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Today’s post is brought to you by guest blogger Charles Baldner, who will be writing a few blog posts this summer on topics related to stellar structure, asteroseismology, and stelalr activity. Charles is a graduate student in the Astronomy Department at Yale University. In his research, he uses helioseismology to study links between the interior of the Sun and solar activity.
Kepler is, first and foremost, an instrument designed to discover and investigate planets around other stars. It will probably not surprise you, however, if I tell you that Kepler data also provides an astounding amount of information about the stars themselves. What the planet hunter sees as noise – that annoying scatter in the data that hides or confuses the telltale signs of a planet – is music to another scientist. I mean that almost literally: like drums, flutes, bagpipes, or guitar strings, stars ‘ring’ at a variety of specific pitches, encoding information about all sorts of stellar properties. Using these `sounds’ to study stars is the science called asteroseismology.
A star is, more or less, a giant sphere of hot gas. Just like in the Earth’s atmosphere or oceans, waves can propagate through a star’s interior. These waves can reflect at the surface, causing it to move up and down, or to brighten or dim. If you can measure the velocity of the surface of a star very precisely, or measure the changes in brightness at the surface, you can detect these waves. If you take enough measurements, you can perhaps see the star ringing just like a musical instrument. In many stars, in fact, the waves you are seeing are sound waves, bouncing back and forth in the stellar interior just as they do inside an organ pipe.
We have used this kind of study to probe the inside of the Sun for more than thirty years. This is called helioseismology, and we have used it to determine the structure of the Sun very precisely. We can measure to great accuracy, for example, exactly where the interior of the Sun changes from `radiative’ to `convective’ (to learn more about the structure of the Sun, you can of course start at Wikipedia: http://en.wikipedia.org/wiki/Sun). We can also see the effects of rotation — different layers and different latitudes of the Sun rotate at different speeds, and we can measure this with helioseismology. Today, I use the tools of helioseismology to probe the regions just beneath sunspots.
In stars, as you can perhaps imagine, measuring these oscillations is much more challenging than it is in the Sun. After all, for most asteroseismic pulsations, we’re talking about minute changes
in velocity or brightness. But that, of course, is precisely what planet search instruments are built to measure, and the Kepler mission is providing us with an immense trove of data with which to use
asteroseismology to study large numbers of stars. In a future post, I’ll go over a few of the sorts of things we hope to glean from Kepler’s asteroseismic measurements.
Image Credit: NASA/ESA/SOHO http://sohowww.nascom.nasa.gov/data/realtime/eit_304/512/
I was talking to last week’s seminar speaker, and we were talking about Planet Hunters and some of the things that might be lurking in the Kepler data. One cool thought is there might be inverse transits so instead of dimming events, instead the star actually appears brighter.
There are lots of eclipsing binaries that you’ve probably seen as you’ve been classified, but another interesting type of eclipsing binary might be a transiting white dwarf orbiting a main sequence star. White dwarfs are about the same size or a little bit bigger than the Earth about half as massive as the Sun. Depending on where the white dwarf orbits, there could be magnification causing a brightening as the white dwarf crosses in front it’s companion star. This magnification is caused by gravitational microlensing, where a massive object bends light of a background source resulting in images of the source that are magnified and distorted. Transiting exoplanets are not massive enough to bend and distort the light of their companion stars significantly. For eclipsing binaries it looks white dwarfs are in the sweet spot, if they are orbiting extremely close to their partner main sequence star. Papers in 2003 by Sahu and Gilliland (2003) and Farmer and Agol predicted that Kepler might be able to detect such events. In these cases during the transiting event, the ligthcurve gets brighter rather than fainter. These events last as long as the transit does so only a few hours (if the white dwarf is orbiting at 1 AU the event is ~10 hours in duration).
Here’s some examples from a paper by Sahu and Gilliland (2003) .
A transiting 0.6 solar mass white dwarf orbiting at 1 AU
0.6 solar mass white dwarf at different orbital radii from a solar-type star
There are some estimates of how many might be there ranging from a few to a about a hundred or so events in the Kepler monitored stars, but we really don’t know. No one has detected them, and there could be 1 or none but with so many eyeballs staring at the data, we might uncover them if they’re there. Anyone seen anything like this in the light curves you’ve classified? It would be very exciting if we found one, it would be the first such discovery – if you see an inverse transit like the examples above, please share on Talk and let us know about your discovery!
We wanted to talk more about the changes to the site and give you all an update on the addition of Quarter 2 data. John’s already talked about the candidates page and some of the new features associated with that, so I wanted to focus on the changes specific to Q2 data release.
NASA and the Kepler team released Quarter 2 on Feb 1st and on Feb 2nd the latest results from the Kepler mission including a complete list of planet candidates and false positives for the first 2 quarters of data. You can read the paper detailing all of this here as well as the Kepler press conference site
The second data release is 90 days so we now have the first approximately 120 days of the Kepler science mission to go through. Q1 was about 35 days, we have chosen to show chunks of the lightcurve in the same size as we were for Q1. So Q2 is broken into three sections. Our aim was to have 5 days worth of overlap in each section, so that we don’t miss any transits that happen at the starts and ends of where we separated the lightcurves. We’re also uploading the Q1 data from the ~400 stars originally withheld and released on Feb 1st. We’ll keep you all posted on the progress.
We have been uploading the new data in batches to make the transition as smooth and seamless as possible. Occasionally the Talk links lag behind because we’re trying to upload as fast as you’re all going through the data. And sometimes you beat us to it
so we’ve increased how fast we’re uploading the Q2 data to keep up with your pace. We’ve appreciated all your patience during this process.
You can tell which part of the lightcurve you are looking at by the APH#. The first two numbers are quarter and section so APH22332480 is section 2 of Quarter 2. We use APH for the lightcurve sections and SPH for referring to the star itself. For the SPH numbers the first two numbers refer to what quarter the star first appeared in the public data set. so SPH21332480 first appeared is Quarter 2 Section 1.
The star source pages (like http://www.planethunters.org/sources/SPH10129795) contain all the sections of lightcurve for you to review and the x-axis is the days from the first observation, so you can look for repeat transits in other sections of the lightcurve easily. Also the downloadable CSV file now contains all the available lightcurve data. We have also updated the gap question (the first question asked) in the classify interface, so now you will now be asked the variability questions regardless of how your answer the gap question (before the variability questions were skipped if you answered yes to their being a data glitch or gap in the lightcurve)
We’ve made some changes to Talk to accommodate the Q2 data. The new planet candidates list and false positive list from the Kepler team are now identified. We’re planning in the near future of marking Planet Hunters planet candidates as well. Each lightcurve section has it’s own object page (ie http://talk.planethunters.org/objects/APH22332480). We now have group pages that gather all the available lightcurve object pages for the star (http://talk.planethunters.org/groups/SPH21332480) which you can access through the “View Star” link on any of the object pages. The “Examine Star” link will take you directly to the star’s source page.
As always we welcome feedback on the new changes, and we are listening to your comments and suggestions on Talk and in your emails. We can’t wait to see what we find in the Quarter 2 data.
Thanks again for your amazing work and feedback. We are working to keep up with you! There is now a data-download button (thanks to Chris, Arfon, Michael, and Stuart!) on the star pages. We are also integrating information about stars that are known eclipsing binaries (EB), Kepler planet candidates (PC) and false positives (FP). Here is an ascii list of light curves with this information. On this list, the APH number is given, followed by the Kepler ID and a flag (EB, PC, FP). For EB objects, D indicates detached binaries, SD is semi-detached, OC is an overcontact binary. Kepler PC stars include columns with the prospective period and planet radius (in Jupiter radii units).
One note about false positives: There are light curves that masquerade as transiting planets. For example, light from a bright foreground star is spread out over several pixels on the CCD detector. The halo of starlight is swept up into a single brightness measurement by the Kepler team’s software. However, in some cases a more distant eclipsing binary (EB) star system blends into the edges of the foreground star. Since the EB is more distant, it is fainter and contributes a smaller fraction of the light. In this case, the background eclipse produces a diluted signal that looks very much like a transiting planet. There are a couple of ways to eliminate these imposters:
- the Kepler team has software that looks for pixel contamination and identifies the star as a false positive (FP). When available, we are listing this information on the light curve and star pages.
- Follow up radial velocity measurements of the bright star will also include the background blended eclipsing binary. A large velocity signal can be a give away sign that the light curve does not arise from a transiting planet.
This follow-up is a critical effort, required to move an object from a transit candidate to a planet.
Dear Planet Hunters: Dr. Natalie Batalha, Deputy Science Team Lead for the Kepler Mission, asked us to post the following message:
Welcome! We are so glad you’re here!
I’m sure I speak for the entire Kepler team when I say how happy we are that Zooniverse is being applied to the Kepler data. For some time now, I’ve watched the public actively work with archived data from other missions. The folks at Unmanned Spaceflight, for example, regularly share the latest images they’ve doctored up from Solar System missions like MER and Cassini. And the SOHO mission recently hit a milestone, discovering its 2000th comet on December 26th, 2010. The discoverer was not part of any formal SOHO science team but rather an astronomy student at Jagiellonian University in Krakow, Poland. I’ve added “Citizen Scientist” to my urban dictionary and appreciate its tremendous potential.
That’s all well and fine when it comes to Martian landscapes, comets, and sunlight glinting off the surface of methane lakes millions of miles away. But how in the world could we entice the public to look at boring old lightcurves? PlanetHunters.org has done exactly that. Not only are thousands of people looking at light curves, they are getting just as hooked on their variety as we are! Welcome to the ranks of those who love light curves.
The Kepler spacecraft is a new piece of technology. Never before have humans stared at stars with such unwavering precision and patience. And whenever humanity does something new, there are sure to be surprises. One of the biggest surprises to me so far is the impact that Kepler is having on stellar astrophysics. Who knew, for example, that a star like RR Lyrae — one of the brightest and well-studied objects in the sky — would blow the dust off textbooks written on this class of star? Who knew we’d see such a symphony of variability occurring just below the noise levels typical of ground-based telescopes?
But the name of the game here is planet hunting. I’ve heard people wonder why they should bother to hunt for planets when the Kepler team has spent years designing savvy computer algorithms to do exactly that — algorithms that can tease signals out of the noise that the human eyes cannot even see. The answer is simple.
Kepler relies, in large part, on automation. We are a relatively small team. There are currently less than 15 scientists working in the Kepler Science Office here at Ames. In the early days, there were only 5 of us! Let’s say we divided up the 150,000 stars we are monitoring amongst the 15 scientists at Ames. We’d each be responsible for 10,000 stars. If we spent only 60 seconds looking at each star, it’d take us over 160 hours to finish out allotment. That’s a solid month of doing nothing else but looking at light curves. Just in time since more data comes down from the spacecraft each month and the process would have to start all over again. Such a plan would never have earned taxpayer dollars. We need our scientists doing other things — like monitoring the instrument and optimizing the software and vetting out the false positives and interpreting the results. And so we write computer software that combs through the data searching for transit-like features.
It’s a challenge to design a one-size-fits-all approach to transit detection. The transit are buried in the light curves of stars with widely different properties and behaviors. You’d build one kind of tool for finding a needle in a haystack but a different kind of tool for finding a needle in a swamp. We don’t even yet know what all the possibilities are because we’ve never looked at stars with this kind of precision.
Another consideration is that the software pipeline requires 3 transits for complete modeling and pipeline generation of they key statistics that are used to vet out the false positives — astrophysical signals masquerading as planet transits. It’s certainly true that we’ve gone back and cherry-picked some of the more compelling light curves displaying less than 3 transits — especially those of the brightest stars. However, many such signals are still lurking in the archive.
So what else did our algorithms miss? Ah, let’s find out, shall we? We’re here with you, ready to help. Come stand here in the crow’s nest and experience the thrill of discovery with us. We welcome your keen eyes!
A huge thank you to the folks at planethunters.org for putting this together.
Deputy Science Team Lead
The reasons for changes in the brightness of a star can be divided into two categories: (1) orbiting companions or (2) stellar astrophysics.
(1) In principle, the variability from orbiting companions (this includes eclipsing binaries or transiting planets) should be as regular as clockwork. In practice, the variability can deviate from clockwork regularity if stellar binaries get too close together, if there are multiple transiting planets, if there is additional background electronic noise or astrophysical noise.
(2) Brightness variations caused by physical processes internal to the star (stellar astrophysics) can arise from pulsations of the star, starspots or flares. Flares are random spikes in the light curve brightness. Pulsations from stars (like RR Lyraes) are quasi-periodic: they can appear to be regular for a while and the cycles are relatively short (generally hours to a day or so). The Figure below shows two variable stars with short periods that might be best classified as “variable” and “pulsating.” These could be short period binary systems – this could quickly be verified with follow-up observations.
Starspots produce complex variations. As the star spins, the spots rotate in and out of view with a periodicity of a day or two (for the most rapidly spinning stars) to several days for slowly rotating stars (the Sun has a rotation period of 25 days). Starspots can form at different latitudes on the star. Since some latitudes rotate faster, spots can show multi-cyclical variations. The light curves below might be best classified as variable and irregular. However, a case could be made for classifying the light curve in the figure below (and left) as variable and regular. Even though the amplitude of the curves changes, the time from one peak to the next is about the same.
I’m Debra Fischer, a Professor of Astronomy at Yale University. Many of you have already discovered some amazing eclipsing binary light curves, and we wanted to provide you with some information. The Figures here show examples that you have put into collections. Some great additional examples are shown in a paper from the Kepler team (Prsá et al. 2010 http://arxiv.org/abs/1006.2815).
The Kepler light curves show how the brightness of the star changes with time. In Figure 1 (APH10135736 = KID 6449358) above, there are two stars orbiting each other. Similar to transiting planets, these stars cross in front of each other. The light curve shows the brightness level of the star, plotted vs time in days. Most of the time, both the larger, hotter star and the smaller cooler star yield a combined brightness measurement for the light curve. When the deep dip in brightness (the primary minimum) occurs it’s because the smaller cooler star is eclipsing the hotter star, which contributes most of the light; when the smaller dip (secondary minimum) occurs, it’s because the larger hotter star is eclipsing the smaller star, which contributes less light to the combined brightness. Stars with flat regions punctuated by relatively sharp dips (e.g. Figure 1) are known as Algol binaries.
A key indicator of eclipsing (or transiting planet) light curves is repeatability.
- you can count the number of days between the large dips to determine the orbital period (about 5 days) of this binary star system in Figure 1
- you can determine how long it takes the stars to cross by the duration of the transit dip (hours for Figure 1)
- you know that one star is larger than the other if the transits don’t have equal dips
Notice that the depth of the brightness dips for an eclipsing binary star can be similar to those for a transiting planet. The transit depth tells us the ratio of the size of the transiting (or eclipsing) object relative to the size of the primary star and the smallest stars have diameters that are similar to Jupiter (stars are gas and the increased gravity from the larger mass star compresses the structure).
Sometimes binary stars are so close that the surfaces are distorted into an elliptical shape and the light curve between the eclipses is rounded, as in the left image of Figure 2 (APH10039007 = KID 9357275), where the orbital period is a little more than one day. You can see both the primary and secondary transit dip in this light curve. The most bizarre eclipsing binary light curves are those where the stars are even closer together, called over-contact binaries. An example of this is shown in the right image of Figure 2 (APH10102932 = KID 4633285). These stars can be so close together that they share a common envelope. The eclipse depth is variable, the light curve looks irregular, and there can be mass transfer between the stars.
Powody zmian jasności gwiazd można podzielić na dwie kategorie: (1) orbitujący towarzysze oraz (2) astrofizyka gwiazd.
(1) W teorii zmienność będąca efektem działania orbitujących towarzyszy (w tym gwiazd i planet) powinna cechować się regularnością szwajcarskiego zegarka. W praktyce mogą wystąpić pewnie odchylenia spowodowane zbytnim zbliżeniem się do siebie gwiazd w układzie podwójnym, jednoczesnym tranzytem kilku planet lub dodatkowymi szumami elektronicznymi bądź astrofizycznymi w tle.
(2) Zmiany jasności gwiazd wynikające z ich wewnętrznych procesów fizycznych (czyli astrofizyki gwiazd) mogą być spowodowane pulsacjami, plamami lub rozbłyskami. Rozbłyski to losowo pojawiające się skoki na krzywej blasku. Pulsacje (np. gwiazd typu RR Lyrae) mają charakter quasiokresowy: przez pewien czas mogą pojawiać się regularnie, a ich cykle są dość krótkie (zwykle trwają od kilku godzin do mniej więcej jednego dnia). Zdjęcie poniżej przedstawia dwie gwiazdy zmienne krótkookresowe, które można określić jako “zmienne” i “pulsujące”. Mogą to być krótkookresowe układy podwójne, co łatwo zweryfikować za pomocą kolejnych badań.
Efektem plam gwiazdowych są złożone wariacje. Kiedy gwiazda się obraca, plamy na zmianę pojawiają się i znikają z pola widzenia w okresach od 1-2 dni (w przypadku najszybciej obracających się gwiazd) do kilku dni w przypadku wolniej obracających się gwiazd (okres obrotu Słońca wynosi 25 dni). Plamy mogą powstawać na różnych szerokościach geograficznych gwiazdy. Ponieważ niektóre szerokości geograficzne obracają się szybciej, a inne wolniej, pomiędzy cyklami poszczególnych plam mogą występować znaczne różnice. Krzywe blasku przedstawione poniżej najlepiej sklasyfikować jako zmienne, nieregularne. Jednak wykres po lewej można by również określić jako zmienny i regularny. Mimo że amplituda krzywych ulega zmianie, czas pomiędzy poszczególnymi szczytami pozostaje taki sam.
Hi I’m Matt, a graduate student at Yale University and a member of the Science Team. We’re really impressed with the turnout so far on planethunters.org and users have already pointed out some really amazing objects! Quite a few people have asked for some clarification on what transits look like, so I’ll address that in this post.
In the figure above, we’ve taken a Kepler light curve from a star that’s about the same size as the Sun and have simulated what the effects would be if a few different types of planets were to transit.
The white dots show the amount of light from the star measured with Kepler with no planets transiting. The blue points show what we would see if a planet just like Jupiter orbiting this star were to transit. This Jupiter-size planet, at about 11.2 times the size of the Earth and one tenth the size of the star, is shown to scale transiting its parent star in the top left blue box.
The green dots show what a planet just like Neptune would look like transiting. Since it is much further away from the star than Jupiter, it would have a slower orbital speed so it would take longer to transit the disk of its parent star, which is what explains the longer duration, or wider width, of the transit event. With Neptune’s much smaller size than Jupiter, at 3.9 times the radius of the Earth, it doesn’t block out as much light, which is why the depth is much shallower.
Both of these events are very noticeable, compared to the effects of an Earth-size planet. The tiny speck on the star in the far right red box shows, to scale, what a transiting Earth-size planet would look like if we could see it. Now you get an idea of how difficult finding Earth-size planets is going to be! If that transiting planet had an orbital period of 1 year just like the Earth, then the dip in light observed from the parent star as the planet transits would be similar to the red points in the light curve. Since the Earth is much closer to the star, it has a much faster orbital speed, which then makes the duration of transit much shorter than the duration of either Jupiter or Neptune. Because the Earth-size planet is much smaller than either Jupiter or Neptune, it also blocks out less light making the dip in light we receive here on Earth barely discernible from no transit at all.
We don’t expect people to see these events all the time, so don’t worry about missing them. That’s why we’ve introduced fake planets into the mix. The fake, or synthetic, planets will help us determine the completeness of Planet Hunters, or how likely we are to detect planets of different sizes and with different orbital periods if they exist.
Greetings from Kevin Schawinski and Meg Schwamb, postdoctoral fellows at Yale and members of the Science Team.
Wow, we’ve been blown away by how enthusiastic everyone has been about the project. In this post, we wanted to talk more about another goal of Planet Hunters, which is to study and better understand stellar variability. The public release Kepler data set is unprecedented, both in observing cadence and in the photometric precision. The lightcurves reveal subtle variability that has never before been documented.
The Kepler lightcurves are complex many exhibiting significant structure including multiple oscillations imposed on top of each other as well as short-lived variations. Most of this variability is due by starspots or stellar pulsations.With Planet Hunters we will not only be looking for stars harboring planets outside of our solar system, but we will be able to study and classify stellar variability in ways that automated routines cannot. Unlike a machine learning approach, human classifiers recognize the unusual and have a remarkable ability to recognize archetypes and assemble groups of similar objects.
Users have the ability to identify strange or unusual lightcurves as well as tag similar curves and come up with their own classes or ”collections” of variability with Planet Hunters Talk. You can add a comment and use the #hashtag like in Twitter to mark an interesting lightcurve and alert others including the science team. Every light curve, or collection of curves has a short-message thread (140 characters) associated with it for general comments. You also can start discussions if you want to chat in a more in-depth fashion.
Mining the Kepler data set will inevitably lead to unexpected discoveries, showcased by the successes of Galaxy Zoo. The prime examples are the discoveries of ”Hanny’s Voorwerp” and the ”green peas” by Galaxy Zoo users. Hanny’s Voorwerp is a cloud of ionized gas in the Sloan Digital Sky Survey image of the nearby galaxy IC 2497. Unlike an automatic classification routine, citizen scientist Hanny van Arkel spotted a blue smudge next to IC 2497, recognized it as unusual, and alerted the Galaxy Zoo team and the other users. Since then, Hanny’s Voorwerp has been identified as a light echo from a recent quasar phase in IC 2497, making it the Rosetta Stone of quasars. The Galaxy Zoo participants started noticing a very rare class of objects of point sources showed as green in the SDSS color scheme. Dubbing them the ”green peas,” the citizen scientists scoured the SDSS database, and assembled a list of these ”pea galaxies.” The ”peas” were revealed to be ultra-compact, powerful starburst galaxies whose properties are highly unusual in the present day universe, but resemble those of primordial galaxies in the early universe. The citizen scientists found veritable fossils living in the present-day universe.
With so many eyes looking at the lightcurves, we are bound to find new variability types! We’re hoping that Planet Hunters, like Galaxy Zoo, will yield exciting new results that we can’t even attempt to speculate or imagine! We can’t wait to see what turns up. | 0.866066 | 3.823315 |
- Carbon Dating | ibohyhozeq.tk
- What type of radiation is used for carbon dating? Alpha,beta or gamma?
- Radiocarbon dating
Carbon is a radioisotope of Carbon. The unstable Carbon is transported down to the lower atmosphere by atmospheric activity such as storms. Carbon reacts identically to Carbon and is rapidly oxidised to form Carbon Dioxide. Since all living organisms on Earth are made up of organic molecules that contain Carbon atoms derived from the atmosphere, they therefore contain Carbon atoms.
The Carbon within a living organism is continually decaying, but as the organism is continuously absorbing Carbon throughout its life the ratio of Carbon to Carbon atoms in the organism is the same as the ratio in the atmosphere. By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known. It must be noted though that radiocarbon dating results indicate when the organism was alive but not when a material from that organism was used.
There are three principal techniques used to measure carbon 14 content of any given sample— gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry. Gas proportional counting is a conventional radiometric dating technique that counts the beta particles emitted by a given sample. Beta particles are products of radiocarbon decay.
In this method, the carbon sample is first converted to carbon dioxide gas before measurement in gas proportional counters takes place. Liquid scintillation counting is another radiocarbon dating technique that was popular in the s. In this method, the sample is in liquid form and a scintillator is added. This scintillator produces a flash of light when it interacts with a beta particle.
A vial with a sample is passed between two photomultipliers, and only when both devices register the flash of light that a count is made. Accelerator mass spectrometry AMS is a modern radiocarbon dating method that is considered to be the more efficient way to measure radiocarbon content of a sample. In this method, the carbon 14 content is directly measured relative to the carbon 12 and carbon 13 present. The method does not count beta particles but the number of carbon atoms present in the sample and the proportion of the isotopes.
Not all materials can be radiocarbon dated. Most, if not all, organic compounds can be dated. Samples that have been radiocarbon dated since the inception of the method include charcoal , wood , twigs, seeds , bones , shells , leather, peat , lake mud, soil , hair, pottery , pollen , wall paintings, corals, blood residues, fabrics , paper or parchment, resins, and water , among others.
Physical and chemical pretreatments are done on these materials to remove possible contaminants before they are analyzed for their radiocarbon content. The radiocarbon age of a certain sample of unknown age can be determined by measuring its carbon 14 content and comparing the result to the carbon 14 activity in modern and background samples. It is not always possible to recognize re-use. Other materials can present the same problem: A separate issue, related to re-use, is that of lengthy use, or delayed deposition.
For example, a wooden object that remains in use for a lengthy period will have an apparent age greater than the actual age of the context in which it is deposited. Archaeology is not the only field to make use of radiocarbon dating. The ability to date minute samples using AMS has meant that palaeobotanists and palaeoclimatologists can use radiocarbon dating on pollen samples. Radiocarbon dates can also be used in geology, sedimentology, and lake studies, for example. Dates on organic material recovered from strata of interest can be used to correlate strata in different locations that appear to be similar on geological grounds.
Dating material from one location gives date information about the other location, and the dates are also used to place strata in the overall geological timeline. The Pleistocene is a geological epoch that began about 2. The Holocene , the current geological epoch, begins about 11, years ago, when the Pleistocene ends.
Before the advent of radiocarbon dating, the fossilized trees had been dated by correlating sequences of annually deposited layers of sediment at Two Creeks with sequences in Scandinavia. This led to estimates that the trees were between 24, and 19, years old, and hence this was taken to be the date of the last advance of the Wisconsin glaciation before its final retreat marked the end of the Pleistocene in North America. This result was uncalibrated, as the need for calibration of radiocarbon ages was not yet understood.
Further results over the next decade supported an average date of 11, BP, with the results thought to be most accurate averaging 11, BP. There was initial resistance to these results on the part of Ernst Antevs , the palaeobotanist who had worked on the Scandinavian varve series, but his objections were eventually discounted by other geologists.
In the s samples were tested with AMS, yielding uncalibrated dates ranging from 11, BP to 11, BP, both with a standard error of years. Subsequently, a sample from the fossil forest was used in an interlaboratory test, with results provided by over 70 laboratories. In , scrolls were discovered in caves near the Dead Sea that proved to contain writing in Hebrew and Aramaic , most of which are thought to have been produced by the Essenes , a small Jewish sect. These scrolls are of great significance in the study of Biblical texts because many of them contain the earliest known version of books of the Hebrew bible.
The results ranged in age from the early 4th century BC to the mid 4th century AD. In all but two cases the scrolls were determined to be within years of the palaeographically determined age. Subsequently, these dates were criticized on the grounds that before the scrolls were tested, they had been treated with modern castor oil in order to make the writing easier to read; it was argued that failure to remove the castor oil sufficiently would have caused the dates to be too young.
Multiple papers have been published both supporting and opposing the criticism. Soon after the publication of Libby's paper in Science , universities around the world began establishing radiocarbon-dating laboratories, and by the end of the s there were more than 20 active 14 C research laboratories. It quickly became apparent that the principles of radiocarbon dating were valid, despite certain discrepancies, the causes of which then remained unknown.
Taylor, " 14 C data made a world prehistory possible by contributing a time scale that transcends local, regional and continental boundaries". It provides more accurate dating within sites than previous methods, which usually derived either from stratigraphy or from typologies e. The advent of radiocarbon dating may even have led to better field methods in archaeology, since better data recording leads to firmer association of objects with the samples to be tested.
These improved field methods were sometimes motivated by attempts to prove that a 14 C date was incorrect. Taylor also suggests that the availability of definite date information freed archaeologists from the need to focus so much of their energy on determining the dates of their finds, and led to an expansion of the questions archaeologists were willing to research. For example, from the s questions about the evolution of human behaviour were much more frequently seen in archaeology.
The dating framework provided by radiocarbon led to a change in the prevailing view of how innovations spread through prehistoric Europe. Researchers had previously thought that many ideas spread by diffusion through the continent, or by invasions of peoples bringing new cultural ideas with them.
Carbon Dating | ibohyhozeq.tk
As radiocarbon dates began to prove these ideas wrong in many instances, it became apparent that these innovations must sometimes have arisen locally. This has been described as a "second radiocarbon revolution", and with regard to British prehistory, archaeologist Richard Atkinson has characterized the impact of radiocarbon dating as "radical More broadly, the success of radiocarbon dating stimulated interest in analytical and statistical approaches to archaeological data.
Occasionally, radiocarbon dating techniques date an object of popular interest, for example the Shroud of Turin , a piece of linen cloth thought by some to bear an image of Jesus Christ after his crucifixion. Three separate laboratories dated samples of linen from the Shroud in ; the results pointed to 14th-century origins, raising doubts about the shroud's authenticity as an alleged 1st-century relic.
Researchers have studied other radioactive isotopes created by cosmic rays to determine if they could also be used to assist in dating objects of archaeological interest; such isotopes include 3 He , 10 Be , 21 Ne , 26 Al , and 36 Cl. With the development of AMS in the s it became possible to measure these isotopes precisely enough for them to be the basis of useful dating techniques, which have been primarily applied to dating rocks.
From Wikipedia, the free encyclopedia.
What type of radiation is used for carbon dating? Alpha,beta or gamma?
Method of chronological dating using radioactive carbon isotopes. Calculation of radiocarbon dates. Calibration of radiocarbon dates. However, this pathway is estimated to be responsible for less than 0. The definition of radiocarbon years is as follows: This effect is accounted for during calibration by using a different marine calibration curve; without this curve, modern marine life would appear to be years old when radiocarbon dated. Similarly, the statement about land organisms is only true once fractionation is taken into account.
For older datasets an offset of about 50 years has been estimated. It can be cited as: Christie M, et al. Journal of the Franklin Institute. Marine radiocarbon reservoir effects MRE in archaeology: Retrieved 11 December Definitions, mechanisms and prospects". Memoirs of the Society for American Archaeology 8: Retrieved 9 December Warren; Blackwell, Paul G.
US Department of State. Retrieved 2 February Woods Hole Oceanographic Institution. Retrieved 27 August Information for Authors" PDF. Archived from the original PDF on 10 August Retrieved 1 January Proceedings of the Royal Society of London B: Canon of Kings Lists of kings Limmu. Chinese Japanese Korean Vietnamese. Lunisolar Solar Lunar Astronomical year numbering. Deep time Geological history of Earth Geological time units. Chronostratigraphy Geochronology Isotope geochemistry Law of superposition Luminescence dating Samarium—neodymium dating.
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Amino acid racemisation Archaeomagnetic dating Dendrochronology Ice core Incremental dating Lichenometry Paleomagnetism Radiometric dating Radiocarbon Uranium—lead Potassium—argon Tephrochronology Luminescence dating Thermoluminescence dating. Fluorine absorption Nitrogen dating Obsidian hydration Seriation Stratigraphy.
Retrieved from " https: Wikipedia articles published in peer-reviewed literature Wikipedia articles published in WikiJournal of Science Externally peer reviewed articles Radiocarbon dating American inventions Carbon Conservation and restoration Isotopes of carbon Radioactivity Radiometric dating. | 0.804704 | 3.470143 |
Researchers at NASA have used data from the Fermi telescope to measure starlight produced over 90% of the Universe’s history and confirm theories regarding the boom-period of star-formation, research published in the latest edition of Science has revealed.
The research focused on Gamma-ray output from distant galaxies to estimate stellar formation rates through the history of the Universe and lay down a template for future examinations of early stellar-development.
The new study hasn’t just independently confirmed previously obtained results, but built upon the findings by removing biases and shortfalls from those studies.
Lead scientist Marco Ajello, an astrophysicist at Clemson University in South Carolina said: “Stars create most of the light we see and synthesize most of the universe’s heavy elements, like silicon and iron.
“Understanding how the cosmos we live in came to be, depends in large part on understanding how stars evolved.”
The primary mission of the Fermi-telescope, launched into orbit 10-years-ago, has been to observe the ‘ cosmic fog’ of all the ultraviolet, visible and infrared light produced by stars over the Universe’s history collectively known as extragalactic light (EBL). This light will long outlast its source continuing to travel across the cosmos, thus measuring the EBL allows astronomers to study the stellar-formation and evolution of long-dead stars.
David Thompson, Fermi’s deputy project scientist describes the recent findings: “This is an independent confirmation of previous measurements of star-formation rates.
“In astronomy, when two completely independent methods give the same answer, that usually means we’re doing something right. In this case, we’re measuring star formation without looking at stars at all but by observing gamma rays that have traveled across the cosmos.”
Gamma rays are the highest frequency and thus the most energetic form of electromagnetic radiation when they interact with interact with other frequencies of light, matter can be created via Einsteins famous energy-mass equivalence, E=mc². An example of this is the creation of electrons and positrons when high-energy gamma-rays interact with infrared light and when lower-energy gamma-rays interact with higher energy light.
Fermi’s ability to detect gamma-rays makes it extremely well-suited for mapping the EBL spectrum. The above-listed interactions are common enough over cosmic distances that the further back cosmologists look, the more evident their effects on gamma-ray sources are, allowing a deep-examination of the Universe’s stellar population.
The researchers led by Vaidehi Paliya examined gamma-ray signals from almost 750 galaxies with supermassive black holes at their center known as blazars collected over a nine-year period by Fermi’s Large Area Telescope (LAT) to estimate how the EBL has built over time.
The study has confirmed previous results that show the peak-period of star-production was 10 -billion years ago. The improvement this new research has made on these studies comes from the fact that previous star-surveys have often missed fainter stars and galaxies. This means that they couldn’t account for star formation in intergalactic space.
This population has previously only been estimated, whereas the EBL includes contributions starlight from these sources, thus providing a more complete picture of star formation. The method has been used before, but the number of blazars surveyed was a fraction of those observed in this new study.
It is expected that the outcome of this study will help guide the future work of the James Webb Telescope (JWST) expected to launch in 2021.
Co-author Kári Helgason, an astrophysicist at the University of Iceland, said: “One of Webb’s primary objectives is to unravel what happened in the first billion years after the big bang.
“Our work places important new limits on the amount of starlight we can expect to see in those first billion years — a largely unexplored epoch in the universe — and provides a benchmark for future studies.” | 0.877572 | 4.088138 |
Solar System Exploration
Io Color Eclipse
December 16, 2004
Io Color Eclipse
The Cassini spacecraft has obtained new images of Saturn's auroral emissions, which are similar to Earth's Northern Lights. Images taken on June 21, 2005, with Cassini's ultraviolet imaging spectro...
This image of Ceres, taken by NASA's Dawn spacecraft, features several craters with bright material within and around them. The image is centered on terrain near the equator of Ceres and faces sout...
Dawn Survey Orbit Image 50
The low angle of the sun over Tethys' massive canyon, Ithaca Chasma (near the terminator, at right), highlights the contours of this enormous rift.
This image shows a high-resolution heat intensity map of part of the south polar region of Saturn's moon Enceladus, made from data obtained by NASA's Cassini spacecraft.
Tiger Stripe Split Ends
This image of Ceres is part of a sequence taken by NASA's Dawn spacecraft on May 22, 2015, from a distance of 3,200 miles (5,100 kilometers) with a resolution of 1,600 feet (480 meters) per pixel.
Dawn OpNav9 Image 1
These images from NASA's Dawn spacecraft are located in asteroid Vesta's Floronia quadrangle, in Vesta's northern hemisphere; distinct sinuous grooves are visible around the rim of the crater.
HAMO and LAMO Images of Floronia Crater
The south pole of the giant asteroid Vesta reveals cliffs that are several miles or kilometers high, deep grooves, and craters. This oblique view is from NASA's Dawn spacecraft.
High Cliffs at Vesta's South Pole
Saturn's moon Janus obscures part of the planet's A ring as the Cassini spacecraft looks toward the main rings and the thin F ring. Janus (179 kilometers, or 111 miles across) appears as a dark ov...
Janus in the Way
It's hard not to speculate about the origins of the narrow, dark features seen in Cassini's new images of Titan's surface. They tantalize the viewer, resembling the dark channels seen elsewhere ...
Channels on Titan?
This view from NASA's Dawn spacecraft shows terrain in the southern hemisphere of Ceres. Most of the image is the impact crater named Annona (37 miles, 60 kilometers across); the smaller, prominent...
Dawn LAMO Image 136
This image from NASA's Dawn spacecraft shows the northeastern rim of Urvara Crater on Ceres at lower left. To the right of the crater, the long, narrow feature that appears to jut out toward the no...
Pongal Catena on Ceres
Comet Siding Spring makes a close pass by Mars and Mars in October 2014.
Mars and Comet Siding Spring
The shepherd moon Pan orbits Saturn in the Encke gap while the A ring surrounding the gap displays wave features created by interactions between the ring particles and Saturnian moons. Pan (17 mil...
Pan and Waves
The cameras on NASA's Cassini spacecraft captured this rare look at Earth and its moon from Saturn orbit on July 19, 2013. Taken while performing a large wide-angle mosaic of the entire Saturn rin...
One Special Day in the Life of Planet Earth
Saturnian Hurricane October 7, 2004 Full-Res: PIA06493 This close-up view shows lots of atmospheric detail, including a dark storm an...
Merging Saturnian Storms
Merging Saturnian Storms
Although the Huygens probe has now pierced the murky skies of Titan and landed on its surface, much of the moon remains for the Cassini spacecraft to explore. Titan continues to present exciting pu...
New Titan Territory
Beyond the Rings: Mimas August 5, 2004 Full-Res: PIA05428 Looking beyond Saturn's magnificent rings, Cassini caught a glimpse of t...
Beyond the Rings: Mimas
Cassini images reveal the existence of a faint arc of material orbiting with Saturn's small moon Anthe. The moon is moving in a counterclockwise direction in this perspective, and is about to reac...
Anthe's Faint Arc
The Cassini spacecraft spies two types of waves in Saturn's A ring: a spiral density wave on the left of the image and a more pronounced spiral bending wave near the middle. See Two Kinds of Wave ...
+ Unannotated version Five images of Saturn's rings, taken by NASA's Cassini spacecraft between 2009 and 2012, show clouds of material ejected from impacts of small objects into the rings. Clockwi...
Meteors Meet Saturn's Rings
In this view, individual layers of haze can be distinguished in the upper atmosphere of Titan, Saturn’s largest moon.
Saturn's moon Prometheus chases Pandora in this Cassini view, but the outcome of their race has already been decided by gravity. Prometheus orbits closer to Saturn and thus moves faster than does P...
NASA is exploring our solar system and beyond to understand the workings of the universe, searching for water and life among the stars.
The Solar System and Beyond is Awash in Water
These two false-color views from NASA's Cassini spacecraft show detailed patterns that change during one Saturn day within the huge storm in the planet's northern hemisphere.
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Lightning creates brief bursts of gamma rays. Researchers measured these bursts using instruments on the ISS.
Space Station Instrument Helps Researchers to Understand Lightning
NASA has assigned astronaut Kate Rubins to a six-month mission to the International Space Station as a flight engineer.
NASA Assigns Astronaut Kate Rubins to Expedition 63/64 Space Station Crew
New results from Hubble suggest the formation of the first stars and galaxies in the early universe took place sooner than previously thought.
Hubble Makes Surprising Find in Early Universe
This view is a mosaic of sample site Osprey on asteroid Bennu created from images collected by NASA’s OSIRIS-REx spacecraft.
OSIRIS-REx Swoops Over Sample Site Osprey
Less than a week into their stay, astronauts Doug Hurley and Bob Behnken are stepping up their advanced science activities.
Science Stepping Up on the International Space Station
NASA's Mars 2020 Perseverance rover will collect the first samples from another planet.
The Extraordinary Sample-Gathering System of Perseverance Rover | 0.842015 | 3.544353 |
Washington, Feb 9 (ANI): The giant black hole at the centre of the Milky Way may be vaporizing and devouring asteroids, which could explain the mysterious X-ray flares detected over a period of several years, a new study has revealed.
For several years NASA's Chandra has detected X-ray flares about once a day from the supermassive black hole known as Sagittarius A-star, or "Sgr A-star" for short.
The flares last a few hours with brightness ranging from a few times to nearly one hundred times that of the black hole's regular output. The flares also have been seen in infrared data from ESO's Very Large Telescope in Chile.
"People have had doubts about whether asteroids could form at all in the harsh environment near a supermassive black hole," said Kastytis Zubovas of the University of Leicester in the United Kingdom, and lead author of the report appearing in the Monthly Notices of the Royal Astronomical Society.
"It's exciting because our study suggests that a huge number of them are needed to produce these flares."
Zubovas and his colleagues suggest there is a cloud around Sgr A* containing trillions of asteroids and comets, stripped from their parent stars.
Asteroids passing within about 100 million miles of the black hole, roughly the distance between the Earth and the sun would be torn into pieces by the tidal forces from the black hole.
These fragments then would be vaporized by friction as they pass through the hot, thin gas flowing onto Sgr A*, similar to a meteor heating up and glowing as it falls through Earth's atmosphere.
A flare is produced and the remains of the asteroid are swallowed eventually by the black hole.
"An asteroid's orbit can change if it ventures too close to a star or planet near Sgr A*," said co-author Sergei Nayakshin, also of the University of Leicester. "If it's thrown toward the black hole, it's doomed."
The authors estimate that it would take asteroids larger than about six miles in radius to generate the flares observed by Chandra.
Meanwhile, Sgr A* also may be consuming smaller asteroids, but these would be difficult to spot because the flares they generate would be fainter.
These results reasonably agree with models estimating of how many asteroids are likely to be in this region, assuming that the number around stars near Earth is similar to the number surrounding stars near the centre of the Milky Way.
"As a reality check, we worked out that a few trillion asteroids should have been removed by the black hole over the 10-billion-year lifetime of the galaxy," said co-author Sera Markoff of the University of Amsterdam in the Netherlands.
"Only a small fraction of the total would have been consumed, so the supply of asteroids would hardly be depleted," Markoff added. (ANI)
Read More: University Grants Commission (UGC) | Mukesh Chandra Mathur | Netherlands | Netherlands Antilles | Chile | Guru Nanak Dev University | Sera | Chandra Nagar | Sera Bera | Chandra Colony Ndtso | S.v.u. P.g .centre | G.s.t.centre | K.p.centre | Chandra Lay Out | Chandra | Chandra Mandi Bo | Chandra Dhipa | K.r.centre | Ram Chandra Pur | Mon | Chandra Dih | 0.888922 | 3.876814 |
Saturn is the sixth planet in the solar system, sitting between the enormous Jupiter and the ice planet Uranus.
The discovery of 20 tiny moons circling Saturn has knocked Jupiter out of the top spot in the moon race; the new additions bring Saturn's total to 82 moons, while Jupiter has just 79. Saturn and Jupiter, with 161 between them, account for almost 80% of these.
Gallic mythology: "One in every of the newly stumbled on moons orbits within the prograde route and has an inclination strategy 36 degrees, which is equivalent to those within the Gallic group, regardless that it is worthy farther away from Saturn than some other prograde moons". It is not yet clear, however, why Venus does not have a moon. The 17 new retrograde moons, or the moons that orbit the opposite direction of Saturn's rotation, joined the Norse group. The discovery was announced by the International Astronomical Union's Minor Planet Center (MPEC). These baby moons could well even contain attain from greater guardian moons that broke apart appropriate after Saturn fashioned. The Carnegie Institution had a moon-naming contest for them; some other is deliberate now for Saturn's fresh moons. The number of Moons is three more than Jupiter, but enough to secure Saturn the first position as the mightiest of them all.
"Studying the orbits of these moons can reveal their origins, as well as information about the conditions surrounding Saturn at the time of its formation", Sheppard said.
Well, a new discovery by scientists has made the planet Saturn, the new moon king!
Last year, Sheppard and his team located 12 new moons around Jupiter, including one with a retrograde orbit. Another three have prograde orbits, meaning they orbit in the same direction as the planet's spin. But the new discovery might provide insight into formation of Saturn facilitating our understanding of an infant solar system.
"Using some of the largest telescopes in the world, we are now completing the inventory of small moons around the giant planets", said Sheppard.
In the Solar System's youth, the Sun was surrounded by a rotating disk of gas and dust from which the planets were born.
Two of the newly discovered prograde moons fit into a group of outer moons with inclinations of about 46 degrees called the Inuit group.
The naming contest runs until December 6, although there are a few rules that will surely disappoint the Moony McMoonFace shippers. The most extreme of these new moons, designated S5613a2 m, requires 1,413 days, or 5.3 years, to revolve around Saturn, making it the farthest known moon from the gas giant.
However, one must remember, two of these moons ought to be named after characters of the Inuit mythology, given they belong to the Inuit group.
The rules mean two of Saturn's moons will have Canadian-inspired names - so start brushing up on your Inuit mythology.
Jane Fonda Arrested During D.C. Climate Change Protest
I got up, and as I started to walk back to the vehicle with the translator, the implication of what had just happened hit me. She was filmed standing beside Oil Change International protesters, who started a chant demanding for "climate justice now".
GM tells workers it's time for the strike to end
Workers and the union are pushing GM on a host of issues, including wages, health care and the use of temporary workers. The UAW did not immediately respond to a request for comment on GM's letter. | 0.825618 | 3.638492 |
Herschel lives up to the family name
The Herschel Space Observatory has been observing the sky at infrared wavelengths since shortly after its launch two years ago, on 14th May 2009. But the name Herschel has a much longer legacy than that. The observatory is named after Sir William Herschel, a leading astronomer, for discovering infrared light around two hundred years ago. The Herschel family was a particularly astronomical one, with both his sister, Caroline, and son, John, playing important roles in the history of astronomy.
Born Friedrich Wilhelm Herschel in Germany in 1738, William moved to England aged 19, and became one of the leading astronomers of his time. In 1800, he discovered infrared light, which has wavelengths longer than visible light that we see. Herschel was also a very accomplished telescope builder, and spent much of his time systematically observing the sky looking for double stars and nebulae. Working from his home in Bath in 1781, one of Williams most famous discoveries was the planet Uranus. He gained favour from King George III by trying to name it the Georgian Star, though the name didnt stick. The favour did, however, and he was appointed The Kings Astronomer in 1782.
Today, the Herschel Space Observatory is still making use of the planet Uranus. The extensive study of our Suns seventh planet means that it is very well understood. Herschels SPIRE instrument regularly observes Uranus so that astronomers can calibrate other measurements against the well-known brightness of Uranus.
Professor Bruce Swinyard, from University College London, said Uranus was one of the first objects we observed with SPIRE, being imaged shortly after the lid over the instruments was opened. One of the reasons Uranus is particularly useful is that its spectrum is very smooth and well understood at our wavelengths, making it an ideal standard to compare other measurements to.
Uranus is too small for the Herschel satellite to see as more than a very bright point of light. In the background of the image are dozens of faint fuzzy blobs, each one a distant galaxy. This is an excellent illustration of Herschels power, as the faint galaxies are typically ten thousand times fainter than the much closer planet Uranus.
Caroline Herschel worked closely with William, and was one of the first female astronomers. She made many discoveries of her own, including a number of comets which bear her name. When she was awarded a £50 annual stipend by King George III, Caroline became the first woman to have an official government appointment. After William's death in 1822, Caroline moved back to Germany and completed his catalogue of nebulae. In recognition of her astronomical work, she was the first woman to be awarded the Gold Medal by the Royal Astronomical Society. The Herschel catalogue of more than 2000 objects formed the basis of the astronomical catalogue which is still used today.
Comets have been important throughout history, and remain so today. They are icy snowballs which were formed at the same time the planets nearly 5 billion years ago. Detailed studies of comets shed light on what the Solar System early in its history, and provide hints as to how the Earth has changed since its formation. While the Herschel Space Observatory isnt observing any of Carolines cometary discoveries, most of which whizzed past Earth and left the Solar System, it has observed a number of others.
Fittingly, the Herschel satellite observes in a very similar way to the technique used by William and Caroline Herschel themselves it methodically and systematically scans the sky recording exactly what is seen over large areas of the heavens. It is the ends of these scans which give the jagged appearance to the Herschel images.
The family connection to the work of the Herschel satellite doesnt end with Caroline. Williams son, Sir John Herschel, was also an astronomer, and added thousands more objects to the catalogue compiled by William and Caroline. He discovered that many of the bright stars in the sky are located in a band which is tilted relative to the disc of stars that makes up most of our Galaxy. It was an American astronomer, Benjamin Gould, who established that there was a full ring around the sky. Now known as the Gould Belt, it contains most of the nearby star forming regions, such as the Orion Nebula, and it provides us with a panoramic view of how stars like the Sun are still forming in the Milky Way today.
The far-infrared light measured by the Herschel Space Observatory makes it the ideal instrument for studying star formation, and the Gould Belt is one of its main targets. Using Herschel, Astronomers have mapped star formation in many areas of the Gould Belt, from the Southern Cross to Cygnus, the Swan.
Those of us working on the Herschel Space Observatory think it's very well named, said Professor Matt Griffin, from Cardiff University and lead scientist of the SPIRE mission. It follows in the footsteps of William and Caroline Herschel in surveying the heavens, and it uses the planet that William Herschel discovered as a standard source. Not only that, our cameras on board the satellite actually use a basic technique used by William Herschel himself to measure the infrared light. Two centuries on, I think William and Caroline would be intrigued and certainly quite pleased to see how what they started has developed. | 0.807226 | 3.501738 |
Once you leave the majestic skies of Earth, the word “cloud” no longer means a white fluffy-looking structure that produces rain. Instead, clouds in the greater universe are clumpy areas of greater density than their surroundings.
Space telescopes have observed these cosmic clouds in the vicinity of supermassive black holes, those mysterious dense objects from which no light can escape, with masses equivalent to more than 100,000 Suns. There is a supermassive black hole in the center of nearly every galaxy, and it is called an “active galactic nucleus” (AGN) if it is gobbling up a lot of gas and dust from its surroundings. The brightest kind of AGN is called a “quasar.” While the black hole itself cannot be seen, its vicinity shines extremely bright as matter gets torn apart close to its event horizon, its point of no return.
But black holes aren’t truly like vacuum cleaners; they don’t just suck up everything that gets too close. While some material around a black hole will fall directly in, never to be seen again, some of the nearby gas will be flung outward, creating a shell that expands over thousands of years. That’s because the area near the event horizon is extremely energetic; the high-energy radiation from fast-moving particles around the black hole can eject a significant amount of gas into the vastness of space.
Scientists would expect that this outflow of gas would be smooth. Instead, it is clumpy, extending well beyond 1 parsec (3.3 light-years) from the black hole. Each cloud starts out small, but can expand to be more than 1 parsec wide — and could even cover the distance between Earth and the nearest star beyond the Sun, Proxima Centauri.
Astrophysicist Daniel Proga at the University of Nevada, Las Vegas, likens these clumps to groups of cars waiting at a highway onramp with stoplights designed to regulate the influx of new traffic. “Every now and then you have a bunch of cars,” he said.
What explains these clumps in deep space? Proga and colleagues have a new computer model that presents a possible solution to this mystery, published in the Astrophysical Journal Letters, led by doctoral student Randall Dannen. Scientists show that extremely intense heat near the supermassive black hole can allow the gas to flow outward really fast, but in a way that can also lead to clump formation. If the gas accelerates too quickly, it will not cool off enough to form clumps. The computer model takes these factors into account and proposes a mechanism to make the gas travel far, but also clump.
“Near the outer edge of the shell there is a perturbation that makes gas density a little bit lower than it used to be,” Proga said. “That makes this gas heat up very efficiently. The cold gas further out is being lifted out by that.”
This phenomenon is somewhat like the buoyancy that makes hot air balloons float. The heated air inside the balloon is lighter than the cooler air outside, and this density difference makes the balloon rise.
“This work is important because astronomers have always needed to place clouds at a given location and velocity to fit the observations we see from AGN,” Dannen said. “They were not often concerned with the specifics of how the clouds formed in the first place, and our work offers a potential explanation for the formation of these clouds.”
This model looks only at the shell of gas, not at the disk of material swirling around the black hole that is feeding it. The researchers’ next step is to examine whether the flow of gas originates from the disk itself. They are also interested tackling the mystery of why some clouds move extremely fast, on the order of 20 million miles per hour (10,000 kilometers per second).
Reference: “Clumpy AGN Outflows due to Thermal Instability” by Randall C. Dannen, Daniel Proga, Tim Waters and Sergei Dyda, 21 April 2020, Astrophysical Journal Letters.
This research, which addresses an important topic in the physics of active galactic nuclei, was supported with a grant from NASA. The co-authors are Dannen, Proga, UNLV postdoctoral scholar Tim Waters, and former UNLV postdoctoral scholar Sergei Dyda (now at the University of Cambridge). | 0.868212 | 4.105795 |
ESA Hubble Space Telescope logo.
7 January 2014
First image from Hubble's Frontier Fields
Hubble Frontier Fields view of Abell 2744
This image of Abell 2744 is the first to come from Hubble's Frontier Fields observing programme, which is using the magnifying power of enormous galaxy clusters to peer deep into the distant Universe. Abell 2744, nicknamed Pandora's Cluster, is thought to have a very violent history, having formed from a cosmic pile-up of multiple galaxy clusters.
Astronomers previously observed Abell 2744 with the NASA/ESA Hubble Space Telescope back in 2011, exploring the cluster's history. They found that at least four galaxy clusters had crashed into one another to form Abell 2744, causing some weird and wonderful effects. This mix of cosmic phenomena, some of which had never been seen before, led to the nickname of Pandora's Cluster (heic1111).
A mix of hazy elliptical galaxies and colourful spirals can be seen clumping together in the centre of this image. The effects of the cluster's gravity can be seen in the blue arcs and distorted shapes that are scattered across the frame, including galaxies that seem to be bleeding into the surrounding space. The arcs are actually the distorted images of galaxies far in the distance.
Abell 2744 is the first of six targets for an observing programme known as Frontier Fields. This three-year, 840-orbit programme will yield our deepest views of the Universe to date, using the power of Hubble to explore more distant regions of space than could otherwise be seen, by observing gravitational lensing effects around six different galaxy clusters.
Gravitational lensing is a phenomenon caused by an object's influence on the space-time around it. Massive objects like galaxy clusters warp and distort this space-time. This causes light from more distant objects hidden behind this makeshift lens to be deflected and bent, leading to a bizarre array of optical effects — for example, it caused a cosmic space invader to appear around cluster Abell 68 (heic1304) by creating mirror images of one galaxy, as well as smearing galaxies out into arcs, and creating multiple images of individual objects.
Hubble Space Telescope
As well as creating these weird shapes, lensing also magnifies the images so that astronomers can see more detail. This means that distant objects that otherwise would be too distant and faint to be seen become visible — something that Frontier Fields aims to exploit over the coming years.
Some results from this programme are already starting to emerge, with Abell 2744 as the first target. In a new paper submitted to The Astrophysical Journal on 29 November 2013 (available on the ArXiv Preprint Server), a group of astronomers detected a large number of distant, gravitationally lensed galaxy candidates — all viewed through Abell 2744, with the galaxy cluster acting as a lens. They also found that five of these candidates are part of distant systems that appear to have been imaged multiple times due to the cluster's gravitational lensing effects. These deep surveys using massive galaxy clusters like Abell 2744 show that looking through cosmic lenses can be an effective and useful way to study the distant Universe. For more information on gravitational lensing see Hubblecast 70: Peering around cosmic corners.
This image is part of the first set of super-deep views of the Universe obtained by the Frontier Fields observing program, and is being released today, 7 January 2014, at the 223rd meeting of the American Astronomical Society in Washington, DC, USA.
A typical Hubble observing programme lasts from a few to a few tens of orbits.
All objects that have mass affect the space around them in this way, but huge clumps of mass like galaxy clusters do so more strongly.
Notes for editors:
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
ESA/Hubble Science Announcement: Start of Hubble Frontier Fields observations: http://www.spacetelescope.org/forscientists/announcements/sci13006/
ArXiv Preprint Server: http://arxiv.org/abs/1311.7670
Hubblecast 70: Peering around cosmic corners: http://www.spacetelescope.org/videos/hubblecast70a/
ESA Hubble site: http://www.spacetelescope.org/
Image, Text, Credits: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI). | 0.890069 | 3.949592 |
First, how much energy does blowing a planet up require?
What holds a planet together is gravity, and the gravitational binding energy of Earth is about 2.5 * 10^32 J. So an approximation, that's how much energy you need to turn the Earth into a bunch of debris. Of course, lighter planets like Mars require less energy, and a super-Earth requires more, at those scales, it won't make that much of a difference anyway.
There will also be losses, so let's round this up to 10^33 J. That's about the total energy output of the Sun in a month. Putting so much energy in a 1-second laser is going to be a problem, though not a physically impossible one.
When you want the biggest, baddest laser possible, the obvious solution is a Nicoll-Dyson beam - that is, a Dyson sphere acting as a giant laser emitter. Using short enough wavelengths, it can very well strike planetary-sized (or even smaller) targets. Problem is, it would need to store energy for a long time - for example, making a few trillion tons of antimatter - and then release it all in one second to generate the laser. Or they could a giant interstellar energy network in order to power a laser emitter. One option is to use the central galactic black hole as an power source (by throwing stuff into it) and interstellar gas clouds as maser transmitter.
Note that the emitter or transmitter will most likely be destroyed by the heat losses. Even if those are very small, a small percentage of apocalyptic energies is still a lot.
Anyway, we have our laser emitter, and it fires a 1-second long beam of 10^33 J at the planet. Then, weird things happen. The details would require simulations, but we can figure out the main effects.
When so much energy hit the atmosphere, it will instantly turn into plasma. If air is transparent to this wavelength (like, say, visible light), enough will hit the ground in the first millisecond to hit it with the force of countless nuclear weapons, but in any case the entire local atmosphere will turn into plasma and thus most of the second-long beam will be absorbed by what was formerly known as the upper atmosphere.
Air will also undergo nuclear fusion, which would add a bit more energy, which may or may not be negligible compared to the laser energy. There will even be some matter-antimatter pair production. This means that whatever the initial wavelength, some X- and gamma rays will be sprayed around, including back to space.
Plasma is opaque, and the laser would more or less be entirely absorbed by it before hitting the surface. That's similar to a nuclear fireball where most of the X-rays are more or less instantly stopped by the atmosphere, which then carry the energy as a giant fireball.
The plasma fireball will then do three things: it will reflect some of the laser back to space, it will expand as a shock-wave and it will radiate energy back all around. The planet is concerned by the last two.
The light will be strong enough to turn even more atmosphere into plasma, as well as a big chunk of the ground. Further away, it will be strong enough to instantly vaporise anything it lights. So expect the continent that is hit to instantly be caught into the plasma ball, and the hemisphere to be flash-vaporised by the fast-expanding plasma ball.
Due to the slight lens effect and the scattering of the atmosphere, the other hemisphere would also be exposed to the light. I would expect everything at the surface to also be instantly be burned, though the antipodean point my be slightly better off. Underground bunkers may also survive, if the detonation of the entire surface flash-vaporising doesn't compress them too much.
So yeah, a million voices suddenly cry out in terror and are suddenly silenced. And many more don't even have time to cry out.
Then, the fireball expands, and causes a giant shock-wave. At those scales, a planet acts like a big blob of liquid (hence its round shape), so it will look like a giant tsunami, but where the crust and upper mantle is making the wave instead of simply the ocean. The shock-wave is also travelling through the interior of the planet, so it will reach the other side before the surface wave. Doing so will cause earthquakes and volcanoes, in a sense that the Halifax explosion made a noise. That is, the crust will break apart and the mantle splash around. I would expect that to take around a few minutes, ten or twenty minutes at most.
This is also the point where the planet starts breaking apart, a bit like a big water drop being hit very hard. It fragments in gobs of varied sizes and shapes, from dust grains to, possibly, some as big as the Moon or Mars. Once settled, the big ones will settled back in round shapes.
Almost all of them are extremely hot, and will stay hot for a long time. Asteroid-sized ones will take years or centuries, the biggest ones may take millions of years to stop glowing - you can look at the history of our planets for details there.
In addition to the atmosphere and hydrosphere being blown to space, a chunk of the planet has been vaporised, and is also blown to space at great speed. In addition, the mantle and core were under tremendous pressure, which is suddenly released. This will make them splash back and/or vaporise with a vengeance. All this will cause the rest of the planet to be pushed in the other direction, as if the planet was a big laser-thermal rocket.
The fragments will, for the most part, still end up in a solar orbit. The push would have been enough to make the orbit vary a bit if they all stayed the same (the details of the new orbit depending on which side of the planet was hit). However, the fragments will not all stay in a roughly Earth-like orbit. Some will have been violently ejected by the energy of the laser, or by how the shock-waves interacted. Other will be destabilised by gravitational interaction with the other fragments.
Starting a few centuries or millennia down the line, and possibly lasting millions of years, the other planets of the system can expect nasty meteoric impacts, some very fast and some very big. Not enough to break another planet apart, but enough to definitely ruin most planetary surfaces at some point.
But even before that, those planets have other problems.
Anything not in the shadow of the planet will have been exposed to the light of the laser being scattered at impact. This scatter, for one second, is emitting as much energy as about a million times the Sun.
If there is something like the Moon and it was in the shadow of the planet, it will take a fair amount of debris in the face, probably breaking bits of it and sending them flying as well. The entire surface is, of course, turned upside-down into a lava ocean.
If this Moon is exposed to the flash, the exposed hemisphere literally explodes into plasma. The vaporised plasma pushes it in the other direction and send it in a slightly more different orbit than the debris. The shock-waves will turn the other hemisphere upside-down as well, and debris will bombard it for a long time, probably starting the following years if not sooner. Again, bits may be sent flying.
The exposed hemispheres of more distant planets will be burned to a crisp, as if by a close nuclear explosion. Atmospheres will be partially blown away. Ice surfaces will explode into steam, some of which may keep around as atmosphere. Surfaces may be vitrified. On the non-exposed hemispheres, all this may also cause earthquakes. The details depend heavily on the planet type and its distance from impact.
There won't be much effect on the local star(s), though weather patterns may be affected in weird ways. Maybe there will be more solar flares in the future, though at that point, few would probably care.
Exposed neighbour star systems will see the flash easily. At a million times the intensity of the Sun, assume a visible wavelength for the laser, anyone looking at the sky will have a hard time missing it, even for a one-second flash. It will be as bright as a thin Moon crescent, but concentrated in a single point, and with a distinct colour.
With access to modern astronomical instruments, probably half the galaxy can see it (by the time the flash arrives, obviously), and possibly neighbouring galaxies as well if they're lucky. Between a very distinct signature and the probably hard-to-miss stellar engineering next to it, it won't take long for them to guess what it was.
Special mention for the Death Star:
Star Wars is apparently taking place in an universe with different physical laws than ours. There is pressure in the vacuum (hence walking on an asteroid with only oxygen masks, flying around as if in atmosphere, space fireballs when things explode...) Flying requires very little energy (no visible radiators or incinerating exhausts). Planets may be smaller, and stars are. Asteroid fields are much, much denser. Star systems are closer together.
In this case, planets are probably much easier to blow up, and their debris cool down near-instantly afterwards. | 0.932326 | 3.681512 |
Notre Dame physics professor instrumental in developing program
Before NASA’s Kepler space telescope was retired October 30, it captured the onset of a supernova, an exploding star in the constellation of Cancer. The data it collected from this nearest and brightest supernova, combined with data from ground-based satellites, resulted from an experiment first proposed by Notre Dame physicist Peter Garnavich.
Garnavich, professor and chair of the Department of Physics, is a co-author on three papers published by NASA on Friday (Nov. 30) about the research. The 130 scientists involved attempted to explain the unusual data revealed during the explosion of the supernova, SN 2018oh. It exploded 170 million years ago in the spiral galaxy UGC 4780, and was detected by the satellite on February 4, 2018. Ten days after Kepler detected the explosion, it was also discovered by the ground-based All-Sky Automated Survey for Supernovae. Soon observatories around the world were monitoring the supernova as part of the Kepler Supernova Experiment, which Garnavich developed to help solve the mystery of how stars explode.
He was the first to propose the use of the Kepler satellite to study supernovae. However, the first two years yielded no discoveries. Instead, astronomers at the University of Maryland found some odd light variations while studying the cores of galaxies, and these became the first crop of supernovae discovered by Kepler. “It was a crazy idea, so I was surprised when NASA approved my early proposals,” Garnavich said. “But by the end of the mission, the search for explosions became a major science driver for the mission.”
Garnavich and others formed the Kepler Extra-Galactic Survey to facilitate the search for explosions outside the Milky Way galaxy. Other leaders of the group include Armin Rest, of the Space Telescope Science Institute in Baltimore, and Bradley Tucker, of the Australian National University, who earned his undergraduate degree in physics from Notre Dame.
NASA retired the Kepler space telescope after nearly 10 years of operation on October 30, following the exhaustion of fuel supplies. But from December 2017 to May 2018, while there was still fuel left, the Kepler team oriented the spacecraft toward two distinct patches of sky that were simultaneously observable from Earth by ground-based observatories. The telescopes were able to view both patches of sky teeming with galaxies. Each of these thousands of galaxies has billions of stars.
SN 2018oh is an example of a Type Ia supernova — the kind that astronomers use to track the expansion of the universe and probe the nature of the invisible “dark energy” that glues together the cosmos. A typical Type Ia supernova brightens over the course of three weeks before gradually fading away. But Kepler observed this particular supernova brightening rapidly a few days after the initial explosion — about three times faster than a typical supernova at this time period — before reaching peak brightness. Meanwhile, color details obtained by the Dark Energy Camera at Cerro Tololo Inter-American Observatory in Chile, and the Panoramic Survey Telescope and Rapid Response System at Haleakala Observatory in Hawaii, showed this supernova gleaming blue during this period of intensity, an indication of high temperatures.
For nearly a decade, scientists have been in search of a signal of a supernova similar to this one. Until Kepler, it was impossible to get an uninterrupted observations of the early stages of Type Ia supernovae.
In addition to Garnavich, the authors of these papers include scientists from dozens of institutions. Additional observatories providing valuable data to support the experiment include the All-Sky Automated Survey for Supernovae, a global network of telescopes managed by Las Cumbres Observatory in Goleta, California and headquartered at Ohio State University; Tsinghua-NAOC and Lijiang Telescopes in China; Konkoly Observatory in Hungary; Lick Observatory in Mount Hamilton, California; Las Campanas Observatory in Chile, and others.
NASA's Ames Research Center in California’s Silicon Valley manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.
Peter Garnavich and Deanna Csomo McCoolcontributed to this article. | 0.881178 | 3.713792 |
Astronomers announced last week the discoveries of the first two potential planets detected by NASA’s Transiting Exoplanet Survey Satellite (TESS), a new exoplanet-hunting telescope that launched earlier this year.
The two exoplanet candidates—called Pi Mensae c and LHS 3844 b—have many similarities. Each is slightly larger than Earth, orbits its star in a very short time, is much too hot to support life, and circles a southern hemisphere star that lies less than 60 light-years from Earth.
“It is rewarding to see years of work that the team—engineers, scientists, and support staff—poured into the dream of [TESS] become the reality of discovered planets,” Patricia Boyd, head of TESS’s Guest Investigator Program, said on Twitter.
Over its 2-year mission, scientists expect TESS to discover more than 20,000 new exoplanets, hundreds of which will likely be Earth sized. One coauthor of the Pi Mensae c discovery expressed excitement that TESS’s first discoveries exceed scientists’ expectations:
Our Pi Mensae c paper is out! Love that TESS’ first result is about a planet orbiting a naked eye star – our predictions that TESS would let you look up at the night sky and point to a star *knowing* that it has a planet came true SO MUCH FASTER than I anticipated 🙂 https://t.co/qpyw8WCChv
— Jennifer Burt (@astrojennb) September 19, 2018
“This is just the beginning,” Boyd said. “We can’t wait to see what’s next.”
Planets Across the Sky
NASA launched TESS on 18 April 2018, and the telescope began its science operations on 25 July. Like its predecessor, the Kepler Space Telescope, TESS looks for signs that a planet transits its host star, temporarily and repeatedly blocking a small fraction of the star’s light from the telescope’s gaze.
The video below explains how TESS will scan nearly the entire sky for exoplanets and what types of planets it will discover.
A Southern Sky Super-Earth
TESS’s first potential exoplanet is Pi Mensae c, which astronomers estimated to be approximately twice the size and 4.5 times the mass of Earth. This planet orbits a star that is only slightly more massive and hotter than the Sun and is a mere 60 light-years away. A planet 10 times the mass of Jupiter, Pi Mensae b, was already known to orbit this star.
The super-Earth planet orbits its star in about 6.3 days, which translates to an orbital distance of about 7% of the separation between Earth and the Sun. Given Pi Mensae c’s close proximity to its star, the researchers estimate that the temperature on the surface of the planet would be a scorching 897°C.
This discovery was announced in a preprint of a paper submitted to the Astrophysical Journal Letters on 16 September. A second team independently announced the same exoplanet in a preprint paper a few days later.
The independent findings came as good news to the exoplanet community:
WEEE! First @NASA_TESS @TESSatMIT planet! Congrats all authors! “The pi Men system has already been generous to the exoplanet community, and with a little luck, the gifts will keep arriving.” https://t.co/GEaLFvzDZu
— Johanna (@johannateske) September 18, 2018
A Red Dwarf Satellite
The second announced exoplanet candidate, LHS 3844 b, is a 1.32-Earth-radius planet that orbits a cool red dwarf star also in the southern sky. The star is about 19% the size and 15% the mass of the Sun and is about half as hot.
Despite LHS 3844 b’s orbital period of 11 hours, the dim red star places the planet’s surface temperature at 532°C. Red dwarf stars are the most common type of star in the galaxy and also will be the most common type of star that TESS will monitor. This exoplanet was announced in a preprint of a paper submitted to the Astrophysical Journal Letters on 19 September.
At only 49 light-years away, LHS 3488 b is one of the closest known exoplanets:
— David Charbonneau (@ExoCharbonneau) September 20, 2018
First Two of Many
Each team cross-checked its TESS discovery using transit observations from ground-based telescopes and also gathered spectroscopic observations of the stars to measure the planets’ mass. The exoplanet candidates must be validated through peer review before becoming confirmed detections.
Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate, called TESS’s first two discoveries “exciting” and said on Twitter that these “will be the first of many planet candidates discovered by the spacecraft. Over the next few years, it will continue to search new parts of the sky for worlds that orbit stars outside our solar system.”
These two planets were detected using the first round of preliminary science data from TESS, which were made available to scientists on 5 September. These data have not yet been peer reviewed or vetted to remove false-positive signals that might mimic that of a planet.
The discovery teams noted that the exoplanets’ close proximity to their host stars mean that neither is likely to have an atmosphere. However, each planet is an ideal target for future observations, for example, with the oft-delayed James Webb Space Telescope, that may seek to uncover any traces of atmosphere that may exist.
“The team is excited about what TESS might discover next,” TESS deputy director of science Sara Seager said via Twitter. “We do know that planets are out there, littering the night sky, just waiting to be found.”
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer | 0.829347 | 3.480771 |
Solar-mass stars form via disk-mediated accretion. Recent findings indicate that this process is probably episodic in the form of accretion bursts1, possibly caused by disk fragmentation2,3,4. Although it cannot be ruled out that high-mass young stellar objects arise from the coalescence of their low-mass brethren5, the latest results suggest that they more likely form via disks6,7,8,9. It follows that disk-mediated accretion bursts should occur10,11. Here we report on the discovery of the first disk-mediated accretion burst from a roughly twenty-solar-mass high-mass young stellar object12. Our near-infrared images show the brightening of the central source and its outflow cavities. Near-infrared spectroscopy reveals emission lines typical for accretion bursts in low-mass protostars, but orders of magnitude more luminous. Moreover, the released energy and the inferred mass-accretion rate are also orders of magnitude larger. Our results identify disk-accretion as the common mechanism of star formation across the entire stellar mass spectrum.
S255IR NIRS 3 (aka S255IR-SMA1) is a well-studied ∼20 M⊙ (Lbol ∼ 2.4 × 104 L⊙) high-mass young stellar object (HMYSO)13,14 in the S255IR massive star-forming region13, located at a distance of ∼1.8 kpc15. It exhibits a disk-like rotating structure13, very likely an accretion disk, viewed nearly edge-on16 (inclination angle ∼80°). A molecular outflow has been detected13 (blueshifted lobe position angle (P.A.) ∼247°) perpendicular to the disk. Two bipolar lobes (cavities), cleared by the outflow, are illuminated by the central source and show up as reflection nebulae towards the southwest (blueshifted lobe) and northeast (redshifted lobe, see Fig. 1, left panel). At ∼25 west of NIRS 3, another HMYSO, NIRS 1 (aka S255IR-SMA2; M∗ ∼ 8 M⊙; ref. 14), is also seen in the near infrared.
Following the detection of a 6.7 GHz class II methanol maser flare in the S255IR star-forming region17, we performed near-infrared imaging with the Panoramic Near Infrared Camera (PANIC) at the Calar Alto Observatory in November 2015 (see Methods), to check whether the flare was triggered by an accretion burst from one of the massive protostars in the region12. Indeed, infrared radiation from heated dust emitting at ∼20–30 μm is thought to be the pumping mechanism of this maser transition18.
Our images in the H (1.65 μm) and Ks (2.16 μm) bands reveal an increase in the infrared brightness (burst) of S255IR NIRS 3, by ΔH ∼ 3.5 mag and ΔK ∼ 2.5 mag with respect to the latest archival images taken with the UKIRT Infrared Deep Sky Survey (UKIDSS) in December 2009 (see Fig. 1, upper left and upper right panels). Moreover, a substantial increase in brightness is also observed in the bipolar outflow cavities, which scatter the light from the central accreting source. These findings provide evidence of an accretion burst onto the HMYSO. The lower left panel of Fig. 1 shows the brightness ratio between the first PANIC Ks-band image and the UKIDSS K-band frame (see Methods). The relative brightness distribution exhibits a bipolar appearance. In principle, this effect could be the result of enhanced scattering in the outflow lobes or extinction variability. However, the former would require an increase in the number density of grains by an order of magnitude, which is impossible to obtain within the short time between the UKIDSS and PANIC images. Extinction variability is also excluded by our multi-wavelength observations, which include near-, mid- and far-infrared spectroscopy and imaging (see Methods). Therefore, the only explanation for this phenomenon is that we are observing the light from the burst scattered by the dust in the outflow cavities (the so-called light echo). Indeed, subsequent PANIC imaging confirms this hypothesis by verifying the motion of the light echo, between November 2015 and February 2016 (see Fig. 1, lower right panel), as it moves away from the source. This discovery allows us to approximately date the onset of the burst to around mid-June 2015 (see Methods). Remarkably, this is the first light echo ever observed from the outburst of a high-mass young star.
The SINFONI/VLT K-band spectrum of NIRS 3 (see Fig. 2, left panel, black spectrum), obtained on the 26th of February 2016, shows a very red and almost featureless continuum, much brighter than that observed with the same instrument in the quiescent phase in 200714 (see Fig. 2, left panel, red spectrum). Notably, no photospheric features in absorption are detected. The lack of prominent features and the extremely reddened continuum are probably due to: the strong veiling, caused by the accretion; the high visual extinction (AV = 44 ± 16 mag, see Methods), resulting from the large inclination of the circumstellar disk to our line of sight; and the presence of a thick envelope surrounding the HMYSO.
In contrast, K-band integral field spectroscopy of the redshifted lobe (the brightest outflow cavity, see Fig. 1), performed with SINFONI/VLT (March 2016) and NIFS/Gemini (April 2016), reveals a wealth of spectral features from the burst (see Fig. 2, right panel, black spectrum). Indeed, the visual extinction towards the lobes (AV ∼ 18 ± 5 mag and 28 ± 9 mag, blue- and redshifted lobe, respectively; see Methods) is smaller than that towards the HMYSO itself. The walls of the outflow cavities are acting as a mirror, scattering the light from the outbursting young star and allowing us to peer directly into the central accretion region. The right-hand panel of Fig. 2 compares our NIFS/Gemini spectrum (in black) of the redshifted outflow lobe with the SINFONI/VLT pre-outburst spectrum14 of the same region (red spectrum). The new spectrum shows an increase in luminosity for both the continuum and lines (H2, Brγ), as well as the appearance of new emission lines, namely CO band-heads, Na I, He I, which are typically observed in young eruptive low-mass stars (EXors, FUors and MNors1,19,20,21,22,23) and are the typical signature of accretion disks, accretion and ejection activity.
Young eruptive low-mass stars (M∗ ≲ 2 M⊙) of these groups produce accretion bursts lasting from a few weeks up to decades, and with accretion luminosities up to thousands of solar luminosities1. During the burst, the mass-accretion rate () usually increases from one (EXors) to several (MNors, FUors) orders of magnitude with respect to quiescence1,23. CO band-heads and Na I lines originate from the outer layer of the disk (within 1 a.u. from the central source in low-mass YSOs). The inner disk atmosphere is heated up to temperatures of a few thousand kelvin (2,000–4,000 K) by the accretion burst1 and these lines show up in emission. In contrast, both He I and Brγ lines are emitted closer to the central source (≲0.1 a.u.) and may originate from accretion onto the star and/or from disk winds20.
The total luminosities of the Brγ (2.2 L⊙), He I (1.2 L⊙), Na I (0.7 L⊙) and COv=2−0 (22 L⊙) lines during the burst of NIRS 3 are from three to four orders of magnitude larger than those observed in EXors and MNors. Drawing a parallel between high-mass and low-mass YSOs, this evidence suggests that the size of the disk emitting region as well as the energy released by the burst are much larger in the present case. Indeed, the luminosity derived from the spectral energy distribution (SED) of NIRS 3 (see Fig. 3) grows from (2.9 ± 0.71) × 104 L⊙ (blue data points) to (1.6 ± 0.30.4) × 105 L⊙ (red data points) during the burst (PANIC, GROND, VLT/SINFONI, SOFIA/FORCAST and FIFI-LS data), corresponding to an increase in accretion luminosity (ΔLacc) of (1.3 ± 0.30.4) × 105 L⊙ and an energy release of (1.2 ± 0.4) × 1046 erg from the beginning of the burst until mid-April 2016 (∼9 months, according to our latest observations), when the source was still in burst. This latter amounts to an accreted mass of about two Jupiter masses (namely ∼3.4 × 10−3 M⊙, see Methods). The derived quantities are about four orders of magnitude larger than what is found in EXors and MNors, making this the most luminous accretion burst ever detected in a YSO. Moreover, assuming that the mass of the central source is ∼20 M⊙ and its radius is equal to 10 R⊙ (approximately the radius of a ∼20 M⊙ star on the zero-age main sequence), from ΔLacc we infer that is boosted to (5 ± 2) × 10−3 M⊙ yr−1 (see Methods). The inferred value is probably a lower limit, as the radius of a massive protostar should be several times larger than that of a main sequence star24,25. Nevertheless, the inferred mass-accretion rate of this HMYSO burst is at least three orders of magnitude higher than those of EXors and MNors.
The accretion burst discovered in S255IR NIRS 3 adds fundamental information to our understanding of the high-mass star formation process. Our observations finally confirm that HMYSOs form through accretion disks at high mass-accretion rates. Moreover, they also provide an observational proof of episodic accretion, possibly originating from disk fragmentation. Here, the timescale and energetics of the outburst are more consistent with disk fragmentation rather than stellar merger26 (see Methods).
In this respect, high-mass star formation can be considered as a scaled up version of the process by which low-mass stars are born. The main differences are that massive stars would form through larger accretion disks with much higher mass-accretion rates (≥10−4 M⊙ yr−1), and on shorter timescales.
High mass-accretion rates and the presence of an accretion disk are fundamental ingredients to circumvent the intense radiation pressure of the massive star, which otherwise might reduce, and even halt accretion. They allow further accretion to proceed even after the hydrogen burning starts7. At variance with low-mass protostars, the timescale for gravitational contraction (Kelvin–Helmholtz time) is shorter than the timescale for accretion in HMYSOs, producing a strong radiation field25. The circumstellar disk reduces the radiation pressure, allowing most of the radiation to escape through the bipolar cavities27. Indeed the light echo and the increase in brightness of the outflow cavities in NIRS 3 confirm this picture.
Finally, as with low-mass protostars, the accretion process would not be continuous but episodic. This would also explain the observation of several knots in jets from HMYSOs28, assuming major outflows events can be linked to major accretion events. Indeed, the morphology of different gas tracers along the outflow axis of NIRS 3, which shows a discrete number of knots, suggests that the source experienced multiple bursts within the past few thousand years13,14,15. Our burst detection proves the erratic behaviour of the accretion process in HMYSOs. Indeed, several radiation hydrodynamic simulations predict the onset of accretion variability in high-mass star formation6,7,11. Notably, episodic accretion might also play an important role in regulating the ionizing radiation, bloating the central source, and prolonging the accretion time during the Ultra-Compact H ii (UCH ii) phase29.
Infrared imaging of the burst.
Near-infrared imaging at various epochs was performed with PANIC30 at the Calar Alto 2.2-m telescope and the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND)31 at the La Silla 2.2-m telescope. Basic image processing was performed by the instrument teams using the corresponding data pipelines. The photometric calibration was done using the Two Micron All Sky Survey (2MASS) catalogue32. Although short detector integration times were applied for the Ks band, partial saturation of the bright target and field stars of similar brightness was unavoidable, in particular under good seeing conditions (our typical seeing was ≲1′′). This was accounted for by a continuous extension of the linear fit between catalogue and instrumental magnitudes with a parabola for the brightest objects. Flux densities for NIRS 3 were generally derived using the APER procedure from the IDL Astronomy Library33, taking the local background into account. Mid- and far-infrared flux densities were obtained by performing target-of-opportunity observations with FORCAST34 and FIFI-LS35,36 aboard SOFIA (principal investigator J. Eislöffel, proposal ID 04_0047). FORCAST images were taken using narrow-band filters centred at 7.7, 11.1, 19.7, 31.5 and 37.1 μm. The spectral windows for FIFI-LS were chosen to match the central wavelengths of the far-infrared AKARI filters—that is, 60, 90, 140 and 160 μm. The FIFI-LS spectral data cubes, calibrated by a FIFI-LS team member (C. F.), were collapsed and photometry was performed on themean image.
To cancel the influence of non-uniform extinction for the assessment of the change of the scattered light distribution due to the burst, and to compensate the decreasing surface brightness with growing distance from the source, a ratio image between PANIC Ks and UKIDSS K frames was calculated. Before doing so, the PSFs of the K frame was convolved with a proper kernel to match that of the Ks frame. The applied photometric scaling factor was derived from the corresponding zero points of the images. This turned out to be correct, since the brightness ratio for field stars is of the order of unity. The resulting distribution has an asymmetric bipolar morphology. The asymmetry results from the inclination of the scattering cavities relative to the sky plane, leading to larger light distances for the blueshifted lobe for a given propagation period and vice versa.
The surfaces of scattered light of fixed travel time can be approximated as paraboloids with the star at the origin. Thereby, it can be shown that, at the onset of an outburst (t = 0), the size ratio between the back- and forward-scattering lobes is zero and increases to unity over time. Thus, an approximately equal extent of the scattering lobes of a YSO seen close to edge-on is expected only for steady-state illumination. Moreover, for the purpose of judging the lobe sizes, it must also be taken into account that forward scattering dominates in the blueshifted lobe, whereas backward scattering is prevalent in the redshifted lobe. Because of the different scattering efficiencies, the redshifted lobe will be less bright in general, and thus appear smaller for a given surface brightness sensitivity.
The same analysis on a later PANIC Ks image (February 2016) confirms the light echo by verifying both its propagation and dilution. For deriving the onset of the burst (mid-June 2015) we estimated the light travel time derived from the mean of the extent of both lobes.
Spectral energy distribution.
As the energy released by the burst is thermalized by dust grains and radiated away in the infrared, pre-burst fluxes in this wavelength range are crucial for deriving the increase in luminosity. For this purpose, pre-outburst non-saturated IRAC images of S255IR (taken in sub-array mode, courtesy of G. Fazio, program ID 40440) were retrieved from the IPAC infrared science archive. Image mosaics were obtained from the dithered images for each channel using a custom IDL (IDL is a trademark of Exelis Visual Information Solutions) procedure. Flux densities for NIRS 3 were estimated as described above. Similarly, flux densities for the N60 and N160 AKARI bands were derived from the corresponding images after retrieval from the ISAS/JAXA archive (the wide AKARI channels centred at 90 and 140 μm are saturated). These data were complemented with an archival ISO/SWS spectrum (courtesy D. Whittet), H and Ks VLT/ISAAC photometry (private communication by S. Correia, ESO proposal ID 074.C-0772(B)) as well as flux densities from the literature13,14,37,38,39 and surveys (AKARI, BGPS, MSX, UKIDSS). The outburst SED was obtained using data from PANIC, GROND, SINFONI, FORCAST and FIFI-LS taken in February 2016. The pre- and burst luminosities were derived by integrating the dereddened SEDs and assuming a distance of 1.8 ± 0.1 kpc. To deredden the SED we adopt our visual extinction AV = 44 ± 16 mag and RV = 3.1 extinction law40. The resulting pre- and outburst luminosities are (2.9 ± 0.71) × 104 L⊙ and (1.6 ± 0.30.4) × 105 L⊙, respectively. The uncertainties were inferred from the small distance error and the uncertainty on the visual extinction. We also note that because of the close to edge-on view of its circumstellar disk, the estimated luminosity might represent a lower limit. The proper value may be up to two times higher41.
Infrared integral field unit spectroscopy.
Our K-band (1.95–2.5 μm) integral field unit (IFU) spectroscopic data of S255IR NIRS 3 consist of three data sets taken with SINFONI42 on VLT (ESO, Chile) with R ∼ 4,000 and NIFS43 on the Gemini North telescope with R ∼ 5,300. Adaptive-optics-assisted mode was used for all runs. The first SINFONI data set (26 February 2016) was centred on NIRS 3 (25 milliarcseconds (mas) pixel scale and field of view - FoV - of 0.8′′ × 0.8′′). The second SINFONI data set (9 March 2016) was taken with the lowest spatial sampling (250 mas pixel scale and FoV of 8′′ × 8′′) and maps an area of ∼11′′ × 11′′ around NIRS 3, covering NIRS 3, NIRS 1 and their outflow cavities. NIFS data (100 mas pixel scale and FoV of 3′′ × 3′′) were collected on the 8 April 2016 and map the redshifted outflow cavity covering an area of ∼6′′ × 6′′.
SINFONI data were reduced with the standard reduction pipeline in GASGANO44, which includes dark and bad pixel removal, flat-field and optical distortion correction, wavelength calibration with arc lamps, and image combination to obtain the final 3D data cube. NIFS data reduction was accomplished in a similar fashion using the Gemini package in IRAF.
All data were corrected for atmospheric transmission and flux calibrated by means of standard stars.
SINFONI pre-outburst IFU spectra, taken between February and March 2007, were retrieved from the ESO Data Archive and have already been published in a previous paper14. They map an area (70′′ × 70′′) larger than our observations. To compare pre- and outburst data, spectra were extracted from our data cubes within an area of 1.5′′ × 1.5′′ (centred on NIRS 3 source; RA(J2000) : 6h12m54.0s; DEC(J2000) : +17°59′23.1′′) and 6′′ × 6′′ (centred on RA(J200) : 6h12m54.4s; DEC(J2000) : +17°59′24.7 ′′) for NIRS 3 (Fig. 2, left panel) and the redshifted outflow cavity (Fig. 2, right panel), respectively.
Visual extinction variability versus accretion burst.
In principle, large variations of the extinction towards NIRS 3 could be a possible cause of the infrared variability of NIRS 3. However, this argument does not fit our observations for the following reasons.
First, the increase in luminosity is detected at NIR, MIR and FIR wavelengths. This implies that the variation in luminosity cannot be due to a change in visual extinction, which would indeed affect the NIR part of the SED but would just marginally affect the MIR part of the spectrum and would not affect its FIR portion. Second, the increase in luminosity at infrared wavelengths temporally matches the flares of the methanol masers in the radio. Moreover the maser positions match that of NIRS 3 (Sanna et al., in preparation). Third, in addition, the light echo observed at NIR wavelengths matches the timing of the CH3OH maser flares. Fourth, the increase in the SED luminosity matches the appearance (CO, He I, Na I, lines) and increase in luminosity (Brγ, H2) of the infrared lines. Fifth, visual extinction affects the intensity of both lines and continuum as well as the continuum’s colour. As the extinction affects both lines and continuum to the same extent, the equivalent width (EW) of the lines should not change. On the other hand, EWs and fluxes of Brγ and H2 lines, already present in the pre-outburst spectrum in the outflow cavity, show a large variability and are anti-correlated, as expected in accretion events45. This cannot be explained with extinction variability. Moreover, the slope of the K-band spectra on source and outflow cavities does not show a significant change before and during the outburst—that is, we do not detect any blueing of the spectra in 2016. Finally, as reported in the next subsection, the visual extinction towards the outflow cavities does not change significantly.
Therefore we infer that the visual extinction did not change significantly between 2007 and 2016.
Visual extinction towards the outflow cavities and on-source.
To estimate the visual extinction towards both blue and redshifted lobes, we use pairs of lines from [FeII] (2.016/2.254 μm) and H2 (2.034/2.437 μm, 2.122/2.424 μm, 2.223/2.413 μm) species that originate from the same upper level. We detect shocked emission lines ([FeII] and H2) in two knots positioned in the blue- and redshifted lobes, respectively. Assuming that the emission arises from optically thin gas, the observed line ratios depend only on the differential extinction. The theoretical values are derived from the Einstein coefficients46 and frequencies of the transitions. We adopt the Rieke & Lebofsky47 extinction law to correct for the differential extinction and compute AV. Values inferred are AV = 18 ± 5 mag (AV([FeII]) = 16 ± 10 mag and AV(H2) = 19 ± 5 mag) for the blueshifted lobe and AV = 28 ± 9 mag (AV([FeII]) = 27 ± 14 mag and AV(H2) = 29 ± 12 mag) for the redshifted lobe. Similar values, but with larger uncertainties, are inferred from the pre-outburst spectra (2007) of the blueshifted (AV(H2) = 18 ± 7 mag) and redshifted (AV(H2) = 27 ± 15 mag) outflow cavities. These latter measurements suggest that the visual extinction towards the lobes did not change significantly.
We also infer the visual extinction towards NIRS 3 from the H2 lines detected in the outburst spectrum (Fig. 2, left panel), obtaining AV(H2) = 44 ± 16 mag. The inferred value is consistent with AV = 46 mag from Simpson and colleagues39. Finally, from the pre-outburst J − H and H − K colours of the UKIDSS photometry, we obtain AV ∼ 48–62 mag by assuming that NIRS 3 is a O6 spectral type positioned on the ZAMS. This latter is consistent with our previous estimate. Therefore we adopt AV(H2) = 44 ± 16 mag towards the source and use this value to deredden the SED.
The line luminosities in the redshifted lobe were inferred from the dereddened line fluxes using AV = 28 ± 9 mag and assuming a distance to the object of 1.8 ± 0.1 kpc15.
Energy of burst, accreted mass and mass-accretion rate.
The burst energy (E = ΔLacc × Δt, where Δt is the length of the burst) delivered so far (until mid-April 2016, the date of the last available observation) by the burst is inferred from ΔLacc = (1.3 ± 0.30.4) × 105 L⊙, obtained from the pre- and outburst SED, and considering that the burst began around mid-June 2015. The accreted mass is inferred assuming that the stellar radius is R∗ = 10 R⊙ and using E = GM∗Macc/R∗, where G is the gravitational constant, M∗ is the mass of the star and Macc is the accreted mass. Finally, the mass-accretion rate is obtained from .
Disk-accretion by fragmentation versus merging.
A conceptual question involves whether our observations can rule out the possibility that what we are seeing is not disk fragmentation but stellar capture and merger via tidal disruption26. This scenario proposes that massive stars build up by capturing other stars in disks, then tidally disrupting them. However, both timescales and energetics of the outburst of S255 NIRS 3 seem to be inconsistent with such a scenario. For example, assuming that the mass of the central object is ∼20 M⊙, the merger with a brown dwarf of 0.1 M⊙ would produce an energy of ∼5 × 1047 erg released in ∼104 yr. These values are much larger than what we inferred from the outburst of NIRS 3.
The data sets generated and analysed during the current study are not publicly available due to a proprietary period restriction of 12 months. After this period ESO/SINFONI and GROND data will become publicly available from the European Southern Observatory science archive (http://archive.eso.org/eso/eso_archive_main.html) under programs ID 296.C-5037(A) and 096.A-9099(A); Gemini/NIFS data from the Gemini Observatory archive (https://archive.gemini.edu/searchform) under program ID GN-2016A-DD-5; SOFIA/FORCAST and FIFI-LS data from the SOFIA science archive (https://dcs.sofia.usra.edu/dataRetrieval/SearchScienceArchiveInfoBasic.jsp) under program ID 04_0047. Upon request the authors will provide all data supporting this study.
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A.C.o.G., R.G.L. and T.P.R. were supported by Science Foundation Ireland, grant 13/ERC/I2907. A.S. was supported by the Deutsche Forschungsgemeinschaft (DFG) Priority Program 1573. We thank the ESO Paranal and Gemini Observatory staff for their support. B.S. thanks Sylvio Klose for helpful discussions concerning the light echo. This research is partly based on observations collected at the VLT (ESO Paranal, Chile) with programme 296.C-5037(A) and at the Gemini Observatory (Program ID GN-2016A-DD-5). Gemini Observatory is operated by the Association of Universities for Research in Astronomy, under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).
The authors declare no competing financial interests.
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Caratti o Garatti, A., Stecklum, B., Garcia Lopez, R. et al. Disk-mediated accretion burst in a high-mass young stellar object. Nature Phys 13, 276–279 (2017). https://doi.org/10.1038/nphys3942
Publications of the Astronomical Society of Japan (2020)
Monthly Notices of the Royal Astronomical Society (2020)
The Astrophysical Journal (2020)
Astronomy & Astrophysics (2020)
Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium
Monthly Notices of the Royal Astronomical Society (2020) | 0.848057 | 4.053647 |
A UC Riverside-led team of astronomers have taken us a step closer to better understand the formation and destruction mechanisms of dust molecules in the distant universe.
The space between stars within galaxies is not empty; it is filled with gas and dust. Dust grains are solid particles with sizes smaller than ~ 1 micron (one millionth of a meter) that absorb energetic ultraviolet and optical photons emitted by stars and other energetic phenomena. They then re-emit them at redder (longer) wavelengths in the infrared. Therefore, the absorption and emission of energy by dust particles modifies our view of galaxies.
An important component of dust in the interstellar medium is organic carbon-based molecules called polycyclic aromatic hydrocarbon (PAH). These molecules are commonly found on Earth in coal, tar, and the exhaust fumes of car engines. These molecules are also thought to have contributed to the origin of life on Earth. In space, PAHs are the most abundant organic molecules and are found in the interstellar medium, reflection nebulae, supernovae remnants, surrounding young and massive stars, and around evolved carbon-rich stars. PAHs play an important role in the physics and chemistry of the interstellar medium by providing surfaces that allow certain molecules to form, such as H2, carrying the electric charge in the interstellar medium, and efficiently heating the gas in regions where ultraviolet starlight is present.
“Despite the ubiquity of PAHs in space, observing them in distant galaxies has been a challenging task,” said Irene Shivaei, a graduate student at UC Riverside, and leader of the study. “A significant part of our knowledge of the properties and amounts of PAHs in other galaxies is limited to the nearby universe.” In the present study astronomers were able to investigate, for the first time, the variations of PAH emissions in distant galaxies with different interstellar medium properties.
The study has been conducted as part of a UC-based survey, the MOSDEF survey, which used the MOSFIRE spectrograph on Keck telescope to observe the emitted visible-light spectra of a large and representative sample of galaxies during the peak-era of star formation activity in the universe. The optical spectra have been used to measure the star-formation rate, chemical abundances, and the properties of ionizing radiation in the interstellar medium of distant galaxies. The authors further incorporated the infrared imaging data from the Spitzer Space Telescope and the Herschel Space Observatory to trace the PAH emission in mid-infrared bands and the thermal dust emission in far-infrared wavelengths.
The study concluded that the emission of PAH molecules is suppressed in low-mass galaxies, which also have lower fraction of metals (for astronomers ‘metals’ are atoms heavier than hydrogen and helium). These results indicate that the PAH molecules are likely to be destroyed in the hostile environment of low-mass and metal-poor galaxies with intense radiation. The authors also found that the PAH emission is relatively weaker in young galaxies compared to older ones, which might be owing to the fact that the PAH molecules are not produced in large quantities in young galaxies. This study take us a step closer to better understand the formation and destruction mechanisms of dust molecules in the distant universe.
The research, which is now published in The Astrophysical Journal, has important implications for the studies of distant galaxies. It shows that the star-formation activity and infrared luminosity per unit of volume in the universe 10 billion years ago is approximately 30% higher than previously measured.
The imminent launch of the James Webb Space Telescope in 2018 will push the boundaries of our knowledge on dust and PAHs in the early universe. Studying the properties of the PAH mid-infrared emission bands in distant universe is of fundamental importance to improving our understanding of the evolution of dust and chemical enrichment in galaxies throughout cosmic time.
The study was published in The Astrophysical Journal.
The research team is comprised of Irene Shivaei and Naveen Reddy (UC Riverside), Alice Shapley (UCLA), Brian Siana (UC Riverside), Mariska Kriek (UC Berkeley), Bahram Mobasher (UC Riverside), Alison L. Coil (UCSD), William R. Freeman (UC Riverside), Ryan L. Sanders (UCLA), Sedona H. Price (UC Berkeley), Mojegan Azadi (UCSD), and Tom Zick(UC Berkeley).
Figure: In this study, astronomers used data from the Keck and Spitzer telescopes to trace the star forming and dusty regions of galaxies at about 10 billion years ago. The picture in the background shows the GOODS field, one of the five regions in the sky that was observed for this study. Credit: Mario De Leo-Winkler and Irene Shivaei with images from the Spitzer Space Telescope, NASA, ESA and the Hubble Heritage Team. | 0.893758 | 4.200006 |
This groundbreaking experiment helped to pave the way for the development of GPS technology. High-tech fused silica from Heraeus made this reflector possible in the first place.
Around 600 million people around the world held their breath in front of the television when Neil Armstrong took his first steps on the lunar surface in July 1969. But after Neil Armstrong and Buzz Aldrin left the moon exactly fifty years ago, the scientific part of the Apollo 11 mission continued. The two astronauts left behind a laser reflector made of Heraeus fused silica, which is still in use today.
Armstrong's "giant leap for mankind" was also a milestone for science: The laser reflector makes it possible to measure the distance between the Earth and the Moon with an accuracy of just a few centimeters.
That’s how it works: A laser beam is directed from the earth to the reflector, which reflects the light precisely to its origin. On Earth, the returning light can be measured, and the distance can be determined by calculating the travel time. The father of this unique experiment – known in scientific circles as Lunar Laser Ranging – is Dr. James Faller. He first developed the idea during his time at Princeton University in the late 1950s.
The moon landing was a quantum leap for science: As far as knowledge about the universe is concerned – but also knowledge about the Earth. The experiment helped scientists to gain essential insights into real-time accuracy that is essential for a space-based GPS system. In order for satellites and ground stations to synchronize, it is necessary to understand the gravitational forces affecting the orbits of the Earth, the Sun, the Moon and space probes.
"Dr. Faller's work was invaluable for the later development of GPS technology," says Dr. Todd Jaeger, former NASA employee and now Global Sales Director of Commercial Optics at Heraeus Conamic in the US. "If the laser reflector experiment had not been selected for Apollo 11, it is doubtful that the development of GPS would have progressed as quickly as before."
The added value of GPS technology for the economy is immeasurable. A recently published study commissioned by the U.S. National Institute of Standards and Technology (NIST)* concludes that 1.4 trillion US dollars have been generated with the Global Positioning System (GPS) since its introduction in 1983 – more than 1000 billion US dollars of this since 2010 alone.
The laser reflector consists of 100 fused silica triple prisms or corner prisms manufactured by Heraeus in Hanau. Originally, the reflector was developed according to NASA requirements in order to remain in operation for ten years. The outcome: On the 50th anniversary of the moon landing, it has far exceeded its expected life span.
One of the main reasons for the reflector's performance is the high-purity and extremely homogeneous fused silica from which Heraeus manufactured the 100 reflectors. High-purity fused silica is one of the few materials that can withstand cosmic rays and extreme temperatures.
No wonder NASA relied on fused silica from Hanau in 1969. The resistant high-tech material is still used today in numerous space projects. For example, in ESA's GAIA space probe, which is currently producing the largest three-dimensional map of our Milky Way.
"In 1962, US President John F. Kennedy based the lunar mission on the pursuit of knowledge and progress. For the last 50 years, the laser reflector has made this vision come true," says Heinz Fabian, Global Head of Heraeus Conamic. "We are proud to have been part of this historic mission."
A globally leading technology group, Heraeus is headquartered in Hanau, Germany. Founded in 1851, it is a family-owned portfolio company which traces its roots back to a pharmacy opened by the family in 1660. Today, Heraeus combines businesses in the environmental, energy, electronics, health, mobility and industrial applications sectors.
In the 2018 financial year, Heraeus generated revenues of €20.3 billion. With approximately 15.000 employees (including staff leasing) in 40 countries, the FORTUNE Global 500-listed company holds a leading position in its global markets. Heraeus is one of the top 10 family-owned companies in Germany.
With technical expertise, a commitment to excellence, a focus on innovation and entrepreneurial leadership, we are constantly striving to improve our performance. We create high-quality solutions for our clients and strengthen their long-term competitiveness by combining unique material expertise with leadership in technology. | 0.848362 | 3.496036 |
In the 18th and 19th centuries, astronomers made some profound discoveries about asteroids and comets within our Solar System. From discerning the true nature of their orbits to detecting countless small objects in the Main Asteroid Belt, these discoveries would inform much of our modern understanding of these bodies.
A general rule about comets and asteroids is that whereas the former develop comas or tails as they undergo temperature changes, the latter do not. However, a recent discovery by an international group of researchers has presented another exception to this rule. After viewing a parent asteroid in the Main Belt that split into a pair, they noted that both fragments formed tails of their own.
The reason asteroids do not do behave like comets has a lot to do with where they are situated. Located predominantly in the Main Belt, these bodies have relatively circular orbits around the Sun and do not experience much in the way of temperature changes. As a result, they do not form tails (or halos), which are created when volatile compounds (i.e. nitrogen, hydrogen, carbon dioxide, methane, etc.) sublimate and form clouds of gas.
As astronomical phenomena go, asteroid pairs are quite common. They are created when an asteroid breaks in two, which can be the result of excess rotational speed, impact with another body, or because of the destabilization of binary systems (i.e. asteroid that orbit each other). Once this happens, these two bodies will orbit the Sun rather than being gravitational bound to each other, and progressively drift farther apart.
However, when monitoring the asteroid P/2016 J1, an international team from the Institute of Astrophysics in Andalusia (IAA-CSIC) noticed something interesting. Apparently, both fragments in the pair had become “activated” – that is to say, they had formed tails. As Fernando Moreno, a researcher at IAA-CSIC who led the project, said in an Institute press release:
“Both fragments are activated, i.e., they display dust structures similar to comets. This is the first time we observe an asteroid pair with simultaneous activity… In all likelihood, the dust emission is due to the sublimation of ice that was left exposed after the fragmentation.”
While this is not the first instance where asteroids proved to be an exception to the rule and began forming clouds of sublimated gas around them, this is the first time it was observed happening with an asteroid pair. And it seems that the formation of this tail was in response to the breakup, which is believed to have happened six years ago, during the previous orbit of the asteroid.
In 2016, the research team used the Great Telescope of the Canary Islands (GTC) on the island of La Palma and the Canada-France-Hawaii Telescope (CFHT) at Mauna Kea to confirm that the asteroid had formed a pair. Further analysis revealed that the asteroids were activated between the end of 2015 and the beginning of 2016, when they reached the closest point in their orbit with the Sun (perihelion).
This analysis also revealed that the fragmentation of the asteroid and the bout of activity were unrelated. In other words, the sublimation has happened since the breakup and was not the cause of it. Because of this, these objects are quite unique as far as Solar System bodies go.
Not only are they two more exceptions to the rule governing comets and asteroids (there are only about twenty known cases of asteroids forming tales), the timing of their breakup also means that they are the youngest asteroid pair in the Solar System to date. Not bad for a bunch of rocks!
Further Reading: IAA | 0.857336 | 4.019917 |
Key questions relevant to fundamental physics and cosmology, namely the nature of the mysterious dark energy and dark matter (Euclid); the frequency of exoplanets around other stars, including Earth-analogs (PLATO); take the closest look at our Sun yet possible, approaching to just 62 solar radii (Solar Orbiter) … but only two! What would be your picks?
These three mission concepts have been chosen by the European Space Agency’s Science Programme Committee (SPC) as candidates for two medium-class missions to be launched no earlier than 2017. They now enter the definition phase, the next step required before the final decision is taken as to which missions are implemented.
These three missions are the finalists from 52 proposals that were either made or carried forward in 2007. They were whittled down to just six mission proposals in 2008 and sent for industrial assessment. Now that the reports from those studies are in, the missions have been pared down again. “It was a very difficult selection process. All the missions contained very strong science cases,” says Lennart Nordh, Swedish National Space Board and chair of the SPC.
And the tough decisions are not yet over. Only two missions out of three of them: Euclid, PLATO and Solar Orbiter, can be selected for the M-class launch slots. All three missions present challenges that will have to be resolved at the definition phase. A specific challenge, of which the SPC was conscious, is the ability of these missions to fit within the available budget. The final decision about which missions to implement will be taken after the definition activities are completed, which is foreseen to be in mid-2011.
Euclid is an ESA mission to map the geometry of the dark Universe. The mission would investigate the distance-redshift relationship and the evolution of cosmic structures. It would achieve this by measuring shapes and redshifts of galaxies and clusters of galaxies out to redshifts ~2, or equivalently to a look-back time of 10 billion years. It would therefore cover the entire period over which dark energy played a significant role in accelerating the expansion.
By approaching as close as 62 solar radii, Solar Orbiter would view the solar atmosphere with high spatial resolution and combine this with measurements made in-situ. Over the extended mission periods Solar Orbiter would deliver images and data that would cover the polar regions and the side of the Sun not visible from Earth. Solar Orbiter would coordinate its scientific mission with NASA’s Solar Probe Plus within the joint HELEX program (Heliophysics Explorers) to maximize their combined science return.
PLATO (PLAnetary Transit and Oscillations of stars) would discover and characterize a large number of close-by exoplanetary systems, with a precision in the determination of mass and radius of 1%.
In addition, the SPC has decided to consider at its next meeting in June, whether to also select a European contribution to the SPICA mission.
SPICA would be an infrared space telescope led by the Japanese Space Agency JAXA. It would provide ‘missing-link’ infrared coverage in the region of the spectrum between that seen by the ESA-NASA Webb telescope and the ground-based ALMA telescope. SPICA would focus on the conditions for planet formation and distant young galaxies.
“These missions continue the European commitment to world-class space science,” says David Southwood, ESA Director of Science and Robotic Exploration, “They demonstrate that ESA’s Cosmic Vision programme is still clearly focused on addressing the most important space science.” | 0.85611 | 3.832603 |
Quarter* ♊ Gemini
Moon phase on 31 August 2094 Tuesday is Waning Gibbous, 21 days old Moon is in Taurus.Share this page: twitter facebook linkedin
Previous main lunar phase is the Full Moon before 5 days on 26 August 2094 at 00:51.
Moon rises in the evening and sets in the morning. It is visible to the southwest and it is high in the sky after midnight.
Moon is passing about ∠23° of ♉ Taurus tropical zodiac sector.
Lunar disc appears visually 0.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1892" and ∠1901".
Next Full Moon is the Harvest Moon of September 2094 after 23 days on 24 September 2094 at 08:33.
There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak.
The Moon is 21 days old. Earth's natural satellite is moving from the middle to the last part of current synodic month. This is lunation 1170 of Meeus index or 2123 from Brown series.
Length of current 1170 lunation is 29 days, 15 hours and 55 minutes. It is 18 minutes shorter than next lunation 1171 length.
Length of current synodic month is 3 hours and 11 minutes longer than the mean length of synodic month, but it is still 3 hours and 52 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠167.4°. At the beginning of next synodic month true anomaly will be ∠190.4°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°).
5 days after point of perigee on 26 August 2094 at 01:39 in ♓ Pisces. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 8 days, until it get to the point of next apogee on 8 September 2094 at 16:37 in ♌ Leo.
Moon is 378 820 km (235 388 mi) away from Earth on this date. Moon moves farther next 8 days until apogee, when Earth-Moon distance will reach 406 544 km (252 615 mi).
9 days after its descending node on 22 August 2094 at 04:41 in ♑ Capricorn, the Moon is following the southern part of its orbit for the next 3 days, until it will cross the ecliptic from South to North in ascending node on 3 September 2094 at 19:00 in ♊ Gemini.
23 days after beginning of current draconic month in ♋ Cancer, the Moon is moving from the second to the final part of it.
8 days after previous South standstill on 22 August 2094 at 13:55 in ♑ Capricorn, when Moon has reached southern declination of ∠-23.409°. Next 3 days the lunar orbit moves northward to face North declination of ∠23.478° in the next northern standstill on 4 September 2094 at 07:14 in ♋ Cancer.
After 9 days on 9 September 2094 at 20:31 in ♍ Virgo, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.848363 | 3.098072 |
Tangled threads weave through cosmic oddity
New observations from the NASA/ESA Hubble Space Telescope have revealed the intricate structure of the galaxy NGC 4696 in greater detail than ever before. The elliptical galaxy is a beautiful cosmic oddity with a bright core wrapped in system of dark, swirling, thread-like filaments.
NGC 4696 is a member of the Centaurus galaxy cluster, a swarm of hundreds of galaxies all sitting together, bound together by gravity, about 150 million light-years from Earth and located in the constellation of Centaurus.
Despite the cluster's size, NGC 4696 still manages to stand out from its companions—it is the cluster's brightest member, known for obvious reasons as the Brightest Cluster Galaxy. This puts it in the same category as some of the biggest and brightest galaxies known in the Universe.
Even if NGC 4696 keeps impressive company, it has a further distinction: the galaxy's unique structure. Previous observations have revealed curling filaments that stretch out from its main body and carve out a cosmic question mark in the sky, the dark tendrils encircling a brightly glowing centre.
An international team of scientists, led by astronomers from the University of Cambridge, UK, have now used new observations from the NASA/ESA Hubble Space Telescope to explore this thread-like structure in more detail. They found that each of the dusty filaments has a width of about 200 light-years, and a density some 10 times greater than the surrounding gas. These filaments knit together and spiral inwards towards the centre of NGC 4696, connecting the galaxy's constituent gas to its core.
In fact, it seems that the galaxy's core is actually responsible for the shape and positioning of the filaments themselves. At the centre of NGC 4696 lurks an active supermassive black hole. This floods the galaxy's inner regions with energy, heating the gas there and sending streams of heated material outwards.
It appears that these hot streams of gas bubble outwards, dragging the filamentary material with them as they go. The galaxy's magnetic field is also swept out with this bubbling motion, constraining and sculpting the material within the filaments.
At the very centre of the galaxy, the filaments loop and curl inwards in an intriguing spiral shape, swirling around the supermassive black hole at such a distance that they are dragged into and eventually consumed by the black hole itself.
Understanding more about filamentary galaxies such as NGC 4696 may help us to better understand why so many massive galaxies near to us in the Universe appear to be dead; rather than forming newborn stars from their vast reserves of gas and dust, they instead sit quietly, and are mostly populated with old and aging stars. This is the case with NGC 4696. It may be that the magnetic structure flowing throughout the galaxy stops the gas from creating new stars. | 0.828075 | 4.027839 |
The results are now in after a year-long, crowdfunded investigation into the star KIC 8462852, and to hardly anyone’s surprise, the strange dimming produced by this star doesn’t appear to be caused by an alien megastructure. That said, astronomers are now significantly closer to knowing the true reasons for the star’s odd behaviour.
Variable star KIC 8462852, also known as Tabby’s Star and Boyajian’s Star, is located more than 1,000 light years from Earth. It’s about 50 per cent larger than our Sun, and nearly 1,000 degrees hotter. But thanks to observations made by the Kepler Space Telescope from 2009 to 2013, we know that this otherwise normal star experiences sporadic and intermittent dimming (at least from our vantage point on Earth). These mysterious drops in luminosity are by as much as 22 per cent, sometimes lasting for days. A recent historical analysis of Tabby’s Star showed that changes to the object’s overall brightness are on timescales lasting for years to centuries.
Astronomers hadn’t seen anything quite like it before, leading to a stream of theories. Explanations included a swarm of comets, a recently-annihilated planet, a distorted star, gravity darkening, and even alien megastructures.
In May 2016, Louisiana State University astronomer Tabby Boyajian set up a Kickstarter in hopes of securing funding for future research, and space fans donated more than £75,000. These funds were used to support a dedicated, ground-based telescopic survey of Tabby’s Star at the Las Cumbres Observatory in Goleta, California, which worked in tandem along with a network of professional and amateur telescopes around the world. In all, nearly 2,000 people were involved in the survey, the results of which have now been published in The Astrophysical Journal Letters.
The star’s behavior was closely monitored from March 2016 to December 2017. Beginning in May 2017, astronomers managed to chronicle four distinct dimming episodes, dubbed Elsie, Celeste, Scara Brae, and Angkor by Kickstarter supporters who got to nominate and vote for the names. The dimming persisted for several days to weeks. After the four dips (collectively known as Elsie, which is derived from the “LC” of Las Cumbres Observatory, the most generous Kickstarter backer), the star exhibited strange and unexpected brightening for a couple of months.
The recurrence of these dimming episodes was a big deal, not least of which because it finally ruled out instrumental effects from Kepler (which was thought unlikely anyway). It was also the first time that scientists were able to observe the dimming in real-time.
Looking at the photometric and spectroscopic data, the researchers were able to rule out an alien megastructure (such as a sun-enveloping Dyson sphere), while affirming a theory proposing that the star is surrounded by ordinary space dust.
Artist’s impression of a Dyson sphere. To get a sense of scale, the outer shell would be located approximately 1 AU from the enveloped star, or roughly 150 million km, depending on the configuration. (Credit: Slawek Wojtowicz)
Tyler Ellis, an astronomy grad student at Louisiana State University and a co-author of the new study, says the data collected by Las Cumbres Observatory and other observatories effectively rules out an alien megastructure, but he admits it’s a tricky issue because we don’t know exactly how an alien civilisation might build a megastructure, or the kinds of materials they would use.
“If we can assume that the construction would be done with normal building materials, then we would expect that it would be opaque and absorb light monochromatically,” Ellis told Gizmodo. “This would result in an overall dimming of the star without selectively absorbing particular colours. This is exactly the opposite of what we are reporting. The Las Cumbres observations show that the occulting material, whatever is blocking the star light, preferentially absorbs blue light. This has the effect of reddening the stellar spectrum.”
What’s more, and as Ellis points out, a Dyson sphere-like object would absorb the star’s light, causing the structure to heat up and subsequently emit infrared radiation that should be detectable from Earth.
“This light radiated by the structure would create an infrared excess,” said Ellis. “Such an excess is observed in young stars with large amounts of coalescing gas and dust. We did not observe any infrared excess. We need to search at longer wavelengths in order to better constrain this though.”
It’s also important to point out that, if the dimming was truly caused by an alien megastructure, the intermittent nature of the flickering would likely be on account of a partial Dyson sphere, or one under construction. If the latter, the odds of our observing such a fleeting event are mind-bogglingly implausible (it shouldn’t take an advanced alien civilisation very long to build such a thing).
Penn State astronomer and study co-author Jason Wright, who first speculated about a potential alien megastructure, says it’s unlikely that large, solid objects are blocking our view of the star’s light.
“If there were opaque objects blocking our view of the light, the star should get equally dim at all wavelengths,” he wrote at his blog. “Instead, [we find] that the blue dips are much deeper—about twice as deep—as they are when we look at infrared wavelengths... the dips are not caused by opaque macroscopic objects (like megastructures or planets or stars) but by clouds of very small particles of dust (less than 1 micron in typical size). We can also say that these clouds are mostly transparent (‘optically thin’ in astrophysics parlance).”
Further analysis ruled out accompanying gas (which favoured the cometary theory), or a companion object in orbit around the star.
But this mystery is far from over. Wright likes the “space dust” hypothesis, but there are several explanations—ranging from the plausible through to the seriously unlikely (such as an orbiting black hole disk), that still need to be ruled out. Our galaxy’s most mysterious star is still ripe for further research.
There’s still plenty of data that needs to be analysed by various groups, explained Ellis, and his team is continuing to refine its observations and analysis. Funds from the Kickstarter campaign have been used to purchase more telescope time for the upcoming observing semester with Las Cumbres. And ideally, Ellis is hoping to use an infrared instrument on a space-based telescope to scan Tabby’s Star during a dimming event to get a better sense of the size of the dust particles and their location around the star.
As the team prepares for this next phase, Ellis is keen to point out that this work was made possible only because of the “trust and generosity” of the Kickstarter backers and the contributions of amateur astronomers and citizen scientists.
“The target was discovered by ordinary people with free time and the follow up work funded by ordinary people with a few spare bucks,” Ellis told Gizmodo. “This target could have very well been left undiscovered in the Kepler data archive. This project would not have stood a chance before any standard funding agency or telescope allocation committee; scientists simply cannot ask for a few minutes every night on a telescope or for funding for essentially a fishing expedition. I hope that we have shown that worthwhile science can be done on crowdfunding platforms.” [The Astrophysical Journal Letters] | 0.863828 | 3.761634 |
Are you ready for the summer of 2015? A showdown of epic proportions is in the making, as NASA’s New Horizons spacecraft is set to pass within 12,500 kilometres of Pluto — roughly a third of the distance of the ring of geosynchronous satellites orbiting the Earth — a little over a year from now on July 14th, 2015.
But another question is already being raised, one that’s assuming center stage even before we explore Pluto and its retinue of moons: will New Horizons have another target available to study for its post-Pluto encounter out in the Kuiper Belt? Researchers say time is of the essence to find it.
To be sure, it’s a big solar system out there, and it’s not that researchers haven’t been looking. New Horizons was launched from Cape Canaveral Air Force Station on January 19th, 2006 atop an Atlas V rocket flying in a 551 configuration in one of the fastest departures from Earth ever: it took New Horizons just nine hours to pass Earth’s moon after launch.
The idea has always been out there to send New Horizons onward to explore and object beyond Pluto in the Kuiper Belt, but thus far, searches for a potential target have turned up naught.
A recent joint statement from NASA’s Small Bodies and Outer Planets Assessment Groups (SBAG and OPAG) has emphasized the scientific priority needed for identifying a possible Kuiper Belt Object (KBO) for the New Horizons mission post-Pluto encounter. The assessment notes that such a chance to check out a KBO up close may only come once in our lifetimes: even though it’s currently moving at a heliocentric velocity of just under 15 kilometres a second, it will have taken New Horizons almost a decade to traverse the 32 A.U. distance to Pluto.
The report also highlights the fact that KBOs are expected to dynamically different from Pluto as well and worthy of study. The statement also notes that the window may be closing to find such a favorable target after 2014, as the upcoming observational apparition of Pluto as seen from Earth — and the direction New Horizons is headed afterwards — reaches opposition this summer on July 4th.
But time is of the essence, as it will allow researchers to plan for a burn and trajectory change for New Horizons shortly after its encounter with Pluto and Charon using what little fuel it has left. Then there’s the issue of debris in the Pluto system that may require fine-tuning its trajectory pre-encounter as well. New Horizons will begin long range operations later this year in November, switching on permanently for two years of operations pre-, during and post- encounter with Pluto.
And there currently isn’t a short-list of “next best thing” targets for New Horizons post-Pluto encounter. One object, dubbed VNH0004, may be available for distant observations in January of next year, but even this object will only pass 75 million kilometres — about 0.5 A.U. — from New Horizons at its closest.
Ground based assets such as the Keck, Subaru and Gemini observatories have been repeatedly employed in the search over the past three years. The best hopes lie with the Hubble Space Telescope, which can go deeper and spy fainter targets.
Nor could New Horizons carry out a search for new targets on its own. Its eight inch (20 cm in diameter) LORRI instrument has a limiting magnitude of about +18, which is not even close to what would be required for such a discovery.
New Horizons currently has 130 metres/sec of hydrazine fuel available to send it onwards to a possible KBO encounter, limiting its range and maneuverability into a narrow cone straight ahead of the spacecraft. This restricts the parameters for a potential encounter to 0.35 A.U. off of its nominal path for a target candidate be to still be viable objective. New Horizons will exit the Kuiper Belt at around 55 A.U. from the Sun, and will probably end its days joining the Voyager missions probing the outer solar system environment. Like Pioneers 10 and 11, Voyagers 1 and 2 and the upper stage boosters that deployed them, New Horizons will escape our solar system and orbit the Milky Way galaxy for millions of years. We recently proposed a fun thought experiment concerning just how much extraterrestrial “space junk” might be out there, littering the galactic disk.
And while the crowd-sourced Ice Hunters project generated lots of public engagement, a suitable target wasn’t found. There is talk of a follow up Ice Investigators project, though it’s still in the pending stages.
Another issue compounding the problem is the fact that Pluto is currently crossing the star rich region of the Milky Way in the constellation Sagittarius. Telescopes looking in this direction must contend with the thousands of background stars nestled towards the galactic center, making the detection of a faint moving KBO difficult. Still, if any telescope is up to the task, it’s Hubble, which just entered its 25th year of operations last month.
Shining at +14th magnitude, Pluto will be very near the 3.5th magnitude star Xi2 Sagittarii during the July 2015 encounter.
New Horizons is currently 1.5 degrees from Pluto — about 3 times the angular size of a Full Moon —as seen from our Earthly vantage point, and although neither can be seen with the naked eye, you can wave in their general direction this month on May 18th, using the nearby daytime Moon as a guide.
July 2015 will be an exciting and historic time in solar system exploration. Does Pluto have more undiscovered moons? A ring system of its own? Does it resemble Neptune’s moon Triton, or will it turn out looking entirely different ?
If nothing else, exploration of Pluto will finally give us science writers some new images to illustrate articles on the distant world, rather than recycling the half a dozen-odd photos and artist’s conceptions that are currently available. An abundance of surface features will then require naming as well. It would be great to see Pluto’s discoverer Clyde Tombaugh and Venetia Burney — the girl who named Pluto — get their due. We’ll even assume our space pundit’s hat and predict a resurgence of the “is it a planet?” debate once again in the coming year as the encounter nears…
Onward to Pluto and the brave new worlds beyond! | 0.912806 | 3.666243 |
Small enough to be an aircraft carry-on, the Juventas spacecraft nevertheless has big mission goals. Once in orbit around its target body, Juventas will unfurl an antenna larger than itself, to perform the very first subsurface radar survey of an asteroid.
ESA’s proposed Hera mission for planetary defence will explore the twin Didymos asteroids, but it will not go there alone: it will also serve as mothership for Europe’s first two ‘CubeSats’ to travel into deep space.
CubeSats are nanosatellite-class missions based on standardised 10-cm boxes, making maximum use of commercial off the shelf systems. Juventas will be a ‘6-unit’ CubeSat, selected to fly aboard Hera along with the similarly-sized APEX Asteroid Prospection Explorer, built by a Swedish-Finnish-German-Czech consortium.
Juventas – the Roman name for the daughter of Hera – is being developed for ESA by the GomSpace company and GMV in Romania, together with consortia of additional partners developing the spacecraft instruments.
“We’re packing a lot of complexity into the mission,” notes GomSpace systems engineer Hannah Goldberg. “One of the biggest misconceptions about CubeSats is that they are simple, but we have all the same systems as a standard-sized spacecraft.
“Another reputation of CubeSats is that they don’t do that much, but we have multiple mission goals over the course of our month-long mission around the smaller Didymos asteroid. One of our CubeSat units is devoted to our low-frequency radar instrument, which will be a first in asteroid science.”
Juventas will deploy a metre and a half long radar antenna, which will unfurl like a tape measure, and was developed by Astronika in Poland. This instrument is based on the heritage of the CONSERT radar that flew on ESA’s Rosetta comet chaser, overseen by Alain Herique of the Institut de Planétologie et d'Astrophysique de Grenoble (IPAG).
The radar signals should reach one hundred metres down, giving insight into the asteroid’s internal structure. “Is it a rubble pile, or something more layered, or monolithic?” adds Hannah, who previously worked at asteroid mining company Planetary Resources before moving to GomSpace.
“This is the sort of information that is going to be essential for future mining missions, to estimate where the resources are, how mixed up they are, and how much effort will be required to extract them.”
ESA radar specialist Christopher Buck has worked on the instrument design with IPAG: “Our radar instrument’s size and power is much lower than those of previous missions, so what we’re doing is using a pseudo-random code sequence in the signals – think of it as a poor man’s alternative. Navigation satellites use a comparable technique, allowing receivers to make up for their very low power.
“We send a series of signals possessing constantly shifting signal phase, then we gradually build up a picture by correlating the reflections of these signals, employing their phase shifts as our guide. One reason we are able to do this is that we will be orbiting around the asteroid relatively slowly, on the order of a few centimetres per second, giving us longer integration times compared to orbits around Earth or other planets.”
The technology proved itself with Rosetta, where the CONSERT radar peered deep inside comet 67P/Churyumov–Gerasimenko and helped locate the Philae lander on the comet’s surface. Juventas uses a more compact ‘monostatic’ version of the design.
As Juventas orbits, the CubeSat will also be gathering data on the asteroid’s gravity field using both a dedicated 3-axis ‘gravimeter’ – first developed by the Royal Observatory of Belgium for Japan’s proposed Martian Moons eXploration mission – as well as its radio link back to Hera, measuring any Doppler shifting of communications signals caused by its proximity to the body.
“But the mission is being designed to operate with minimal contact with its mothership and the ground, operating autonomously for days at a time,” says Hannah.
“This is a big difference from Earth orbit, where communications are much simpler and more frequent. So we will fly in what is called a ‘self-stabilising terminator orbit’ around the asteroid, perpendicular to the Sun, requiring minimal station-keeping manoeuvring.”
The final phase of the mission will come with a precisely-controlled attempt to land on the asteroid.
“We’ll have gyroscopes and accelerometers aboard, so we will capture the force of our impact, and any follow-on bouncing, to gain insight into the asteroid’s surface properties – although we don’t know how well Juventas will continue to operate once it finally touches down. If we are able to successfully operate after the impact, we will continue to take local gravity field measurements from the asteroid surface.”
The Hera mission, including its two CubeSats, will be presented to ESA’s Space19+ meeting this November, where Europe’s space ministers will take a final decision on flying the mission.
Space Safety at ESA
Solar activity, asteroids and artificial space debris all pose threats to our planet and our use of space.
ESA's Space Safety activities aim to safeguard society and the critical satellites on which we depend, identifying and mitigating threats from space through projects such as the Flyeye telescopes, the Lagrange space weather mission and the Hera asteroid mission.
As asteroid experts meet for the international Planetary Defense Conference, ESA is focusing on the threat we face from space rocks. How likely is an asteroid impact? What is ESA doing to mitigate impact risks? Follow the hashtag #PlanetaryDefense to find out more. | 0.829384 | 3.588502 |
The weird "neck" between the lobes of Comet 67P/Churyumov-Gerasimenko spotted by the Rosetta spacecraft formed in part because the comet had a brittle interior, a new study shows.
Pictures of 67P taken by Rosetta between 2014 and 2016 — coupled with new modeling and three-dimensional analyses — revealed networked faults and fractures in the comet that stretched as far as 1,640 feet (500 meters) underground and hundreds of feet or meters wide. The stress peaked at the thinnest part of the comet's neck, which connected the two lobes of 67P.
The discovery not only helps scientists understand 67P, but also how comets in general were formed around the solar system, researchers said in a statement about the new research. These tiny worlds of ice and dust circle the Sun; as they move closer to the star's warmth and particle pressure, ice boils off directly into space in a process called sublimation. This process often creates a tail of water vapor protruding from the comet. But sublimation alone cannot explain the presence of the newly found cracks in 67P, the researchers said. [In Images: Rosetta Spacecraft's Last Comet Photos During Crash-Landing]
"These geological features were created by shear stress, a mechanical force often seen at play in earthquakes or glaciers on Earth and other terrestrial planets, when two bodies or blocks push and move along one another in different directions," Christophe Matonti, lead author of the new report and an astrophysicist at Aix-Marseille University in France, said in the statement. "This is hugely exciting: it reveals much about the comet's shape, internal structure, and how it has changed and evolved over time."
"It's as if the material in each hemisphere is pulling and moving apart, contorting the middle part — the neck — and thinning it via the resulting mechanical erosion," co-author Olivier Groussin, an astronomer at Aix-Marseille University, added in the same statement. "We think this effect originally came about because of the comet's rotation combined with its initial asymmetric shape. A torque formed where the neck and 'head' meet, as these protruding elements twist around the comet's center of gravity."
While sublimation dies down during 67P's furthest point from the Sun — beyond Jupiter's orbit to almost 6 Earth-sun distances (called astronomical units) away — the stress would continue to act over the billions of years since the comet was formed, the researchers said.
While the stress is small, the effects would accumulate over time. Sublimation would affect the comet much more rapidly over millions of years, researchers said in the statement. Sublimation is maximal when 67P skirts inside Mars' orbit for its closest approach to the sun, every 6.5 years. (A billion years is equal to 1,000 million years; the solar system is roughly 4.5 billion years old, for perspective.)
After swinging past Pluto in 2015, NASA's New Horizons spacecraft came close to another dual-lobed object when it flew by 2014 MU69 (which NASA nicknamed Ultima Thule) on Jan. 1. The object is embedded in a region called the Kuiper Belt, a huge reservoir of comets and small objects beyond Neptune. While analysis is ongoing, so far researchers haven't spotted any sign of shear stress in MU69, Mantoni said.
A study based on the research was published Feb. 18 in the journal Nature Geoscience. | 0.839558 | 3.951654 |
The science of shooting stars owes much to a storied episode of crowdsourcing, a new historical report shows, kicked off by a stunning 1833 meteor shower.
Astronomers have increasingly turned to “citizen science” in the Internet era, setting up everyday folks to look for everything from alien worlds to the Milky Way’s galactic gas bubbles. But in a new Endeavour journal report, Mark Littmann and Todd Suomela of the University of Tennessee in Knoxville show that there is nothing new about the practice, with one Yale astronomer pioneering crowdsourced astronomy well over a century ago.
The astronomer, Denison Olmsted, was awakened by neighbors on November 13, 1833, and walked into the cold November night to see a sky filled with shooting stars, 72,000 or more per hour. It was the November meteor shower we now call the Leonids, but at the time, no one knew what caused the display or where meteors came from. But because of the number of shooting stars filling the heavens—20 a second—Olmsted saw clearly a pattern that had escaped other astronomers.
“Olmsted realized for the first time that they came from one point, one he first called the radiant,” Littmann says. Astronomers today still use the radiant to name meteor showers: The Leonids take their name from their seeming origin in the constellation Leo, the Lion. And the Perseids seen in early August every summer take their name from their origin in the constellation Perseus.
Citizen Science Starts
But Olmsted didn’t stop with that discovery. “Just as dawn was brightening the sky, causing the meteors to disappear from view, Olmsted rushed inside and dashed off a brief report on the meteor storm for the New Haven Daily Herald newspaper,” says the study.
“As the cause of ‘Falling Stars’ is not understood by meteorologists, it is desirable to collect all the facts attending this phenomenon, stated with as much precision as possible,” Olmsted wrote to readers, in a report subsequently picked up and pooled to newspapers nationwide. Responses came pouring in from many states, along with scientists’ observations sent to the American Journal of Science and Arts.
“This was a seminal moment in American science journalism, really in science journalism worldwide,” says Littmann, author of The Heavens on Fire: The Great Leonid Meteor Storms. “Until then, the newspapers were mostly political rags, filled with opinion, but here they did a very good job of dispassionately reporting on the meteors, calming people down that it wasn’t ‘The End of Days.'”
The responses also let Olmsted make a series of scientific breakthroughs, ending the 2,200-year grip of Greek philosopher Aristotle on explanations for meteors, which he saw as bubbles of gas lofted high into the sky and ignited. Olmsted’s contemporaries suspected the bodies were electrified by lightning.
Aristotle’s Last Gasp
Instead, Olmsted’s crowdsourced observations showed that meteor showers were seen nationwide and fell from space under the influence of gravity. The crowd also noted that the showers had appeared before in yearly cycles, something that had eluded scientists, but not European farmers, for centuries.
Olmsted realized that the meteors must be smacking into Earth’s atmosphere from outer space. He estimated their speed at about 4 miles per second (6.4 kilometers per second), which he thought was fantastically fast. If he had been less conservative in the calculation, the observations from the crowd would have suggested their actual speed, about ten times faster. Because he didn’t realize that friction, instead of conventional burning, was firing up the shooting stars, Olmsted calculated their size as very large, up to a mile (1.6 kilometers) wide instead of the pinprick-size comet dust particles they actually are.
He did get their altitude nearly correct, triangulating the height of the fireballs with another scientific observer in New York at 30 to 50 miles (50 to 80 kilometers) high. He also surmised they originated from a body in a very elongated orbit around the sun, but it would not be until 1867 that astronomers made the connection between meteors and the dust left behind in comet tails, linking the trail of comet Tempel-Tuttle to the Perseids.
“He was ahead of his time, a remarkable guy, not least in using crowdsourcing for the first time, as far as we know, in mass media,” Littmann says. “Meteor astronomy really began with this shower.”
Every 30 years or so, particularly in 1966, the Leonids have produced remarkably strong showers as a reminder of the 1833 event, although they have declined overall as the comet-tail cloud spawning the meteors has thinned over time. The Leonids are expected to peak around November 16 and 17 this year.
Follow Dan Vergano on Twitter. | 0.863725 | 3.420171 |
High School Earth Science/Stars
When you look at the sky on a clear night, you can see dozens, perhaps even hundreds, of tiny points of light. Almost every one of these points of light is a star, a giant ball of glowing gas at a very, very high temperature. Some of these stars are smaller than our Sun, and some are larger. Except for our own Sun, all stars are so far away that they only look like single points, even through a telescope.
- Define constellations.
- Describe the flow of energy in a star.
- Classify stars based on their properties.
- Outline the life cycle of a star.
- Use light-years as a unit of distance.
For centuries, people have seen the same stars you can see in the night sky. People of many different cultures have identified constellations, which are apparent patterns of stars in the sky. Figure 26.1 shows one of the most easily recognized constellations. The ancient Greeks thought this group of stars looked like a hunter from one of their myths, so they named it Orion after him. The line of three stars at the center of the picture is "Orion's Belt".
The patterns in constellations and in groups or clusters of stars, called asterisms, stay the same night after night. However, in a single night, the stars move across the sky, keeping the same patterns. This apparent nightly motion of the stars is actually due to the rotation of Earth on its axis. It isn't the stars that are moving; it is actually Earth spinning that makes the stars seem to move. The patterns shift slightly with the seasons, too, as Earth revolves around the Sun. As a result, you can see different constellations in the winter than in the summer. For example, Orion is a prominent constellation in the winter sky, but not in the summer sky.
Apparent Versus Real Distances
Although the stars in a constellation appear close together as we see them in our night sky, they are usually at very different distances from us, and therefore they are not at all close together out in space. For example, in the constellation Orion, the stars visible to the naked eye are at distances ranging from just 26 light-years (which is relatively close to Earth) to several thousand light-years away. A light-year is the distance that light can travel in one year; it is a large unit of distance used to measure the distance between objects in space.
Energy of Stars
Only a small portion of the light from the Sun reaches Earth; yet that light is enough to keep the entire planet warm and to provide energy for all the living things on Earth. The Sun is a fairly average star. The reason the Sun appears so much bigger and brighter than any of the other stars is that it is very close to us. Some other stars produce much more energy than the Sun. How do stars generate so much energy?
Stars are made mostly of hydrogen and helium. These are both very lightweight gases. However, there is so much hydrogen and helium in a star that the weight of these gases is enormous. In the center of a star, the pressure is great enough to heat the gases and cause nuclear fusion reactions. In a nuclear fusion reaction, the nuclei, or centers of two atoms join together and create a new atom from two original atoms. In the core of a star, the most common reaction turns two hydrogen atoms into a helium atom. Nuclear fusion reactions require a lot of energy to get started, but once they are started, they produce even more energy.
The energy from nuclear reactions in the core pushes outward, balancing the inward pull of gravity on all the gas in the star. This energy slowly moves outward through the layers of the star until it finally reaches the outer surface of the star. The outer layer of the star glows brightly, sending the energy out into space as electromagnetic radiation, including visible light, heat, ultraviolet light, and radio waves.
Scientists have built machines called accelerators that can propel subatomic particles until they have attained almost the same amount of energy as found in the core of a star. When these particles collide with each other head-on, new particles are created. This process simulates the nuclear fusion that takes place in the cores of stars. It also simulates the conditions that allowed for the first Helium atom to be produced from the collision of two hydrogen atoms when the Universe was only a few minutes old. Two well-known accelerators are SLAC in California, USA and CERN in Switzerland.
How Stars Are Classified
Stars come in many different colors. If you look at the stars in Orion (as shown in Figure 26.1), you will notice that there is a bright, red star in the upper left and a bright, and a blue star in the lower right. The red star is named Betelgeuse (pronounced BET-ul-juice), and the blue star is named Rigel.
Color and Temperature
If you watch a piece of metal, such as a coil of an electric stove as it heats up, you can see how color is related to temperature. When you first turn on the heat, the coil looks black, but you can feel the heat with your hand held several inches from the coil. As the coil gets hotter, it starts to glow a dull red. As it gets hotter still, it becomes a brighter red, then orange. If it gets extremely hot, it might look yellow-white, or even blue-white. Like a coil on a stove, a star's color is determined by the temperature of the star’s surface. Relatively cool stars are red, warmer stars are orange or yellow, and extremely hot stars are blue or blue-white.
The most common way of classifying stars is by color. Table 26.1 shows how this classification system works. The class of a star is given by a letter. Each letter corresponds to a color, and also to a range of temperatures. Note that these letters don’t match the color names; they are left over from an older system that is no longer used.
|Class||Color||Temperature Range||Sample Star|
|O||Blue||30,000 K or more||Zeta Ophiuchi|
|F||Yellowish-white||6,000-7,500 K||Procyon A|
|K||Orange||3,500-5,000 K||Epsilon Indi|
|M||Red||2,000-3,500 K||Betelgeuse, Proxima Centauri|
For most stars, surface temperature is also related to size. Bigger stars produce more energy, so their surfaces are hotter. Figure 26.2 shows a typical star of each class, with the colors about the same as you would see in the sky.
Lifetime of Stars
As a way of describing the stages in a star's development, we could say that stars are born, grow, change over time, and eventually die. Most stars change in size, color, and class at least once during this journey.
Formation of Stars
Stars are born in clouds of gas and dust called nebulas, like the one shown in Figure 26.3. In Figure 26.1, the fuzzy area beneath the central three stars across the constellation Orion, often called Orion's sword, contains another nebula called the Orion nebula.
The Main Sequence
For most of a star's life, the nuclear fusion in the core combines hydrogen atoms to form helium atoms. A star in this stage is said to be a main sequence star, or to be on the main sequence. This term comes from the Hertzsprung-Russell diagram, that plots a star's surface temperature against its true brightness or magnitude. For stars on the main sequence, the hotter they are, the brighter they are. The length of time a star is on the main sequence depends on how long a star is able to balance the inward force of gravity with the outward force provided by the nuclear fusion going on in its core. More massive stars have higher pressure in the core, so they have to burn more of their hydrogen "fuel" to prevent gravitational collapse. Because of this, more massive stars have higher temperatures, and also run out of hydrogen sooner than smaller stars do.
Our Sun, which is a medium-sized star, has been a main sequence star for about 5 billion years. It will continue to shine without changing for about 5 billion more years. Very large stars may be on the main sequence for "only" 10 million years or so. Very small stars may be main sequence stars for tens to hundreds of billions of years.
Red Giants and White Dwarfs
As a star begins to use up its hydrogen, it then begins to fuse helium atoms together into heavier atoms like carbon. Eventually, stars contain fewer light elements to fuse. The star can no longer hold up against gravity and it starts to collapse inward. Meanwhile, the outer layers spread out and cool. The star becomes larger, but cooler on the surface and red in color. Stars in this stage are called red giants.
Eventually, a red giant burns up all of the helium in its core. What happens next depends on how massive the star is. A typical star like the Sun, stops fusion completely at this point. Gravitational collapse shrinks the star’s core to a white, glowing object about the size of Earth. A star at this point is called a white dwarf. Eventually, a white dwarf cools down and its light fades out.
Supergiants and Supernovas
A star that has much more mass than the Sun will end its life in a more dramatic way. When very massive stars leave the main sequence, they become red supergiants. The red star Betelgeuse in Orion is a red supergiant.
Unlike red giants, when all the helium in a red supergiant is gone, fusion does not stop. The star continues fusing atoms into heavier atoms, until eventually its nuclear fusion reactions produce iron atoms. Producing elements heavier than iron through fusion takes more energy than it produces. Therefore, stars will ordinarily not form any elements heavier than iron. When a star exhausts the elements that it is fusing together, the core succumbs to gravity and collapses violently, creating a violent explosion called a supernova. A supernova explosion contains so much energy that some of this energy can actually fuse heavy atoms together, producing heavier elements such as gold, silver, and uranium. A supernova can shine as brightly as an entire galaxy for a short time, as shown in Figure 26.4.
Neutron Stars and Black Holes
After a large star explodes in a supernova, the leftover material in the core is extremely dense. If the core is less than about four times the mass of the Sun, the star will be a neutron star, as shown in Figure 26.5. A neutron star is made almost entirely of neutrons. Even though it is more massive than the sun, it is only a few kilometers in diameter.
If the core remaining after a supernova is more than about 5 times the mass of the Sun, the core will collapse so far that it becomes a black hole. Black holes are so dense that not even light can escape their gravity. For that reason, black holes cannot be observed directly. But we can identify a black hole by the effect that it has on objects around it, and by radiation that leaks out around its edges.
Measuring Star Distances
The Sun is much closer to Earth than any other star. Light from the Sun takes about 8 minutes to reach Earth. Light from the next nearest star, Proxima Centauri, takes more than 4 years to reach Earth. Traveling to Proxima Centauri in spacecraft similar to those we have today would take tens of thousands of years.
Because astronomical distances are so large, it helps to use units of distance that are large as well. A light-year is defined the distance that light travels in one year. One light-year is 9,500,000,000,000 (9.5 trillion) kilometers, or 5,900,000,000,000 (5.9 trillion) miles. Proxima Centauri is 4.22 light-years away, which means that its light takes 4.22 years to reach us.
One light-year is approximately equal to 60,000 AU and 4.22 light-years is almost 267,000 AU. Recalling that Neptune, the farthest planet from the Sun, orbits roughly 30 AU from the Sun, we can realize that the distance from the Earth to stars other than our own Sun is much greater than the distance from the Earth to other planets within our own solar system.
So how do astronomers measure the distance to stars? Distances to stars that are relatively close to us can be measured using parallax. Parallax is an apparent shift in position that takes place when the position of the observer changes.
To see an example or parallax, try holding your finger about 1 foot (30 cm) in front of your eyes. Now, while focusing on your finger, close one eye and then the other. Alternate back and forth between eyes, and pay attention to how your finger appears to move. The shift in position of your finger is an example of parallax. Now try moving your finger closer to your eyes, and repeat the experiment. Do you notice any difference? The closer your finger is to your eyes, the greater the position changes due to parallax.
As Figure 26.6 shows, astronomers use this same principle to measure the distance to stars. However, instead of a finger, they focus on a star. And instead of switching back and forth between eyes, they use the biggest possible difference in observing position. To do that, they first look at the star from one position, and they note where the star appears to be relative to more distant stars. Then, they wait 6 months; during this time, Earth moves from one side of its orbit around the Sun to the other side. When they look at the star again, parallax will cause the star to appear in a different position relative to more distant stars. From the size of this shift, they can calculate the distance to the star.
For stars that are more than a few hundred light years away, parallax is too small to measure, even with the most precise instruments available. For these more distant stars, astronomers use more indirect methods of determining distance. Most of these other methods involve determining how bright the star they are looking at really is. For example, if the star has properties similar to the Sun, then it should be about as bright as the Sun. Then, they can compare the observed brightness to the expected brightness. This is like asking, "How far away would the Sun have to be to appear this dim?"
- Constellations and asterisms are apparent patterns of stars in the sky.
- Stars in the same constellation are often not close to each other in space.
- A star generates energy by nuclear fusion reactions in its core.
- The color of a star is determined by its surface temperature.
- Stars are classified by color and temperature. The most common system uses the letters O (blue), B (bluish white), A (white), F (yellowish white), G (yellow), K (orange), and M (red), from hottest to coolest.
- Stars form from clouds of gas and dust called nebulas. Stars collapse until nuclear fusion starts in the core.
- Stars spend most of their lives on the main sequence, fusing hydrogen into helium.
- Typical, Sun-like stars expand into red giants, then fade out as white dwarfs.
- Very large stars expand into red supergiants, explode in supernovas, then end up as neutron stars or black holes.
- Astronomical distances can be measured in light-years. A light year is the distance that light travels in one year. 1 light-year = 9.5 trillion kilometers (5.9 trillion miles).
- Parallax is an apparent shift in an object's position when the position of the observer changes. Astronomers use parallax to measure the distance to relatively nearby stars.
- What distinguishes a nebula and a star?
- What kind of reactions provide a star with energy?
- Which has a higher surface temperature: a blue star or a red star?
- List the seven main classes of stars, from hottest to coolest.
- What is the primary reaction that occurs in the core of a star, when the star is on the main sequence?
- What kind of star will the Sun be after it leaves the main sequence?
- Suppose a large star explodes in a supernova, leaving a core that is 10 times the mass of the Sun. What would happen to the core of the star?
- What is the definition of a light-year?
- Why don't astronomers use parallax to measure the distance to stars that are very far away?
- A group or cluster of stars that appear close together in the sky.
- black hole
- The super dense core left after a supergiant explodes as a supernova.
- An apparent pattern of stars in the night sky.
- The distance that light travels in one year; 9.5 trillion kilometers.
- main sequence star
- A star that is fusing hydrogen atoms to helium; a star in the main portion of its "life".
- An interstellar cloud of gas and dust.
- neutron star
- The remnant of a massive star after it explodes as a supernova.
- nuclear fusion reaction
- When nuclei of two atoms fuse together, giving off tremendous amounts of energy.
- A method used by astronomers to calculate the distance to nearby stars, using the apparent shift relative to distant stars.
- red giant
- Stage in a star's development when the inner helium core contracts while the outer layers of hydrogen expand.
- A tremendous explosion that occurs when the core of a star is mostly iron.
- A glowing sphere of gases that produces light through nuclear fusion reactions.
Points to Consider
- Although stars may appear to be close together in constellations, they are usually not close together out in space. Can you think of any groups of astronomical objects that are relatively close together in space?
- Most nebulas contain more mass than a single star. If a large nebula collapsed into several different stars, what would the result be like? | 0.892609 | 3.896815 |
A team of astronomy researchers from Stony Brook University, the National Astronomical Observatory of Japan, and Tsuru University are the first to reveal clear details about the rapidly changing plasma tail of the comet C/2013 R1 (Lovejoy). The observation and details behind the discovery are published in a paper in the March 2015 edition of the Astronomical Journal.
The team, Led by Jin Koda, PhD, Assistant Professor in the Department of Physics and Astronomy at Stony Brook University, captured the images by using the Subaru Telescope’s wide-field prime-focus camera, called Suprime-Cam, which resulted in gaining new knowledge regarding the extreme activity in that tail as the comet neared the Sun.
“My research is on galaxies and cosmology, but I always want to explore beyond these boundaries. Lovejoy was up in the sky after my targets were gone, and we started taking other images for educational and outreach purposes, and for curiosity,” said Dr. Koda. “The single image from one night revealed such delicate details along the tail that it inspired us further to take a series of images on the following night. When we analyzed these additional images, we realized that the tail was displaying rapid motion in a matter of only a few minutes. This was an incredible discovery.”
In their paper, “Initial Speed of Knots in the Plasma Tail of C/213 R1 (Lovejoy),” the researchers report short-time variations in the plasma tail of Lovejoy.
They suggest that “these rapid motions suggest the need for high time-resolution studies of comet plasma tails with a large telescope,” and that, “A series of short (2-3 minutes) exposure images with the 8.2 m Subaru telescope shows faint details of filaments and their motions over a 24 minutes observing duration. We identified rapid movements of two knots in the plasma tail near the nucleus. Their speeds are 20 and 25 kms along the tail and 2.8 and 2.2 kms across it respectively. These set a constraint on an acceleration model of plasma tail and knots as they set the initial speed just after their formation. We also found a rapid narrowing of the tail.”
Dr. Koda explained that the plasma tail of a comet forms when gas molecules and atoms coming out from the comet encounter the solar wind. Changes and disturbances in the solar wind can affect the behavior and appearance of this plasma tail, causing it to form clumps of ionized material. The material in the plasma tail departed from the comet’s coma and floats away on the solar wind. At these times, the plasma tail can take on a “kinked” or twisted look.
In 2013, the team reported highly resolved fine details of this comet captured in B-band filter in Subaru Telescope’s Image Captures the Intricacy of Comet Lovejoy’s Tail. They used I-band filter which includes H2O+ line emissions and V-band filter which includes CO+ and H2O+ line emissions. During the observations, the comet exhibited very rapid changes in its tail in the course of only 20 minutes (Figure 1). Such extreme short-term changes are the result of the comet’s interactions with the solar wind where charged particles constantly sweeping out from the Sun. They explain that the reason for the rapidity of these changes is not well understood.
By using the Subaru Telescope, they also discovered that clumps located in the plasma tail at about 300 thousand kilometers from the nucleus moved fairly slow speed at about 20-25 kilometers per second (Figure 2). That is much slower than reported in other comets, such as P/Halley, which gave off clumps that moved as fast as 58 kilometers per second or the value 44 +/- 11 kilometers per second (Note 2) as derived from several bright comets in the past.
The speed of the solar wind ranges from 300 to 700 kilometers per second, and the intensity and velocity that the comet encounters depends on where it is located with respect to the Sun. The solar wind helps to accelerate the clumps in the tail out away from the Sun. Dr. Koda explained that eventually the clumps in the comet’s tail reach this high speed.
The observation team believes they witnessed the beginning of the acceleration of the clumps by the solar wind, however it is still under investigation how these ion clumps form and what parameters determine the initial speed of them.
The team concluded that because of the Subaru Telescope capacity for large photon collection coupled with the wide field-of-view camera they were able to and fortunate enough to catch the rare tail condition before it disappeared. Dr. Koda says their discovery is the first such demonstration underscoring the need for use of a large telescope to capture rapid motions of comets’ tails in action. They also conclude that with such a powerful instrument, more observations will help to contribute to the better understanding of comets. Such observations would include a series of images for longer periods of time, which would help the team learn more about how the comet tail moves and evolves. | 0.894343 | 4.008474 |
The Extrasolar Planets Encyclopedia counted 548 confirmed extrasolar planets at 6 May 2011, while the NASA Star and Exoplanet Database (updated weekly) was today reporting 535. These are confirmed findings and the counts will significantly increase as more candidate exoplanets are assessed. For example, there were the 1,235 candidates announced by the Kepler mission in February, including 54 that may be in a habitable zone.
So what techniques are brought to bear to come up with these findings?
Pulsar timing – A pulsar is a neutron star with a polar jet roughly aligned with Earth. As the star spins and a jet comes into the line of sight of Earth, we detect an extremely regular pulse of light. Indeed, it is so regular that a slight wobble in the star’s motion, due to it possessing planets, is detectable.
The first extrasolar planets (i.e. exoplanets) were found in this way, actually three of them, around the pulsar PSR B1257+12 in 1992. Of course, this technique is only useful for finding planets around pulsars, none of which could be considered habitable – at least by current definitions – and, in all, only 4 such pulsar planets have been confirmed to date.
To look for planets around main sequence stars, we have…
The radial velocity method – This is similar in principle to detection via pulsar timing anomalies, where a planet or planets shift their star back and forth as they orbit, causing tiny changes in the star’s velocity relative to the Earth. These changes are generally measured as shifts in a star’s spectral lines, detectable via Doppler spectrometry, although detection through astrometry (direct detection of minute shifts in a star’s position in the sky) is also possible.
To date, the radial velocity method has been the most productive method for exoplanet detection (finding 500 of the 548), although it most frequently picks up massive planets in close stellar orbits (i.e. hot Jupiters) – and as a consequence these planets are over-represented in the current confirmed exoplanet population. Also, in isolation, the method is only effective up to about 160 light years from Earth – and only gives you the minimum mass, not the size, of the exoplanet.
To determine a planet’s size, you can use…
The transit method – The transit method is effective at both detecting exoplanets and determining their diameter – although it has a high rate of false positives. A star with a transiting planet, which partially blocks its light, is by definition a variable star. However, there are many different reasons why a star may be variable – many of which do not involve a transiting planet.
For this reason, the radial velocity method is often used to confirm a transit method finding. Thus, although 128 planets are attributed to the transit method – these are also part of the 500 counted for the radial velocity method. The radial velocity method gives you the planet’s mass – and the transit method gives you its size (diameter) – and with both these measures you can get the planet’s density. The planet’s orbital period (by either method) also gives you the distance of the exoplanet from its star, by Kepler’s (that is Johannes’) Third Law. And this is how we can determine whether a planet is in a star’s habitable zone.
It is also possible, from consideration of tiny variations in transit periodicity (i.e regularity) and the duration of transit, to identify additional smaller planets (in fact 8 have been found via this method, or 12 if you include pulsar timing detections). With increased sensitivity in the future, it may also be possible to identify exomoons in this way.
The transit method can also allow a spectroscopic analysis of a planet’s atmosphere. So, a key goal here is to find an Earth analogue in a habitable zone, then examine its atmosphere and monitor its electromagnetic broadcasts – in other words, scan for life signs.
To find planets in wider orbits, you could try…
Direct imaging – This is challenging since a planet is a faint light source near a very bright light source (the star). Nonetheless, 24 have been found this way so far. Nulling interferometry, where the starlight from two observations is effectively cancelled out through destructive interference, is an effective way to detect any fainter light sources normally hidden by the star’s light.
Gravitational lensing – A star can create a narrow gravitational lens and hence magnify a distant light source – and if a planet around that star is in just the right position to slightly skew this lensing effect, it can make its presence known. Such an event is relatively rare – and then has to be confirmed through repeated observations. Nonetheless, this method has detected 12 so far, which include smaller planets in wide orbits such as OGLE-2005-BLG-390Lb.
These current techniques are not expected to deliver a complete census of all planets within current observational boundaries, but do offer us an impression of how many there may be out there. It has been speculatively estimated from the scant data available so far, that there may be 50 billion planets within our galaxy. However, a number of definitional issues remain to be fully thought through, such as where you draw the line between a planet versus a brown dwarf. The Extrasolar Planets Encyclopedia currently set the limit at 20 Jupiter masses.
Anyhow, 548 confirmed exoplanets for only 19 years of planet spotting is not bad going. And the search continues. | 0.826312 | 3.831611 |
The upshot of the book is that there is a developing intelligent species on Europa, one of the so-called "Galilean" moons of Jupiter. It's not such a far-fetched idea; Europa has a water-ice crust and might well have liquid water underneath it, so it's entirely possible there's some life form or another living down there. (In the book, there was, and the super-intelligent civilization that sent the famous monolith to Earth in the previous book starts broadcasting the message, "All these worlds are yours -- except Europa. Attempt no landings there" in an attempt to keep humans from dropping in and fucking things up, which you have to admit we have a tendency to do.)
Europa is only one candidate for hosting life, however. An even better bet is Titan, the largest moon of Saturn and the second largest (after Jupiter's moon Ganymede) moon in the Solar System. It's larger than the planet Mercury, although less than half as massive, and its surface seems to be mostly composed of water and ammonia -- although in 2004 the Cassini-Huygens probe found liquid hydrocarbon geysers at its poles, which is certainly suggestive of some fancy organic chemistry going on underneath the surface.
A photograph of Titan taken by Cassini-Huygens. Its featurelessness is because we're seeing the tops of the clouds -- thought to be, basically, photochemical smog. [Image is in the Public Domain, courtesy of NASA/JPL]
One limitation of any probe we've sent out is that even if it's working optimally, it still can only survey a minuscule percentage of the target's surface. What the planned Shapeshifter mission does is to send a spacecraft out there that's composed of hundreds (or more) smaller, self-propelled, robotic spacecrafts that can then roam around exploring the surface or dive down and puncture the crust and see what's down in the oceans that we believe exist below it.
"We have very limited information about the composition of the surface," said team leader Ali Agha, of NASA's Jet Propulsion Laboratory. "Rocky terrain, methane lakes, cryovolcanoes – we potentially have all of these, but we don't know for certain. So we thought about how to create a system that is versatile and capable of traversing different types of terrain but also compact enough to launch on a rocket."
The difficulty -- well, one of the many difficulties -- is whether we'll recognize life on Titan if we find it. Besides an atmosphere that seems to be mostly made of ammonia and methane, Titan has an average surface temperature of around -180 C, which is a little chilly. So any living thing there would have to be adapted to seriously different conditions than anything we've found on Earth. There's no reason to believe that it would share characteristics with any terrestrial life form besides the most basic requirements for life -- reproduction, metabolism, and some kind of inheritable genetic code -- so we'll have to be pretty willing to expand our definition of "living thing" or we'll likely miss it entirely. (Remember the Horta from the famous original Star Trek episode "The Devil in the Dark?" It was a silicon-based life form that used hydrofluoric acid instead of water as its principal circulatory solvent -- and also as a defense mechanism, as various red-shirted unfortunates found out. The intrepid crew of the Enterprise at first thought the Horta was some bizarre geological formation -- which, of course, it sort of was.)
In any case, I hope Agha's project gets off the ground, both figuratively and literally. If we can't develop faster-than-light travel, and unfortunately Einstein's ultimate universal speed limit seems to be strictly enforced in most jurisdictions, investigating other star systems is kind of impractical. So we probably should focus on what's going on here at home -- and hope we're not told, "Attempt no landings on Titan."
Although if we were, that would be eye-opening in an entirely different way.
This week's Skeptophilia book recommendation is especially for those of you who enjoy having their minds blown. Niels Bohr famously said, "Anyone who is not shocked by quantum theory has not understood it." Physicist Philip Ball does his best to explain the basics of quantum theory -- and to shock the reader thereby -- in layman's terms in Beyond Weird: Why Everything You Thought You Knew About Quantum Physics is Different, which was the winner of the 2018 Physics Book of the Year.
It's lucid, fun, and fascinating, and will turn your view of how things work upside down. So if you'd like to know more about the behavior of the universe on the smallest scales -- and how this affects us, up here on the macro-scale -- pick up a copy of Beyond Weird and fasten your seatbelt.
[Note: If you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!] | 0.844585 | 3.472394 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2000 April 12
Explanation: What surrounds the Sun in this neck of the Milky Way Galaxy? Our current best guess is depicted in the above map of the surrounding 1500 light years constructed from various observations and deductions. Currently, the Sun is passing through a Local Interstellar Cloud (LIC), shown in violet, which is flowing away from the Scorpius-Centaurus Association of young stars. The LIC resides in a low-density hole in the interstellar medium (ISM) called the Local Bubble, shown in black. Nearby, high-density molecular clouds including the Aquila Rift surround star forming regions, each shown in orange. The Gum Nebula, shown in green, is a region of hot ionized hydrogen gas. Inside the Gum Nebula is the Vela Supernova Remnant, shown in pink, which is expanding to create fragmented shells of material like the LIC. Future observations should help astronomers discern more about the local Galactic Neighbourhood and how it might have affected Earth's past climate.
Authors & editors:
Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
& Michigan Tech. U. | 0.859047 | 3.028924 |
The brightest stars in Libra organize a quadrilateral that distinguishes it for the unaided perceiver. Alpha Librae. called Zubenelgenubi. is a binary star divisible in field glassess. 77 light years from Earth. The primary is a bluish-white star of magnitude 2. 7 and the secondary is a white star of magnitude 5. 2. Its traditional name means “the southern claw” . Zubeneschamali ( Beta Librae ) is the corresponding “northern claw” to Zubenelgenubi. The brightest star in Libra. it is a green-tinged star of magnitude 2. 6. 160 light years from Earth. Gamma Librae is called Zubenelakrab. which means “the scorpion’s claw” . finishing the suite of names mentioning to Libra’s archaic position. It is an orange giant of magnitude 3. 9. 152 light years from Earth. Libra is home to several other binary and dual stars. Iota Librae is a complex multiple star. 377 light years from Earth. with both optical and true binary constituents. The primary appears as a bluish-white star of magnitude 4. 5 ; it is a binary star indivisible in even the largest recreational instruments with a period of 23 old ages.
The secondary. seeable in little telescopes as a star of magnitude 9. 4. is a binary with two constituents. magnitudes 10 and 11. There is an optical comrade to Iota Librae ; 25 Librae is a star of magnitude 6. 1. 219 light years from Earth and seeable in field glassess. Mu Librae is a binary star divisible in medium-aperture recreational telescopes. 235 light years from Earth. The primary is of magnitude 5. 7 and the secondary is of magnitude 6. 8. There are many variable stars in Libra every bit good. Delta Librae is an Algol-type eclipsing variable star. 304 lightyears from Earth. It has a period of 2 yearss. 8 hours ; its minimal magnitude of 5. 9 and its maximal magnitude is 4. 9. FX Librae. designated 48 Librae. is a shell star of magnitude 4. 9. Shell stars. like Pleione and Gamma Cassiopeiae. are bluish supergiants with irregular fluctuations caused by their abnormally high velocity of rotary motion. This ejects gas from the star’s equator.
The star Thuban ( ? Draconis ) was the northern pole star from 3942 BC. when it moved farther north than Theta Bootis. until 1793 BC. The Egyptian Pyramids were designed to hold one side confronting north. with an entryway transition designed so that Thuban would be seeable at dark. Due to the effects of precession. it will one time once more be the pole star around the twelvemonth 21000 AD. It is a bluish-white elephantine star of magnitude 3. 7. 309 light years from Earth. The traditional name of Alpha Draconis. Thuban. means “head of the serpent” . Draco is home to several dual stars and binary stars. ? Draconis is a dual star with a yellow-hued primary of magnitude 2. 8 and a white-hued secondary of magnitude 8. 2 placed South of the primary. The two are separated by 4. 8 arcseconds. Mu Draconis. traditionally called Alrakis. is a binary star with two white constituents. Magnitude 5. 6 and 5. 7. the two constituents orbit each other every 670 old ages. The Alrakis system is 88 light years from Earth. Nu Draconis is a similar binary star with two white constituents. 100 light years from Earth. Both constituents are of magnitude 4. 9 and can be distinguished in a little amateur telescope or a brace of field glassess.
Omicron Draconis is a dual star divisible in little telescopes. The primary is an orange giant of magnitude 4. 6. 322 light years from Earth. The secondary is of magnitude 7. 8. Psi Draconis is a binary star divisible in field glassess and little amateur telescopes. 72 light years from Earth. The primary is a yellowish-white star of magnitude 4. 6 and the secondary is a xanthous star of magnitude 5. 8. 16 Draconis and 17 Draconis are portion of a ternary star 400 light years from Earth. divisible in moderate-sized recreational telescopes. The primary. a bluish-white star of magnitude 5. 1. is itself a binary with constituents of magnitude 5. 4 and 6. 5.
The secondary is of magnitude 5. 5 and the system is 400 light-years off. [ 1 ] 20 Draconis is a binary star with a white-hued primary of magnitude 7. 1 and a yellow-hued secondary of magnitude 7. 3 placed east-northeast of the primary. The two are separated by 1. 2 arcseconds at their upper limit and have an orbital period of 420 old ages. As of 2012. the two constituents are nearing their maximal separation. 39 Draconis is a ternary star 188 light years from Earth. divisible in little recreational telescopes. The primary is a bluish star of magnitude 5. 0. the secondary is a xanthous star of magnitude 7. 4. and the Tertiary is a star of magnitude 8. 0 ; the third appears to be a close comrade to the primary. 40 Draconis and 41 Draconis are a binary star divisible in little telescopes. The two orange midget stars are 170 light years from Earth and are of magnitude 5. 7 and 6. 1. | 0.827884 | 3.326976 |
This is a long overdue review of this book. Leaving the Planet by Space Elevator is co-authored by Dr. Bradley Edwards and Philip Ragan and is intended, according to the blurb about it on Amazon.com, to be “An easy guide to the most exciting development in space travel since the rocket. Stripped of the technical jargon, this is a layman’s guide to the breathtaking developments surrounding the space elevator: a plan to string a 100,000 km from Earth to space, revolutionizing space access.”
The book certainly succeeds in doing this. Anyone who reads this book, assuming they have at least the intelligence of the average 8th grader and are paying attention, will be able to understand a) what a space elevator is b) how it would be constructed c) how it would work d) why it would work (i.e., the physical principles involved) and e) why it is such a great idea.
Edwards and Ragan discuss everything from the practical issues one will run into in building their version of a space elevator (for example, you need the capability to get 80 tons of parts into space, assemble them together and then lift it all to the appropriate point in geosynchronous orbit), to where it could be actually be anchored on earth. This latter point is most interesting; the authors specify six locations where the factors of nearness to the equator, lack of storms and lack of lightning strikes favor the location of a Space Elevator earthport; the largest being on the equator and west of South America, but also including three locations in the Atlantic Ocean and two locations in the Indian Ocean. As an aside, I found the maps of places on our planet which have/do not have storms and lightning strikes over the measured period to be fascinating.
The book also addresses a common misunderstanding; the example of whirling an object attached to a string around your hand (or head) is often used to indicate how/why the elevator cable would remain straight. This is correct of course, but people often misinterpret this to mean that anchoring the cable to the earth is necessary in order to keep it from flying away into space; as if there are going to be some gigantic clamps holding on to the end of the cable (as the hand is holding on to the end of the string). I still use the ‘object-on-a-string’ example, but emphasize that it is gravity, acting on the entire cable (rather than on just the endpoint) which is holding it in place; i.e. it really is a cable hanging from geosynchronous orbit. This book makes this same point in a very easy to understand way.
This is truly a fine book and is a wonderful introduction to the potential of a Space Elevator. Highly, highly recommended.
Oh, and what’s the difference between this book and the previous effort (The Space Elevator) by Dr. Edwards and Eric Westling? I think you can summarize it this way; The Space Elevator is more technical while Leaving the Planet by Space Elevator is more current. I have both books and am glad I do – I refer to both of them often.
Leaving The Planet by Space Elevator is available from Amazon.com and Lulu.com. For you eBook afficianados, Lulu.com also offers the book in downloadable format.
(Click on the thumbnail to see a larger version of the books front and back cover.)
Update January 20, 2007 – There is a website dedicated to this book too – you can find it here.
Update January 24, 2007 – Well, I stand corrected. I had written in this post that it was not really necessary to clamp the earthbound end of the tether in order to hold it to the planet – the centrifugal force pulling the tether outwards (and upwards) and the gravitational force pulling the tether downwards would be in balance. But, as both Ben Shelef and Dr. Brad Edwards have informed me, there IS a slight, outwards (upwards) pull on the tether; otherwise when the climber was put onto the ribbon, it would have the effect of pulling the ribbon downwards. So, to correct my earlier posting, yes, there must be a clamp holding the space elevator to earth; otherwise the tether will fly away from the planet. But it’s not much – only about 20+ tons worth (in a system massing more than 1400 tons). Once a 20 ton climber is placed on the ribbon, the system is then, essentially, in balance. I apologize for my mistake… | 0.824791 | 3.293774 |
ESO’s Very Large Telescope (VLT) has noticed the central a part of the Milky Way with spectacular resolution and uncovered new details in regards to the history of star birth in our galaxy. Due to the new observations, astronomers have discovered proof for a dramatic event within the life of the Milky Way – a burst of star formation is so intense that it resulted in over a hundred thousand supernova explosions.
Within the research, revealed today in Nature Astronomy, the group discovered that about 80% of the stars within the Milky Way central region formed within the beginning years of the galaxy, between 8 and 13.5 billion years ago. This starting period of star formation was followed by about six billion years throughout which only a few stars have been born, and this was brought to an end by an intense burst of star formation around 1 billion years ago when, over a period of fewer than 100 million years, stars with a combined mass probably as high as just a few tens of million Suns formed on this central region.
This research was possible because of observations of the Galactic central region carried out with ESO’s HAWK-I instrument on the VLT within the Chilean Atacama Desert. This infrared-sensitive camera peered by means of the dust to provide us a remarkably detailed image of the Milky Way’s central region, revealed in October in Astronomy & Astrophysics by Nogueras-Lara and a group of astronomers from Spain, the US, Japan, and Germany.
The survey studied over 3 million stars, covering an area corresponding to more than 60 000 square light-years on the distance of the Galactic center. | 0.887355 | 3.219054 |
|Olympus Mons, NASA/MOLA Science Team/ O. de Goursac, Adrian Lark|
Topics: Mars, Planetary Science, Space Exploration, Spaceflight
Olympus Mons is the most extreme volcano in the solar system. Located in the Tharsis volcanic region, it's about the same size as the state of Arizona, according to NASA. Its height of 16 miles (25 kilometers) makes it nearly three times the height of Earth's Mount Everest, which is about 5.5 miles (8.9 km) high.
Olympus Mons is a gigantic shield volcano, which was formed after lava slowly crawled down its slopes. This means that the mountain is probably easy for future explorers to climb, as its average slope is only 5 percent. At its summit is a spectacular depression some 53 miles (85 km) wide, formed by magma chambers that lost lava (likely during an eruption) and collapsed.
Mars is a planet mostly shaped by wind these days, since the water evaporated as its atmosphere thinned. But we can see extensive evidence of past water, such as regions of "ghost dunes" found in Noctis Labyrinthus and Hellas basin. Researchers say these regions used to hold dunes that were tens of meters tall. Later, the dunes were flooded by lava or water, which preserved their bases while the tops eroded away.
Old dunes such as these show how winds used to flow on ancient Mars, which in turn gives climatologists some hints as to the ancient environment of the Red Planet. In an even more exciting twist, there could be microbes hiding in the sheltered areas of these dunes, safe from the radiation and wind that would otherwise sweep them away.
Touring Mars, Elizabeth Howell, Space.com | 0.821852 | 3.291807 |
NASA's Next Exoplanet-Hunter, TESS, Arrives at Kennedy Space Center Ahead of Launch
TESS is the next exoplanet-hunting mission following the Kepler Space Telescope mission. Kepler has already discovered thousands of exoplanets and TESS is expected to find thousands more. Unlike Kepler however, TESS will survey almost the entire sky over at least two years, looking at 200,000 of the nearest and brightest stars. Kepler focused on one small patch of sky, examining stars further away. It is expected that TESS will be able to catalog more than 1,500 transiting exoplanet candidates, including a sample of about 500 Earth-sized and “super-Earth” planets, with radii less than twice that of the Earth.
TESS will be able to identify exoplanets which may be capable of supporting some form of life, and those findings can then be followed up by even more advanced telescopes, such as the upcoming James Webb Space Telescope, scheduled for launch in 2019.
Jeff Seibert and Alan Walters from AmericaSpace were in the clean room yesterday at Kennedy to view the activities first-hand. As noted to Walters by Robert Lockwood, Orbital ATK Spacecraft Program Director, TESS is a photometry mission, not an imaging mission, so it does not take images directly of any exoplanets, but instead collects other data about them.
According to Lockwood, “The TESS mission is an exoplanet planet finder. We are surveying the entire sky to find star i our solar neighborhood, that is 300 light-years around us, that have exoplanets for follow-up observations by ground and future space telescopes. We would hope to find many Earth-sized planets orbiting around stars near us, and then follow-up observations would look to see if they had atmospheres, if the atmospheres have signatures in them like water or methane. But what we will be doing is just finding the planets for follow-up observations.”
He also noted that the accuracy of the cameras is 3.6 arc seconds, with a stability measure of 50 milli-arc seconds per hour.
TESS will be the first NASA science mission to be launched on a Falcon 9 rocket by SpaceX.
“That’s our first Falcon from the East Coast, for our program,” said Chuck Dovale, deputy manager of NASA’s Launch Services Program at Kennedy Space Center. “It’s a big step for us.”
TESS will be launched into an unusual orbit, orbiting around Earth once every two weeks in a 2:1 resonance with the Moon; the orbit will range from 67,000 miles (108,000 kilometers) to 233,000 miles (376,000 kilometers) from Earth. It will take TESS about two months to settle into its desired orbit.
“The Falcon 9 does a lot of the lifting for us, and then the Moon does most of the rest of it,” said Robert Lockwood, TESS program director at Orbital ATK.
TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. More information is available on the TESS website. | 0.887521 | 3.445401 |
While mapping the solar system’s edge for the first time, NASA’s Interstellar Boundary Explorer (IBEX), spacecraft has discovered a ‘space ribbon’ two billion miles long.
As the solar wind reaches the edge of the solar system and collides with the interstellar medium, a shock wave forms, heating particles which then stream away from the boundary.
“We have discovered an arc-shaped ribbon of high-pressure material that looks to be piled-up material from the Sun,” says team member Herbert Funsten. “The IBEX maps and the discovery of the ribbon are completely different from what we thought it should look like. We were expecting tie-dye and instead found noodle soup.”
What the mission has not found is what it was expecting – evidence of large-scale dynamic processes like the storms and tornados that result from the collision of a cold front and a warm front.
“The ribbon follows a circular arc of high pressure that we believe is centered on the direction of the magnetic field of the interstellar cloud through which we are moving,” Funsten said. This magnetic field seems to fundamentally organize the interaction region.
The sky map was produced with data collected by two detectors on the spacecraft over a six-months period. The detectors measured and counted particles known as energetic neutral atoms.
“For the first time, we’re sticking our heads out of the sun’s atmosphere and beginning to really understand our place in the galaxy,” said David J McComas, IBEX principal investigator. “The IBEX results are truly remarkable, with a narrow ribbon of bright details or emissions not resembling any of the current theoretical models of this region.” | 0.866994 | 3.715864 |
Gas pillars in the Eagle Nebula: One of Hubble's most famous images. Image courtesy NASA.
On May 19, 2009, the Space Shuttle Atlantis released the Hubble Space Telescope (HST) back into orbit after a hugely successful servicing mission, during which two new instruments have been installed on board the telescope, and two existing ones have been repaired. This marked the beginning of the next phase in the life of this incredible observatory. During its 19 years of operation, HST has produced 39 terabytes of data in the HST archive. At the time of this writing, 7,917 refereed scientific articles have been written based on HST data. With such a record, it is clearly impossible to even just list the HST's scientific accomplishments in a short article. In what follows, I have attempted to briefly describe (in no particular order) what I regard as the top five scientific discoveries. I should also note that rarely do astronomical discoveries belong to just one telescope. Usually it is many observatories, from the ground and from space, working in concert to produce a complete and multihued view of phenomena. Nevertheless, in the topics that I have selected, there is no doubt that HST played a crucial role.
The Hubble Constant
The astronomer Edwin Hubble, after whom the Hubble Space Telescope is named, determined in the 1920s that our Universe is expanding. The fabric of space between any two distant galaxies is stretching, just like the rubber of an inflating balloon. The rate at which galaxies are currently moving apart from one another is known as the Hubble constant, or H0. For a constant rate of expansion, the inverse of H0 gives the time at which the expansion started. But even in the presence of deceleration and acceleration H0 is the dominant factor in determining the age of the Universe.
Before HST, the value of H0 was known only to within a factor of two. The main reason for this large uncertainty was the fact that the determination of distances in astronomy is notoriously difficult. To overcome this obstacle, astronomers have constructed a distance ladder in which they use a series of standard candles — objects whose brightnesses are relatively well known — to infer distances to objects that are increasingly farther away.
Figure 1: Cepheid variable star in galaxy M100. Image courtesy NASA.
Key standard candles are certain pulsating stars — stars that show periodic variations in their brightness — known as Cepheid variables. These are luminous stars, about a thousand times more luminous than the Sun, whose intrinsic brightness is tightly correlated to their pulsation period. By measuring the period of the variation, astronomers deduce the intrinsic brightness, and by comparing that to the apparent brightness, they can determine the distance (the apparent brightness decreases like the inverse square of the distance). The superb resolution of HST has allowed astronomers to isolate the light from numerous Cepheids in dozens of galaxies (figure 1), and the uncertainty in the value of the Hubble constant has initially been reduced to about 10%. Most recently, detailed HST observations of Cepheids in the galaxy NGC 4258 — whose distance is very accurately known through radio observations — coupled with observations of well-calibrated supernova explosions in more distant galaxies, have reduced the error in the value of H0 to less than 5%.
In 1998, two teams of astronomers working independently discovered that the expansion of our Universe is in fact speeding up, propelled by the repulsive force of a mysterious dark energy. This came as a shock, because the prevailing assumption was that cosmic expansion should be slowing down due to the mutual gravitational attraction of all matter within the Universe. The precise nature of the dark energy that powers the acceleration is arguably the biggest puzzle that physics is facing today. Since the discovery, observations of the cosmic microwave background radiation have shown that dark energy makes up more than 70% of the total energy density of the Universe. The Hubble observations relied on a particular type of supernova explosion (known as Type Ia supernovae) to trace the expansion history of the Universe (figure 2), and thereby to place constraints on the properties of dark energy. There are two factors that make type Ia supernovae particularly useful in this regard. First, they are extremely bright, and therefore can be observed half way across cosmic time. Second, they are good standard candles — their luminosities are nearly constant — and therefore their distances can be determined quite accurately. Hubble's sharp vision has allowed astronomers to pinpoint distant supernovae in galaxies that are as far as nine billion light-years away, and to determine that dark energy was already present (though not dominant) even at that early stage, when gravity still had the upper hand and the expansion of the cosmos was decelerating.
Figure 2: Hubble spots distant supernovae in search of properties of dark energy. Image courtesy NASA.
All the observations to date are consistent with dark energy being the energy of empty space. Quantum mechanics, the theory that most accurately describes the sub-atomic world, says that the physical vacuum, far from being empty, is teeming with virtual particles that appear and disappear in split seconds. The energy density associated with the vacuum is constant, and characterised by an equation of state parameter w (the ratio of pressure to density), which, according to the theory, satisfies w = -1. Most of the current observational efforts are directed at determining whether w is indeed constant across cosmic time, and whether its value is equal to –1. However, even if the characteristics of dark energy will be found to be fully consistent with it being the energy of the vacuum, many open questions will remain. In particular, naive attempts to theoretically calculate the expected value of the vacuum energy density produce results that are more than 50 orders of magnitude higher than the observed value (see Plus article Lambda marks the spot for more information). Consequently, a true understanding of dark energy will require a combination of observational efforts coupled with significant theoretical developments.
Galaxy formation and evolution
Figure 3: The heart of the Whirlpool Galaxy. Image courtesy NASA.
Everyone is familiar with the shapes of the galaxies that we see in the relatively local Universe. Galaxies such as the Milky Way and the Andromeda galaxy are disc galaxies: they are flattened like pancakes, and are characterised by a prominent spiral structure traced by young stars (figure 3). Other galaxies are elliptical: they are shaped like oval concentrations of relatively old stars. One of the key goals of astronomy is to understand how galaxies form and how they evolve. Astronomers using HST produced the deepest images of the Universe in optical light. These observations were dubbed the Hubble Deep Fields and the Hubble Ultra Deep Field (figure 4). The observations revealed that galaxies in the distant past were smaller in physical size, and that their shapes were much more irregular. These two properties are consistent with a scenario of hierarchical structure formation, in which smaller building blocks of galaxies collided and coalesced frequently in the early, dense Universe, to form the larger galaxies we observe today. Using HST's exquisite spatial resolution and photometric stability, astronomers were also able to observe in detail the stellar populations in the old halos of nearby galaxies, which allowed them to reconstruct how mass was assembled in these galaxies.
Figure 4: The Hubble Ultra Deep Field image reveals galaxies galore. Image courtesy NASA.
Finally, the deep-field observations yielded the history of the global rate of star formation in the cosmos. Even before the Hubble observations, astronomers knew that our Universe as a whole is past its peak in terms of the rate of birth of new stars. The peak occurred about 7 to 8 billion years ago. The Hubble Ultra Deep Field showed that when the Universe was less than one billion years old (the Universe today is 13.7 billion years old) the rate of cosmic star formation was lower than the peak value by about a factor of three, but already higher than the rate today, which is about a factor of ten lower than at the peak. In other words, once the Universe started forming stars, it did so furiously.
Supermassive black holes
Figure 5: Hubble confirms the existence of a massive black hole at the heart of an active galaxy. Image courtesy NASA.
Astrophysicists have long suspected that active galactic nuclei — the extremely bright cores of galaxies that show violent activity — and quasi-stellar objects (QSOs) create their extraordinarily high luminosities by accreting mass at a high rate onto a black hole that lies at their centre. The power emitted simply reflects the rate of release of gravitational potential energy. However, before HST it was virtually impossible to detect the host galaxies of QSOs, and it was extremely difficult to confirm the presence of a black hole, except in a couple of relatively nearby galaxies, and in our own Milky Way Galaxy. HST changed all that. First, it has unambiguously detected the host galaxies in a few relatively nearby QSOs. Second, by following the motions of individual stars (or of gas discs) around the centres of tens of galaxies, it has shown that essentially all the galaxies that have a central bulge of stars harbor a supermassive black hole at their centres (figure 5). The masses of these black holes range from a few millions to a few billions of solar masses. But in addition to the mere discovery of the black holes, HST provided two other significant pieces of information. First, high-resolution images of the hosts of QSOs revealed that many of them were interacting galaxies and the others were bright elliptical galaxies. This suggests that certain environments (such as the one resulting from an interaction) may be needed to funnel gas into the central regions to fuel the black holes.
Second and more important, the masses of the black holes were found to be tightly correlated with the masses of the smooth, spherical bulges of stars surrounding the galactic centres. This indicates that the black holes and their host galaxies do not evolve independently, but rather that their evolutions are intimately connected — massive black holes are apparently a generic feature of galaxy formation and evolution.
Figure 6: A planet's telltale signature. Image courtesy NASA.
Until 1992, we did not know of a single planet outside our solar system. In 1992, the first so-called extrasolar planets were detected, but they did not orbit an ordinary star such as the Sun. Rather, they were found around a pulsar — an extremely compact object with a mass of about 1.4 solar masses, but a radius of only about 10km. The first planet around a Sun-like star was discovered in 1995. Since then, astronomers have discovered about 350 extrasolar planets. Most of these planets were discovered by ground-based telescopes. Still, HST has contributed a few unique observations to this field. First, Hubble focused on transiting planets — planets whose orbital planes are aligned with our line of sight, so that the planets periodically eclipse their host stars. When the planet passes in front of the star, it blocks some of the star's light. From the amount of dimming (typically 1-2%) the radius of the planet can be deduced (figure 6). But this is not all. Some of the starlight passes through the planet's atmosphere, where part of it is absorbed by various atoms. By concentrating on particular spectral lines, the presence and abundance of certain atoms and molecules can be determined (see Plus article Hunting for life in alien worlds for more on this technique). In this way, HST observations showed that the atmosphere of the planet around the star HD 209458 contains sodium, carbon, oxygen, and hydrogen. In another case, even water and methane were detected. These were the first determinations of the composition of atmospheres of extrasolar planets.
The Hubble Space Telescope against the Earth's horizon. Image courtesy NASA.
Most of the extrasolar planets were found around stars in the solar neighborhood. This still left open the question of whether the local fraction of stars hosting planets is typical of the Galaxy at large. To answer this question, HST observed about 180,000 stars in the crowded central bulge of our Galaxy, half-way across the Milky Way. These observations led to the discovery of 16 planet candidates, a tally consistent with the frequency of planets in the solar neighborhood, and they showed that the Galaxy is indeed teeming with billions of planets. Five of the planet candidates were found to whirl around their stars in less than one Earth day, and they were dubbed Ultra-Short-Period Planets.
Finally, HST produced the first visible-light snapshot of a planet orbiting another star. The planet, known as Fomalhaut b since it circles the bright southern star Fomalhaut, was resolved inside a large debris disc, somewhat similar to the Kuiper Belt in our own solar system. The planet's distance from its host star is about ten times the distance of the planet Saturn from the Sun.
Following Servicing Mission 4, Hubble has the largest complement of functioning instruments it has ever had. Assuming that the Wide Field Camera 3 (WFC3), the Cosmic Origins Spectrograph (COS), the Advanced Camera for Surveys (ACS), and the Space Telescope Imaging Spectrograph (STIS) will work as expected, many Hubble discoveries are still to come. In particular, WFC3, with its infrared capabilities, will take us even closer to the very first galaxies, and COS will reveal to us the structure and composition of the cosmic web — the filamentary intergalactic gas. You can be almost certain that five years from now, the list of the top five Hubble discoveries will have to be revisited.
About the author
Mario Livio is a theoretical astrophysicist at the Space Telescope Science Institute, which conducts the scientific program of the Hubble Space Telescope. He has published more than four hundred scientific articles in a wide range of topics in astrophysics. Dr Livio's recent book, Is god a mathematician? was reviewed in Issue 49 (December 2008) of Plus. | 0.908326 | 4.027081 |
Finding extraterrestrial life in our solar system just got a huge boost. NASA’s Cassini space probe has detected molecular hydrogen in the plumes of saltwater that burst from the oceans buried beneath the icy surface of Saturn’s moon Enceladus. Scientists remain cautiously agnostic, but the discovery of key ingredients for life is a game changer. With subsurface oceans found beneath other moons in our solar system, most famously Jupiter’s frozen moon Europa, the chances of finding extraterrestrial life (at the bacterial level at least) is exciting. It also has implications for the possibility of alien life elsewhere in the galaxy. We’re only now able to detect atmospheres on planets orbiting distant stars — what about their moons?
Above: Colour-enhanced image from Cassini.
Below: Plumes of saltwater burst from the icy surface of Enceladus. | 0.837516 | 3.010068 |
Kepler Mission launched by NASA has discovered another world, two months after the Kepler spacecraft ran out of the fuel. They took nine years to complete their mission and meanwhile they unveiled 2,600 confirmed planets in addition to many more which are not yet confirmed.
This time NASA has come up with all new planet-hunter, the Transition Exo-planet Survey Satellite, which is being used for the new discoveries. With the aid of Kepler’s Space Telescope, the scientists have found that there is a planet in the habitable zone of stars which is found to be twice the size of Earth. This new world is named as K2-288Bb. It is also a dense ball of gases resembling that of Neptune.
The scientists were very happy with this great discovery as it was uncommon. It resides in the K2-288 stellar system from where it get its name. This stellar system comprises a dim set of stars (M-type stars) among which the brightest star is half massive as the sun.
A team comprising of an undergraduate student and an astrophysicist at NASA searched the dimming of stars while the planet moves across them. The team noticed two planetary transits in the same system. But they needed the presence of a third transit before confirming the presence of the neighboring planet but they didn’t notice any.
From 2014-2018, the spacecraft reposition itself at the start of every year to search other parts of the sky. While orienting the equipments toward the sun, the equipment has to suffer shape alteration due to elevated temperature. To cope with all these concerns, the software was used but it ignored that signals where third transit lied.
To ensure the accuracy, the data was re-analyzed and the planets were re-evaluated to confirm the presence of the entities but due to the occurrence of other noises in space that mimics the transits, the accuracy wasn’t assured.
All the collected data was sent to Exoplanet Explorers to re-process the data. In 2017, volunteers confirmed the third transit. They had a meeting a discussed all the shortcomings that have hindered them to notice it.
For this mission, they employed Spitzer Space Telescope, K II telescope, and the NASA’s Infrared Telescope Facility to discover all these. | 0.893962 | 3.178663 |
Image credit: Hubble
A new photograph taken by the Hubble Space Telescope shows a nebula formed around a group of young, hot, stars. Designated N44C, the nebula is located in the Large Magellanic Cloud, a nearby, small companion galaxy to the Milky Way. It’s peculiar because the star located at the centre of the nebula is inexplicably hot – it could be that the star has a black hole or neutron star companion.
Resembling the hair in Botticelli’s famous portrait of the birth of Venus, softly glowing filaments stream from a complex of hot young stars. This image of a nebula, known as N44C, comes from the archives of NASA’s Hubble Space Telescope (HST). It was taken with the Wide Field Planetary Camera 2 in 1996 and is being presented by the Hubble Heritage Project.
N44C is the designation for a region of glowing hydrogen gas surrounding an association of young stars in the Large Magellanic Cloud, a nearby, small companion galaxy to the Milky Way visible from the Southern Hemisphere.
N44C is peculiar because the star mainly responsible for illuminating the nebula is unusually hot. The most massive stars, ranging from 10-50 times more massive than the Sun, have maximum temperatures of 54,000 to 90,000 degrees Fahrenheit (30,000 to 50,000 degrees Kelvin). The star illuminating N44C appears to be significantly hotter, with a temperature of about 135,000 degrees Fahrenheit (75,000 degrees Kelvin)!
Ideas proposed to explain this unusually high temperature include the possibility of a neutron star or black hole that intermittently produces X-rays but is now “switched off.”
On the top right of this Hubble image is a network of nebulous filaments that inspired comparison to Botticelli. The filaments surround a Wolf-Rayet star, another kind of rare star characterized by an exceptionally vigorous “wind” of charged particles. The shock of the wind colliding with the surrounding gas causes the gas to glow.
N44C is part of the larger N44 complex, which includes young, hot, massive stars, nebulae, and a “superbubble” blown out by multiple supernova explosions. Part of the superbubble is seen in red at the very bottom left of the HST image.
The data were taken in November 1996 with Hubble’s Wide Field Planetary Camera 2 by Donald Garnett (University of Arizona) and collaborators and stored in the Hubble archive. The image was composed by the Hubble Heritage Team (STScI/AURA).
Original Source: Hubble News Release | 0.865374 | 3.923518 |
Here on Earth, we're used to a certain kind of weather. It might be unpredictable and scary at times, but at least we know that everything falling out of our atmosphere and onto the ground is water in some form or another. You'd be excused, therefore, for thinking "water" when considering the question of rain on other planets. But you'd be wrong all the same -- Earth is the only planet that has liquid water. There is indeed rain falling from clouds on other planets, but it's not water. Not even close.
Let's start with perhaps the most intriguing substance that might be raining down on a number of planets. Diamonds. Yes, diamonds. About 1,000 tons (907 metric tons) a year fall on Saturn [source: Morgan]. But before you start devising a way to make a fortune by collecting diamonds in outer space, we need to tell you that this isn't a cold, hard fact. It's still an unpublished theory -- a theory by planetary scientists at the NASA Jet Propulsion Laboratory, but unproven nonetheless.
According to the findings, diamond rain falls on Saturn, Neptune and Jupiter, among others, but Saturn might have the best conditions for it. Saturn's intense lightning storms (10 strikes per second!) can cause the methane molecules in its atmosphere to break up, leaving carbon atoms to float freely and start falling to the ground [source: Jaramillo]. They transform into graphite as they travel through Saturn's dense, layered atmosphere and eventually get pressurized into tiny diamond pieces (most are less than a millimeter in diameter). But about 22,000 miles (36,000 kilometers) in, things get too hot and the diamonds decompose into a mushy liquid [source: Dattaro].
Not into diamonds? Head to Venus for some refreshing, incredibly hot sulfuric acid rain. Venus' atmosphere is full of sulfuric acid clouds, but because the surface of the planet hovers at a balmy 894 degrees Fahrenheit (480 Celsius), the rain only gets about as close as 15.5 miles (25 kilometers) to the surface before it becomes a gas [source: Hammonds].
Over on Titan, Saturn's largest moon, there are icy methane rainstorms. Just as Earth has a water cycle, Titan has a methane cycle: There are seasonal rains, the methane rain fills up lakes, the lakes eventually evaporate and the vapor ascends into the clouds, starting the whole thing over again. Methane is in its liquid form on Titan because the surface temperature is an extremely chilly minus 290 degrees F (minus 179 C) [source: Space.com]. There are also solid-ice mountains on Titan.
These cases are just the start of the conversation about rain on other planets. We didn't even get into dry-ice snow on Mars, liquid helium rain on Jupiter and plasma rain on the sun. It's fascinating stuff, but we'll leave the horrific flesh-melting precipitation to the rest of the solar system, please. We're just fine stuck with good old lukewarm rainwater.
- Arcale, Calli. "What the Weather is Like on Other Moons and Planets." Mental Floss, Sept. 21, 2012. (July 5, 2014) http://mentalfloss.com/article/12596/what-weather-other-moons-and-planets
- Dattaro, Laura. "Diamonds Rain Down on Saturn and Jupiter." Weather.com, Oct. 9, 2013. (July 5, 2014) http://www.weather.com/news/science/diamonds-rain-down-saturn-and-jupiter-20131009
- Hammonds, Markus. "The Metallic Snow-Capped Mountains of Venus." Discovery News. http://news.discovery.com/space/the-metallic-snows-of-venus-130610.htm
- NASA Jet Propulsion Laboratory. "NASA Observations Point to 'Dry Ice' Snowfall on Mars." Sept. 11, 2012. (July 5, 2014) http://www.jpl.nasa.gov/news/news.php?release=2012-286&cid=release_2012-286
- Jimenez Jaramillo, Juliana. "Bizarre Weather Around the Solar System." Slate, Dec. 11, 2012. July 5, 2014) http://www.slate.com/articles/health_and_science/science/2012/12/space_weather_tornadoes_dust_storms_hurricanes_acid_rain_on_other_planets.html
- Morgan, James. "'Diamond Rain' falls on Saturn and Jupiter.'" BBC News, Oct. 14, 2013. (July 5, 2014) http://www.bbc.com/news/science-environment-24477667
- Space.com. "Titan, Saturn's Largest Moon, Facts and Discovery." April 13, 2012. (July 5, 2014) http://www.space.com/15257-titan-saturn-largest-moon-facts-discovery-sdcmp.html | 0.800104 | 3.838737 |
Almost in spite of its decline, Spitzer’s last months will be jam-packed with science. The biggest challenge between now and its end will be avoiding any anomaly that could render the telescope unusable before its appointed end. But presuming everything runs smoothly, Spitzer will collect a vast hoard of data during the next seven months that will take decades to analyze and soften the blow of the gap until the JWST—including observations of dwarf stars, the center of our galaxy and, of course, exoplanets.
Delays to the James Webb Space Telescope will result in at least a yearlong hiatus in space-based infrared observations
Editor’s Note (1/21/20): On January 30, 2020, spacecraft controllers will transmit the final shutdown commands to NASA’s Spitzer Space Telescope, bringing the observatory’s 16-year mission to a close. This story from 2019 details the reasons for the shutdown, reflects on Spitzer’s legacy and discusses the gap in infrared astronomy that will persist until the debut of the observatory’s successor, the James Webb Space Telescope.
In 2016 NASA’s Spitzer Space Telescope observed a distant star called TRAPPIST-1 for 500 hours. Around the star, using the telescope’s unique infrared capabilities, scientists were able to discover four roughly Earth-sized exoplanets, adding to three others previously found in the system. To date, no other star has been shown to harbor so many small worlds. Most impressive of all was that Spitzer had never been designed to find exoplanets. “When Spitzer was first conceived of in the 1980s, [exoplanets] hadn’t even been discovered,” says Charles Beichman, Executive Director of the NASA Exoplanet Science Institute at the California Institute of Technology.
Spitzer’s observations of TRAPPIST-1 were a testament to just how far the telescope has exceeded expectations. Launched in 2003 as the last of NASA’s four “great observatories”—the others being the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-ray Observatory—Spitzer has helped usher in a new Golden Age of astronomical discovery. Even today, despite its aging hardware, the telescope continues to produce vital scientific contributions—in large part because Earth’s atmosphere blocks most infrared light, making space-based observations the only option to see the entire infrared sky. It remains, for instance, arguably the best presently available telescope for investigating exoplanet atmospheres for signs of habitability and life.
But Spitzer’s mission is now set to end. In May 2019 NASA confirmed that the telescope will be retired on January 30, 2020, bringing to a close an incredible mission that originally was planned to last only two and a half years. With modest operational costs of just $14 million a year, however, and suggestions that Spitzer could have operated until at least November 2020—bridging the gap between itself and the much-delayed James Webb Space Telescope (JWST), NASA’s next infrared space telescope—this conclusion leaves some astronomers with decidedly mixed feelings.
“It’s slightly complicated,” says Lisa Storrie-Lombardi, project manager for Spitzer at NASA’s Jet Propulsion Laboratory. “They’re going to be spending the money on something else. Originally it all made a lot of sense. JWST was going to be flying if we retired Spitzer now, but that’s a little less clean now. Spitzer has been able to do great science, and it’s still doing that; it’s going to end on a high note. $14 million is an excellent price for what Spitzer can do.”
The Spitzer mission last came up for formal consideration of its retirement in spring of 2016, when the JWST—50 times larger than Spitzer and offering vast improvements on its infrared capabilities—was planned to launch in 2018. Back then, the space agency’s decision was that Spitzer would be retired in 2019, overlapping with JWST and perfectly handing off the infrared baton. Soon, however, NASA was forced to push back the launch of JWST, first to 2019, then to 2020 and ultimately to March 2021 at the earliest. NASA officials opted to extend Spitzer’s mission to January 2020 to compensate, but calculated that beyond this date continued operation of the telescope offered dramatically diminishing returns.
This leaves a gap in infrared capabilities between Spitzer and JWST that could negatively affect astronomy as a whole. Having an infrared space telescope ready and waiting is useful to follow-up on certain events, such as exoplanet finds from NASA’s Transiting Exoplanet Survey Satellite, or gravitational-wave discoveries from the LIGO consortium, as was done with two merging stars in 2017, or even the detection of mysterious objects passing through our solar system from interstellar space. “Without Spitzer it may not have been possible to get that information,” says Michael Werner, the Project Scientist for Spitzer at JPL.
Although Spitzer’s operating costs are relatively modest, there are sound reasons to shutter the telescope in the not-too-distant future. It is slowly moving away from our planet in its Earth-trailing orbit, requiring Spitzer to pitch at higher angles to beam its transmissions home and reducing the amount of sunlight striking the spacecraft’s solar panels. Where once it could transmit indefinitely, it can now manage just two and a half hours a day before its batteries drain. Spitzer’s greater distance from Earth also means communicating with home is becoming more difficult just as the telescope’s hardware is reaching its limits. “The hardware is ageing, and rather than go to a failure where we couldn’t recover, we just want to end the mission gracefully,” says Kartik Sheth, Deputy Program Scientist at NASA headquarters in Washington, D.C.
In 2009 the mission also ran out of coolant to keep its infrared instrument cold. Rather than bring the mission to a close, scientists decided instead to enter a “warm phase,” using Spitzer’s two remaining operational infrared detectors to perform deep surveys of the universe and hunt for exoplanets. “We definitely lost some capabilities,” Beichman says. “But the warm mission, which was thought to be a little addendum to the cold mission, has gone on spectacularly well. I think that surprised [Spitzer’s] builders.”
Paul Hertz, NASA’s Astrophysics Division director, insists the decision to end the mission was based not on money but on the operational capability of the telescope. “We are not retiring Spitzer because of cost,” he says. “We are retiring it because of increasingly difficult and risky operations, which is reducing the science value of the mission. This is not something that was decided recently; rather we have been working towards end-of-mission since the decision in spring 2016.”
There had been some suggestions the telescope could endure until November 2020, and in 2017 NASA attempted to find a private entity to take over the funding of the spacecraft to see it through its final stage of operations. They were unsuccessful and, Storrie-Lombardi notes, any extension would likely have been a somewhat reduced mission owing to the aforementioned problems. “What would happen in the 2020s is the rate at which we can downlink data would be lowered,” she says. “We could take science data, but we might take less. In terms of operating the way we are now, early 2020 is a reasonable time to end.” | 0.854127 | 3.692751 |
Another day, another exoplanet discovery! At least, that's certainly what it feels like as of late, with astronomers successfully seeking out the celestial objects and stumbling upon some pretty impressive discoveries. Most recently, two new exoplanets that scientists are referring to as "Super-Earths" as well as a record-smashing "cold Neptune" were added to the veritable menagerie of space objects it feels like we've added to our galactic reach thus far. Is this the path forward to finally choosing a "replacement" Earth for the far-off future if (or when) Earth finally becomes uninhabitable?
It certainly feels that way sometimes, especially since the new "Super-Earth" exoplanets are possibly habitable. Orbiting red dwarf stars GJ229A and GJ180, these planets are about 19 lightyears and 39 lightyears from Earth, respectively. Red dwarf stars are similar to our sun in the solar system, but much smaller, and less bright. That means the habitable zones on the exoplanets, or the areas on the planet where liquid water could remain surface-stable, are closer to the stars they orbit around than they are with Earth and our solar system.
We've seen habitable zone red dwarf planets before, which was the case with the most recent discovery thanks to NASA's TESS finding the newly-christened exoplanet TOI 700 d. But TOI 700 d, like most similar exoplanets orbiting red dwarf planets are, is tidally locked. That means that the stars red dwarf planets orbit around only ever shows them the same side, much like Earth only sees one side of the moon.
It looks like that isn't the case with these new exoplanets, which actually happen to orbit far enough away from the red stars that they aren't forced into tidal locking. That alone makes GJ180 d, along with its partner exoplanet GJ229A c significant discoveries.
"GJ180 d is the nearest temperate super-Earth to us that is not tidally locked to its star, which probably boosts its likelihood of being able to host and sustain life," said Fabo Feng, Carnegie Institution for Science in Washington, D.C., team lead, in a statement.
GJ180 d is actually a bit bigger than Earth, with 7.5 times the mass of our planet. GJ229A c is also larger than the Earth, with about 7.9 times Earth's masses. But as the letters in the planets' names indicate, there are additional worlds in their systems as well. There's also GJ 433 d, which isn't quite a candidate for supporting life. It is, however, the "nearest, widest, and coldest Neptune-like planet" that's ever been detected, according to Feng. But while it's similar in size to the other planets, it's not really a good fit for people to actually live on.
Beyond those details, astronomers still don't know a lot about the new exoplanets, the so-called "Super-Earths." It may be a while, potentially when NASA's upcoming James Webb Space Telescope finally launches next year, before additional research becomes possible.
With the new telescope in the works for next year and continued study into exoplanets, their potential methods of supporting life, and all the other findings scientists are seemingly reporting every other week or so, it feels like we're painfully close to finding a planet that might actually act as a decent surrogate for humanity at one point far off in the future. There's still plenty left to explore, so that means we've hardly even scratched the surface when it comes to the possibilities the human race has kindly been afforded.
This article was originally published on | 0.912694 | 3.708663 |
Cold Gas and the Evolution of Early-type Galaxies
Lisa Young, New Mexico Tech
A major theme of galaxy evolution is understanding how today’s Hubble sequence was
established — what makes some galaxies red spheroidals and others blue disks, and what
drives their relative numbers and their spatial distributions. One way of addressing these
questions is that galaxies themselves hold clues to their formation in their internal
structures. Recent observations of early-type galaxies in particular (ellipticals and
lenticulars) have shown that their seemingly placid, nearly featureless optical images can
be deceptive. Kinematic data show that the early-type galaxies have a wide variety of
internal kinematic structures that are the relics of dramatic merging and accretion
events. A surprising number of the early-type galaxies also contain cold atomic and
molecular gas, which is significant because their transitions to the red sequence must
involve removing most of their cold gas (the raw material for star formation). We can now
also read clues to the evolution of early-type galaxies in the kinematics and the
metallicity of their gas, and possibly also in the rare isotope abundance patterns in the
cold gas. Numerical simulations are beginning to work on reproducing these cold gas
properties, so that we can place the early-type galaxies into their broader context.
Starless clumps and the earliest phases of high-mass star formation in the Milky Way
Brian Svoboda, NRAO Jansky Fellow
High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. In order to understand the physical conditions during the earliest phases of high-mass star formation, I will present observational studies we have carried out on dense starless clump candidates (SCCs) that show no signatures of star formation activity. We identify 2223 SCCs from the 1.1 mm Bolocam Galactic Plane Survey, systematically analyse their physical properties, and show that the starless phase is not represented by a single timescale, but evolves more rapidly with increasing clump mass. To investigate the sub-structure in SCCs at high spatial resolution, we investigate the 12 most high-mass SCCs within 5 kpc using ALMA. We find previously undetected low-luminosity protostars in 11 out of 12 SCCs, fragmentation equal to the thermal Jeans length of the clump, and no starless cores exceeding 30 solar masses. While uncertainties remain concerning the star formation efficiency in this sample, these observational facts are consistent with models where high-mass stars form from initially low- to intermediate-mass protostars that accrete most of their mass from the surrounding clump. I will also present on-going research studying gas inflow signatures with GBT/Argus and ALMA, and the dense core mass function with the JVLA.
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An Observer’s Examination of the Circumgalactic Medium using Cosmological Simulations
Rachel Marra, NMSU
A significant aspect to understanding galaxy evolution is having an understanding of the intricacies involving the inflow and outflow of baryons onto a galaxy. Gas needs to accrete onto the galaxy in order for star formation to occur, while stellar winds, supernovae, and radiation pressure result in the outflow of gas from the galaxy. The diffuse region around the galaxy that has gas from interstellar medium (ISM) inflows and intergalactic medium (IGM) outflows interacting is the circumgalactic medium (CGM). Studying the CGM will help us learn about the baryon cycle and give us a better understanding of galactic evolution.
The primary method to studying the CGM is through absorption, as the density is too low to detect emission. Studying these absorption features allows us to learn about the physical properties of the gas giving rise to the absorption. Other than through observations, cosmological simulations play a large role in how we learn about the CGM of galaxies. Using MOCKSPEC, the Quasar Absorption Line Analysis Pipeline, to create mock quasar sightlines through the VELA simulation suite of galaxies, we use the absorption features seen in the sightlines to study the CGM in the simulations. While there are many ions that are used to study the CGM, we focus on OVI.
We intend to study how effective our methods are for studying the CGM with both observations and simulations. The covering fraction of OVI for a sample of observed galaxies will be compared with the covering fraction that is found from a selection of LOS that probe simulated, Milky-Way type galaxies. This tells us if the simulations can reproduce the observations, and if they do not, we can gain insights as to why the simulations do not match observed data. We will also investigate if the metallicity calculated from an observed absorption feature reflects the actual metallicity of the probed gas by using mock sightlines through simulations. Additionally, we will do a comparison of different methodologies used to study the CGM in simulations, to determine if using mock quasar sightlines is a more realistic and accurate method to compare to observed data. | 0.897842 | 4.125922 |
Scientists will now be able to measure how fast the universe is truly expanding with the kind of precision not possible before. This, after an international team of astronomers led by Stockholm University, Sweden, captured four distinct images of a gravitationally lensed Type Ia supernova, named iPTF16geu.
Since its arrival at comet 67P/Churyumov-Gerasimenko in August 2014, ESA’s Rosetta spacecraft has been surveying the surface and the environment of this curiously shaped body. Now that the comet is experiencing a brief, hot southern hemisphere summer, its south polar regions have emerged from almost five years of total darkness and it has been possible to observe them with other Rosetta instruments.
The origin of of Comet 67P/Churyumov-Gerasimenko’s double-lobed form has been a key question since Rosetta first revealed its surprising shape in July 2014. By studying the layers of material seen all over the nucleus, scientists have shown that the shape arose from a low-speed collision between two fully fledged, separately formed comets.
Scientists from Rosetta’s OSIRIS team have discovered an extraordinary formation in the Aker region on the larger lobe of comet 67P/Churyumov-Gerasimenko. The largest of a group of three boulders with a diameter of approximately 30 metres appears to perch on the rim of a small depression. There seems to be only a very small contact area with the nucleus. | 0.836853 | 3.530889 |
Petroleum in space? Ain’t that a Gas! – Part 3
Saturn, the sixth planet out from the Sun, orbits 1.2 billion km from us, at its closest approach—eight times the distance between Earth and Sun.
Titan is the largest of Saturn’s 62 moons. With a diameter of 5,150 kilometers, it is wider than the planet Mercury (though less massive), comprising 96 percent of Saturn’s orbiting mass.
According to Wikipedia, the icy moon gets only about one percent as much sunlight as Earth. Hence frigid conditions on this moon, where the temperature is 94 to 98 K.
Titan holds the distinction, of being the solar systems only planetary satellite, with a thick atmosphere—which, like that of Earth, is nitrogen-rich.
In contrast to our planet though, the air on Titan consists of one to six percent methane and smaller quantities of heavier natural gases, such as ethane (C2H6) propane (C2H8) and ethalyne (C2H4).
These heavier species, explains a Case Western Reserve University (U.S.A.) posting, are created when Ultraviolet radiation from the Sun interacts with the methane in the moon’s atmosphere.
“Titan is just covered in carbon-bearing material,” Ralph Lorenz, of John Hopkins University, told Jet Propulsion Laboratory’s Carolina Martinez, “It’s a giant factory of organic chemicals…”
Investigators attribute conditions on Titan, to a temperature and pressure regime, in which methane remains at the triple point—where a substance can exist simultaneously, as liquid, solid, and vapour.
On Earth, for example, water occurs as an atmospheric vapour (clouds), a liquid (fresh and salt water) or a solid (polar and season ice).
But instead of water, the NASA press release noted, “liquid hydrocarbons in the form of methane and ethane are present on the moon’s surface”.
Methane and other hydrocarbons rain from the sky, it reports, “collecting in vast deposits that form lakes and dunes”. A space probe detected surface channels, which the flow of liquid methane has cut.
Space.Com notes as well, “Nitrogen and methane extend around the moon 10 times as far into space as Earth’s atmosphere, sometimes falling to the surface in the form of methane rain”.
In light of this, astronomers are convinced that atmospheric methane is somehow being replaced. The most likely source, they reason, is a layer of methane ice beneath Titan’s surface.
“They believe this crust of methane is floating on top of an ocean of liquid water mixed with ammonia,” writes Fraser Cain, in Universe Today.
Citing a European Space Agency (ESA) news release, Cain explains that the methane has been oozing out in periodic outgassing over millions of years.
Researchers suspect, he says, that heat generated by the gradual crystallization of Titan’s water-ammonia ocean, dissociates methane from the moon’s floating “clathrate hydrate” crust.
The resulting spurts of gas “could produce temporary flows of liquid methane on the surface, accounting for the river-like features seen on Titan’s surface”.
Uranus and Neptune, orbiting beyond Saturn, are gaseous worlds with rocky cores. But they also have methane in their atmospheres.
In the case of Uranus, for instance, University of Oregon astronomers estimate atmospheric methane at two percent, with traces of acetylene and other hydrocarbons.
Methane in the upper atmosphere, the university’s online article says, absorbs red light, giving Uranus its blue-green color.
Astronomers have also found ethane (C2H6) and acetylene (C2H2) in the hazy atmospheres of these two ice giants—as Uranus and Neptune are now known.
This “ice” cognomen comes from the extreme environment of the outer planets: Where temperatures of below 70 K freeze ammonia into ice crystals, which drop out of the atmosphere.
To be continued. | 0.851394 | 3.705489 |
Zooming in on our odds of finding a hospitable planet.
Astronomers’ cups have runneth over with alien worlds since NASA launched its (now retired) exoplanet-hunting Kepler space telescope in 2009. But sussing out which orbiting rocks could support life as we know it isn’t an exact science; our current deep-space-searching technology can’t peer closely enough to determine surface and atmospheric compositions on faraway places. Here’s what experts have managed to work out so far.
1. Confirmed planets
Orbiting bodies dim starlight as they pass in front of their respective suns, which makes the fireballs appear to flicker out at regular intervals from our perspective. Astronomers think they’ve already spotted potentially telltale winks from more than 8,000 planets but have confirmed the existence of only around half that number.
2. Rocky planets
Mass really does matter. Rocks much smaller than ours lack the gravity to hold an atmosphere, so liquid surface water won’t stick around. Anything twice our size or larger is likely to gather dust, gas, and ice, creating a barren world like Jupiter or Neptune. Orbs 0.8 to 1.5 times Earth’s radius can be both rocky and wet, and we’ve found around 1,000 of them.
3. Habitable-zone planets
Life is a Goldilocks game; too close to the sun and you roast, too far and you freeze. A few dozen worlds seem to spin in an orbit that’s just right. They could receive anywhere from half to double the radiation that hammers Earth and still harbor life, but factors like how often host stars spit plasma flares could eliminate many contenders.
4. Earth-like planets
Headlines oft herald worlds as “Earth-like,” and a couple dozen could be. But we can’t yet tell whether bodies in other star systems share crucial atmospheric similarities with our home. The closest of our planetary twins is Proxima Centauri b, roughly 4 light-years away. Current probes and scopes can’t gather the intel we need at that distance—yet. | 0.914448 | 3.311364 |
Massive catalog issued exuding high energy gamma ray sources galaxy as The HESS international alliance to which CNRS and CEA bestow has published the outcome of fifteen years of gamma ray surveillance of the Milky Way. Its telescopes positioned in Namibia have explored populations of pulsar wind nebulae and supernova remnants, as well as microquasars, were never found by gamma rays.
These educations are augmented by exact measurements like those of the dispersed emission at the galaxy’s center. The whole data set will from now onwards perform as a citation for the international scientific community.
In the universe, cosmic ray particles are expedited by galaxy clusters, supernovae, binary stars, pulsars and specific types of supermassive black holes. Through a dismally comprehended apparatus they accomplish very high energies, made perceptible by the release of gamma rays. Upon reaching the earth’s atmosphere, these gamma rays are absorbed, emanating a temporary shower of secondary particles that exude weak flashes of bluish light known as Cherenkov radiation, lasting just a few billionths of a second.
To examine these exceptionally short flashes, and consequently gamma ray emissions that fourteen countries for the organization configured the HESS array, the world’s largest gamma ray observatory in Namibia in 2002. The huge mirrors of the five telescopes gather Cherenkov radiation and display it onto exceptionally fragile cameras. Each image offers the direction of the oncoming gamma ray photon, and the quantity of light gathered furnishes instructions about its energy. | 0.876925 | 3.537017 |
The orbits of the new extreme dwarf planet 2015 TG387 and its fellow Inner Oort Cloud objects 2012 VP113 and Sedna as compared with the rest of the Solar System. 2015 TG387 was nicknamed 'The Goblin' by the discoverers, as its provisional designation contains TG and the object was first seen near Halloween. 2015 TG387 has a larger semi-major axis than either 2012 VP113 or Sedna, which means it travels much further from the Sun at its most distant point in its orbit, which is around 2300 AU. Credit: Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science.
Oct. 2, 2018 (Phys.org) -- Carnegie's Scott Sheppard and his colleagues -- Northern Arizona University's Chad Trujillo, and the University of Hawaii's David Tholen -- are once again redefining our Solar System's edge. They discovered a new extremely distant object far beyond Pluto with an orbit that supports the presence of an even-farther-out, Super-Earth or larger Planet X.
The newly found object, called 2015 TG387, was announced Tuesday by the International Astronomical Union's Minor Planet Center. A paper with the full details of the discovery has also been submitted to the Astronomical Journal.
2015 TG387 was discovered about 80 astronomical units (AU) from the Sun, a measurement defined as the distance between the Earth and Sun. For context, Pluto is around 34 AU, so 2015 TG387 is about two and a half times further away from the Sun than Pluto is right now.
The new object is on a very elongated orbit and never comes closer to the Sun, a point called perihelion, than about 65 AU. Only 2012 VP113 and Sedna at 80 and 76 AU respectively have more-distant perihelia than 2015 TG387. Though 2015 TG387 has the third-most-distant perihelion, its orbital semi-major axis is larger than 2012 VP113 and Sedna's, meaning it travels much farther from the Sun than they do. At its furthest point, it reaches all the way out to about 2,300 AU. 2015 TG387 is one of the few known objects that never comes close enough to the Solar System's giant planets, like Neptune and Jupiter, to have significant gravitational interactions with them. | 0.857631 | 3.591677 |
LPSC, Day 2: Morning sessions on our Moon and Saturn's moons
This morning at the Lunar and Planetary Science Conference would have presented a challenge to me. On the one hand, there's the Moon, with a whole session devoted to Chandrayaan-1 and Chang'e 1 (actually, upon reading the abstracts, it was mostly Chandrayaan-1). But it was scheduled back-to-back with a session on the icy satellites of Jupiter and Saturn. I'll confess I probably would have made an effort to attend the lunar sessions, because you just don't get many results out of the Asian missions, but would eventually have crept away to the outer planets moons sessions.
For the most part, the abstracts from the lunar session contain descriptive information about each science instrument and about the commissioning phase of the mission, before science data was available, so there's not a lot of new stuff to report on. There was one abstract, reporting on the first results from the Moon Mineralogy Mapper, that did dare to put in writing some analysis: "A major new result is that the existence and distribution of massive amounts of anorthosite as a continuous stratigraphic crustal layer is now irrefutable." Anorthosite is the igneous rock that makes up the bright highlands areas of the Moon, in contrast to the much darker, basaltic igneous rocks that makes up the lunar maria. This statement was based upon mineralogical and stratigraphic analysis of the Orientale basin, one of the youngest big impact features on the Moon and one of the few that hasn't been entirely filled with basalts. The Moon Mineralogy Mapper team's conclusion basically states that underneath all those lunar basalts is more anorthosite.
By contrast, the abstracts from the icy satellites sessions had a lot more in-depth analysis of the geophysics underlying the surface features and shapes of icy moons. But after reading the abstracts it seems like an awful lot of the analysis is still producing more questions about the icy moons of Saturn and Jupiter than they are answers.
NASA / JPL / SSI / Animation by Emily Lakdawalla
Cassini flies over Iapetus' equatorial ridge
As Cassini flew by Iapetus on September 10, 2007, it took 13 images of the equatorial ridge rising over the horizon. Most of the flight is over Iapetus' dark terrain, but at the very end of the animation, the white flanks of the Voyager moutains begin to appear.
For example, two different presenters talked about how the bizarre equatorial ridge on Iapetus may have formed. James Roberts and Francis Nimmo explored the possibility that the ridge formed as a result of the stresses that happened when Iapetus "despun." To explain, originally, all the moons of Saturn would have been spinning at some relatively fast rate, but stresses due to the tides raised on the moons decreased their spin rates over time until they became tidally locked with Saturn, a state in which they complete one rotation for every orbit and keep the same face pointed at Saturn at all times. This condition is also called "synchronous rotation." A faster-spinning moon will have an equatorial bulge that is larger than a slower-spinning moon. Iapetus, being relatively big (so it has relatively large gravity) and relatively distant from Saturn (so it orbits slowly, and consequently had a lot of slowing to do in order to get into synchronous rotation) would have experienced relatively large stresses due to despinning; that much isn't in doubt. But it's quite hard to get those stresses to make a very narrow ridge just at Iapetus' equator. Roberts wrote, "While our models produce elevated topography at the equator, we note there remain significant differences between our models and the observed ridge on Iapetus. In particular, the actual ridge is much taller and narrower that the one shown" as a result of his modeling.
The next presentation, by Jay Melosh and Francis Nimmo, looked at the narrow, steep shape of the ridge and asked: what structure that we've studied on Earth does it most resemble? They decided that Iapetus' ridge most resembles a dike, a volcanic structure that forms when a fissure opens in a stiff crust and is filled by intrusive magma. The abstract goes through a possible scenario that could create the right kind of stresses to make a dike form along the equator: it involves despinning happening at exactly the same time that there is unusual heating along the equator. They conclude that "Although one could complain that this combination of despinning stresses and equatorial heating is somewhat contrived, there seem to be few other scenarios that can fit the observations." Scientists don't like having to argue that two different processes were just coincidentally happening at the same time, but they conclude that the coincidence is "not unreasonable" and that "further exploration of an intrusive, extensional origin of the bulge is likely to be fruitful."
The next paper in the session is by Paul Schenk and Jeff Moore, two scientists who do a lot of comparative studies of icy moons all over the outer solar system. For this talk they focused on Dione, in particular on the evidence for eruptive volcanism on Dione's surface. They found that Dione has all sorts of geomorphological features that are probably associated with volcanusm that are just not observed on other icy satellites -- smooth plains centered on a couple of possible big volcanic complexes, and chasms that radiate out from those complexes. Just another indication that each moon is a world unto itself, with its own fascinating and unique geologic history. Naturally, some of the most interesting features on Dione march off into an area that hasn't yet been imaged very well by Cassini -- the north pole. It hasn't been imaged very well yet because it's been in winter darkness since the spacecraft arrived at Saturn. That's changing soon, and Paul and Jeff argue that mapping the north pole should be "a priority target during future close encounters with Dione."
NASA / JPL / SSI / Gordan Ugarkovic
Dione in approximate true color
Cassini took the images for this mosaic of Dione on December 24, 2005. Infrared, green, and ultraviolet images have been processed to make the mosaic resemble Dione's approximate true color. In between larger craters, Dione's plains are very smooth, indicating a possible history of volcanism. Chasms and chains of craters are also evidence for an interesting geologic history.
NASA / JPL / SSI / Gordan Ugarkovic
Phoebe in false color
The next paper, by Torrence Johnson and a few coauthors, looked closely at the shape of Phoebe. Remember Phoebe? It's an outer, irregular satellite of Saturn, so distant from the planet that Cassini got its one and only close look at it more than two weeks before it got into Saturn orbit, on its way into the system. Its orbit indicates it has more in common with the irregular outer moons than the classical inner icy moons, and scientists have always suspected it didn't form in the Saturn system, but is instead a body that formed elsewhere and was later captured into Saturn orbit. Johnson's abstract discusses Phoebe's shape and finds that, lumpy as Phoebe looks, it's actually more regular than you'd expect for a body its size, and that regular shape combined with its unusually (for a Saturnian moon) high density of 1.9 grams per cubic centimeter suggests that it has a layered internal structure, meaning it's differentiated, and that "it may be typical of any objects in the outer solar system including the present KBOs and TNOs" (Kuiper belt objects and trans-Neptunian objects). That's been suggested before, but it's always satisfying when further research bears out the results of preliminary studies.
The next abstract, by Sami Asmar and coauthors, provided one of the first reports I've seen on attempts to determine the internal structure of a moon (in this case, Rhea) from radio tracking data. In brief, the results are inconclusive. The problem is that they don't know whether Rhea is "hydrostatic" or not, meaning that it's not known if its shape represents an equilibrium between the forces due to gravity and the forces due to its spin. In brief, despite approaching the problem from a couple of different directions (radio tracking and looking at topographic profiles of the moon from observations of the shape of its limb silhouetted against black space), they still don't know whether it's hydrostatic or not.
The next paper, by Zhang and Nimmo, looked at the orbital evolution of Enceladus and Dione (the two are linked: Enceladus and Dione are in an orbital resonance, where Enceladus orbits twice for every single Dione orbit) and went through some mathematical modeling to see if there was likely to be an ocean underneath either of the two. The result: Enceladus probably does have one, and the idea that Dione does "cannot be ruled out."
The next paper, by Susan Kieffer and coauthors, is notable because it overturns an earlier result that I've quoted a lot. In the past, it's been argued that Enceladus' plumes are made of roughly equal amounts (by mass) of vapor and solid ice. But Kieffer's study shows "that the mass of ice in the column is significantly less than the mass of water vapor....This implies that the plume is dominated by vapor and can easily be produced by sublimation with recondensation. Therefore, [there is] no compelling criterion for consideration of a liquid water reservoir." To translate, you don't need near-surface liquid water to produce the amount of ice crystals seen in the plumes. (However, I don't think this study addresses another argument for the presence of near-surface liquid water, which is the high heat flow observed at the surface.)
The final abstract in the session, by Francis Nimmo and Bruce Bills, takes issue with the conclusions of the Cassini radar team, that Titan's crust is spinning faster than its core, evidence for its crust being "decoupled" from its core by an internal ocean of liquid water. They argue that Titan's orbit may be precessing, in which case "the spin rate must be somewhat faster in order to match the sum of orbital mean motion and apsidal precession rates," so that it is a synchronous rotator through and through.
All in all, icy moons seem to be a really dynamic field of study, and there's a lot more for Cassini to do to illuminate what's going on at Saturn's moons, and lots more to learn from a future Jupiter satellite mission, and a later mission back to study Saturn's moons will not be a waste. Also, based on my writeup above, it seems like Francis Nimmo is a real troublemaker, throwing a wrench into a lot of people's conclusions, and sometimes advocating for two different explanations for something that's going on at an icy moon. (No criticism meant here: when nobody really knows what's going on, it seems that exploring lots of different possibilities is the right way to go!) | 0.847994 | 3.597058 |
In 1988, the astrophysicist Jack Hills at Los Alamos National Laboratories wondered what might happen if a binary star system were to wander too close to the supermassive black hole at the centre of our galaxy. He reasoned that it ought to be possible for the black hole to swallow one star while sending the other shooting away, like a galactic catapult.
These runaway stars would be no ordinary objects. Hills calculated that they would have velocities exceeding 1000 km/s relative to the Milky Way’s rest frame. That’s more than the escape velocity of the galaxy.
The only trouble was that no astronomer had ever seen such a runaway star. Hills told them to look harder and sure enough, astronomers began to spot otherwise ordinary stars travelling at hypervelocities. Their discovery was a testament to the predictive powers of gravitational theory and a triumph for Hills.
Now there’s a puzzle. Although astronomers have found several hypervelocity runaways they’ve been able to measure the proper motion of only one–HD 271791, a star about 11 times the mass of the sun and the first known to be escaping our galaxy.
Knowing the proper motion is handy because it allows astronomers to trace the trajectory of the star back to its origin.
The trouble is that when researchers do this for HD 271791, it leads to the edge of the galactic disc, more than 3000 light years from the supermassive black hole at the galactic centre. Whichever way you look at it, that’s bad news for Hills’ theory.
So what else can accelerate stars beyond the galactic escape velocity, asks Vasilii Gvaramadze at Moscow State University. There are several possibilities. One idea is that the star might have been torn from the clutches of the Milky Way by the tidal forces associated with a close encounter with satellite galaxy. Gvaramadze says that doesn’t seem likely because there is no sign of such an encounter that could have occurred within the lifetime of HD 271791.
Another possibility (and the one most popular with other astronomers) is that HD 271791 was once part of a binary system whose partner exploded in a supernova. This sent HD 271791 on its current trajectory. But Gvaramadze dismisses this too because HD 271791’s velocity is just too big to have been kick-started in this way.
That leaves one other idea: that HD 271791’s velocity is the result of a much more complex interaction between three or four stars. Gvaramadze suggests that this might have involved two binary systems or a binary system interacting with a giant star some 300 times the size of the sun. The end result of this would have been a catapult effect that ejected HD 271791 at hypervelocities.
Of course, that doesn’t exclude the possibility that there may have been a supernova involved somewhere. Proponents of the supernova idea are likely to say that Gvaramadze has overcomplicated matters.
How to settle the matter? More clues are likely to come from the study of the composition of HD 271791. A nearby supernova would have taken its toll on this star’s make up.
And determining the proper motions of other runaway stars would help to give us a better understanding of this population of extraordinary stars.
Astronomers may even find that some of them do come from the galactic centre, which would give Hills the experimental evidence he needs to confirm his idea, albeit a little later than expected.
Ref: arxiv.org/abs/0909.4928: On the Origin of the Hypervelocity Runaway Star HD271791 | 0.83673 | 4.022033 |
When the Sloan Digital Sky Survey (SDSS) was conceived, there wasn’t anything like it. At the time, astronomical survey research was conducted by exposing and developing photographic plates—a slow and laborious process—and the data, owned by the scientists who gathered it, was difficult for others to access.
The Sloan Digital Sky Survey changed all of this, transforming how astronomical research gets done. Designed to create a map of the sky hundreds of times larger than any other map to date, it collected digital astronomical research data from a 2.5-meter telescope at Apache Point Observatory in New Mexico, making the data much easier to catalog, search, and use. The digitization multiplied the amount of data captured and shared with all scientists, thus facilitating new analysis. Today, SDSS, which has already produced a spectroscopic map of over a third of the night sky, is among the most highly-cited surveys in the history of astronomy, and its data platforms serve as models for other large-scale astronomical surveys. SDSS research has made headlines with precise measures of the expansion rate of the universe, studies of the habitability of planets, and newly-discovered modes of activity of the supermassive black holes at the centers of galaxies.
But it took a long time for all the pieces of the SDSS to come together—the instruments, the data collection, the procedures, and the funding. The Alfred P. Sloan Foundation, founded in 1934 by Alfred P. Sloan, Jr., the former head of General Motors, played an important role in supporting the project. It was an early supporter of the Sloan Digital Sky Survey in 1992 and has invested approximately $60 million across 16 grants, with another $16 million grant recently approved to continue SDSS through at least 2024. The project is considered one of the big success stories in science philanthropy, but the road to success was not without lessons about how to conduct big, collaborative, data-based scientific projects.
Deciding to fund SDSS
The Sloan Digital Sky Survey was initially conceptualized in the late 1980s by astrophysicist Jim Gunn. Jim had pioneered the use in astronomy of a new digital camera called a charge-coupled device, which records images by converting light into digital information. The new device could create the first digital, searchable, and computable map of the universe.
The Sloan Foundation was intrigued by the digital sky survey’s promise, which aimed to transform astronomy by moving to digital images and engendering a dramatic increase in information about stars and galaxies. Access to this data would facilitate the study of many new and important questions in astronomy that scientists were starting to explore.
“To understand questions such as what stars and galaxies are made of, how they are born and how they interact with one another, the nature of dark matter and dark energy, what the relationships between galaxies imply for the expansion of the universe, scientists need to be able to do statistical analysis on large data sets,” said Evan Michelson, the Sloan Foundation’s current program director overseeing SDSS grantmaking. “Without digitization, these questions would have been very challenging to pursue.”
In addition, the foundation was attracted by Jim’s proposed open data model that would, after an embargo year, provide collected data for free and hold them in an archive open to the world. The potential of such a model was apparent.
Access to this data would facilitate the study of many new and important questions in astronomy.
“The foundation wanted to nurture a culture of data-sharing in astronomy,” Evan said. “We wanted to try to move folks away from ‘I collected this; it’s my data; you can’t have it’ to a shared data model that could accelerate discovery.”
“We didn’t, and still don’t, have a broader astronomy portfolio, so this investment might have seemed a little surprising at the time,” said Evan. “But in fact, it was right in the foundation’s wheelhouse: it focused on basic science, it was about data access and facilitated the participation of many scientists for a relatively modest investment, and it was cutting-edge science. Here was an opportunity to transform astronomy. How could we say no?”
As with all its major grants, Sloan vetted the idea with outside expert advisors and presented the proposal to its board for approval. Jim and his team needed $25 million for the first phase of funding. With the board’s approval, the foundation contributed $8 million over three to four years for the survey’s first phase. Eight million, Evan said, was a figure decided upon by assessing what researchers needed, what the foundation could give, and what the scientists could secure in complementary contributions from other sources. “Determining how much money is needed at the outset is always a challenge,” said Evan. “Having our proposals externally reviewed by experts in the field helps us figure out what that percentage of project funding should be.” The SDSS grants are the largest and longest individual grants that the Sloan Foundation makes.
“Getting in early on the project meant our support would be meaningful, but the size of the project was also an important consideration,” said Evan. “If the project cost was an order of magnitude more, we may not have been able to participate.”
Early stumbling blocks
As with any novel scientific endeavor, it wasn’t easy in the beginning. Besides having to come up with new data platforms, the researchers hit problems right from the start. The camera sometimes wouldn’t function correctly. New technologies needed to be developed to finish the telescope. Costs were higher than expected. Progress was delayed.
“The question in these situations is always: How long do we stay with this? Supporting novel, large-scale science projects requires a degree of patience and willingness to take risks. Sometimes that patience can be difficult to maintain,” said Evan. Although the build-out of the telescope took longer than expected, the original SDSS team finally reached some success with the telescope recording starlight for the first time—astronomers call it achieving “first light”—in 1997. Though this took longer than planned, it was a sign of forward momentum, and the foundation decided to continue funding the project.
Engaging the scientific community
While the Sloan Foundation helped ensure that SDSS research plans were strong and that the collaboration was moving in the right direction, it took a mostly hands-off approach to the day-to-day operation of the project. The key to success, it believed, was to ensure the scientific community was at the helm and fully engaged.
Since its early development, SDSS has undergone four phases, each of which was about five years long and focused on a specific set of research questions. The scientific community itself identified the most important questions for each phase of the project. The first phase focused on mapping 10,000 square degrees of the sky, while future phases focused on more specific research questions. Phase II (2005–2008), for example, included an investigation of the stars in the Milky Way’s halo, and the study of the universe’s acceleration and dark energy. Phase III (2008–2014) mapped an even larger region of the universe, probed the role dark energy played in the early universe, hunted for planets, and built an infrared spectrograph able to study the Milky Way more completely than previously possible. Phase IV (2014–2020) is creating yet larger and deeper maps using quasars, is writing a development history of 10,000 nearby galaxies, and is expanding the study of the Milky Way to the southern hemisphere with a newly installed spectrograph. The next phase, Phase V (2020–2024), will take full advantage of this dual hemisphere presence and conduct observations at both sites across two different light wavelengths.
“Identifying the right scientific questions was critical to the program’s success,” said Evan. “The scientific community weighed in to select topics that offered the most exciting opportunities for discovery and these questions drove the type of data that was collected.”
A sustainable funding model
In addition to deciding on the topics worth studying, the SDSS team recruited subscribers to support the costs of the project. This innovative funding model for the program was proposed by Jerry Ostriker, one of SDSS’s early team leaders.
The Sloan Foundation has provided about 20 to 25 percent of the SDSS costs at each phase of its implementation—the rest has been funded mainly by university subscribers that join as members. Members get a say in project governance, can shape the survey design, and get privileged access to collected data prior to its release to the general public. Each university subscriber typically contributes $1 million over five years, which allows its astronomers, postdoctoral researchers, and graduate and undergraduate students to get a sneak peek at SDSS data. The SDSS team estimates that this translates to approximately $10,000 per participant per year. The project now has over 54 university partners who contribute most of the funding for SDSS.
Today, the Astrophysical Research Consortium (ARC) has responsibility for overseeing all budgetary aspects of the project, and SDSS itself has a central collaboration team, a steering committee, a separate scientific team to lead each component of the survey, a data team, and an instrument development team, among others.
The Sloan Foundation asks questions upfront, holds annual check-ins with researchers, and assists the consortium when needed, but doesn’t have daily influence on the research. The foundation also ensures that a strong management plan is in place. For such a large, collaborative project, the Sloan Foundation must be sure that the project has strong leadership and management.
“A lot of it is getting the right people in place and allowing them the freedom and flexibility to build the infrastructure they need,” Evan said.
Emphasizing open data and diversity
There are two areas where Evan thinks the Sloan Foundation has been most influential in shaping the development of SDSS: open data and diversity. SDSS Phase IV director Michael Blanton agrees, noting that “the foundation converted these from ‘nice-to-haves’ to ‘got-to-haves.’ ”
The success of SDSS in accelerating scientific discovery across the astronomy community has been based in its open data principles, which have allowed for open-ended discovery and examination of questions in astronomy that were not envisioned at the outset of SDSS. After a one-year period during which the data is made available to participating members, all the data is then made public. Anyone, from professional astronomers to museum staff to high school students, can use the data without restrictions.
SDSS also developed a data citation policy which standardized references to data collected by the collaboration and makes experts available to answer questions and troubleshoot problems once data sets are shared. In addition, its two-decade history of data collection allows researchers to track changes in celestial objects over time. These practices worked. Studies show that SDSS is among the most highly-used and cited data sets in astronomy. SDSS data has been used in over 7,800 papers and 390,000 citations, 80 percent of which have been published by scientists with no formal relationship with the SDSS.
Challenges remain. With the open data model, the SDSS team must continually work to keep track of who is using the data. The collaboration has no direct control over how the publicly-released data is used. There is always a need to update data practices and infrastructure, which takes time and financial resources.
The success of SDSS in accelerating scientific discovery has been based in its open data principles.
The Sloan Foundation has also required the integration of diversity and inclusion considerations throughout the collaboration, ranging from how senior management teams are constructed to ensuring participation of underrepresented minorities. The foundation provided funding for a Faculty and Student Team mentoring program that helps underrepresented minority students and faculty from non-member institutions become full members of SDSS. “As a condition of our grantmaking, we require that SDSS leadership pay close attention to engaging women and underrepresented minorities,” said Evan. “While there are always strides to be taken in this area, I am proud that promoting diversity and inclusion have become core values of SDSS.”
The recently named director of SDSS V, Juna Kollmeier, echoed this point. “The Sloan Foundation is helping to make fundamental changes regarding diversity that have stymied other funding institutions for decades,” she said.
As a result of the foundation’s generous grants and early support of the project, consortium leaders named the survey and telescope after the Sloan Foundation early in its history. Evan noted that naming a project after the foundation has its advantages and disadvantages: While it can give the foundation recognition for its support, it can also hinder fundraising with other sources.
“If you are going to put your foundation’s name on it, you should be prepared to support the project for the long haul, or else be open to project renaming when you depart,” cautioned Evan. In the case of SDSS, the project was successful in getting funding from the Sloan Foundation for additional phases, as well as from university subscribers and government agencies, such as the National Science Foundation. While it has proven more difficult to secure additional philanthropic support for SDSS given the Sloan name, the collaboration is working to make progress.
The SDSS proposal goes through the same rigorous, external peer-review process that the Sloan Foundation has established for all proposals.
“The phased nature of the SDSS program and our grant renewal process forces the SDSS team to justify the plans for each subsequent phase every few years,” said Evan. To report on its progress, each year the SDSS consortium sends the Sloan Foundation a summary of its progress. Each grant comes with a set of metrics—some are about management and budget goals and others are about specific hardware installation milestones. The primary metrics relate to achieving scientific research objectives, such as observing a certain number of stars or galaxies. The Sloan Foundation reviews progress each year and toward the end of each SDSS phase, determines whether to consider funding for the next phase.
In determining funding for future phases, the Sloan Foundation asks whether the telescope instrumentation and collaboration would still be relevant for the period of the project as the landscape of astronomical research changes and evolves, whether the methods and research questions proposed by the SDSS team are likely to remain at the forefront of science in this area during this period, whether the management team and plan remain strong, whether plans for data access, storage, archiving, and dissemination continue to be on the leading edge, whether SDSS has made substantial strides in terms of diversity, and whether there is demand for this project from the astronomical research community.
“Our responsibility is to ensure the SDSS team is asking the right questions, that oversight and management are sound, and that they address any operational issues,” Evan said.
To plan for the next phase, Evan works closely with the SDSS team as they write up a proposal, which is first reviewed internally by foundation staff and then by external subject matter experts in astronomy and cosmology. Principal investigators respond to reviews and make clarifications and adjustments, after which Evan presents the review and response document internally a second time before deciding whether the Sloan Foundation board of trustees should consider it for final approval.
“We just completed this process in approving their proposal for a $16 million grant that will allow the fifth phase of SDSS to go forward, with observations starting in 2020,” said Evan. Although more than three years out, the foundation needed to consider the proposal earlier because of the infrastructure upgrades and hardware build-out that would be needed.
Before even submitting a proposal for SDSS V, the collaboration spent nearly a year planning its future scientific program, presenting its initial ideas to the foundation’s staff before a formal proposal was invited. The proposal preparation and review process to consider support for SDSS V then took another six months. “The original proposal was nearly 200 pages long. We got 12 external reviews, which provided them with over 50 pages of comments. The SDSS team’s response to reviews exceeded 25 pages. It was a lot of material, but we had to do our due diligence,” said Evan. “Without a doubt, they did an excellent job navigating the process, which resulted in a top-notch plan for SDSS V.”
“In the end, it was worth it,” he said. “When our board approved the proposal in October, I could not have been happier to make that phone call to let them know the grant was approved.”
Evolving with the times
One of the notable things about SDSS is how successful it has been over a long period—25 years. The process of periodic grant reviews and renewals helped ensure that the project evolved. The subscription model helped ensure that SDSS was responding to the changing demands in the field—including to topics for research, as well as to changes in technology.
For instance, as it became clear that the digital imaging technology used in Phases I and II was soon to be surpassed by other facilities, SDSS switched its focus exclusively to wide-field spectroscopy, which allowed SDSS to remain the forefront facility in astronomy. In addition to spectroscopy conducted on visible light, SDSS has been a pioneer of infrared spectroscopy (studying infrared light from distant objects), ensuring its relevance to astronomical research for years to come.
Other developments expanded the project over successive phases. The first telescope at Apache Point Observatory in New Mexico could only cover the northern half of the sky. In the fourth and most recent phase of SDSS, Sloan Foundation funding helped the consortium expand to a second telescope in Chile to capture astronomical data from the southern half of the sky. SDSS V will expand this partnership with the Chilean telescope, as it will be fully dedicated to SDSS observations. This collaboration across multiple telescopes located in different sites is rather rare in astronomy.
Keys to success
In retrospect, SDSS is an accomplishment that revolutionized astronomy and far exceeded expectations. It is one of the most productive astronomical facilities in history, a relatively modest investment that has brought a greater understanding of our universe.
“One of the important reasons for its success,” said Evan, “is that it focused on the important questions in astronomy and astrophysics, and on using big data to answer them more accurately, more quickly, more efficiently, and more transparently.”
SDSS also advances a model of international scientific collaboration that improves how institutions work together, how data is shared, and even how the public can engage in scientific discovery. Its open data policies and the multi-institution subscription model helped ensure the engagement of the scientific community in the project.
The fact that the project was and is completely driven by “passionate researchers who were and are willing to lead this and put in their blood, sweat, and tears is the key ingredient that helps SDSS thrive,” Evan said. “It was important that the project was not foundation-driven, but community-driven.”
Ultimately, many factors contributed to the success of the project.
“You need a combination of dedicated people asking important scientific questions, the right technology, an effective management structure, data policies to facilitate broader use, and an innovative and collaborative funding model,” Evan said. “There’s no magic formula, but for SDSS, the right leadership that was committed to science and open collaboration made it work.” | 0.8071 | 3.755896 |
Dr. Sahu is an astronomer at the Space Telescope Science Institute, and an instrument scientist for HST. His research efforts have focused on applying microlensing, transit, and relativistic deflection techniques to detect and study exoplanets, nearby stars and black holes. He currently leads two HST projects to detect isolated, stellar-mass black holes and determine their masses through gravitational lensing.
Dr. Sahu’s early work showed that the microlensing events detected towards the Magellanic Clouds are mainly caused by the stars within the Magellanic Clouds, and not by MACHOs (Sahu, 1994, Nature, 370, 275). He then cofounded the PLANET (Probing Lensing Anomalies NETwork) collaboration, to detect planets around the lensing stars through frequent monitoring of microlensing events. This project has led to the discovery of several exoplanets, including terrestrial planets beyond the snow line.
Dr. Sahu led a program of HST observations which showed, for the first time, that a Gamma-Ray Burst (GRB 970228) was associated with an external galaxy (Sahu et al. 1997, Nature, 387, 479).
Dr. Sahu led a large HST program called SWEEPS (Sagittarius Window Eclipsing Extrasolar Planet Search) which led to the discovery of 16 transiting planet candidates in the Galactic bulge; these planet candidates remain the farthest planets detected to date (Sahu et al. 2006, Nature, 443, 1038).
Recently, Dr. Sahu led the first ever measurement of relativistic deflection caused by a star outside the solar system, as predicted by Einstein just over a century ago, and measured the mass of the nearby white dwarf Stein 2051 B--- the first mass measurement through this technique (Sahu et al. 2017, Science 356, 1046). This work was listed by Discover magazine as one of the “Top 100 Science Stories” of 2017.
Dr. Sahu has over 300 scientific publications, including 9 in Nature and one in Science. His work has received extensive coverage in national news media (including The Washington Post, New York Times, LA Times and National Geographic), as well as international press (such as The Economist, Times of India, New Scientist, De Volkskrant, El Mercurio, etc.).
PhD in Physics, Gujarat University, India
- Determining masses of nearby stars through relativistic deflections
- Detecting and measuring the masses if isolated, stellar-mass black holes through astrometric microlensing
- Detection and study of Exoplanets through transits and microlensing
- Study of the different stellar populations of the Galactic bulge
Research Topics: Exoplanets; Gravitational Microlensing; Stallar Remnants
ORCID ID: 0000-0001-6008-1955 | 0.877669 | 3.402445 |
An ocean (from Ancient Greek Ὠκεανός, transc. Okeanós) is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. The phrases "the ocean" or "the sea" used without specification refer to the interconnected body of salt water covering the majority of the Earth's surface. As a general term, "the ocean" is mostly interchangeable with "the sea" in American English, but not in British English. Strictly speaking, a sea is a body of water (generally a division of the world ocean) partly or fully enclosed by land.
Saline seawater covers approximately 361,000,000 km2 (139,000,000 sq mi) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of Earth's surface and 90% of the Earth's biosphere. The ocean contains 97% of Earth's water, and oceanographers have stated that less than 20% of the World Ocean has been mapped. The total volume is approximately 1.35 billion cubic kilometers (320 million cu mi) with an average depth of nearly 3,700 meters (12,100 ft).
As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, and influences climate and weather patterns. The World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger, possibly over two million. The origin of Earth's oceans is unknown; oceans are thought to have formed in the Hadean eon and may have been the cause for the emergence of life.
Extraterrestrial oceans may be composed of water or other elements and compounds. The only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, and a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many dwarf planets and natural satellites; notably, the ocean of the moon Europa is estimated to have over twice the water volume of Earth. The Solar System's giant planets are also thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone. Ocean planets are a hypothetical type of planet with a surface completely covered with liquid.
The word ocean comes from the figure in classical antiquity, Oceanus (//; Greek: Ὠκεανός Ōkeanós, pronounced [ɔːkeanós]), the elder of the Titans in classical Greek mythology, believed by the ancient Greeks and Romans to be the divine personification of the sea, an enormous river encircling the world.
The concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases.
Earth's global ocean
Though generally described as several separate oceans, the global, interconnected body of salt water is sometimes referred to as the World Ocean or global ocean. The concept of a continuous body of water with relatively free interchange among its parts is of fundamental importance to oceanography.
|1||Pacific Ocean||Separates Asia and Australasia from the Americas[NB]||168,723,000
|2||Atlantic Ocean||Separates the Americas from Europe and Africa||85,133,000
|3||Indian Ocean||Borders southern Asia and separates Africa and Australia||70,560,000
|4||Southern Ocean||Encircles Antarctica. Sometimes considered an extension of the Pacific, Atlantic and Indian Oceans,||21,960,000
|5||Arctic Ocean||Borders northern North America and Eurasia and covers much of the Arctic. Sometimes considered a sea or estuary of the Atlantic. ||15,558,000
|Total – World Ocean||361,900,000
|Arabian Sea||Between the Arabian peninsula and the Indian subcontinent||3,862,000||1|
|Bay of Bengal||Between the Indian subcontinent and the Malay Peninsula||2,173,000||2|
Sources: Encyclopedia of Earth, International Hydrographic Organization, Regional Oceanography: an Introduction (Tomczak, 2005), Encyclopædia Britannica, and the International Telecommunication Union.
The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system that is part of every ocean and the longest mountain range in the world. The continuous mountain range is 65,000 km (40,000 mi) long (several times longer than the Andes, the longest continental mountain range).
The total mass of the hydrosphere is about 1.4 quintillion tonnes (1.4×1018 long tons or 1.5×1018 short tons), which is about 0.023% of Earth's total mass. Less than 3% is freshwater; the rest is saltwater, almost all of which is in the ocean. The area of the World Ocean is about 361.9 million square kilometers (139.7 million square miles), which covers about 70.9% of Earth's surface, and its volume is approximately 1.335 billion cubic kilometers (320.3 million cubic miles). This can be thought of as a cube of water with an edge length of 1,101 kilometers (684 mi). Its average depth is about 3,688 meters (12,100 ft), and its maximum depth is 10,994 meters (6.831 mi) at the Mariana Trench. Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep. The vast expanses of deep ocean (anything below 200 meters or 660 feet) cover about 66% of Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea.
The bluish ocean color is a composite of several contributing agents. Prominent contributors include dissolved organic matter and chlorophyll. Mariners and other seafarers have reported that the ocean often emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow. It is most likely caused by bioluminescence.
Oceanographers divide the ocean into different vertical zones defined by physical and biological conditions. The pelagic zone includes all open ocean regions, and can be divided into further regions categorized by depth and light abundance. The photic zone includes the oceans from the surface to a depth of 200 m; it is the region where photosynthesis can occur and is, therefore, the most biodiverse. Because plants require photosynthesis, life found deeper than the photic zone must either rely on material sinking from above (see marine snow) or find another energy source. Hydrothermal vents are the primary source of energy in what is known as the aphotic zone (depths exceeding 200 m). The pelagic part of the photic zone is known as the epipelagic.
The pelagic part of the aphotic zone can be further divided into vertical regions according to temperature. The mesopelagic is the uppermost region. Its lowermost boundary is at a thermocline of 12 °C (54 °F), which, in the tropics generally lies at 700–1,000 meters (2,300–3,300 ft). Next is the bathypelagic lying between 10 and 4 °C (50 and 39 °F), typically between 700–1,000 meters (2,300–3,300 ft) and 2,000–4,000 meters (6,600–13,100 ft), lying along the top of the abyssal plain is the abyssopelagic, whose lower boundary lies at about 6,000 meters (20,000 ft). The last zone includes the deep oceanic trench, and is known as the hadalpelagic. This lies between 6,000–11,000 meters (20,000–36,000 ft) and is the deepest oceanic zone.
The benthic zones are aphotic and correspond to the three deepest zones of the deep-sea. The bathyal zone covers the continental slope down to about 4,000 meters (13,000 ft). The abyssal zone covers the abyssal plains between 4,000 and 6,000 m. Lastly, the hadal zone corresponds to the hadalpelagic zone, which is found in oceanic trenches.
The pelagic zone can be further subdivided into two subregions: the neritic zone and the oceanic zone. The neritic zone encompasses the water mass directly above the continental shelves whereas the oceanic zone includes all the completely open water.
In contrast, the littoral zone covers the region between low and high tide and represents the transitional area between marine and terrestrial conditions. It is also known as the intertidal zone because it is the area where tide level affects the conditions of the region.
If a zone undergoes dramatic changes in temperature with depth, it contains a thermocline. The tropical thermocline is typically deeper than the thermocline at higher latitudes. Polar waters, which receive relatively little solar energy, are not stratified by temperature and generally lack a thermocline because surface water at polar latitudes are nearly as cold as water at greater depths. Below the thermocline, water is very cold, ranging from −1 °C to 3 °C. Because this deep and cold layer contains the bulk of ocean water, the average temperature of the world ocean is 3.9 °C. If a zone undergoes dramatic changes in salinity with depth, it contains a halocline. If a zone undergoes a strong, vertical chemistry gradient with depth, it contains a chemocline.
The halocline often coincides with the thermocline, and the combination produces a pronounced pycnocline.
The deepest point in the ocean is the Mariana Trench, located in the Pacific Ocean near the Northern Mariana Islands. Its maximum depth has been estimated to be 10,971 meters (35,994 ft) (plus or minus 11 meters; see the Mariana Trench article for discussion of the various estimates of the maximum depth.) The British naval vessel Challenger II surveyed the trench in 1951 and named the deepest part of the trench the "Challenger Deep". In 1960, the Trieste successfully reached the bottom of the trench, manned by a crew of two men.
Oceanic maritime currents
Oceanic maritime currents have different origins. Tidal currents are in phase with the tide, hence are quasiperiodic; they may form various knots in certain places,[clarification needed] most notably around headlands. Non-periodic currents have for origin the waves, wind and different densities.
The wind and waves create surface currents (designated as “drift currents”). These currents can decompose in one quasi-permanent current (which varies within the hourly scale) and one movement of Stokes drift under the effect of rapid waves movement (at the echelon of a couple of seconds).). The quasi-permanent current is accelerated by the breaking of waves, and in a lesser governing effect, by the friction of the wind on the surface.
This acceleration of the current takes place in the direction of waves and dominant wind. Accordingly, when the sea depth increases, the rotation of the earth changes the direction of currents in proportion with the increase of depth, while friction lowers their speed. At a certain sea depth, the current changes direction and is seen inverted in the opposite direction with current speed becoming null: known as the Ekman spiral. The influence of these currents is mainly experienced at the mixed layer of the ocean surface, often from 400 to 800 meters of maximum depth. These currents can considerably alter, change and are dependent on the various yearly seasons. If the mixed layer is less thick (10 to 20 meters), the quasi-permanent current at the surface adopts an extreme oblique direction in relation to the direction of the wind, becoming virtually homogeneous, until the Thermocline.
Ocean currents greatly affect Earth's climate by transferring heat from the tropics to the polar regions. Transferring warm or cold air and precipitation to coastal regions, winds may carry them inland. Surface heat and freshwater fluxes create global density gradients that drive the thermohaline circulation part of large-scale ocean circulation. It plays an important role in supplying heat to the polar regions, and thus in sea ice regulation. Changes in the thermohaline circulation are thought to have significant impacts on Earth's energy budget. In so far as the thermohaline circulation governs the rate at which deep waters reach the surface, it may also significantly influence atmospheric carbon dioxide concentrations.
The Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans.
The ocean has a significant effect on the biosphere. Oceanic evaporation, as a phase of the water cycle, is the source of most rainfall, and ocean temperatures determine climate and wind patterns that affect life on land. Life within the ocean evolved 3 billion years prior to life on land. Both the depth and the distance from shore strongly influence the biodiversity of the plants and animals present in each region.
As it is thought that life evolved in the ocean, the diversity of life is immense, including:
- Bacteria : ubiquitous single-celled prokaryotes found throughout the world
- Archaea : prokaryotes distinct from bacteria, that inhabit many environments of the ocean, as well as many extreme environments
- Algae : algae is a "catch-all" term to include many photosynthetic, single-celled eukaryotes, such as green algae, diatoms, and dinoflagellates, but also multicellular algae, such as some red algae (including organisms like Pyropia, which is the source of the edible nori seaweed), and brown algae (including organisms like kelp).
- Plants : including sea grasses, or mangroves
- Fungi : many marine fungi with diverse roles are found in oceanic environments
- Animals : most animal phyla have species that inhabit the ocean, including many that are only found in marine environments such as sponges, Cnidaria (such as corals and jellyfish), comb jellies, Brachiopods, and Echinoderms (such as sea urchins and sea stars). Many other familiar animal groups primarily live in the ocean, including cephalopods (includes octopus and squid), crustaceans (includes lobsters, crabs, and shrimp), fish, sharks, cetaceans (includes whales, dolphins, and porpoises).
In addition, many land animals have adapted to living a major part of their life on the oceans. For instance, seabirds are a diverse group of birds that have adapted to a life mainly on the oceans. They feed on marine animals and spend most of their lifetime on water, many only going on land for breeding. Other birds that have adapted to oceans as their living space are penguins, seagulls and pelicans. Seven species of turtles, the sea turtles, also spend most of their time in the oceans.
|Gas||Concentration of seawater, by mass (in parts per million), for the whole ocean||% Dissolved gas, by volume, in seawater at the ocean surface|
|Carbon dioxide (CO2)||64 to 107||15%|
|Nitrogen (N2)||10 to 18||48%|
|Oxygen (O2)||0 to 13||36%|
|Characteristic||Oceanic waters in polar regions||Oceanic waters in temperate regions||Oceanic waters in tropical regions|
|Precipitation vs. evaporation||P > E||P > E||E > P|
|Sea surface temperature in winter||−2 °C||5 to 20 °C||20 to 25 °C|
|Average salinity||28‰ to 32‰||35‰||35‰ to 37‰|
|Annual variation of air temperature||≤ 40ªC||10 °C||< 5 °C|
|Annual variation of water temperature||< 5ªC||10 °C||< 5 °C|
|Constituent||Residence time (in years)|
A zone of rapid salinity increase with depth is called a halocline. The temperature of maximum density of seawater decreases as its salt content increases. Freezing temperature of water decreases with salinity, and boiling temperature of water increases with salinity. Typical seawater freezes at around −2 °C at atmospheric pressure. If precipitation exceeds evaporation, as is the case in polar and temperate regions, salinity will be lower. If evaporation exceeds precipitation, as is the case in tropical regions, salinity will be higher. Thus, oceanic waters in polar regions have lower salinity content than oceanic waters in temperate and tropical regions.
Salinity can be calculated using the chlorinity, which is a measure of the total mass of halogen ions (includes fluorine, chlorine, bromine, and iodine) in seawater. By international agreement, the following formula is used to determine salinity:
- Salinity (in ‰) = 1.80655 × Chlorinity (in ‰)
The average chlorinity is about 19.2‰, and, thus, the average salinity is around 34.7‰
Absorption of light
|Color: Wavelength (nm)||Depth at which 99 percent of the wavelength is absorbed (in meters)||Percent absorbed in 1 meter of water|
|Ultraviolet (UV): 310||31||14.0|
|Violet (V): 400||107||4.2|
|Blue (B): 475||254||1.8|
|Green (G): 525||113||4.0|
|Yellow (Y): 575||51||8.7|
|Orange (O): 600||25||16.7|
|Red (R): 725||4||71.0|
|Infrared (IR): 800||3||82.0|
Many of the world's goods are moved by ship between the world's seaports. Oceans are also the major supply source for the fishing industry. Some of the major harvests are shrimp, fish, crabs, and lobster.
Waves and swell
The motions of the ocean surface, known as undulations or waves, are the partial and alternate rising and falling of the ocean surface. The series of mechanical waves that propagate along the interface between water and air is called swell.
The gas giants, Jupiter and Saturn, are thought to lack surfaces and instead have a stratum of liquid hydrogen; however their planetary geology is not well understood. The possibility of the ice giants Uranus and Neptune having hot, highly compressed, supercritical water under their thick atmospheres has been hypothesised. Although their composition is still not fully understood, a 2006 study by Wiktorowicz and Ingersall ruled out the possibility of such a water "ocean" existing on Neptune, though some studies have suggested that exotic oceans of liquid diamond are possible.
The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, though the water on Mars is no longer oceanic (much of it residing in the ice caps). The possibility continues to be studied along with reasons for their apparent disappearance. Astronomers now think that Venus may have had liquid water and perhaps oceans for over 2 billion years.
A global layer of liquid water thick enough to decouple the crust from the mantle is thought to be present on the natural satellites Titan, Europa, Enceladus and, with less certainty, Callisto, Ganymede and Triton. A magma ocean is thought to be present on Io. Geysers have been found on Saturn's moon Enceladus, possibly originating from an ocean about 10 kilometers (6.2 mi) beneath the surface ice shell. Other icy moons may also have internal oceans, or may once have had internal oceans that have now frozen.
Large bodies of liquid hydrocarbons are thought to be present on the surface of Titan, although they are not large enough to be considered oceans and are sometimes referred to as lakes or seas. The Cassini–Huygens space mission initially discovered only what appeared to be dry lakebeds and empty river channels, suggesting that Titan had lost what surface liquids it might have had. Later flybys of Titan provided radar and infrared images that showed a series of hydrocarbon lakes in the colder polar regions. Titan is thought to have a subsurface liquid-water ocean under the ice in addition to the hydrocarbon mix that forms atop its outer crust.
Dwarf planets and trans-Neptunian objects
Not enough is known of the larger trans-Neptunian objects to determine whether they are differentiated bodies capable of supporting oceans, although models of radioactive decay suggest that Pluto, Eris, Sedna, and Orcus have oceans beneath solid icy crusts approximately 100 to 180 km thick.
Some planets and natural satellites outside the Solar System are likely to have oceans, including possible water ocean planets similar to Earth in the habitable zone or "liquid-water belt". The detection of oceans, even through the spectroscopy method, however is likely extremely difficult and inconclusive.
Theoretical models have been used to predict with high probability that GJ 1214 b, detected by transit, is composed of exotic form of ice VII, making up 75% of its mass, making it an ocean planet.
Other possible candidates are merely speculated based on their mass and position in the habitable zone include planet though little is actually known of their composition. Some scientists speculate Kepler-22b may be an "ocean-like" planet. Models have been proposed for Gliese 581 d that could include surface oceans. Gliese 436 b is speculated to have an ocean of "hot ice". Exomoons orbiting planets, particularly gas giants within their parent star's habitable zone may theoretically have surface oceans.
Terrestrial planets will acquire water during their accretion, some of which will be buried in the magma ocean but most of it will go into a steam atmosphere, and when the atmosphere cools it will collapse on to the surface forming an ocean. There will also be outgassing of water from the mantle as the magma solidifies—this will happen even for planets with a low percentage of their mass composed of water, so "super-Earth exoplanets may be expected to commonly produce water oceans within tens to hundreds of millions of years of their last major accretionary impact."
Non-water surface liquids
Oceans, seas, lakes and other bodies of liquids can be composed of liquids other than water, for example the hydrocarbon lakes on Titan. The possibility of seas of nitrogen on Triton was also considered but ruled out. There is evidence that the icy surfaces of the moons Ganymede, Callisto, Europa, Titan and Enceladus are shells floating on oceans of very dense liquid water or water–ammonia. Earth is often called the ocean planet because it is 70% covered in water. Extrasolar terrestrial planets that are extremely close to their parent star will be tidally locked and so one half of the planet will be a magma ocean. It is also possible that terrestrial planets had magma oceans at some point during their formation as a result of giant impacts. Hot Neptunes close to their star could lose their atmospheres via hydrodynamic escape, leaving behind their cores with various liquids on the surface. Where there are suitable temperatures and pressures, volatile chemicals that might exist as liquids in abundant quantities on planets include ammonia, argon, carbon disulfide, ethane, hydrazine, hydrogen, hydrogen cyanide, hydrogen sulfide, methane, neon, nitrogen, nitric oxide, phosphine, silane, sulfuric acid, and water.
Supercritical fluids, although not liquids, do share various properties with liquids. Underneath the thick atmospheres of the planets Uranus and Neptune, it is expected that these planets are composed of oceans of hot high-density fluid mixtures of water, ammonia and other volatiles. The gaseous outer layers of Jupiter and Saturn transition smoothly into oceans of supercritical hydrogen. The atmosphere of Venus is 96.5% carbon dioxide, which is a supercritical fluid at its surface.
- Blue carbon
- Brackish water
- Effects of global warming on oceans
- European Atlas of the Seas
- Four Seas
- International Maritime Organization
- List of bodies of water by salinity
- List of largest lakes and seas in the Solar System
- List of oceans with alternative names
- List of seas
- Marine debris
- Marine pollution
- Ocean acidification
- Ocean current
- Ocean general circulation model
- Ocean governance
- Ocean rowing
- Oceans (film)
- Pelagic zone
- Physical oceanography
- Polar seas
- Sea ice
- Sea in culture
- Sea level and sea level rise
- Sea salt
- Sea state
- Seven Seas
- United Nations Convention on the Law of the Sea
- Water distribution on Earth
- Wind wave
- World Ocean Atlas
- World Oceans Day
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- Elkins-Tanton (2010). "Formation of Early Water Oceans on Rocky Planets". Astrophysics and Space Science. 332 (2): 359–364. arXiv:1011.2710. Bibcode:2011Ap&SS.332..359E. doi:10.1007/s10509-010-0535-3.
- McKinnon, William B.; Kirk, Randolph L. (2007). "Triton". In Lucy Ann Adams McFadden; Lucy-Ann Adams; Paul Robert Weissman; Torrence V. Johnson (eds.). Encyclopedia of the Solar System (2nd ed.). Amsterdam; Boston: Academic Press. p. 485. ISBN 978-0-12-088589-3.
- Coustenis, A.; Lunine, J.; Lebreton, J.; Matson, D.; et al. (2008). "The Titan Saturn System Mission". American Geophysical Union, Fall Meeting. 21: 1346. Bibcode:2008AGUFM.P21A1346C.
the Titan system, rich in organics, containing a vast subsurface ocean of liquid water
- Nimmo, F.; Bills, B. G. (2010). "Shell thickness variations and the long-wavelength topography of Titan". Icarus. 208 (2): 896–904. Bibcode:2010Icar..208..896N. doi:10.1016/j.icarus.2010.02.020.
observations can be explained if Titan has a floating, isostatically-compensated ice shell
- Goldreich, Peter M.; Mitchell, Jonathan L. (2010). "Elastic ice shells of synchronous moons: Implications for cracks on Europa and non-synchronous rotation of Titan". Icarus. 209 (2): 631–638. arXiv:0910.0032. Bibcode:2010Icar..209..631G. doi:10.1016/j.icarus.2010.04.013.
A number of synchronous moons are thought to harbor water oceans beneath their outer ice shells. A subsurface ocean frictionally decouples the shell from the interior
- "Study of the ice shells and possible subsurface oceans of the Galilean satellites using laser altimeters on board the Europa and Ganymede orbiters JEO and JGO" (PDF). Retrieved 2011-10-14.
- "Tidal heating and the long-term stability of a subsurface ocean on Enceladus" (PDF). Retrieved 2011-10-14.
- Hinrichsen, D (2011-10-03). "The ocean planet". People Planet. 7 (2): 6–9. PMID 12349465.
- "Irrigating Crops with Seawater". Scientific American. August 1998. Archived from the original on 2011-06-10. Retrieved 2014-03-16.
- Schaefer, Laura; Fegley, Bruce, Jr. (2009). "Chemistry of Silicate Atmospheres of Evaporating Super-Earths". The Astrophysical Journal Letters. 703 (2): L113–L117. arXiv:0906.1204. Bibcode:2009ApJ...703L.113S. doi:10.1088/0004-637X/703/2/L113.
- Solomatov, V. S. (2000). "Fluid Dynamics of a Terrestrial Magma Ocean" (PDF).
- Leitner, J.J.; Lammer, H.; Odert, P.; Leitzinger, M.; et al. (2009). "Atmospheric Loss of Sub-Neptune's and Implications for Liquid Phases of Different Solvents on Their Surfaces" (PDF). EPSC Abstracts. 4: 542. Bibcode:2009epsc.conf..542L. EPSC2009-542.
- Tables 3 and 4 in Bains, William (2004). "Many Chemistries Could Be Used to Build Living Systems" (PDF). Astrobiology.
- Atreya, S.; Egeler, P.; Baines, K. (2006). "Water-ammonia ionic ocean on Uranus and Neptune?" (PDF). Geophysical Research Abstracts. 8: P11A–0088. Bibcode:2005AGUFM.P11A0088A.
- Guillot, T. (1999). "A comparison of the interiors of Jupiter and Saturn" (PDF). Planetary and Space Science. 47 (10–11): 1183–200. arXiv:astro-ph/9907402. Bibcode:1999P&SS...47.1183G. doi:10.1016/S0032-0633(99)00043-4.
- Lang, Kenneth R. (2003). "Jupiter: a giant primitive planet". NASA. Retrieved 2007-01-10.
- Matthias Tomczak and J. Stuart Godfrey. 2003. Regional Oceanography: an Introduction. (see the site)
- Pope, F. 2009. From eternal darkness springs cast of angels and jellied jewels. in The Times. November 23. 2009 pp. 16–17.
- Oceans at Curlie
- Smithsonian Ocean Portal
- NOAA – National Oceanic and Atmospheric Administration – Ocean
- Ocean :: Science Daily
- Ocean-bearing Planets: Looking For Extraterrestrial Life In All The Right Places
- Titan Likely To Have Huge Underground Ocean | Mind Blowing Science
- Origins of the oceans and continents". UN Atlas of the Oceans. | 0.887213 | 3.69194 |
- Through which city does the prime meridian run?
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- What are the dates of the solstices and equinoxes?
Summer solstice: June 21 Winter solstice: December 22
Vernal equinox: March 21 Autumnal equinox: September 22
- Describe Earth–Sun relationships in terms of orbit, the Sun’s position, tilt and direction of Earth’s axis as it revolves around the Sun.
Earth’s orbit around the sun is not circular, and the sun is not in the center of
the orbit. Earth is closest to the sun during January, and farthest during July, so
Earth-Sun distance does not cause the seasons, but it does affect the severity of the
winter and summer seasons. The changing orientation of Earth’s tilt relative to the
position of the sun as Earth revolves around it is the cause of the seasons. The tilt
and revolution cause all lines of latitude to receive differing amounts of solar
radiation throughout the year and the direct rays of the sun to strike at latitudes
varying from 23.5°N to 23.5°S. Tilt and revolution also cause day length to vary over
the course of the year for each line of latitude (except the equator).
- Does water have a low or high specific heat?
- What is the equation of state for an ideal gas? What are the variables?
P = ρRdT where P = pressure, ρ = density, Rd = the dry grass constant, and
T = temperature in Kelvins
- What are isobars?
a line on a map that connects locations having the same atmospheric pressure
- What forces apply to winds near the surface and in the free atmosphere?
free atmosphere: pressure gradient force (PGF), Coriolis effect (CE), centrifugal
- To what depths in the ocean do Ekman spirals exist?
- Do winds diverge or converge in cyclones and anticyclones in the northern and southern
Northern hemisphere: winds converge in cyclones and are deflected to the left,
winds diverge in anticyclones and are deflected to the right. Southern hemisphere: winds
converge in cyclones and are deflected to the right, winds diverge in anticyclones and are
deflected to the left.
- What is the change in wind direction toward the right (in the northern hemisphere) with increasing height called?
- How is air directed relative to the isobars by pressure gradient?
Air is directed at some across PGF isobars at the surface, from areas of high pressure to low. (Parallel to isobars in “free atmosphere”)
How is air directed (in the northern hemisphere) relative to wind direction by the Coriolis effect?
Air is deflected to the right.
How is air directed for an object moving on a curved trajectory by centrifugal force?
Air is pulled slightly back toward its initial trajectory (to the outside of the curve).
How is air affected by friction?
Friction slows air (wind), thus affecting the speed and reducing the amount of
Deflection from both CE and CA.
- Pounds per square inch, inches of mercury, the Pascal, and the millibar are units associated with what atmospheric characteristic?
Correction to the textbook: A newton is not a unit of pressure (and not force per square meter). A newton (abbreviated as N) is the force required to give a mass of 1 kilogram (1 kg) an acceleration of 1 meter per second per second (1 m/sec2).
- The law of motion or thermodynamics governs the movement of energy inequalities from areas of higher concentration to areas of lower concentration to balance them?
the second law of thermodynamics
- What are density, specific heat, sensible energy, and pressure?
density: a physical property of matter represented by the ratio of mass to volume
specific heat: the amount of heat (energy) required to raise the temperature of a 1 g mass
by 1°C or 1 K
sensible energy: radiant energy that heats the Earth-ocean-atmosphere system rather than
pressure: the amount of force exerted on a given area
- In what orbital positions does every latitude experience 12 hours of daylight and 12 hours of darkness?
vernal and autumnal equinoxes
- Are summer temperatures near oceans, on average, warmer or colder than temperatures at locations far inland?
- During which season do bodies of water store energy? During which season do bodies of water slowly release energy?
store in summer, release in winter
- What does leeward mean?
downwind; the side of a topographic feature facing away from the wind
- Is evaporation is a cooling or heating process?
- For a given temperature, would the heat index usually be higher or lower in the desert of Arizona than in the Amazon rain forest?
lower heat index in Arizona
- How many Navier-Stokes equations of motion are there that form the fundamentals of
numerical weather forecasting?
- Are strong pressure gradients associated with weaker or stronger winds?
- What Earth process is solely responsible for the existence of the Coriolis effect?
rotation; Earth’s angular velocity about the local vertical
- Describe the pressure of and circulation around cyclones and anticyclones in the northern and southern hemispheres.
Northern hemisphere: winds converge in cyclones and are deflected to the left,
winds diverge in anticyclones and are deflected to the right. Southern hemisphere:
winds converge in cyclones and are deflected to the right, winds diverge in
anticyclones and are deflected to the left. Cyclones are areas of low pressure, and
anticyclones are areas of high pressure.
- Do high diurnal temperature variations exist at higher or lower altitudes?
- Why is the maritime effect for San Francisco greater than it is for Washington, DC?
The maritime effect for Washington is much less than San Francisco due to the westerly direction of the prevailing winds. Washington is windward of the moderating influence of the ocean, while San Francisco is leeward (AIR AND OCEAN CIRCULATION)
- How does advection transfer energy or matter through a fluid?
- What is the average distance between the Earth and the Sun?
149.67 million km (92.96 million miles)
- How does convection transfer energy or matter through a fluid?
- How are for the wind direction named?
wind is named after the direction in which it originates (coming from)
- What is the term for the transfer of atmospheric mass from one location to another?
- What is the difference between heat and temperature with respect to the kinetic energy of molecules? (You’ll need some help from the internet)
All molecules contain some amount of kinetic energy, that is to say, they have some intrinsic motion. … Thus, the heat of an object is the total energy of all the molecular motion inside that object. Temperature, on the other hand, is a measure of the average heat or thermal energy of the molecules in a substance.
- What is the difference between revolution and rotation?
revolution: Earth’s orbit around the sun; rotation: the spin of the Earth on its axis
- What is absolute zero? How close have scientists been able to approach this temperature in the laboratory?
The theoretical temperature at which all molecular motion ceases and no internal
energy is present. Scientists were able to approach absolute zero within a few
billionths of a degree. (0 K, -273°C, -460°F)
- What are some units of energy or work?
calorie, Joule, British Thermal Unit (BTU), horsepower
Which is used in the metric system?
- What are some units of pressure? Which is used in the metric system?
inches of mercury (inHg), Newton (N), Pascal (Pa), millibar (mb)…Newton
- What are axial parallelism, axial tilt, the circle of illumination, and the plane of the ecliptic?
Axial parallelism is the property of Earth’s axis of remaining tilted at the same
fixed angle throughout its revolution about the Sun. Axial tilt is the angle between
the vertical and Earth’s axis, which corresponds approximately to 23.5° currently
in geological history. The circle of illumination is an imaginary line, as viewed from
space, that separates the illuminated and dark halves of Earth at any given time.
The plane of the ecliptic is the imaginary plane bisecting Earth and the sun, on
which Earth and other planets revolve about the sun.
- What is special regarding daylight hours at the Arctic and Antarctic Circles, equator, and Tropics of Cancer and Capricorn on the days of solstices and equinoxes?
Arctic Circle: June 21; 24 hours of sunlight, December 22; 0 hours of sunlight
Equator: 12 hours of sunlight every day of the year
Antarctic Circle: June 21; 0 hours of sunlight, December 22; 24 hours of sunlight
Tropic of Cancer: June 21; 12 hours of sunlight
Tropic of Capricorn: December 22; 12 hours of sunlight
*12 hours of daylight everywhere on March 21 and September 22
- What is the difference between latent energy and sensible energy?
Latent energy is radiant energy that evaporates water in the Earth-ocean-
atmosphere system rather than heating the atmosphere or surface. Sensible
energy is radiant energy that heats the Earth-ocean-atmosphere system rather
than evaporates water.
- Which are the six controls of climate?
latitude, Earth-Sun relationships, position in the continent, atmospheric and
oceanic circulation, topography, and local features
- Why do is urban heat islands form in cities?
lack of vegetation, decreased evaporative cooling, waste heat from domestic and
industrial processes, and thermal properties of construction material
- What is orographic precipitation?
precipitation caused by clouds formed from cool air moving uphill (windward side)
- What is refraction?
the bending of light when it encounters a medium of different density
- What is the name of the current of warm water that circulates across the North Atlantic keeping maritime Europe warmer than regions farther inland?
North Atlantic Drift
- In what latitudes do wave cyclones typically occur?
The middle latitudes (mid-latitudes, sometimes mid latitudes) are between 23°26’22” North and 66°33’39” North, and between 23°26’22” South and 66°33’39” South latitude, or, the Earth’s temperate zones between the tropics and the Arctic and Antarctic polar regions.
- As latitude and wind speed increase, does the Coriolis effect get stronger or weaker?
- According to the equation of state (ideal gas law), which factors determine the pressure of a gas?
density, the dry gas constant, and temperature in Kelvin
- How would places affected by continentality experience summer and winter temperatures?
very cold winters and fairly hot summers
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Since the angular separation of Mercury from the Sun is never more than 28 degrees at maximum elongation, visual observation and study of the planet is fraught with technical difficulty. In fact, the rugged, little planet spends more time lost in the Sun’s glare than it does out of it, meaning that much about Mercury remains unknown. However, the two NASA missions to visit Mercury, namely Mariner 10 and MESSENGER, have yielded much useable information, and while much about the “Swift Planet” remains unknown, many questions have been answered, albeit only partially in some cases. Below are some details of these questions and their answers, and it is our hope that at least some of the information presented here is new to you.
Getting into orbit around Mercury is not easy
Although the mean distance between Earth and Mercury is only 77 million km (48 million miles), a space probe that is required to enter into a stable orbit around the little planet needs to travel at least 91 million km (57 million miles) before it can do so. The issue revolves around the facts that Mercury’s orbital velocity is 48 km/sec (30 mi/sec) as compared to Earth’s, which is only 30km/sec (19 mi/sec), and that to reach Mercury in the first place, the space probe is forced to dip deeply into the Sun’s gravitational well.
The latter problem means that the probe gains a lot of speed, which can only be bled off by orbiting Venus repeatedly to slow it down, since Mercury does not have an atmosphere that is dense enough for a probe to use aero-braking maneuvers as a means to lose velocity. In practice, this means that a space probe bound for a stable orbit around Mercury uses more fuel than would be required for that same probe to escape the solar system completely. As a result, only two space probes have visited Mercury, the first being the Mariner 10 fly-by mission.
The Mariner 10 fly-by mission
The image oposite shows the first view of Mercury taken by a spacecraft, in this case, the Mariner 10 craft that also visited several other planets. Mariner 10 orbited Mercury three times after using the gravity of Venus to slow it down sufficiently, and it came to within 327 km (203 miles) at closest approach.
The image clearly shows the planet’s heavily cratered surface, as well as some of the scarps that formed when the planet’s crust cracked after the core shrank as it cooled down. This mission also gathered extensive data on the planet’s magnetic field, which turned out to be remarkably similar to Earth’s, albeit a lot weaker. The mission ended on March 24, 1975, when the craft ran out of fuel after its third close approach. Mission controllers shut down the craft but it is still thought to orbit the Sun, and to pass close by Mercury every few months.
…and then the Messenger mission
This image shows the image of Mercury’s surface taken by the MESSENGER probe (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) which left Earth on August 3, 2004, and made one orbit around our planet, and two braking orbits of Venus in October 2006 and June 2007, respectively. MESSENGER then made three fly-by orbits of Mercury to further slow it down (Jan 14, 2008, a second on Oct 6, 2008, and a third on Sept 29, 2009), before entering a stable orbit around the planet on March 18, 2011.
The mission had six objectives, which were to investigate the cause(s) of Mercury’s high density, its geological history and evolution, the nature and extent of its magnetic field, the planets’ internal structure, whether or not it has ice at its poles, and the origin of the planet’s tenuous atmosphere. The mission was also used to map parts of the planet’s surface that escaped mapping during the Mariner 10 mission.
By all accounts, the MESSENGER mission was successful in all respects. The crafts’ last maneuver happened on April 24, 2015 and it was allowed to crash onto the planets’ surface after running out of fuel, which happened on 3:26 PM EDT on April 30, 2015, leaving an estimated 16-meter (52 ft) wide crater.
MESSENGER found many volcanic flows
The MESSENGER probe located a total of 51 pyroclastic lava flows on Mercury, with 90% of the flows located inside huge impact craters. Analysis of the flows and the state of degradation of the craters suggest that volcanic activity on Mercury had occurred over very long time scales, and perhaps for much, if not most of the planet’s history.
The image opposite is a colour enhanced view of the western side of the Sholem Aleichem Crater situated on the planet’s northern hemisphere. Clearly apparent is the brightly haloed volcanic hollows, with the dark staining also possibly suggestive of ash.
Another such volcanic system in the Caloris Basin, located north of the planet’s equator, which consists of at least nine overlapping, or intersecting volcanic vents whose floors are more than one km below their brinks. This indicates that the entire system had spewed lava explosively, before the lava had retreated back down into the mantle, thus creating the system of pits. A color enhanced image of the feature can be seen at the bottom of the page, and based on MESSENGER data, this particular volcanic system is at least one billion years old.
MESSENGER was five times faster than the Space Shuttles
The MESSENGERS’ average speed during its 6.5 years in space was a respectable 136,000 km/h (84,500 m/ph), which is about five times higher than the highest speeds attained by the Space Shuttles in low Earth orbit. However, at some points during its journey, the MESSENGER probe had reached speeds in excess of 225,000 km/h (140,000 mph), nearly matching the speed record for space craft held by NASA’s Helios-2 spacecraft, which was clocked at speeds of 241,000 km/ph (150 000 m/ph) in 1976.
Mercury has ice caps
Although Mercury approaches the Sun to within 47 million km (29 million miles), images from the Arecibo Radio telescope suggested that the areas of high radio reflectivity near Mercury’s North Pole might be frozen water ice. This was confirmed by the MESSENGER probe when images from various sources were superimposed on one another. In the image above, the red areas are in permanent shadow, while the yellow spots are areas of high reflectivity, which MESSENGER’s instruments have confirmed as water ice that coincide exactly with the highly reflective spots detected by the Arecibo instrument. While the presence of water ice on super hot Mercury might sound implausible, it must be remembered that the planets’ axis is tilted by less than half a degree, which guarantees that some areas on the planet will always be in shadow.
Mercury has a weird magnetic field
Although Mercury is only marginally larger than Earth’s Moon, it has a large-scale magnetic field that is not typically associated with an object of its size and mass. The only other bodies in the solar system with comparable magnetic fields are Earth, Saturn, Jupiter, and Jupiter’s moon Ganymede. Weirder still is the fact the Mercury’s magnetic field is three times stronger in its northern hemisphere than it is in the southern hemisphere, which to date, is a mystery that remains unresolved.
Mercury is not tidally locked to the Sun
Prior to 1965, it was thought by most investigators that Mercury was tidally locked to the Sun, since they always observed the same face of the planet turned towards us whenever they looked at it. However, improved observational techniques developed during the mid-1960’s showed that Mercury is locked into a 3:2 spin/orbital resonance with the Sun, meaning that it rotates twice around its own axis during the time it takes to complete three orbits around the Sun.
In practice, this means that whenever Mercury is best placed for observation it is at, or very nearly at the same point in its orbit around the Sun, which explains why observers always saw the same side of the planet.
Mercury consists mostly of its iron core
Unlike other solid bodies in the solar system whose cores comprise only a small percentage of their diameters, Mercury’s core comprises about 55% of its diameter. The reasons for this are still unclear, but current theories include speculation that a huge impact or a series of impacts over extended time periods had stripped off the planet’s outer layers, or that the planet had formed before the Sun had stabilized its energy output. If the latter were the case, the planet’s outer layers would have been vaporized as the proto-Sun heated up as it contracted further. The vaporized rock would then have formed a silicate based “atmosphere”, and been blown away by the Sun’s energetic solar wind.
The MESSENGER mission showed that both of these hypotheses are improbable due to the presence of relatively light elements such as sulfur on the planet’s surface, which leaves the possibility that Mercury did not attract lighter material during its formation from the nebula out of which the rest of the solar system had formed, for reasons that remain unclear.
Mercury’s biggest crater is 1,550 km in diameter
Mercury has some of the biggest craters in the solar system, with the biggest example of a major impact on Mercury being the Caloris Basin, which stretches over 1,525 km. The image above shows a (partial) perspective view, with the highest part of the basin rendered in red, and the lowest parts in blue. The main impact site is visible toward the bottom edge of the frame- note the crater rim that is more than 2,000 meters high.
It is also worth noting that the impact that created the Caloris Basin was so powerful that the shockwaves from the impact travelled right round the planet to create an area of chaotic terrain known as “The Weird Terrain” at a point on the planets’ surface that is exactly antipodal (diametrically opposite) to the impact site. Part of “The Weird Terrain” can be seen in the image above. | 0.871345 | 3.778257 |
Crescent ♈ Aries
Moon phase on 23 June 2030 Sunday is Last Quarter, 22 days old Moon is in Aries.Share this page: twitter facebook linkedin
Last Quarter is the lunar phase on . Seen from Earth, illuminated fraction of the Moon surface is 42% and getting smaller. The 22 days old Moon is in ♈ Aries.
* The exact date and time of this Last Quarter phase is on 22 June 2030 at 17:19 UTC.
Moon rises at midnight and sets at noon. It is visible to the south in the morning.
Moon is passing about ∠11° of ♈ Aries tropical zodiac sector.
Lunar disc appears visually 4.3% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1807" and ∠1888".
Next Full Moon is the Buck Moon of July 2030 after 21 days on 15 July 2030 at 02:12.
There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak.
The Moon is 22 days old. Earth's natural satellite is moving through the last part of current synodic month. This is lunation 376 of Meeus index or 1329 from Brown series.
Length of current 376 lunation is 29 days, 15 hours and 13 minutes. It is 1 hour and 36 minutes longer than next lunation 377 length.
Length of current synodic month is 2 hours and 29 minutes longer than the mean length of synodic month, but it is still 4 hours and 34 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠189°. At the beginning of next synodic month true anomaly will be ∠213.7°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°).
8 days after point of perigee on 14 June 2030 at 23:37 in ♐ Sagittarius. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 4 days, until it get to the point of next apogee on 27 June 2030 at 14:14 in ♉ Taurus.
Moon is 396 568 km (246 416 mi) away from Earth on this date. Moon moves farther next 4 days until apogee, when Earth-Moon distance will reach 405 881 km (252 203 mi).
8 days after its ascending node on 15 June 2030 at 05:24 in ♐ Sagittarius, the Moon is following the northern part of its orbit for the next 5 days, until it will cross the ecliptic from North to South in descending node on 28 June 2030 at 23:50 in ♊ Gemini.
8 days after beginning of current draconic month in ♐ Sagittarius, the Moon is moving from the beginning to the first part of it.
8 days after previous South standstill on 15 June 2030 at 07:44 in ♐ Sagittarius, when Moon has reached southern declination of ∠-22.735°. Next 5 days the lunar orbit moves northward to face North declination of ∠22.734° in the next northern standstill on 29 June 2030 at 02:45 in ♊ Gemini.
After 7 days on 30 June 2030 at 21:34 in ♋ Cancer, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.848363 | 3.148351 |
If the moon was large enough to hold an atmosphere, then in principle there is no reason that it could not be capable of being terraformed. There would be some interesting complications, however.
First off, a moon orbiting a Gas Giant would likely be tidally locked with one face towards the primary. Days would be very short, but the hemisphere facing the primary would be illuminated by the primary itself, as well as the primary and the sun during part of the orbit, and in darkness for a very short period of time. The side facing the primary would have the "hot pole" where the primary is at the zenith, while the opposite side would have the "cold pole", so atmospheric and hydrospheric circulation and heat flows would be dominated by this.
The leading hemisphere of the moon would be bathed by the energetic radiation trapped in the primary's magnetosphere, while the trailing hemisphere would be relatively shielded. The interaction between the energy deposited from the hot pole and the "leading pole" could be defined as a series of concentric bands at 90 degrees from each other, leaving the moon covered in a sort of checkerboard of ecosystems based on energy inputs.
Depending on the numbers of other moons, the core of this moon might be "kneaded" by multiple and overlapping gravitational pulls during its orbit, making the moon quite active tectonically. Lots of volcanoes and active plates would make the surface quite active, as well as subducting lots of water and carbonate rocks. The hydrothermal and carbon dioxide cycles on this moon would be much faster than on Earth.
Since we are in the middle of a very deep gravity well, you should expect the moon is also subject to lots of collisions with asteroids and comets. This would add lots of water to the moon, but also reset ecological "squares" that were hit, meaning evolution would be going in fits and starts if the moon already had or was seeded with some sort of "native" life.
IF the Primary was tipped over like Uranus and the moons were in orbiting facing the sun at all times, then the positions of the "Hot" and "Leading" poles would be different. There would actually be a third pole, where the primary is overhead at all times, with the sun coming down at a high angle but also being permanently illuminated by the primary as well. There would be no diurnal cycle as we understand it, but the solar and hot poles would always be illuminated, while the dark pole (opposite the solar pole)would be in darkness and the cold pole would only have solar illumination, but more constant than the cold pole of the first example. Trying to trace the energy flows in these moons would be very interesting indeed. | 0.854283 | 3.8376 |
The International Astronomical Union has chosen the names Aegis and Gorgoneion for the two moons of the asteroid (93) Minerva. My team discovered the small moons in 2009 using the W. M. Keck Telescope and its adaptive optics system. We proposed the names after receiving input from the public.
Astronomer J.C. Watson discovered (93) Minerva, a large 150 km diameter asteroid located in the main belt, on Aug. 24, 1867 and named the body after the Roman equivalent of Athena, the Greek goddess of wisdom. On Aug. 16, 2009, astronomers discovered two moons around the asteroids with the temporary names S/2009 (93) 1 and S/2009 (93) 2 from direct imaging with the 10 m Keck II Telescope on Mauna Kea, Hawaii. A follow-up study published this year in Icarus Journal revealed that the moons are small, with an estimated diameter of 2 to 5 km, and orbit at 375 and 625 km from the primary.
The convention for naming asteroidal moons is to pick a child or close relative of the historical figure after whom the asteroid is named. For example, the moons of the triple main-belt asteroid system (87) Sylvia are named Romulus and Remus, founders of Rome and twin sons of the Rhea Sylvia. Minerva was a virgin goddess who did not have descendants, however, which makes it impossible to follow this rule.
That’s why I asked the public for help naming the moons after announcing their discovery and presenting his analysis of the data at meeting of the European Planetary Science Congress and the Division of Planetary Science in Nantes, France in Oct. 2011.
The decision to crowd-source the names caught the attention of the public, so whenever I had the opportunity I repeated the request when giving presentations to groups of amateur astronomers and in interviews to astronomy magazines. Over the following year, I received a lot of emails with suggestions. Interestingly, several of them used mythological attributes of the goddess Minerva as potential names for the moons.
Several space aficionados proposed naming the moons after magical weapons used by goddess. Athena was the favorite daughter of Zeus, and that’s why he let her use his insignia, his terrible shield, the aegis, and his devastating weapon, the ray. Gorgoneion was a special apotropaic amulet showing the Gorgon head, and was used as a protective pendant. The Aegis was the shield worn by Athena, bore Medusa’s head, and could paralyze any enemy who looked at it.
We submitted a formal proposal with the names Aegis and Gorgoneion to the International Astronomical Union, which is in charge of naming comets, asteroids and their moons. In Dec. 2013, the names were officially accepted by the organization and published in the Minor Planet Center MPC batch. “S/(93) 1 Aegis” the outer, larger 4 km moonlet, was the first one spotted by the observers. “S/(93) 2 Gorgoneion” orbits closer to the primary and may be smaller (3 km). The pendant is normally smaller than the shield, and held closer—a tool for remembering which moon is Gorgoneion.
It is a great privilege for astronomers to name celestial bodies such as the moons of an asteroid. We wanted to share this privilege with members of the public, who as taxpayers fund our research and consequently play an essential role in it. Plus, it is reassuring to find out through emails sent by people around the world that astronomy gets a lot of attention.
Thanks for my colleagues and co-discoverers Pascal Descamps, Jerome Berthier and Frederic Vachier from IMCCE-Obs de Paris.
Additional references if you want to know more:
Guidelines for the names of Minor Planets, Committee on Small Body Nomenclature, IAU Division III, 2000, http://www.ss.astro.umd.edu/IAU/csbn/mpnames.shtml
James Craig Watson:
Marchis et al., Icarus, Volume 224, Issue 1, May 2013, Pages 178–191, 2013. Characteristics and large bulk density of the C-type main-belt triple asteroid (93) Minerva http://www.sciencedirect.com/science/article/pii/S0019103513000808
The encyclopedia of Goddess Athena | 0.87912 | 3.182356 |
Radio astronomy is the observation of astronomical phenomena via the reception of radio waves originating in the cosmos. ITU has identified the frequency bands necessary for these observations based on the physical characteristics of the chemical molecules under observation: hydrogen, water vapour, methanol or carbon monoxide, for example. Radio astronomical measurements are often carried out as part of an international framework involving research laboratories in several countries.
Because they measure radio emissions from celestial objects at cosmic distances from the Earth, radio astronomy receivers are designed to detect extremely weak signals, without comparison with those used in terrestrial applications. There are two types of radio astronomy observations:
- observation of spectral lines, where the radiation detected by the radio telescope is the result of spontaneous emissions (associated with changes of quantum state) by certain atoms or molecules (hydrogen or hydroxyl radical, for example). These lines are characterized by precise central frequencies, determined by the characteristics of and physical changes to the molecules under observation;
- observation of continuum emissions, whether thermal or non-thermal in origin (planetary magnetosphere, for example, or solar flares), for which radio spectrum is wide-band.
To observe these cosmic sources, radio astronomers use either an extremely large antenna providing sufficient spatial resolution to distinguish the various celestial objects under observation, or interferometry systems combining simultaneous measurements by a number of radio telescopes thousands of kilometres apart. These systems achieve resolutions so fine that they are able to study the detailed structure of distant radio sources. Observations made by high spatial resolution interferometry therefore rely on simultaneous reception of the same radio frequency by widely dispersed reception systems, further emphasizing the international scope of the protection afforded to radio astronomy: if just one of the observation systems is affected by interference, all the other international measurements are compromised.
There are four radio astronomy observatories in France: Nançay, the plateau de Bure, Maïdo on the island of Réunion and Floirac.
While radio astronomy studies the cosmos from Earth, satellites, too, can be used to observe celestial objects. Scientific space research is set firmly in a dynamic of international cooperation: costly programmes (astronomical missions such as the Herschel infrared space telescope or the Planck cosmic microwave background mapping mission) are conducted by the European Space Agency (ESA) and financed by a budget to which member states contribute. Onboard instruments are supplied by member states following requests for proposals. France’s participation in ESA is coordinated by the French space research agency, CNES.
In addition to its European initiatives, CNES conducts national programmes (such as the MICROSCOPE project launched in April 2016, designed to verify the principle of equality of gravitational and inertial mass, one of the foundations of the theory of general relativity) and engages in multilateral cooperation (such as the CoRoT satellite carrying a space telescope designed to study the internal structure of stars and search for exoplanets). These programmes are generally based on micro or mini-satellites. For projects such as these, CNES brings in scientific and industrial partners to carry out the space programmes it designs.
Because they are so intrinsically international in nature, space research systems rely solely on frequencies that have been globally harmonised under the ITU Radio Regulations. In France, CNES operates a space research station, based on the Kourou site, in the 8400-8500 MHz band, for the needs of projects such as Mars-Express, Rosetta, Herschel or Planck. | 0.885189 | 4.032562 |
While astronomers and scientists hunt for signs of alien life on other planets, researchers closer to home are still trying to establish the origins of life on Earth.
By knowing how life got kickstarted on our planet, it could help us more accurately study evolution, cure disease and even pinpoint similar conditions elsewhere in the Universe.
One theory is that comets delivered the building blocks for life eons ago. This week, Speaking of Chemistry explained the chemistry behind how these icy, lumpy space rocks might have seeded life on Earth in an explainer video.
Where are all the aliens? WIRED explains the Fermi Paradox
As the video explains, comets are "leftovers after the birth of stars and planets," meaning comets in our solar system are more than 4 billion years old.
While Earth was cooling down, comets were in abundance and are thought to have crashed into Earth, the Moon and many other celestial bodies. Because comets are made up of the debris of planetary formation, they are believed to have had the same sort of basic chemicals found on nascent planet Earth. In particular, methane, carbon monoxide, methanol, and ammonia.
Researchers have recently created lab models of comets and showed that ultraviolet radiation, even in the frigid temperatures of outer space, can transform these basic molecules into more complex carbon compounds.
Another possibility is that complex carbon molecules formed at the same time as the solar system itself, but vaporised close to the hot cores of planets and stars. The molecules, however, survived on cooler comets.
Rosetta spots the lifeless body of its long-lost Philae lander on Comet 67P
The theory dictates that comets would have smashed into primordial Earth, bringing with them the complex carbon molecules required to kickstart life, such as components of nucleic acids, lipids and amino acids, at the same time the planet was cooling enough to not incinerate them.
In 2004, Nasa’s Stardust mission picked up some dust around a comet called Wild Two and found evidence of the amino acid glycine, as well as methylamine and ethylamine, chemicals formed en route to glycine.
Then, in 2014 while the Philae lander was en route to the surface of 67P, two instruments detected organic molecules methyl isocyanate, acetone, propanal, and acetamide, as well as organic polymers, most likely from the radiation-induced polymerisation of formaldehyde. These findings all add to the theory.
However, deep sea vents, for example, are also likely candidates for producing complex carbon compounds needed for life start and work will continue on trying to determine the cause. | 0.900728 | 3.560624 |
Vast quantities of water have poured across the surface of Mars in ages past. The evidence is obvious in dozens of outflow channels, large and small. The waters emerged, scientists think, from subsurface reservoirs when the frozen ground capping them was broken open.
But where did the water end up? And what about eroded sediment carried along by the floods?
Studying Hebrus Valles and Hephaestus Fossae in the Utopia impact basin, the dozen authors of a new paper in Geophysical Research Letters write, “Our investigation indicates that outflow channel floodwaters were captured and reabsorbed into the subsurface in zones where caverns developed within the northern plains.”
Led by Alexis Rodriguez (Planetary Science Institute), the scientists used images from CTX and THEMIS coupled with topographic data from MOLA. “At some locations within the study region,” they write, “features interpreted as mud volcanoes cluster into linear ridges. These ridge patterns align with networks of individual pits, pit chains, and troughs.”
Linking the features, the team argues, are open voids in the subsurface, or caverns. “We suggest that within the study region, collapsed sections of cavern systems are expressed at the surface by these linear depressions.” The apparent connectivity of mud volcanoes with the pit and trough networks suggests a genetic link between mud volcanism and the development of cavern networks.
The scientists note that streams on Earth disappear into sinkholes, and underground conduits can carry large amounts of water and sediment.
They acknowledge that the estimated volume of the Hebrus outflow is 100 times greater than the trough networks where they end. However, they say, “we note that these trough networks likely represent only the portions of the cavern networks that collapsed.”
Caverns on Earth commonly form in carbonate rocks, such as limestone, where acidic rain and groundwater dissolves the rock starting along joints and cracks. However, if Mars has extensive carbonate rocks in the northern lowlands, geologists have yet to find them. The team, instead, proposes an alternative method of making caverns.
“Our model invokes the role of mud volcanism in the formation of subsurface caverns. High hydraulic pressures are thought to have led to mud volcanism along the southeast margins of the Utopia basin, as well as within other regions of the northern plains,” they explain.
They note that the occurrence of mud volcanoes along boundary plains fits with the idea of a pressurized hydraulic head within water-bearing rocks that extend across the highland-lowland boundary. Something – perhaps hot magma – increased the water pressure or melted the frozen ground, thus opening pathways for the water to reach the surface.
“Fluid circulation along the fractures led to the development of feeder conduits through which fluid-sediment mixtures erupted to construct mud volcanoes,” says the team. It was the enlargement of these conduits by subsurface erosion that led to the development of caverns.
How long would such caverns remain open? Potentially a very long time. The write, “At -60°C [–76°F], a predicted typical mean annual surface temperature for the investigated latitudes, permafrost could have had a mechanical strength close to that of limestone.” This could allow the formation of longterm, structurally stable caverns.
The researchers explain that “the gravity of Mars is 0.38 times that of Earth, which would have allowed for the development of 2.5 times deeper cavern systems.” Terrestrial caverns occur down to a maximum depth of about 2,000 meters (6,500 feet), thus gravity differences alone could allow Martian caverns to remain open to about 5,000 m (16,500 ft) depth – especially if deep-seated carbonates form extensive deposits within the northern lowlands’ upper crust.
Finally, the researchers note that Martian caverns could be bigger than those on Earth. “The maximum stable width of a cavern increases with the inverse square root of gravitational acceleration. Consequently, on Mars caverns within geologic materials that have similar mechanical strength could have about 60 percent wider roofs than on Earth.”
This means, they say, “If maximum cavern dimensions all scale similarly, Martian caverns could be more voluminous than Earth’s, perhaps four times greater.” | 0.808578 | 3.766009 |
The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF).
|ジャーナル||EPJ Web of Conferences|
|出版物ステータス||Published - 2015 5 29|
|イベント||3rd International Conference on New Frontiers in Physics, ICNFP 2014 - Kolymbari, Crete, Greece|
継続期間: 2014 7 28 → 2014 8 6
ASJC Scopus subject areas
- Physics and Astronomy(all) | 0.849995 | 3.196686 |
New research re-creates planet formation, super-earths and giant planets in the laboratory
New laser-driven compression experiments reproduce the conditions deep inside exotic super-Earths and giant planet cores, and the conditions during the violent birth of Earth-like planets, documenting the material properties that determined planets' formation and evolution processes.
The experiments, reported in the Jan. 23 edition of Science, reveal the unusual properties of silica - the key constituent of rock - under the extreme pressures and temperatures relevant to planetary formation and interior evolution.
Using laser-driven shock compression and ultrafast diagnostics, Lawrence Livermore National Laboratory (LLNL) physicist Marius Millot and colleagues from Bayreuth University (Germany), LLNL and University of California, Berkeley were able to measure the melting temperature of silica at 500 GPa (5 million atmospheres), a pressure comparable to the core-mantle boundary pressure for a super-Earth planet (5 Earth masses), Uranus and Neptune. It is also the regime of giant impacts that characterize the final stages of planet formation.
"Deep inside planets, extreme density, pressure and temperature strongly modify the properties of the constituent materials," Millot said. "How much heat solids can sustain before melting under pressure is key to determining a planet's internal structure and evolution, and now we can measure it directly in the laboratory."
In combination with prior melting measurements on other oxides and on iron, the new data indicate that mantle silicates and core metal have comparable melting temperatures above 300-500 GPa, suggesting that large rocky planets may commonly have long-lived oceans of magma - molten rock - at depth. Planetary magnetic fields can be formed in this liquid-rock layer.
"In addition, our research suggests that silica is likely solid inside Neptune, Uranus, Saturn and Jupiter cores, which sets new constraints on future improved models for the structure and evolution of these planets," Millot said.
Those advances were made possible by a breakthrough in high-pressure crystal growth techniques at Bayreuth University in Germany. There, Natalia Dubrovinskaia and colleagues managed to synthesize millimeter-sized transparent polycrystals and single crystals of stishovite, a high-density form of silica (SiO2) usually found only in minute amounts near meteor-impact craters.
Those crystals allowed Millot and colleagues to conduct the first laser-driven shock compression study of stishovite using ultrafast optical pyrometry and velocimetry at the Omega Laser Facility at the University of Rochester's Laboratory for Laser Energetics.
"Stishovite, being much denser than quartz or fused-silica, stays cooler under shock compression, and that allowed us to measure the melting temperature at a much higher pressure," Millot said. "Dynamic compression of planetary-relevant materials is a very exciting field right now. Deep inside planets hydrogen is a metallic fluid, helium rains, fluid silica is a metal and water may be superionic."
In fact, the recent discovery of more than 1,000 exoplanets orbiting other stars in our galaxy reveals the broad diversity of planetary systems, planet sizes and properties. It also sets a quest for habitable worlds hosting extraterrestrial life and shines new light on our own solar system. Using the ability to reproduce in the laboratory the extreme conditions deep inside giant planets, as well as during planet formation, Millot and colleagues plan to study the exotic behavior of the main planetary constituents using dynamic compression to contribute to a better understanding of the formation of the Earth and the origin of life. | 0.877867 | 3.79743 |
Now here’s something I guarantee you’ve never seen before: a video of the dwarf planet Pluto and its largest moon Charon showing the two distinctly separate worlds actually in motion around each other! Captured by the steadily-approaching New Horizons spacecraft from July 19–24, the 12 images that comprise this animation were acquired with the Long Range Reconnaissance Imager (LORRI) instrument from distances of 267 million to 262 million miles (429 million to 422 million km) and show nearly a full orbital rotation. Absolutely beautiful!
For a close-up video of the two worlds in motion, click below:
Pluto and Charon are seen circling a central gravitational point known as the barycenter, which accounts for the wobbling motion. Since Charon is 1/12th the mass of Pluto the center of mass between the two actually lies a bit outside Pluto’s radius, making their little gravitational “dance” readily apparent.
(The same effect happens with the Earth and Moon too, but since the barycenter lies 1,700 km below Earth’s surface it’s not nearly as obvious.)
“The image sequence showing Charon revolving around Pluto set a record for close range imaging of Pluto—they were taken from 10 times closer to the planet than the Earth is,” said New Horizons mission Principal Investigator Alan Stern, of the Southwest Research Institute. “But we’ll smash that record again and again, starting in January, as approach operations begin.”
Launched January 19, 2006, New Horizons is now in the final year of its journey to the Pluto system. On August 25 it will pass the orbit of Neptune – which, coincidentally, is 25 years to the day after Voyager 2’s closest approach – and then it’s on to Pluto and Charon, which New Horizons will become the first spacecraft to fly by on July 14, 2015, at distances of 10,000 and 27,000 km respectively. Find out where New Horizons is right now here.
Source: New Horizons
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute | 0.871309 | 3.376352 |
Evidence for the ancient, 1.2 billion years old, meteorite strike, was first discovered in 2008 near Ullapool, NW Scotland by scientists from Oxford and Aberdeen Universities. The thickness and extent of the debris deposit they found suggested the impact crater—made by a meteorite estimated at 1km wide—was close to the coast, but its precise location remained a mystery.
In a paper published today in Journal of the Geological Society, a team led by Dr. Ken Amor from the Department of Earth Sciences at Oxford University, show how they have identified the crater location 15-20km west of a remote part of the Scottish coastline. It is buried beneath both water and younger rocks in the Minch Basin.
Dr. Ken Amor said: ‘The material excavated during a giant meteorite impact is rarely preserved on Earth, because it is rapidly eroded, so this is a really exciting discovery. It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.
‘The next step will be a detailed geophysical survey in our target area of the Minch Basin.’
Using a combination of field observations, the distribution of broken rock fragments known as basement clasts and the alignment of magnetic particles, the team was able to gauge the direction the meteorite material took at several locations, and plotted the likely source of the crater.
Dr. Ken Amor said: ‘It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area.’
1.2 billion years ago most of life on Earth was still in the oceans and there were no plants on the land. At that time Scotland would have been quite close to the equator and in a semi-arid environment. The landscape would have looked a bit like Mars when it had water at the surface.
Earth and other planets may have suffered a higher rate of meteorite impacts in the distant past, as they collided with debris left over from the formation of the early solar system.
However, there is a possibility that a similar event will happen in the future given the number of asteroid and comet fragments floating around in the solar system. Much smaller impacts, where the meteorite is only a few meters across are thought to be relatively common perhaps occurring about once every 25 years on average.
It is thought that collisions with an object about 1 km (as in this instance) across occur between once every 100,000 years to once every one million years—but estimates vary.
One of the reasons for this is that our terrestrial record of large impacts is poorly known because craters are obliterated by erosion, burial and plate tectonics.
More information: Kenneth Amor et al. The Mesoproterozoic Stac Fada proximal ejecta blanket, NW Scotland: constraints on crater location from field observations, anisotropy of magnetic susceptibility, petrography and geochemistry. Journal of the Geological Society (2019). DOI: 10.1144/jgs2018-093
Michael J. Simms et al. A reassessment of the proposed ‘Lairg Impact Structure’ and its potential implications for the deep structure of northern Scotland. Journal of the Geological Society (2019). DOI: 10.1144/jgs2017-161
Image Credit: CC0 Public Domain | 0.860559 | 3.778014 |
Portrait of Galileo Galilei, 1636 (detail),
by Justus Sustermans (1597-1681).
As a youth, Galileo was taught at the Cestello monastery by court mathematician Ostilio Ricci. This was around 1580 when Galileo was sixteen, and Neri was a four year old toddler, living only a block away and attending the Cestello church with his family. Neri's father and grandfather had just been granted citizen status, already well known for their medical prowess, and his father served on the board of the artist's guild based at Cestello. Galileo would go on to become good personal friends with Prince Don Antonio de' Medici, Neri's sponsor. Later, the astronomer would have telescope tubes made by Jacopo Ligozzi, a regular at the Casino di San Marco, where Neri worked as an alchemist and took his first steps into the craft of glassmaking. As Galileo started to experiment with lenses, Neri was leaving Italy for Antwerp and would be absent for seven years. Meanwhile Galileo landed a job at the Florentine court as mathematics tutor to Grand Duke Ferdinando's son, Cosimo II.
Both Galileo and Neri worked hard for their achievements. In the hindsight of history, innovations are often romanticized into shining moments of inspiration, forgetting the painstaking effort and dogged persistence required to bring those ideas to fruition. For his telescopes, Galileo encountered tremendous difficulty both in the production of suitable glass and in grinding that glass into usable lenses. His celestial observations included sunspots, lunar craters and the planet Jupiter with its moons, which he named "Medicea Sideria" after his Medici benefactors. As these revelations became known, there was a clamor of orders for telescopes from princes throughout Europe and Galileo struggled to keep up. He maintained a circle of trusted craftsmen on Murano in Venice, and elsewhere, but still, the majority of output was unusable.
Initially, he had reasonable success grinding and polishing broken pieces of mirrors. In early 1610, Galileo held a demonstration in Pisa for his former pupil, Grand Duke Cosimo II. A short time later, the grand duke ordered that a special batch of glass be made for Galileo by Niccolò Sisti, for whom Antonio Neri had worked just a few years earlier. At the time, Neri himself was still in Antwerp and would not return until the following year.
Neri returned to Tuscany and wrote his book on glassmaking, L'Arte Vetraria, but then turned his attention to other pursuits. This, just as Galileo's quest for high quality glass to make his lenses took off in earnest. Neri’s final manuscript places him in Pisa working on alchemical recipes. There was no more optimal moment for the two men to meet; both were working in Pisa, both knew Niccolò Sisti, Neri had just published his book and the astronomer was becoming desperate for clear flawless glass. If such a meeting ever occurred, it has not been recorded, and shortly thereafter, in 1614, Neri died of an unspecified illness.
On 20 December of that same year, four days before Christmas, Tommaso Caccini, Neri's childhood next-door neighbor, delivered a scathing denouncement of Galileo from the pulpit of Santa Maria Novella church. While the sermon earned Caccini a reprimand, and was an embarrassment to his family, it did also serve as a start to Galileo's troubles with the inquisition.
While Antonio Neri may have never encountered the astronomer, shortly after the time of the priest’s death, the astronomer acquired Neri's book on glassmaking. One copy was sent to Rome, to Federico Cesi, founder of the Accademia dei Lincei, a scientific society to which Galileo belonged, and another copy was saved for the astronomer's personal library. Galileo continued his quest for flawless glass and in his correspondence he takes on the same obsession with purity of ingredients that Neri exhibits throughout his book. | 0.849087 | 3.097614 |
NASA’s Voyager 2 becomes second spacecraft to reach interstellar space
PTI, Nov 5, 2019, 5:04 PM IST
Washington: More than four decades after beginning its epic journey, NASA’s Voyager 2 spacecraft has crossed the elusive boundary that marks the edge of the Sun’s realm and the start of interstellar space, scientists have announced.
According to the researchers at the University of Iowa in the US, Voyager 2 has entered the interstellar medium (ISM), the region of space outside the bubble-shaped boundary produced by wind streaming outward from the Sun.
This makes Voyager 2 the second human-made object to journey out of the Sun’s influence, following the US space agency’s Voyager 1’s solar exit in 2012.
The study, published in the journal Nature Astronomy, confirmed Voyager 2’s passage on November 5, 2018, into the ISM by noting a definitive jump in plasma density detected by a plasma wave instrument on the spacecraft.
The marked increase in plasma density is evidence of Voyager 2 journeying from the hot, lower-density plasma characteristic of the solar wind to the cool, higher-density plasma of interstellar space, the researchers said.
It is also similar to the plasma density jump experienced by Voyager 1 when it crossed into interstellar space, they said.
“In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true,” said Professor Don Gurnett from the University of Iowa, and corresponding author on the study.
“We show with Voyager 2 — and previously with Voyager 1 — that there’s a distinct boundary out there. It’s just astonishing how fluids, including plasmas, form boundaries,” Gurnett said.
Voyager 2’s entry into the ISM occurred at 119.7 astronomical units (AU), or more than 11 billion miles from the Sun. Voyager 1 passed into the ISM at 122.6 AU.
The spacecraft were launched within weeks of each other by NASA in 1977, with different mission goals and trajectories through space. Yet they crossed into the ISM at basically the same distances from the Sun.
That gives valuable clues to the structure of the heliosphere — the bubble, shaped much like a wind sock, created by the Sun’s wind as it extends to the boundary of the solar system, the researchers said.
“It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed,” said Bill Kurth, University of Iowa research scientist and a co-author on the study.
“That says that these two points on the surface are almost at the same distance,” Kurth said.
“There’s almost a spherical front to this. It’s like a blunt bullet,” Gurnett added.
Data from the instrument on Voyager 2 also gives additional clues to the thickness of the heliosheath, the outer region of the heliosphere and the point where the solar wind piles up against the approaching wind in interstellar space, which Gurnett likens to the effect of a snowplow on a city street.
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Pak Army claims to shoot down ‘Indian spying quadcopter’ along LoC | 0.839715 | 3.483658 |
Crazy things can happen when galaxies collide, as they sometimes do. Although individual stars rarely impact each other, the gravitational interactions between galaxies can pull enormous amounts of gas and dust into long streamers, spark the formation of new stars, and even kick objects out into intergalactic space altogether. This is what very well may have happened to SDSS1133, a suspected supermassive black hole found thousands of light-years away from its original home.
Seen above in a near-infrared image acquired with the Keck II telescope in Hawaii, SDSS1133 is the 40-light-year-wide bright source observed 2,300 light-years out from the dwarf galaxy Markarian 177, located 90 million light-years away in the constellation Ursa Major (or, to use the more familiar asterism, inside the bowl of the Big Dipper.)
The two bright spots at the disturbed core of Markarian 177 are thought to indicate recent star formation, which could have occurred in the wake of a previous collision.
“We suspect we’re seeing the aftermath of a merger of two small galaxies and their central black holes,” said Laura Blecha, an Einstein Fellow in the University of Maryland’s Department of Astronomy and a co-author of an international study of SDSS1133. “Astronomers searching for recoiling black holes have been unable to confirm a detection, so finding even one of these sources would be a major discovery.”
Interactions between supermassive black holes during a galactic collision would also result in gravitational waves, elusive phenomena predicted by Einstein that are high on astronomers’ most-wanted list of confirmed detections.
Watch an animation of how the suspected collision and subsequent eviction may have happened:
But besides how it got to where it is, the true nature of SDSS1133 is a mystery as well.
The persistently bright near-infrared source has been detected in observations going back at least 60 years. Whether or not SDSS1133 is indeed a supermassive black hole has yet to be determined, but if it isn’t then it’s a very unusual type of extremely massive star known as an LBV, or Luminous Blue Variable. If that is the case though, it’s peculiar even for an LBV; SDSS1133 would have had to have been continuously pouring out energy in a for over half a century until it exploded as a supernova in 2001.
To help determine exactly what SDSS1133 is, continued observations with Hubble’s Cosmic Origins Spectrograph instrument are planned for Oct. 2015.
“We found in the Pan-STARRS1 imaging that SDSS1133 has been getting significantly brighter at visible wavelengths over the last six months and that bolstered the black hole interpretation and our case to study SDSS1133 now with HST,” said Yanxia Li, a UH Manoa graduate student involved in the research.
And, based on data from NASA’s Swift mission the UV emission of SDSS1133 hasn’t changed in ten years, “not something typically seen in a young supernova remnant” according to Michael Koss, who led the study and is now an astronomer at ETH Zurich.
Regardless of what SDSS1133 turns out to be, the idea of such a massive and energetic object soaring through intergalactic space is intriguing, to say the least.
The study will be published in the Nov. 21 edition of Monthly Notices of the Royal Astronomical Society.
Source: Keck Observatory | 0.933352 | 4.103959 |
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as Venus entered on the solar disc, the sweep of light round the dark disc of Venus would enable a very precise observation to be made. The Transit of Venus in 1874, in which the present writer assisted, overthrew this delusion. In 1877 Sir David Gill used Lord Crawford's heliometer at the Island of Ascension to measure the parallax of Mars in opposition, and found the sun's distance 93,08o,ooo miles. He considered that, while the superiority of the heliometer had been proved, the results would be still better with the points of light shown by minor planets rather than with the disc of Mars. In 1888–9, at the Cape, he observed the minor planets Iris, Victoria, and Sappho, and secured the co-operation of four other heliometers. His final result was 92,870, ooo miles, the parallax being 8”,802 (Cape Obs., Vol. VI.). So delicate were these measures that Gill detected a minute periodic error of theory of twenty-seven days, owing to a periodically erroneous position of the centre of gravity of the earth and moon to which the position of the observer was referred. This led him to correct the mass of the moon, and to fix its ratio to the earth's mass = o.o.1 2240. Another method of getting the distance from the sun is to measure the velocity of the earth's orbital motion, giving the circumference traversed in a year, and so the radius of the orbit. o This has been done by comparing observation and experiment. The aberration of light is an angle 2 o'' 48, giving the ratio of the earth's velocity to the velocity of light. The velocity of light is 186, ooo miles a second; whence the distance to the sun is 92,78o, ooo miles. There seems, however, to be some uncertainty about the true value of the aberration, any determination of which is subject to irregularities due to the “seasonal errors.” The velocity of light was experimentally found, in 1862, by Fizeau and Foucault, each using an independent method. These methods have been developed, and new values found, by Cornu, Michaelson, Newcomb, and the present writer. Quite lately Halm, at the Cape of Good Hope, measured spectroscopically the velocity of the earth to and from a star by observations taken six months apart. Thence he obtained an accurate value of the sun's distance." But the remarkably erratic minor planet, Eros, discovered by Witte in 1898, approaches the earth within 15, ooo, ooo miles at rare intervals, and, with the aid of photography, will certainly give us the best result. A large number of observatories combined to observe the opposi
tion of 1900. Their results are not yet completely reduced, but the best value deduced so far for the parallax' is 8”.807 to".oo28.”
II. HISTORY OF THE TELEscoPE
Accounts of wonderful optical experiments by Roger Bacon (who died in 1292), and in the sixteenth century by Digges, Baptista Porta, and Antonio de Dominis (Grant, Hist. Ph. Ast.), have led some to suppose that they invented the telescope. The writer considers that it is more likely that these notes refer to a kind of camera obscura, in which a lens throws an inverted image of a landscape on the wall. The first telescopes were made in Holland, the originator being either Henry Lipperhey,” Zacharias Jansen, or James Metius, and the date 1608 or earlier. In 1609 Galileo, being in Venice, heard of the invention, went home and worked out the theory, and made a similar telescope. These telescopes were all made with a convex object-glass and a concave eye-lens, and this type is spoken of as the Galilean telescope. Its defects are that it * The parallax of the sun is the angle subtended by the earth's radius at the sun's distance. * A. R. Hinks, R.A.S.; Monthly Notices, June, 1909. * In the Encyclopædia Britannica, article “ Tele
scope,” and in Grant's Physical Astronomy, good reasons are given for awarding the honour to Lipperhey. has no real focus where cross-wires can be placed, and that the field of view is very small. Kepler suggested the convex eye-lens in 1611, and Scheiner claimed to have used one in 1617. But it was Huyghens who really introduced them. In the seventeenth century telescopes were made of great length, going up to 3oo feet. Huyghens also invented the compound eye-piece that bears his name, made of two convex lenses to diminish spherical aberration. But the defects of colour remained, although their cause was unknown until Newton carried out his experiments on dispersion and the solar spectrum. To overcome the spherical aberration James Gregory," of Aberdeen and Edinburgh, in 1663, in his Optica Promota, proposed a reflecting speculum of parabolic form. But it was Newton, about 1666, who first made a reflecting telescope; and he did it with the object of avoiding colour dispersion. * Will the indulgent reader excuse an anecdote which may encourage some workers who may have found their mathematics defective through want of use? James Gregory's nephew David had a heap of MS. notes by Newton. These descended to a Miss Gregory, of Edinburgh, who handed them to the present writer, when an undergraduate at Cambridge, to examine. After perusal, he lent them to his kindest of friends, J. C. Adams (the discoverer of Neptune), for his opinion. Adams's final verdict was: “I fear they are of no value. It is pretty evident that, when Some time elapsed before reflectors were much used. Pound and Bradley used one presented . to the Royal Society by Hadley in 1723. Hawksbee, Bradley, and Molyneaux made some. But James Short, of Edinburgh, made many excellent Gregorian reflectors from 1732 till his death in 1768.
Newton's trouble with refractors, chromatic aberration, remained insurmountable until John Dollond (born 1706, died 1761), after many experiments, found out how to make an achromatic lens out of two lenses — one of crown glass, the other of flint glass — to destroy the colour, in a way originally suggested by Euler. He soon acquired a great reputation for his telescopes of moderate size; but there was a difficulty in making flint-glass lenses of large size. The first actual inventor and constructor of an achromatic telescope was Chester Moor Hall, who was not in trade, and did not patent it. Towards the close of the eighteenth century a Swiss named Guinand at last succeeded in producing larger flint-glass discs free from striae. Frauenhofer, of Munich, took him up in 1805, and soon produced, among others, Struve's Dorpat refractor of 9.9 inches diameter and 13.5 feet focal length, and another, of 12 inches diameter and 18 feet focal length, for Lamont of Munich.
In the nineteenth century gigantic reflectors | 0.862087 | 3.777165 |
THE TIME TRAVEL RECORD is held by retired cosmonaut Sergei Krikalev, who trumps us all with 23 milliseconds more reality than you or I. Yes, it’s a stretched qualification for ‘time traveller’ — the sharper way to put it is that for Krikalev, time has been slightly dilated. Slowed down, as it were, leaving him with a fraction of a second more existence than he might otherwise have been allowed.
Fiddly business. The physicists refer to this phenomenon as time dilation, a consequence of Einstein’s Special Theory of Relativity. The effect is this: time slows down when you approach the speed of light.
It’d be generous to say that Krikalev ever ‘approached the speed of light’ (because that’s really quite fast). What the man has done is spend just over 803 days living in space, spent between missions aboard the International Space Station (ISS) and its Russian counterpart, the Mir (sunk and obliterated, as of 2001). This means cruising at 27,600 km/h (17,100 mph) as you orbit Earth — that’s 7.66 kilometres every second.
Comparatively, the speed of light is just short of 300,000 kilometres per second. That’s faster than anything we’ve ever known. Current scientific thinking is that the speed of light represents the ‘speed limit of the universe’: nothing but light could go so fast and certainly nothing may travel faster.
At 7.66 km/s Krikalev is no contender. But he is moving far more quickly than any human on Earth has the means to achieve. And across 803 days, the miniscule effects of time dilation had room to swell, quietly bulging to the slim but noteworthy 23 milliseconds of existential drag.
Krikalev is a fraction of a second ‘younger’ than what he would’ve been if he stayed at home. In a sense, he has travelled 0.23 seconds into the future.
Over the dinner table this figure has less kick than anything Doctor Who might arouse. The juice really lies in what Krikalev’s time dilation represents. Scientists measure this sort of thing with hyper-accurate atomic clocks. If you leave one clock on a desk and send its exact double on an aeroplane trip around the world, the clocks will come back to you reading slightly different times (as per the famous Hafele-Keating experiment). It’s not the outcome of dodgy clocks. Time dilation has been challenged and tested with all sorts of rigour. Today the phenomenon is a routine consideration in the mathematics of spaceflight, GPS satellites and other scientific endeavours requiring high speeds and knifepoint accuracy.
The heart of the concept begins with light. The speed of light, no matter which way you look at it, is constant. Run as fast as you can, you will still get the same measurement of light’s speed as would your colleague standing still. The speed of light remains weirdly the same for all observers, regardless of your relative velocity. To make up for this, time must personally accommodate itself to different perspectives. You might recall the formula, ‘Speed = Distance/Time’. Between these three, balance must be kept. Where light speed is stubbornly fixed, time is compliantly fluid. The faster you go, the more distance you cover, the closer you get to the speed of light, your subjective flow of time will begin to slow down.
Click here for a Lapsus dip into Einstein’s Theory of Special Relativity, where the whole idea may begin to sound a little less preposterous.
The time dilation phenomenon has ghostly implications. Physicists speak of something called the twin paradox. Your identical twin stays on Earth, operating from mission control, and you’re the space traveller, taking off in ship that travels at 80 percent of the speed of light. You fly out to a nearby star system then turn around and head home. By mission control’s calculations the whole journey will take ten years. And it does: when you return, everyone on Earth has aged ten years and the date is ten years on. However, travelling at such a high speed for so long, something odd has happened. By your clock only six years have passed. There’s nothing wrong with the clock, it is time itself that has changed. When you arrive back on Earth, your twin has aged ten years while you have only aged six.
The twin paradox is a trifle more pronounced than Krikalev’s 23 milliseconds. But it will be a while still before our spaceships can travel anything like the speed of light—and with this, dilate the process of ageing. Perhaps the real wonder here lies in the question: you and your twin disagree on the length of the trip… but which one of you is correct? How much time has really passed?
The question prods against our common understanding of time. For Earthly purposes time is straightforward and absolute. The sense of this is in your bones, unquestioned and fundamental. While we’re all on Earth, travelling together with the planet’s rotation and orbit and so forth, this might as well be the case. But in the great mix of velocities out in space, behind the scenes of reality, there is really no unifying piece of clockwork. The speed of time is fluid and disjointed. It is not absolute: you and your older twin may disagree, but you are both correct. There is no objective answer to how much time has really passed; ten and six years are both equally valid measurements. The answer depends entirely on one’s subjective frame of reference.
How about a time-machine then?
Well! If theoretically a 1981 DeLorean (or any vehicle) could be accelerated to the speed of light, the events unfolding around you would begin to lag so drastically that at maximum speed, time would cease to exist. At the speed of light time dilation reaches one-hundred percent. From its own perspective, light departs from and reaches its destination instantaneously. By the breath of the same instant, it reaches everywhere it shall ever be.
Current thinking is that it would be really quite difficult for matter (let alone a person) to reach light speed. Burried beneath the French-Swiss border in an oval-shaped tunnel running 27 kilometres, physicists make sporting use of a machine called the Large Hardon Collider. With this they have scratched the ceiling, accelerating molecules to about 99.9999991% the speed of light. Immense amounts of energy are pumped into reaching this speed. But at a certain speed increasing energy ceases to make a molecule travel any faster, instead it gets bigger. As mass increases so too does the amount of energy required to make the molecule move. This leads to the bothersome conclusion that accelerating matter to the speed of light requires an infinite amount of energy.
99.9999991% is a lot further off light speed than it sounds. But it is pretty good going. At this velocity the ‘clock’ of a speeding molecule would be running 7,460 times slower than yours. So for a vehicle moving this close to light speed, travelling 7,460 years into the future should only take one year of driving. Going backwards in time might not be as doable (unless you travelled faster than light…?)
If you’re at all softened up to the idea of time dilation, it may now be of interest that gravity, as well as relative velocity, affects the flow of time.
In modern physics, space and time are regarded as interwoven and part of the same fabric called spacetime. Massive bodies like the Earth, our sun or a black hole are conceptualised to ‘curve’ this spacetime.
The dent is referred to as a gravitational well. Right now, you’re sitting deep inside the well of the Earth. Experiments have demonstrated that the flow of time is susceptible to the dent-like wells. The deeper you are in the well, the slower time runs. The film Interstellar dealt with this, with characters experiencing time more slowly when in close proximity to a massive black hole.
So, would a time-machine work simply because it was really heavy? Running the numbers, a person could travel forward in time at a rate four times faster than that of distant observers by sitting inside a spherical tank with a diameter of five meters and the mass of Jupiter. For every day that passed in the tank, four days would pass elsewhere.
Not a brilliant time-machine, but it would do well as a place to keep milk from going off. | 0.828874 | 3.778756 |
There’s still so much we don’t know about our universe. Why are black holes so terrifying? Can we live on Mars? And most importantly, are we alone in the universe? Well, according to a new study published in Nature, we might not be after all.
A star about 40 lightyears from Earth, known as TRAPPIST-1 or an ‘ultracool dwarf’ for it’s low temperatures, is orbited by 3 planets that may be the most temperate and Earth-like ones ever discovered outside of our own solar system.
The research, conducted by investigators from the Massachusetts Institute of Technology, the University of Liège in Belgium and elsewhere involved extensive observations of stars with a 60-centimetre telescope to find exoplanets. When located, TRAPPIST-1 indicated the existence of at least 3 planets, all of them about the diameter of Earth and all of them orbiting at a distance where water (the ingredient for life) could exist in liquid form.
There a couple of hitches though. Two of the three planets complete a single orbit once every 1.5 and 2.4 days, respectively, which is much faster than Earth’s 365-day orbit. This makes the planets closer to TRAPPIST-1 than we are to the sun. While we would flame up being that close to the sun, these planets are comfortably close as TRAPPIST-1 isn’t as hot.
Before we all get excited about new space adventures, or perhaps the existence of aliens, spacecrafts won’t be visiting TRAPPIST-1 any time soon. Even though the planet is only 40 light years from Earth, it’s still far beyond the reach of our probes.
The discovery of TRAPPIST-1, however, means that telescopes around the world can study other planets in great detail and look for biosignatures of methane, oxygen, CO2 and more, and see if they could one day bear human life. | 0.860868 | 3.297807 |
Psyche, NASA's Discovery Mission to a unique metal asteroid, has been moved up one year with launch in the summer of 2022, and with a planned arrival at the main belt asteroid in 2026 -- four years earlier than the original timeline.
"We challenged the mission design team to explore if an earlier launch date could provide a more efficient trajectory to the asteroid Psyche, and they came through in a big way," said Jim Green, director of the Planetary Science Division at NASA Headquarters in Washington. "This will enable us to fulfill our science objectives sooner and at a reduced cost."
The Discovery program announcement of opportunity had directed teams to propose missions for launch in either 2021 or 2023. The Lucy mission was selected for the first launch opportunity in 2021, and Psyche was to follow in 2023. Shortly after selection in January, NASA gave the direction to the Psyche team to research earlier opportunities.
"The biggest advantage is the excellent trajectory, which gets us there about twice as fast and is more cost effective," said Principal Investigator Lindy Elkins-Tanton of Arizona State University in Tempe. "We are all extremely excited that NASA was able to accommodate this earlier launch date. The world will see this amazing metal world so much sooner."
The revised trajectory is more efficient, as it eliminates the need for an Earth gravity assist, which ultimately shortens the cruise time. In addition, the new trajectory stays farther from the sun, reducing the amount of heat protection needed for the spacecraft. The trajectory will still include a Mars gravity assist in 2023.
"The change in plans is a great boost for the team and the mission," said Psyche Project Manager Henry Stone at NASA's Jet Propulsion Laboratory, Pasadena, California. "Our mission design team did a fantastic job coming up with this ideal launch opportunity."
The Psyche spacecraft is being built by Space Systems Loral (SSL), Palo Alto, California. In order to support the new mission trajectory, SSL redesigned the solar array system from a four-panel array in a straight row on either side of the spacecraft to a more powerful five-panel x-shaped design, commonly used for missions requiring more capability. Much like a sports car, by combining a relatively small spacecraft body with a very high-power solar array design, the Psyche spacecraft will speed to its destination at a faster pace than is typical for a larger spacecraft.
"By increasing the size of the solar arrays, the spacecraft will have the power it needs to support the higher velocity requirements of the updated mission," said SSL Psyche Program Manager Steve Scott.
The Psyche Mission
Psyche, an asteroid orbiting the sun between Mars and Jupiter, is made almost entirely of nickel-iron metal. As such, it offers a unique look into the violent collisions that created Earth and the terrestrial planets.
The Psyche Mission was selected for flight earlier this year under NASA's Discovery Program, a series of lower-cost, highly focused robotic space missions that are exploring the solar system.
The scientific goals of the Psyche mission are to understand the building blocks of planet formation and explore firsthand a wholly new and unexplored type of world. The mission team seeks to determine whether Psyche is the core of an early planet, how old it is, whether it formed in similar ways to Earth's core, and what its surface is like. The spacecraft's instrument payload will include magnetometers, multispectral imagers, and a gamma ray and neutron spectrometer.
For more information about NASA's Psyche mission go to:
News Media ContactD.C. Agle
Jet Propulsion Laboratory, Pasadena, Calif.
Arizona State University School of Earth and Space Exploration, Tempe
Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
[email protected] / [email protected] | 0.862927 | 3.016816 |
The Cigar Galaxy (also known as M82) is famous for its extraordinary speed in making new stars, with stars being born 10 times faster than in the Milky Way. Now, data from the Stratospheric Observatory for Infrared Astronomy, or SOFIA, have been used to study this galaxy in greater detail, revealing how material that affects the evolution of galaxies may get into intergalactic space.
Researchers found, for the first time, that the galactic wind flowing from the center of the Cigar Galaxy (M82) is aligned along a magnetic field and transports a very large mass of gas and dust - the equivalent mass of 50 million to 60 million Suns.
"The space between galaxies is not empty," said Enrique Lopez-Rodriguez, a Universities Space Research Association (USRA) scientist working on the SOFIA team. "It contains gas and dust - which are the seed materials for stars and galaxies. Now, we have a better understanding of how this matter escaped from inside galaxies over time."
Besides being a classic example of a starburst galaxy, which means it is forming an extraordinary number of new stars compared with most other galaxies, M82 also has strong winds blowing gas and dust into intergalactic space. Astronomers have long theorized that these winds would also drag the galaxy's magnetic field in the same direction, but despite numerous studies, there has been no observational proof of the concept.
Researchers using the airborne observatory SOFIA found definitively that the wind from the Cigar Galaxy not only transports a huge amount of gas and dust into the intergalactic medium, but also drags the magnetic field so it is perpendicular to the galactic disc. In fact, the wind drags the magnetic field more than 2,000 light-years across - close to the width of the wind itself.
"One of the main objectives of this research was to evaluate how efficiently the galactic wind can drag along the magnetic field," said Lopez-Rodriguez. "We did not expect to find the magnetic field to be aligned with the wind over such a large area."
These observations indicate that the powerful winds associated with the starburst phenomenon could be one of the mechanisms responsible for seeding material and injecting a magnetic field into the nearby intergalactic medium. If similar processes took place in the early universe, they would have affected the fundamental evolution of the first galaxies.
The results were published in January 2019 in the Astrophysical Journal Letters.
SOFIA's newest instrument, the High-resolution Airborne Wideband Camera-Plus, or HAWC+, uses far-infrared light to observe celestial dust grains, which align along magnetic field lines. From these results, astronomers can infer the shape and direction of the otherwise invisible magnetic field. Far-infrared light provides key information about magnetic fields because the signal is clean and not contaminated by emission from other physical mechanisms, such as scattered visible light.
"Studying intergalactic magnetic fields - and learning how they evolve - is key to understanding how galaxies evolved over the history of the universe," said Terry Jones, professor emeritus at the University of Minnesota, in Minneapolis, and lead researcher for this study. "With SOFIA's HAWC+ instrument, we now have a new perspective on these magnetic fields."
The HAWC+ instrument was developed and delivered to NASA by a multi-institution team led by the Jet Propulsion Laboratory. JPL scientist and HAWC+ Principal Investigator Darren Dowell, along with JPL scientist Paul Goldsmith, were part of the research team using HAWC+ to study the Cigar Galaxy.
SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR. NASA's Ames Research Center in California's Silicon Valley manages the SOFIA program, science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA's Armstrong Flight Research Center Hangar 703, in Palmdale, California.
News Media ContactCalla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
Written by Kassandra Bell and Arielle Moullet, USRA SOFIA Science Center | 0.848695 | 4.179398 |
Compiled by Carl Slaughter: (1) Black hole pairs: “Scientist Find Treasure Trove of Giant Black Hole Pairs”.
For decades, astronomers have known that Supermassive Black Holes (SMBHs) reside at the center of most massive galaxies. These black holes, which range from being hundreds of thousands to billions of Solar masses, exert a powerful influence on surrounding matter and are believed to be the cause of Active Galactic Nuclei (AGN). For as long as astronomers have known about them, they have sought to understand how SMBHs form and evolve.
In two recently published studies, two international teams of researchers report on the discovery of five newly-discovered black hole pairs at the centers of distant galaxies. This discovery could help astronomers shed new light on how SMBHs form and grow over time, not to mention how black hole mergers produce the strongest gravitational waves in the Universe.
(2) It’s for you: “Scientists made the first ‘unhackable’ quantum video call”.
Traditional methods of digital communication rely on certain mathematical functions, which can be hacked with the right tools and know-how. Quantum communications, however, send information embedded in entangled particles of light, in this instance by a satellite named Micius, in a process which is said to be completely unhackable. It’s so secure that anyone even attempting to infiltrate the communication without authorization will be uncovered. As Johannes Handsteiner from the Austrian Academy of Sciences explained, “If somebody attempts to intercept the photons exchanged between the satellite and the ground station and to measure their polarization, the quantum state of the photons will be changed by this measurement attempt, immediately exposing the hackers.”
(3) NASA / Russia moon station: “NASA and Russia agree to work together on Moon space station”.
This is part of NASA’s expressed desire to explore and develop its so-called “deep space gateway” concept, which it intends to be a strategic base from which to expand the range and capabilities of human space exploration. NASA wants to get humans out into space beyond the Moon, in other words, and the gateway concept would establish an orbital space station in the vicinity of the Moon to help make this a more practical possibility.
(4) I like ?. Pi, the Golden Number, impossible engineering, and the Egyptian pyramids.. | 0.840882 | 3.001592 |
A NASA spacecraft has broken records by successfully going into orbit around an ancient asteroid.
The Osiris-Rex spacecraft is now orbiting Bennu – a tiny asteroid that is just 500m (1,600ft) long and found 70 million miles from Earth.
Bennu is the smallest celestial body to ever be orbited by a spacecraft, and Osiris-Rex's laps are barely one mile above the asteroid's surface.
NASA says the spacecraft's objective is to grab samples of gravel from the asteroid in 2020 and return them to Earth by 2023 – a manoeuvre described as a "gentle high-five".
The $800 million unmanned spaceship launched two years ago from Cape Canaveral in Florida – arriving at its destination on 3 December.
After closely studying the asteroid for several weeks, Osiris-Rex fired its thrusters to bring it into orbit around Bennu at 7.43pm UK time on New Year's Eve.
Dante Lauretta, Osiris-Rex's principal investigator, said: "Entering orbit around Bennu is an amazing accomplishment that our team has been planning for years."
NASA has described the achievement as a "leap for humankind" because no spacecraft has ever "circled so close to such a small space object – one with barely enough gravity to keep a vehicle in a stable orbit".
Bennu has a gravity force that is just five-millionths as strong as Earth's.
From now until mid-February, Osiris-Rex will use a suite of five scientific instruments to map Bennu in high resolution, enabling scientists to decide where to take the sample.
A reverse vacuum and a circular device, not dissimilar from a car's filter, will then be used to collect about 60g of material.
Bennu is also regarded as potentially dangerous, as there is a one in 2,700 chance of the asteroid colliding with Earth in 2135.
It is one of the oldest asteroids known to NASA, and scientists hope it will reveal more about the early formation of the solar system.
The start of 2019 is shaping up to be a busy one for NASA, as its New Horizons spacecraft is also due to pay a visit to a tiny, icy world that lies one billion miles beyond Pluto in the early hours of New Year's Day.
It will fly past a mysterious object nicknamed Ultima Thule, which lies four billion miles from Earth, at 5.33am UK time – but it will take 10 hours for flight controllers to find out whether New Horizons survives the close encounter.
Roughly 20 miles long and shaped like a giant peanut, Ultima Thule was discovered using the Hubble Space Telescope in 2014, and will become the most distant world ever explored by humankind.
Clear images of the cosmic body are expected to emerge in the coming days.
Alan Stern, the lead planetary scientist on the New Horizons mission, said: "The object is in such a deep freeze that it is perfectly preserved from its original formation.
More from Science & Tech
"Everything we are going to learn about Ultima – from its composition to its geology to how it was originally assembled, whether it has satellites and an atmosphere and those kinds of things – are going to teach us about the original formation conditions of objects in the solar system.
"I think that the kinds of things NASA is doing are the envy of the world." | 0.88933 | 3.329472 |
I have heard many times about interstellar travels. Are centrifuge space craft (artificial gravity) and warp drives technologies being built or still it is just concepts ? Nearest start system is alpha centauri so is it possible to reach there by mentioned technologies ? and if yes then how.
Manned interstellar space flight is not going to happen anytime soon. Definitely not within the next 50 years, most likely not within the next 100. There are too many basic issues that are hard to work around.
The biggest issue (apart from politics and funding) is propulsion. So far, nobody's figured out how to build an engine that doesn't require some form of reaction mass (propellant) to accelerate, meaning your total ΔV (change in velocity) is limited by how much reaction mass you can carry along, and the amount of reaction mass you need grows exponentially as ΔV increases (i.e., for N times more ΔV, you need eN times more reaction mass). Conventional chemical and ion engines are simply not up to the task of interstellar travel; either the amount of propellant necessary is many orders of magnitude larger than the spacecraft itself1, or you accept travel times of thousands to tens of thousands of years (which brings up issues with power, life support, spacecraft maintenance, etc.).
There are ideas for engines that use nuclear fission or fusion that provide better performance, but the best of them would still require on the order of a century or so to reach the nearest star. And again, you're limited by the amount of reaction mass you can carry.
The logical step up from that is to not carry your reaction mass with you; instead, you either gather reaction mass from the interstellar medium as you travel (like the Bussard ramjet), or you use a sail to exchange momentum with the solar wind or a powerful EM source, like a laser array. There's a project called Breakthrough Starshot that intends to use a massive bank of ground-based lasers to accelerate a gram-scale spacecraft with a large sail to something like 20% c.
The problem with ramjets is that there just isn't that much material to gather, and the drag from the scoops would probably cancel out whatever thrust you could generate. And the problem with sails in general (and Starshot in particular) is that you have no way to slow down once you reach your destination.
Basically, interstellar travel with reaction drives is not going to happen. We need to develop some kind of reactionless drive, one that doesn't require you to exhange momentum with some kind of reaction mass in order to accelerate.
There's the EmDrive, which allegedly provides thrust without reaction mass. There's a lot of skepticism associated with this, with good reason. At first blush, it seems to violate conservation of momentum. Also, people who've tried to replicate the results using sane test setups have not been able to reproduce the effect.
So, that pretty much leaves us with warp drives, which...aren't going to happen anytime soon, if ever. They're mathematically possible, but that doesn't mean that they will ever be physically possible, and even if they're physically possible, the energy requirements are such that we could probably never build one.
- To reach 1% c (3000000 m/s) using the ion engine on the Dawn spacecraft, you'd need on the order of 1088 kg of propellant for every kg of spacecraft mass. To reach that same velocity using an RL-10 chemical (hydrogen/oxygen) engine, you'd need on the order of 10295 kg of propellant for every kg of spacecraft mass.
A sucessful flight of humans to mars and back might be possible in some years or some decades. But we don't have the technology for a human flight to the outer planets and their moons. Before we did not manage to send an orbiter to pluto and land a rover on pluto we are not able to leave our solar system with human passengers. We should send some spacecrafts to the oort cloud before. There is so much work to be done before. We did not even try a space station in an earth orbit with artifical gravity in a centrifuge yet and we would need many years of experience with humans living there.
Humans will NEVER travel to another star!
It requires either so much time, or so radically new technology, that humans cannot exist under such conditions. We are not created to be star travelers, we're deeply rooted in Earth. We're just the guys in the post office. We'll send Earth life out there, but not ourselves. | 0.846292 | 3.638543 |
INDIANAPOLIS — The sun was probably an active, "feisty" star in the early days of its evolution, scientists suspect.
A group of researchers have been examining a young star similar in mass to the sun to understand what Earth's closest star could have looked like early in the solar system's history. The star, called TW Hydrae, shines about 190 light-years from Earth and weighs about 80 percent as much as the sun.
"By studying TW Hydrae, we can watch what happened to our sun when it was a toddler," Nancy Brickhouse of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said in a statement.
TW Hydrae is about 10 million years old and could be going through a process that the 4.6 billion-year-old sun undertook early in its stellar existence. The young star is still accreting gas from a disk that surrounds it. The gas is being funneled into the star along magnetic field lines.
Brickhouse and her team observed the infalling gas using NASA's Chandra X-ray Observatory as well as other ground-based methods. The researchers saw the gas crash into the star, which can create a shock wave and heat the gas to more than 5 million degrees Fahrenheit (2.8 million degrees Celsius). The gas cools once it falls further into the star.
"By gathering data in multiple wavelengths we followed the gas all the way down," Brickhouse said. "We traced the whole accretion process for the first time."
Through tracking the gas on its path into the star, Brickhouse noticed that the accreting gas didn't fall into the star at an even rate. Instead, the star grew by fits and starts, changing from one day to the next.
The observations are giving researchers a window into the relationship between the star's magnetic fields and its orbiting disk of material that could clarify how magnetism affects similar processes around the galaxy, the scientists said. | 0.859273 | 3.667838 |
The flow characteristics of the light ions H(+) and He(+) have been studied in the midnight region of the ionosphere of Venus. Measurements of ion composition, electron and ion temperatures and magnetic fields by instruments onboard the Pioneer Venus Orbiter have been used in rite electron and ion equations of conservation of mass and momentum to derive the vertical flow velocities of H(+) and He(+). When average height profiles of the measured quantities were used, H(+) was found to flow upward, accelerating to speeds of almost 1 km/s at the ion-exobase. In a similar fashion, He(+) was found to flow downward into the neutral atmosphere where it is readily quenched by charge transfer reactions. The polarization electric field played an important role in forcing H(+) upward, but did not contribute enough to the He(+) force balance to produce upward flow. At the ion-exobase, the outward electric polarization force on H(+) was shown to be five times the gravitational force. Using an analogy with the terrestrial ion-exosphere, H(+) was inferred to flow upward into the ionotail of Venus and accelerate to escape speeds. A planet averaged escape flux of 1.4 x 10 exp 7/sq cm/s was calculated, which is comparable to hydrogen loss rates estimated by other investigators.
LUNAR AND PLANETARY EXPLORATION
Journal of Geophysical Research (ISSN 0148-0227); 98; E4; p. 7437-7445. | 0.87631 | 3.66901 |
New SPHERE view of Vesta
Sitting between Mars and Jupiter, the doughnut-shaped asteroid belt is packed full of rocky bodies and debris. Despite its fragmented, rubbly nature, the total mass contained within the belt is considerable — roughly four per cent of that of the Moon! The majority of this mass is contained within two distinctive bodies: Ceres, a dwarf planet estimated to make up a third of the mass of the belt, and the asteroid Vesta, which holds around nine per cent of it. Vesta is pictured here.
Vesta was recently observed by the SPHERE/ZIMPOL instrument on ESO’s Very Large Telescope (VLT) — the SPHERE image is shown on the left (see the single image here), produced using the MISTRAL algorithm, with a synthetic view derived from space-based data shown on the right for comparison. SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, is a powerful planet-finding and direct imaging instrument. ZIMPOL is one of its subsystems: a specialised camera perfectly suited to taking very sharp images of small objects — like Vesta.
The synthetic image was generated using a tool developed for space missions called OASIS. Factors such as the reflectance of Vesta’s surface and the geometric conditions of the VLT/SPHERE observations where accounted for by OASIS, which used a 3D model of Vesta’s shape based on images from NASA’s Dawn spacecraft (which completed a 14-month survey of Vesta between 2011 and 2012).
SPHERE’s image of Vesta is impressive given the separation between Earth and Vesta, and the small size of the asteroid — it lies twice as far from the Sun as our planet does, and has a mean diameter of just 525 kilometres. It shows Vesta’s main features: the giant impact basin at Vesta's south pole, and the mountain at the bottom right. This is the central peak of the Rheasilvia basin, and is roughly 22 kilometres high — over twice as high as the tallest mountain on Earth, Mauna Kea, which rises roughly 10 kilometres from the basin of the Pacific Ocean floor, and nearing the height of the mammoth Martian volcano Olympus Mons.Credit:
ESO/L. Jorda et al., P. Vernazza et al.
About the Image
|Release date:||25 June 2018, 06:00|
|Size:||3618 x 1840 px|
About the Object | 0.820193 | 3.799568 |
Galaxies are enormous conglomerations of stars and interstellar material. The qualifying morphological properties of these objects, however, remain flexible due to two principal factors: continuity and irregularity.
This is a one-page note on the basics of calculus. Introduction to the study of change, Differential Calculus, Integral Calculus, Fundamental Theorem of Calculus, formula of Newton and Leibnitz. Full note in PDF.
Subrahmanyan Chandrasekhar (1910–1995) was born into a Brahmin family in Lahore, then India. At the age as early as 21, he was responsible for deriving a theoretical mass limit an ideal white dwarf star can achieve without collapsing in on itself, now referred to as the Chandrasekhar limit, and accepted at 1.39 M⊙. This was one of the most important discoveries in the 20th century as it paved the way for better understanding of the processes occurring during the collapses of degenerate stars that may lead to such phenomena as black holes—ingredients crucial for the development of our modern cosmological theories.
Stellar-mass black holes are the result of a gravitational collapse of a massive star at the end of its life. The core of such star collapses to singularity – a point of infinite density and space-time curvature – that is cloaked in the event horizon. The gravitational force of the resulting black hole is so strong that no light or signal can escape its event horizon. This essay will address how astronomers search for stellar-mass black holes, will attempt to describe their characteristics, and will also discuss the current knowledge on Milky Way black hole candidates and their companion stars, and the connection between X-ray sources and black holes.
Tracing the origins of the discovery and the development of observations of NGC 1555, also referred to as the Hind’s Variable Nebula in the constellation Taurus, reveal an interesting story of how a faint glow in the sky became on the most discussed objects in the sky.
The CMD submitted in the previous fortnight shows members of NGC 4755 – an open cluster in Crux. The stars were selected in the SIMBAD database as they all belong to the cluster – all at more or less the same distance, and this simplifies working with apparent mag- nitudes that are available in the database.
As an amateur astronomer, I was to an unnecessary degree opposed to the concept of astrology, especially if questioned about its scientific impact. The more I progress through the history course at Swinburne, the more I realize how naive that position was. It is too easy to underestimate the contributions of astrology from the pinnacles of modern astrophysics and freedom of thought, especially after it has been decoupled from the mainstream science. | 0.888143 | 4.005544 |
Talking about a planetary orbit,Mercury has the most eccentric orbit (after excluding Pluto from the planets list) while Venus has the most circular orbit.
One of the most interesting things that I came across while reading a book was about a horseshoe orbit. How could something like that be possible? What can cause an object to move in a horseshoe orbit? Well, mathematics or equations were never in the list of my “top favorites”, till I came across their practical aspects. Physics or mathematics becomes interesting when we start looking out of the books, into nature (which is as important). Here, I will try to explain it simply, which is the main focus of ours for creating this website. These articles are for everyone, especially for those who love nature’s beauty and want to understand it but are afraid. Fear disappears when everything becomes simple and that is when you start exploring the knowledge and the universe around you.
Let’s come back from philosophy to science, a horseshoe orbit, as the name suggests, is the path followed by a small body orbiting a larger orbiting body, as seen from the larger body. The orbital periods (time taken by the body to complete one revolution around the Sun) of both the bodies are almost same. One of the fascinating examples is the asteroids orbiting Earth in a similar way, for example, 54509 YORP, 2002 AA29, 2010 SO16 etc. Saturn’s moons Epimetheus and Janus occupy horseshoe orbits with respect to each other
The main cause of the existence of a horseshoe orbit is the change in an elliptical orbit (press a circular orbit from two sides and you will get an elliptical one) of the asteroid because of the gravitational influence of the Earth. When the asteroid tries to catch up with Earth while orbiting the Sun, it gives rise to a horseshoe orbit.
The following diagram shows it beautifully;
While the satellite is orbiting faster than the larger body (Earth) and is about to pass between Earth and Sun. Earth’s gravity pulls the satellite into a higher orbit, thus decreasing its angular speed (Kepler’s third law). Angular speed is the rate at which an object changes its angle (measured) in radians, in a given time period. At the point B, the satellite is moving at almost the same speed as that of Earth while the satellite is still being pulled higher. After reaching a high enough point C where it is slow enough which makes it lag behind Earth. It takes a century or more for the satellite to reach point D as it appears to drift backward when viewed relative to Earth. The gravity of Earth now reduces the orbital velocity of the satellite which makes it fall into a lower orbit which thus increases the angular speed of the satellite. It continues till its orbit is lower and faster than the Earth’s. It takes another century for it to reach the point A thus completing the horseshoe shape.
Now, according to classical mechanics (Mechanics is an area of science concerned with the behavior of physical bodies when subjected to forces or displacements and the subsequent effects of the bodies on their environment) the energy of a body that is moving in a time independent field will be conserved (E= T+V). E is the total energy, T is the kinetic energy (the kinetic energy of an object is the energy that it possesses due to its motion) and V is the potential energy (Potential energy is the energy that an object has due to its position in a force field, gravitational potential energy of a mass m at height h near the surface of the Earth is more than the potential energy would be at height 0 \). T is non-negative and V is negative here.
Now, V will increase when the smaller body (Asteroid) is behind M (Earth) because it is lagging behind and V will decrease when the smaller body is in front of M. Then why does it fall and rise in its orbit? The body as it is moving in front of M will lose energy and will fall into a shorter orbit because orbits with lower total energy have shorter periods and will thus be repelled (as seen in the given figure). If the asteroid is behind Earth,it will gain energy, its orbit will rise and in the process, it will lag behind or get repelled. While dancing or moving the body, as we see, will never come too near to the planet. Sighs!!
Sit back and enjoy the dance without getting hurt. | 0.837794 | 3.604363 |
13 relations: Apparent magnitude, Aquila (constellation), Carnegie Institution for Science, Celestial equator, Constellation, Delta Scuti variable, Durchmusterung, Flamsteed designation, Henry Draper Catalogue, Hipparcos, Smithsonian Astrophysical Observatory Star Catalog, Star, Variable star.
The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth.
Aquila is a constellation on the celestial equator.
The Carnegie Institution of Washington (the organization's legal name), known also for public purposes as the Carnegie Institution for Science (CIS), is an organization in the United States established to fund and perform scientific research.
The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth.
A constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices.
A Delta Scuti variable (sometimes termed dwarf cepheid) is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface.
In astronomy, Durchmusterung or Bonner Durchmusterung (BD), is the comprehensive astrometric star catalogue of the whole sky, compiled by the Bonn Observatory (Germany) from 1859 to 1903.
A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England.
The Henry Draper Catalogue (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension (HDE), published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the Henry Draper Extension Charts (HDEC), published from 1937 to 1949 in the form of charts, which gave classifications for 86,933 more stars.
Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993.
The Smithsonian Astrophysical Observatory Star Catalog is an astrometric star catalogue.
A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates. | 0.808635 | 3.319527 |
copyright © 2014 James J. Hurtak, Ph.D., Ph.D. and Desiree Hurtak, Ph.D.
NASA’s Cassini spacecraft is currently orbiting the ring system of Saturn. It has been on an extended mission since 2008 and amazingly continues to send back advanced data on Saturn, its moons and extensive ring system. The ring system has proved most amazing as it contains myriads of ringlets, moonlets composed of dust and icy rocks. It operates as an accretion disk with primordial matter, ice and micro debris. What is most interesting is that the rings are not as stable as they have appeared. Originally, the rings were observed by the Voyager mission when it passed by Saturn (1980-1981), but a comparison with the Cassini images has revealed great differences in almost all the rings, especially the F-ring, over the period of less than thirty years. Thus, in a relatively short period of time the vast changes in the rings have shown spectacular morphologies.1
The changes in the rings of Saturn have completely overturned the classical picture of a stable system. The current study of the massive ring system has produced evidence of gravitational resonance, but, more importantly and stunning, is the finding of the “F-ring” having a strangely, continuously changing pattern, from helical formations to propeller-like mini-spokes. Some scientists even believe that the rings are producing small moonlets from the collisions of fragments that exist in and around the rings, especially the F-ring which exists in the Roche limit, a point where the gravitational tug from the planet could tear a larger moon apart. Again, the rings are made of dusty ice, in the form of boulder-sized and smaller chunks that often collide with each other as they orbit Saturn. Saturn’s gravitational field constantly disrupts these ice chunks, causing, as well as preventing them from forming moons. Saturn, itself, has the most moons of any of the planets in our solar system, over 60 objects of this type, but they are mainly outside the more familiar inner ring system with just a few in the area of the A- and B-rings, more towards the F-ring, but the majority lying in the G- and E-rings and beyond. Another question is the age of the rings. They may be as old as 4.4 billion years, but if they are so old why are they changing so rapidly? Did they always do this or is there something new taking place?
The analysis of the changing rings has become one of the most important topics surrounding Saturn over the past 7 years. Not surprising, The Keys of Enoch® proposed that Saturn would be a sign of change, revealing how we, the human race, should take a closer look at our evolving Solar system. Specifically, Key 304:11- 12 tells us: “Our sun, by virtue of being a variable star, will be seen as having great limitations for future evolutions. This will be observable by visible exchange of the solar polarity fields and by the magnetic mapping of inner-solar magnetic lines rotating faster than the surface of the sun. These changes will also affect the rotation of Saturn. This will be seen as a periodic effect which will be noticed in the activity of Saturn’s rings. It will illustrate new changes that will take place throughout the entirety of the solar system.”2
This indicates that Saturn holds one of the clues to the next phase of our solar system’s evolutionary future. The first part of this quote was confirmed in the same words by Lika Guhathakurta of NASA headquarters in Washington DC that our sun is “a variable star.” 3 Thinking like that was unheard of before 2010 when observations of variations in the sun’s magnetic field were noted by NASA. Additionally, some research scientists (e.g., MGS MOC Release No. MOC2-297, 6 December 2001) have recently considered that Mars itself is going through climate change.4 So all planets may be experiencing some changes, it may just be more obvious within Saturn’s rings and possibly the polar regions of Mars.
It is fortunate that we have a 30-year comparison made by Voyager (1980-81) from colleagues at JPL and the team of Dr. Jim Warwick in Colorado. So why are the rings revolving and changing into strange patterns? Theories still abound. The answer to these deeper questions may lie in the nature of the outer planets and especially how the rings themselves seem to have rain affecting Saturn’s ionosphere.5 Saturn’s moon Rhea may also have rings around it, although this has not been confirmed. The rings of Saturn themselves although varying in width are incredibly thin, ranging from about 30 feet (10 meters) to several kilometers thick at most. The rings have slight pink, grey and brown colors due to the presence of dusty material mixed with the water ice.
A definite change in the appearance of the rings is at work. Whatever the result of the new research, keep looking upward for we are about to learn more valuable information about how Saturn’s rings, as well as how its planets and moons, are forming and evolving as a miniature solar system.
1. Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009)
“Origin and Evolution of Saturn’s Ring System” Chapter 17 of the book Saturn After Cassini-Huygens pp. 537-575.
2. Hurtak, JJ (1973)The Book of Knowledge: The Keys of Enoch® Los Gatos: Academy For Future
3. Solar Dynamics Observatory: The ‘Variable Sun’ Mission http://science.nasa.gov/ science-news/science-at-nasa/ 2010/05feb_sdo/
4. Malin Space Science Systems “MOC Observes Changes in the South Polar Cap:
Evidence for Recent Climate Change on Mars”MGS MOC Release No. MOC2-297, 6 December 2001, http://www.msss.com/mars_ images/moc/CO2_Science_rel/
5. Blame it on the Rain (from Saturn’s Rings) NASA, http://www.jpl.nasa.gov/news/ news.php?release=2013-130
For more pictures see:
http://lasp.colorado.edu/home/ wp-content/uploads/2011/07/ albers-unexpected-surprises. pdf | 0.890466 | 4.011759 |
Set against the cold morning sky, the warm red of Mars and its stellar counterpart Antares lends a note of cheer to the January darkness.
Mars begins the year as a glimmering red dot somewhat low in the southeast, above Antares, the heart of Scorpius. Day by day, the stars of Scorpius approach and sweep past Mars.
Between the 6th and 9th, the three stars known as the Crown of Scorpius sail by the red planet. Earth’s orbital motion is pushing both Mars and the stars of Scorpius westward, but the stars outstrip Mars because the planet, moving eastward in its own orbit, is able to slow its drift.
Before Scorpius gets too far west, we have a good chance to compare Mars to gigantic Antares, the red star whose name means rival, or antagonist, of Mars. The star and planet come closest on the 18th, when they’ll be 4.8 degrees apart, with Antares to the lower right of Mars. Mars and its rival are now of comparable brightness, but Mars is slowly cranking up the wattage. A waning crescent moon hangs above the pair on the 20th.
Jupiter breaks into the southeastern morning sky late in the month. Saturn follows, but won’t be easily visible until February. Both planets will rendezvous with Mars before winter is over.
In the west, Venus dominates the early evening sky. As the month goes by, Venus climbs toward the slightly dim, ring-shaped Circlet of Pisces. Above the Circlet, the Great Square of Pegasus is now tipped as it heads into the sunset, along with the Circlet and other autumn stars. On the 27th and 28th, a waxing crescent moon appears with Venus.
January’s full moon arrives at 1:21 p.m. on the 10th, just a few hours before rising for the night. It travels the night sky near the Gemini twins Pollux (the brighter) and Castor.
Earth reaches perihelion, its closest approach to the sun in an orbit, on the 5th. At that point we’ll be 91.4 million miles from our parent star. We in the Northern Hemisphere can feel lucky that perihelion happens during winter, because the nearer the Earth is to the sun, the faster it moves along in its orbit. That means it moves through the fall and winter part of its orbit faster than it moves through the spring and summer part. As a result, the Northern Hemisphere gets about five more days of spring and summer than does the Southern Hemisphere.
Deane Morrison is a writer and editor with the University of Minnesota Office of University Relations. Minnesota Starwatch is a service of the Minnesota Institute for Astrophysics, located in the Tate Laboratory of Physics and Astronomy. The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. | 0.858093 | 3.68494 |
Table of contents
About this book
Casual stargazers are familiar with many classical figures and asterisms composed of bright stars (e.g., Orion and the Plough), but this book reveals not just the constellations of today but those of yesteryear. The history of the human identification of constellations among the stars is explored through the stories of some influential celestial cartographers whose works determined whether new inventions survived. The history of how the modern set of 88 constellations was defined by the professional astronomy community is recounted, explaining how the constellations described in the book became permanently “extinct.” Dr. Barentine addresses why some figures were tried and discarded, and also directs observers to how those figures can still be picked out on a clear night if one knows where to look. These lost constellations are described in great detail using historical references, ennabling observers to rediscover them on their own surveys of the sky. Treatment of the obsolete constellations as extant features of the night sky adds a new dimension to stargazing that merges history with the accessibility and immediacy of the night sky.
Forgotten Constellations Historical Asterisms History of Astronomical Nomenclature History of Star Cartography History of Star Maps IAU Constellation Commission Modern 88 Constellations Single-sourced Constellations Western Catalog of Constellations | 0.823018 | 3.117327 |
Finally, we have the whole family portrait of the Solar System together in one place. Pluto is so far away from the rest of the pack that is has been difficult getting clear shots of its terrain and singular moon. The New Horizons space probe sent solely for the purpose of studying the icy planet has re-established contact with the NASA headquarters and sent some amazing pictures of the remote heavenly body. It is a great breakthrough for the space agency, and it will shed further light on unexplored parts of the solar system.
Pluto is a mammoth 4.47 billion kilometers away from our planet. It is so far that the radio signal travelling at the speed of light takes approximately four hours and twenty-five minutes just to reach us. Now that is a lot of distance. The magnified pictures that Hubble Telescope has been providing us over the years are not suitable for studying the minute details of the dwarf planet. So, NASA sent this probe to take real pictures of it from a relatively closer distance.
The project had to face several technical problems to get these elusive snaps. Since it takes 4.5 hours to transmit and receive a message, a re-alignment, no matter how minor it is can take 18 hours to be confirmed, and that is precisely what happened. When the probe was in the position to take the pictures, the main antennae weren’t pointing in the right direction towards Earth. It was realigned, and then those photos were sent. The Horizons probe thankfully has an HD camera in its inventory and was able to capture the planet in much detail.
So, finally, here is Pluto itself. Seems a lot like the Moon.
These pictures finally presented a visual tool to calculate the real diameter of Pluto, which had been debated quite a lot in recent times due to its status of dwarf planet. It came out to be 2370 Kilometers which is by far the largest heavenly body in the solar system beyond Neptune. The pictures have also shed light on Pluto’s history. A plain-like feature was discovered covering one thousand miles that had amassed meteor impacts during millions of years of planet’s existence.
The future of the unmanned space traveller is yet unclear as it has fulfilled its primary objective. It could rendezvous to further routes in the Kuiper belt, but it all depends on the fuel left in the probe. It was launched in 2006 from a Lockheed Martin rocket, and it is the fastest one ever built as it reached the Lunar orbit within nine hours. It was able to cover such enormous distance after a gravity-assisted push from planet Jupiter in 2007 helped it achieve 52,000 miles per hours speed. Still, it took nine years for the probe to make a flyby near the frozen planet at a distance of 12,500 Km. It is the final planet to be photographed entirely. Sun would be so proud to have its family in the same snap! | 0.878393 | 3.072898 |
30 Dec The Pulse of the Earth
The Pulse of the Earth
This article essays to respond to a complex question: whether the planet Earth can have an identifiable heartbeat of its own.
“Our solid earth, apparently so stable, inert and finished, is changing, mobile and still evolving… And the secret of it all – the secret of the earthquake, the secret of the “temple of fire,” the secret of the highland – is in the heart of the earth, forever invisible to the human eyes. These words that Canadian geologist R.A. Daly wrote in 1926 are still very much relevant. According to Victor Hugo Forjaz, a renowned volcanologist – with expertise in astrophysics, cartography and hydrogeology – working at the Volcanological and Geothermal Observatory in Azores, the planet Earth is “young and it’s in expansion”. From an astrophysics’ point of view our planet is still in its infancy, only 4 billion years old. At the time of death from a geological perspective, it will be 50 billion years old. Its core, currently at 5000° degrees is cooling off 100° degrees every billion years. So, by the time the 50-billion-year mark comes around, the planet will be completely cold. Besides, as Dutch geologist J.H.F. Umbgrove wrote: “as the Earth disposes of the youthful power to withstand the destructive work of denudation I cannot detect any symptoms of senility in the pulse of the Earth.”
Therefore, is there a way to identify what exactly can be recognized as the pulse of the earth? Answering this question became challenging because in trying to find the answer it quickly became apparent that this Earthly pulse may actually differ even among the various disciplines under the Geophysics umbrella, the subject of natural science that studies Earth’s internal structure, composition and shape, gravitational and magnetic fields, and dynamics, which is what many consider to be the key to Earth’s heartbeat.
Some scientists consider the planet’s pulse to be linked to its magnetic field, specifically when taking into account the Schumann’s resonance; others consider it to be connected with the geodynamics of Earth, specifically volcanism, given the fact that it’s the study of plate tectonics, volcanoes and magma; some to the gravitational field, which, in turn, affects Earth’s tides, a phenomenon that can be deemed as the regular heartbeat of the world. But even geothermal energy can be thought of as the pulsation of our planet.
“The most identifiable phenomena which form the pulse of the Earth is connected to seismology, volcanology and tectonic plates”.
VICTOR HUGO FORJAZ, VOLCANOLOGIST
Tides are a way of identifying this pulse. The natural phenomenon of gravity causes the ocean’s tides: the systematic rise and fall of sea levels, a result of the combined forces exerted by both the moon and sun, as well as the Earth’s rotation. Renowned ecologist H. H. Shugart writes, in “Foundations of the Earth” (2014), that tides “are the most obvious pulsations of the seas, its heartbeats”. This way, it produces a regular, constant ebb and flow of tides can be considered as Earth’s own steady, unfaltering heartbeat. However, Victor Hugo Forjaz reveals that there are also earth tides, a “tide of what’s solid”, that can only be measured in nano-units. This “is a kind of pulsation” that can also “affect the magnetic field of our planet because iron, one of the components of magma that creates this field, is oriented according to the moon – an example of what Umbgrove calls “the pulse of the deep-seated forces”. This magnetic field extends from the Earth’s core into outer space. The magnetic field and electric currents that envelop our planet, invisible to our eyes, create intricate forces that affect life on Earth. It’s like an enormous bubble, protecting the planet from cosmic radiation and electrically charged atomic particles, that is pulsating because it’s in a permanent state of flux. A more specific set of electromagnetic waves that surround the Earth was identified by German physicist W.O. Schumann – now known as Schumann’s Resonance.
According to NASA, its produces a recurring atmospheric heartbeat. Inevitably, however, Victor Hugo Forjaz argues that “the most identifiable phenomena which form the pulse of the Earth is connected to seismology, volcanology and tectonic plates”, such as the crust and upper mantle, such as permanent volcanoes, earthquakes and mountain building – “the pulsation of folding and mountain building”. Furthermore, Forjaz claims that, “if we think about tectonic activity as the pulse of the earth”, then we would be living a period of “relative calm” that may very well “correspond to a cycle whereas in half a million years we’ll go through another period of great plate activity”.
Forjaz also believes that geothermal energy can also be a possible measure of the Earth’s heartbeat or pulse, “both due to medicinal thermalism and new or renewable sources of energy”. This resource has as a source – the so-called hot spots – that pulsate magma periodically – at 15 million year intervals, another potential heartbeat. These “hot spots” are located at tectonic plate boundaries, which are also seismically active. There is also a supply of balmier heat at shallower depths effectively anywhere on the planet, a naturally occurring “hydrothermal convection” system: an authentic circulatory system.
In terms of identifying Earth’s ultimate heart, the volcanologist doesn’t hesitate to nominate the planet’s mantle because it pulsates and moves in a very similar way to that of a human heart.
RESTING BETWEEN PLATES
Portugal rests near the intersection between the major Eurasian and African plates, however the plate boundary of Southern Iberia is not properly defined. A new study, helmed by Marc-Andre Gutscher, a researcher for the European Institute for Marnie Studies, notes that Portugal’s 1755 earthquake was the result of subduction, where the oceanic lithosphere (outer, solid part) submerged under the continental lithosphere. This subduction is still active but its consequences won’t be felt for a long time (1,000 to 2,000 years). Additionally, the Azores and Madeira archipelagos have a long history of volcanism, with the Serreta volcano as the one with the most recent activity (2001).
A digital illustration of map showing the Earth’s tectonic plates, specifically the boundaries between plates beneath the Iberia Peninsula
A CARIBBEAN “HOT SPOT”
Colombia’s emerged territory covers a vast area of the South American plate. At the same time, there is submerged Colombian territory that lies in the Caribbean and the Nazca plates, all very close together. As a result of being in a “hot spot” location, Colombia experiences tectonic movement and frequent seismic activity. One of Colombia’s strongest and worst earthquakes was shared with Ecuador – along the line between the Nazca Plate and the South American Plate – in January 1906. The 8.8 Richter magnitude was catastrophic and it triggered a destructive tsunami that caused, at least, 500 casualties on the Colombian coast, near Esmeraldas.
Aerial view of Nevado del Tolima and Nevado del Ruiz volcano showing a plume of smoke and ashes on November 21, 2016 in Colombia.
These “hot spots”, located at tectonic plate boundaries, are also seismically active.
Poland, which also has three volcanoes (Ostrzyca, Grodczyn, Wilcza Góra) – although extinct – has significant resources of geothermal energy. The results of research and estimations have been able to prove that geothermal energy has the greatest potential in this country when it comes to renewable sources. In fact, Poland has one of the largest low-enthalpy (resources that typically present temperatures below 150 °C) geothermal potentials in Europe, with temperatures ranging from 30° to 130° at depths of 1 to 4 km. There are seven geothermal plants: three in the Podhale region (Zakopane, Bukowina Tatrzańska and Bańska Niżna), in Stargard Szczeciński and Pyrzyce (both in the northwest) and in Mszczonów and Uniejow, both in central Poland. | 0.821522 | 3.179264 |
The possibility that Saturn’s moon Enceladus could support life has strengthened after researchers determined its ocean is likely 1 billion years old, placing it in the sweet spot.
“In the scenario that best matches the real moons, the ocean of Enceladus is about a billion years old,” Neveu wrote in an abstract, discussing the research. “That’s good news for life: it should have had enough time to arise and there should still be some energy to power it.”
With its global ocean, unique chemistry and internal heat, Enceladus has become a promising lead in our search for worlds where life could exist. (NASA/JPL-Caltech)
Speaking with Live Science, Neveu said he was surprised when the Cassini spacecraft had discovered an ocean on Enceladus, given its size. “It’s a very tiny moon and, in general, you expect tiny things to not be very active [but rather] like a dead block of rock and ice,” he told the news outlet.
Fifty simulations were created using data from the Cassini spacecraft, which intentionally plunged itself into Saturn’s atmosphere in September 2017. However, there was some guesswork that led Neveu and co-author Alyssa Rhoden to estimate the age of Enceladus’ ocean, which was based on a single simulation, one that best replicated the conditions seen on the celestial satellite, Live Science added.
Additional research is needed to make the simulation faster and get a more precise date for the exact age of Enceladus’ ocean.
Neveu’s study was published in April in the scientific journal, Nature Astronomy.
The prospect for life on Enceladus has been raised before, including by NASA in 2017. The space agency found the presence of hydrogen in its atmosphere, something Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, said at the time could be meaningful.
“It could be a potential source for energy from any microbes,” Spilker said at the time. “We now know that Enceladus has almost all of the ingredients you would need for life here on Earth.”
In the 2017 announcement, Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate, said these findings were the closest the space agency had come at the time “to identifying a place with some of the ingredients needed for a habitable environment,” adding that NASA’s missions “are getting us closer to answering whether we are indeed alone or not.”
Complex organic molecules were discovered on Enceladus in 2018, which scientists said are the “building blocks” for life.
Cassini was launched in 1997 at a total cost of $3.9 billion ($2.5 billion in pre-launch costs and $1.4 billion in post-launch) and spent 13 years circling, studying and taking data of Saturn and its moons, including Titan, Saturn’s largest moon, which may also be home to extraterrestrial life. | 0.813059 | 3.166932 |
Astronomers have spotted an ultrafast star, traveling at a blistering 6 million km/h, that was ejected by the supermassive black hole at the heart at the Milky Way five million years ago. The discovery of the star, known as S5-HVS1, was made as part of the Southern Stellar Stream Spectroscopic Survey (S5). Located in the constellation of Grus – the Crane – S5-HVS1 was found to be moving ten times faster than most stars in the Milky Way.
Astronomers have spotted an ultrafast star, traveling at a blistering 6 million km/h, that was ejected by the supermassive black hole at the heart at the Milky Way five million years ago.
The discovery of the star, known as S5-HVS1, was made by Carnegie Mellon University Assistant Professor of Physics Sergey Koposov as part of the Southern Stellar Stream Spectroscopic Survey (S5). Located in the constellation of Grus — the Crane — S5-HVS1 was found to be moving ten times faster than most stars in the Milky Way.
“The velocity of the discovered star is so high that it will inevitably leave the galaxy and never return,” said Douglas Boubert from the University of Oxford, a co-author on the study.
Astronomers have wondered about high velocity stars since their discovery only two decades ago. S5-HVS1 is unprecedented due to its high speed and close passage to the Earth, “only” 29 thousand light years away. With this information, astronomers could track its journey back into the center of the Milky Way, where a four million solar mass black hole, known as Sagittarius A*, lurks.
“This is super exciting, as we have long suspected that black holes can eject stars with very high velocities. However, we never had an unambiguous association of such a fast star with the galactic center,” said Koposov, the lead author of this work and member of Carnegie Mellon’s McWilliams Center for Cosmology. “We think the black hole ejected the star with a speed of thousands of kilometers per second about five million years ago. This ejection happened at the time when humanity’s ancestors were just learning to walk on two feet.”
Superfast stars can be ejected by black holes via the Hills Mechanism, proposed by astronomer Jack Hills thirty years ago. Originally, S5-HSV1 lived with a companion in a binary system, but they strayed too close to Sagittarius A*. In the gravitational tussle, the companion star was captured by the black hole, while S5-HVS1 was thrown out at extremely high speed.
“This is the first clear demonstration of the Hills Mechanism in action,” said Ting Li from Carnegie Observatories and Princeton University, and leader of the S5 Collaboration. “Seeing this star is really amazing as we know it must have formed in the galactic center, a place very different to our local environment. It is a visitor from a strange land.”
The discovery of S5-HVS1 was made with the 3.9-meter Anglo-Australian Telescope (AAT) near Coonabarabran, NSW, Australia, coupled with superb observations from the European Space Agency’s Gaia satellite, that allowed the astronomers to reveal the full speed of the star and its journey from the center of the Milky Way.
“The observations would not be possible without the unique capabilities of the 2dF instrument on the AAT,” said Daniel Zucker, an astronomer at Macquarie University in Sydney, Australia, and a member of the S5 executive committee. “It’s been conducting cutting-edge research for over two decades and still is the best facility in the world for our project.”
These results were published on November 4 online in the Monthly Notices of the Royal Astronomical Society, and the S5 collaboration unites astronomers from the United States, United Kingdom, Australia and Chile.
“I am so excited this fast-moving star was discovered by S5,” says Kyler Kuehn, at Lowell Observatory and a member of the S5 executive committee. “While the main science goal of S5 is to probe the stellar streams — disrupting dwarf galaxies and globular clusters — we dedicated spare resources of the instrument to searching for interesting targets in the Milky Way, and voila, we found something amazing for ‘free.’ With our future observations, hopefully we will find even more!” | 0.923873 | 3.853123 |
An artistic interpretation of a secondary supermassive black hole orbiting the main one in the galaxy Cygnus A.
For the first time in the past 20 years, scientists sent a Very Large Telescope to a famous galaxy and received an unexpected gift. It turned out that something new had formed near the galactic nucleus. This may be a rare type of supernova, or (more likely) a flash in another supermassive black hole.
Cygnus A was discovered by Grotto Rebert in 1939. The received radio signal was compared with the survey data in 1951 and found a galaxy remote for 800 million light years. Beautiful pictures in 1984 helped to better understand the ultra-fast jets of subatomic particles pushed into space by the gravity of a black hole.
Researchers studied the galaxy in detail and did not look at it until 1996. Then expanded the radio frequency range. But nothing new was found. Meanwhile, in 2012, the Very Large Telescope was updated and more powerful, so they wanted to look at Cygnus A. again. Observations were made in 2015-2016. Surprisingly, something unexpected appeared near the galactic nucleus, which was not the case in 1996. In November 2016, researchers noticed an object that was already weak in the infrared observations of Hubble and Keck (1994 and 2002). At first they thought it was a dense star cluster, but everything turned out to be even more interesting.
Radio image (orange) of Cygnus A superimposed on Hubble data (1989-2015)
What is this? Analyzing the characteristics, the scientists found out that this is the death of a supernova or a flash of a supermassive black hole (already the second) near the nucleus. Of course, to make sure, you need to follow the phenomenon for a long time. But scientists say that for a supernova it lasts too long. Therefore, this option is losing.
The find is located in 1500 light years from the central hole, but very similar to it in characteristics. Most likely, at one time Cygnus A merged with another galaxy and formed a pair of supermassive black holes approaching a rapprochement.
Why didn't she see her before? It is believed that now it is actively feeding, therefore, it creates radiation, noticed by a telescope. It may be gas destroyed after a galactic merger, or it may be a star. | 0.888933 | 3.688292 |
These discoveries have excited the astronomical community and the broader public as well. Since then, the pace of exoplanet discovery has increased each year. There are now nearly 1000 confirmed exoplanets and Kepler has identified thousands of candidates that await confirmation. Nature has surprised astronomers with the enormous and unexpected diversity of exoplanetary systems, containing planets with physical properties and orbital architectures that are radically different from our own Solar System. Since the very first discoveries, we have struggled to understand this diversity of exoplanets, and in particular how our solar system fits into this menagerie.
These two complementary approaches will provide the most comprehensive view of the formation, evolution, and physical properties of planetary systems. In addition, information and experience gained from both approaches will lay the foundation for, and take the first steps toward, the discovery and characterization of a "pale blue dot " -- a habitable Earth-like planet orbiting a nearby star.
The first exoplanets to be discovered were gas giants, but today it is becoming clear that there are probably many more "small" planets, in the Earth to Super-Earth range, than there are giants. Discovering the statistics of these planets is crucial for understanding their formation and commonality. Gravitational microlensing is an observational effect that was predicted in 1936 by Einstein using his General Theory of Relativity. When one star in the sky appears to pass nearly in front of another, the light rays of the background source star become bent due to the gravitational "attraction" of the foreground star. This star is then a virtual magnifying glass, amplifying the brightness of the background source star, so we refer to the foreground star as the lens star. If the lens star harbors a planetary system, then those planets can also act as lenses, each one producing a short deviation in the brightness of the source. Thus we discover the presence of each exoplanet, and measure its mass and separation from its star. This technique will tell us how common Earth- like planets are, and will guide the design of future exoplanet imaging missions.
More than 20 planets have been discovered from the ground using this technique. The WFIRST microlensing survey will detect many more such planets, including smaller mass planets since the planet "spike" will be far more likely to be observed from a space-based platform. This will lead to a statistical census of exoplanets with masses greater than a tenth of the Earth's mass from the outer habitable zone out to free floating planets. The results from the WFIRST microlensing survey will complement the exoplanet statistics from Kepler, and will provide answers to questions about planet formation, evolution, and the prevalence of planets in the galaxy.
Our understanding of the internal structure, atmospheres, and evolution of planets was originally developed through models that were tuned to explain the detailed properties of the planets in our own solar system.
Surveys of exoplanetary systems have led to the realization that there exists a diversity of worlds with very different properties and environments than those in our solar system. Models of planet formation and evolution have had to be expanded and generalized to explain the properties of these new worlds, often including new and uncertain physics. Our understanding of these new worlds therefore remains primitive. The best hope of understanding the physical properties of this diversity of worlds is through comparative planetology: detailed measurements of, and comparisons among, the properties of individual planets and their atmospheres. Understanding the structure, atmospheres, and evolution of a diverse set of exoplanets is an important step in the larger goal of assessing the habitability of Earth-like planets discovered in the habitable zones of nearby stars. It is unlikely that any such planets will have exactly the same size, mass, or atmosphere as our own Earth. Measuring a large sample of systems with a range of properties will be necessary to understand which properties permit habitability and to properly interpret these discoveries.
Direct imaging provides the critical approach to studying the detailed properties of exoplanets. Images and spectra of directly imaged planets provide some of the most powerful information about the structure, composition, and physics of planetary atmospheres. This information can in turn help scientists better understand the origin and evolution of these systems. The direct imaging technique is also naturally applicable to the nearest and brightest, and thus best-characterized, solar systems.
Advancing the technology for direct imaging of exoplanets was the top priority medium-scale space investment recommended by NWNH. Coronagraphy on WFIRST will be a major step towards the long-term goal of a mission that can image habitable Earth-mass planets around nearby stars and measure their spectra for signs of life. | 0.915249 | 4.024468 |
Life of Stars – Birth
We always live our daily life without understanding the mechanics of our world. If we give close thought to mechanics of it, life is possible because of our sun. And if we look in the clear sky at night we see a sky full of ghosts.
Our whole universe is filled of these giants and we call them as stars. And our sun is one of them. Stars give us life by burning themselves. But is there a limit to their burning? Do they have a life? How they are formed? Do they have a death? What do we know about them? And where do they go? What happens with them? But due to recent breakthroughs in physics, throughout the last century made the picture clear and give the answers to those questions.
If we see it all started with the Big Bang as it is the best explanation we have. Many people must have heard of it to. But what is the Big Bang? It is like our entire universe is condensed in a single point less than an atom and it contained not only all energy but also every atom that exists. Even time and space didn’t exist before this massive event. Scientists call this as The Big Bang Singularity. This huge event happened around 13.7 billion years ago. This tiny particle exploded and threw a large amount of matter and energy in a matter of microseconds and universe started to build and went on expanding till the moment what we see now and it is still expanding.
And here gravity played the main role, due to gravity some atoms came close and made clouds. Clouds went on becoming denser and denser and hence first stars were formed from the clouds of hydrogen and helium. And the death of these first stars built our universe which we see now.
We’ll see the death of stars further. From the nebula or clouds of hydrogen and helium stars born. Our sun is also born in this way. The gravitational waves spread across universe due to supernovas (i.e. death of star by the explosion) causes nearby nebulas to accumulate the matter to the center, the matter starts revolving around this small globe, this is called as an accretion disc.
When the fusion of hydrogen starts and optimum pressure is generated this pressure keeps the balance with its own gravity and fusion reaction keeps taking place and this is how a star is born.
Life of Stars – Journey
Now we have seen the birth of stars. Our sun was born around 5 billion years ago as a protostar and so as the other stars and some of them are older than our sun and some of them are younger. But the question rises what keeps them burning so many years? How do they last long in some billion years? And how many years they will burn this way? How do they measure the age of stars? But thanks to the genius scientist because of whom we can not only calculate their ages but also what will happen to them when their fuel burns up completely.
Stars start their life as a protostar. At the start, they are super hot. Proto stars transform into the blue supergiants or into sun-like stars or into the dwarf stars. This transformation of stars tells us how the star will die. Supergiants turn either into supernovas or into red giants or in some of the cases into black holes. Sun-like stars convert into red giants and further into the planetary nebula and white dwarfs. And dwarf stars transform into red dwarfs and brown dwarfs.
Stars are mainly massive spheres of hydrogen and helium. Four hydrogen atoms come together and form a single atom of helium but it is in general. Energy is given out in this process. When 2 hydrogen collides with each other and creates deuterium. While this reaction 1.44 MeV energy is given out. Previously formed deuterium collides with another hydrogen atom and forms Helium-3 (3He), which is a light isotope of Helium. 5.49 MeV energy is given out in this process. From this, there are 2 ways in which He-3 is converted into the helium atom. Either by fusing 2 3He atoms with each other or by fusing 3He and pre-existing Helium (4He) atom, which produces 7Be which again undergoes in fission reaction and forms 2 helium (4He) atom. And throughout all this reaction a tremendous amount of energy is given out. This reaction is called as P-P cycle.
But this is not the only reaction that happens into the stars, which produces energy. There is another reaction known as the CNO cycle. In this process reaction takes place from carbon atoms to nitrogen formation to oxygen formation, while this process is taking place at the end of the cycle helium is given out with a large amount of energy. But the P-P cycle takes place in those stars which are same or lesser than our sun in size. While the CNO cycle takes place in the stars which are more than 1.3 times the size of our sun. In those bigger stars, these reactions are more in the core that’s why some of the elements are formed there up to iron.
The classification of stars is made on the basis of their luminosity. The colors of the stars represent their temperatures. Blue stars are very hot, their surface temp. ranges between 50000 K to 28000 K. Whereas red stars are comparatively cool, their surface temp. ranges between 3500 K to 2000 K.
Life of Stars – Death
Stars also have aged. They born, they live their life and they face death also. And their death depends upon their mass. After their death stars leave behind the marks of their existence in the forms of dwarfs or neutron stars or pulsars or black holes.
1. Brown Dwarfs: Very small stars mainly brown or red dwarf stars when reaching their limits they collapse and becomes brown dwarfs.
2. White Dwarfs: When a star nearly same size of our sun dies, the whole mass of sun contracts under its own gravity and collapse completely that a small spoon fully filled from this dwarf weighs more than a large city. Our sun will be a white dwarf after 5 billion years so we don’t have to worry about it.
3. Neutron stars and pulsars: When a star weighing more than 1.44 times than our sun collapse under its own gravity it becomes a neutron star. Its matter is denser than the matter from the white dwarf. The 1.44 limit is known as C-limit and named after the Indian Scientist Chandrashekhar Subrahmanyam. Pulsars are also regular neutron stars but they throw out the matter from their poles. And their spinning is so fast hence it seems like a beam of light or like a pulse and therefore called a pulsar. Pulsar from crab nebula spins 33 revolutions per second. Mostly neutron stars and pulsars are formed by the supernovas i.e. explosion of the star. It is so humongous that it shines like hundreds of stars are present there. It appears brighter than the stars to the eyes. This supernova after becomes nebulas from where stars are born.
4. Black Holes: Black holes are formed by mostly 2 ways. When a blue supergiant in his old age transforms into red supergiant, then the giant collapse under its own gravity and the black holes are formed. Or when a blue supergiant in his old age transforms into red supergiant, then the giant can’t stabilize the balance between internal pressure and its own gravity and a huge supernova is formed and the core of it becomes a Black hole. But to happen all this mass of the star must be more than 3 times than our sun.
Our universe is filled with the trillions of stars but the distance between two stars is so large that we can’t even imagine. They are very very far from us. We just see their old forms only as the light left from them requires hundreds even thousands of years to reach to us. Some of them are still living but some of them are dead decades ago. We are just seeing their souls only. The sky is full of ghosts.
Read Also – 1. Life of Small Stars
1. A Brief History of Time By Stephen Hawking
2. The Universe in Nutshell By Stephen Hawking
3. The Structure And Composition of Cosmos (University of Copenhagen) By Jorgen Balslev | 0.82698 | 3.064312 |
Crescent ♎ Libra
Moon phase on 14 August 2064 Thursday is Waxing Crescent, 2 days young Moon is in Virgo.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 1 day on 12 August 2064 at 17:49.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing about ∠17° of ♍ Virgo tropical zodiac sector.
Lunar disc appears visually 3.5% wider than solar disc. Moon and Sun apparent angular diameters are ∠1963" and ∠1895".
Next Full Moon is the Sturgeon Moon of August 2064 after 12 days on 26 August 2064 at 21:35.
There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak.
The Moon is 2 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 799 of Meeus index or 1752 from Brown series.
Length of current 799 lunation is 29 days, 8 hours and 22 minutes. This is the year's shortest synodic month of 2064. It is 1 minute shorter than next lunation 800 length.
Length of current synodic month is 4 hours and 22 minutes shorter than the mean length of synodic month, but it is still 1 hour and 47 minutes longer, compared to 21st century shortest.
This lunation true anomaly is ∠325.7°. At the beginning of next synodic month true anomaly will be ∠344°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°).
Moon is reaching point of perigee on this date at 20:26, this is 11 days after last apogee on 2 August 2064 at 22:45 in ♈ Aries. Lunar orbit is starting to get wider, while the Moon is moving outward the Earth for 16 days ahead, until it will get to the point of next apogee on 30 August 2064 at 14:46 in ♈ Aries.
This perigee Moon is 362 724 km (225 386 mi) away from Earth. It is 216 km closer than the mean perigee distance, but it is still 7 632 km farther than the closest perigee of 21st century.
2 days after its descending node on 12 August 2064 at 09:26 in ♌ Leo, the Moon is following the southern part of its orbit for the next 10 days, until it will cross the ecliptic from South to North in ascending node on 25 August 2064 at 09:06 in ♒ Aquarius.
16 days after beginning of current draconic month in ♒ Aquarius, the Moon is moving from the second to the final part of it.
5 days after previous North standstill on 8 August 2064 at 13:25 in ♊ Gemini, when Moon has reached northern declination of ∠27.403°. Next 6 days the lunar orbit moves southward to face South declination of ∠-27.397° in the next southern standstill on 21 August 2064 at 06:25 in ♐ Sagittarius.
After 12 days on 26 August 2064 at 21:35 in ♒ Aquarius, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.221863 |
NASA is plunging into the solar system’s origins, selecting two planetary missions to visit mysterious asteroids. The agency has chosen Lucy, which will visit Jupiter's Trojan asteroids, and Psyche, which will orbit a large metallic asteroid, for its next Discovery missions, its low-cost planetary science mission line.
Lucy, set for a 2021 launch, will take advantage of a unique orbital moment to fly past six of Jupiter's Trojan asteroids, which precede and follow the gas giant's orbit, a region previously unexplored by spacecraft. Launching in 2023, Psyche will orbit a rare iron and nickel asteroid of the same name, believed to be the stripped-bare core of an ancient planetesimal, and will test whether such bodies could have been hot enough to have formed molten, spinning cores.
“Lucy and Psyche will take us to unique worlds that humankind has never explored before," says Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington, D.C. "With this, NASA is continuing its legacy of firsts.”
The Jupiter Trojans have long been an exploratory goal for NASA. But Harold Levison, Lucy's principal investigator and a planetary scientist at the Southwest Research Institute in Boulder, Colorado, came to the project from his theoretical work. A decade ago, he helped devise a leading model of the solar system's formation that, among its virtues, gave birth to objects with orbits like the Jupiter Trojans. These are the fossils of planet formation, he says. "If we're going to detangle what happened out there, the Trojans are the place to look."
Lucy will make a grand tour, examining its targets with an infrared spectrometer and new versions of the black-and-white and color cameras found on New Horizons, the Pluto explorer. After passing one asteroid in the main belt, in 2027 it will fly past four Jupiter Trojans over the course of a year and a half. And then, 5 years later, it will pass a rare binary asteroid system in an orbit highly tilted from Jupiter’s orbital plane. It's a complicated trajectory that was only possible with the 2021 launch, which may have helped its selection. "I've been worshipping at the feet of the celestial mechanics god for the last 30 years," Levison says, "and they're paying us back."
Little is known about Lucy's targets. The team knows their colors, from which they infer composition, and some of their reflectivity. From this limited information, it's clear they are diverse in type, and not homogenous leftovers from the formation of Jupiter. It's likely they originated farther out from their current orbit, Levison says, and found their way to Jupiter during the reconfiguration of the planets. The most interesting target is the binary pair Patroclus and Menoetius, Levison adds. Binaries are rare in much of the solar system, but common in the Kuiper belt beyond Neptune, far from the gravity of planets. That could indicate the duo are nearly pristine leftovers from that early era.
Psyche, meanwhile, has its origins in research conducted by Lindy Elkins-Tanton, the project's principal investigator and planetary scientist at Arizona State University in Tempe. With several colleagues, Elkins-Tanton identified remnant magnetic fields in meteorites that could be linked to ancient planetesimals, the building blocks of planets. Such magnetism was thought only to come from the spinning molten cores of full-fledged planets, not cooler, smaller protoplanets. But they surmised that a radioactive isotope of aluminum may have been abundant enough to heat the planetesimals from the inside-out, forming a molten core.
It was controversial. At the first meeting where they presented this idea, in 2011, "they lined up three deep at the microphones to rebut me even before I started talking," Elkins-Tanton says. But it gradually caught on, and then the Jet Propulsion Lab called, suggesting a mission to test their hypothesis.
They settled on 16 Psyche as a target. At 210 kilometers in diameter, it is one of the largest known members of the asteroid belt, and thought to be largely iron and nickel in composition, similar to Earth's core. They suspect it could have once been the molten core of a planetesimal that might have neared Mars in size. And late last year, observations from NASA's Infrared Telescope Facility also discovered signs of what looks to be water or hydroxyl on Psyche's surface, which could make it a promising resource-rich depot for human exploration in the future.
After its launch in October 2023, Psyche will arrive at its target in 2030. While orbiting, it will use a magnetometer to search for signs of a remnant magnetic field, which could have once been half as strong as Earth’s. "A little fridge magnet in space," Elkins-Tanton says. It will also employ a gamma-ray and neutron spectrometer to study radiation emitted by the asteroid, to judge its metallic composition. It's not an asteroid mission in the classic sense, Elkins-Tanton adds. "We want to understand the interior of a planet. It just happens this planet is categorized as an asteroid."
NASA has supported many missions to small bodies in recent years, but its appetite has not waned. Lucy and Psyche are different, but worthy, missions, says Michael A'Hearn, an astronomer at the University of Maryland in College Park. "Psyche is important because it will tell of the evolution of bodies in the solar system, whereas Lucy is telling us more about the origins of Trojans." Many scientists suspect the Jupiter asteroids are similar in composition to comets, he adds.
Each capped at $450 million in costs, these proposals were selected from five final candidates, all focused either on Venus or small solar system bodies. After an initial cull in 2015, the teams received $3 million to flesh out their proposals. After weeks of waiting over the holidays, the candidates learned of their selection only hours before the final announcement today.
The agency also announced it would extend another year of funding to the Near-Earth Object Camera (NEOCam), one of the finalists, though its plans beyond that were not immediately clear. “This mission is an important capability for the agency,” says Jim Green, NASA’s planetary science division director in Washington, D.C.
The final five candidates were:
- Lucy and Psyche;
- NEOCam, a space-based telescope that would discover and study 10 times more Earth-threatening asteroids and comets than known today;
- DAVINCI (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging), a probe that would plunge into Venus's atmosphere for 63 minutes and study its chemical and isotopic composition; and
- VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy), a Venus orbiter that would map the planet with radar at high resolutions, hunting for active volcanism.
The announcement comes as a particular rebuke for planetary scientists focused on Venus. For years, these researchers have been frustrated by NASA's refusal to return the planet, which it last directly targeted in the early 1990s. After failing to win selection in the previous Discovery round earlier this decade, scientists worked to clarify their scientific questions and needed measurements. By selecting two Venus missions among its final five candidates, NASA seemed to signal their success in coming together.
Many planetary scientists were also wary of the NEOCam mission. NASA faces a congressional mandate to identify 90% of mid-sized near-Earth objects by 2020. Although NEOCam would provide worthy scientific research, scientists feared it would take a Discovery slot away from more deserving work—fears that were ultimately unfounded. But bypassing NEOCam means it is unlikely that NASA will meet its congressional obligation, unless Congress ultimately decides to separately finance the mission.
The B612 Foundation, which once promised to launch a private asteroid telescope similar to NEOCam, has backed away from its plans. The $650 million Large Synoptic Survey Telescope (LSST), currently being built in Chile with the support of the National Science Foundation and the Department of Energy, will identify many near-Earth asteroids as it surveys the entire sky every 3 nights once it begins operations in 2023. But simulations suggest the LSST is unlikely to meet the 90% threshold on its own. According to a White House strategy memo released late last month, the best strategy may be to combine a space-based telescope with the LSST.
For 2 decades, NASA's Discovery program has supported low-cost planetary missions, with a goal of launching a new probe every 2 to 3 years. However, it has been 5 years since the last launch, and the most recent selection, the InSight probe to Mars, has been plagued by delays, with its launch falling back to 2018. NASA had a goal of selecting two Discovery missions this round to help it get back on schedule, though there had been concerns whether federal budget uncertainty would allow it. Green says missions should launch every 32 to 36 months going forward. “The program is now back, now healthy.” | 0.924492 | 3.575441 |
Interstellar objects entering the solar system are a bit like buses, you wait centuries for one to turn up and then two come (in astronomical terms) more or less at once. This second object (following on the heels of ‘Oumuamua seen back in 2017) first turned up on NASA’s radar back in August but has now come within camera range for a decent snapshot. And boy, is it a beauty.
The interstellar comet, 2I/Borisov, as it’s rather unromantically known (the I stands for ‘interstellar’) has now been snapped by the Hubble Space Telescope, at the comparatively close proximity of 300 million kilometers, and the images are far sharper than the earlier fuzzy, blurry shots taken in November. Now we can more clearly make out details of size and shape and learn how much earlier observations got wrong.
For instance, initial observations overestimated the size of the comet’s nucleus, its central, solid core. This now looks to be just a half a kilometer across, about one-fifteenth the estimates made on first viewing. In fact, early estimates suggested that the area around the nucleus, the coma and tail, were 14 times the size of the Earth.
The coma surrounding 2/I Borisov is made up frozen dust and gases, thawed out by proximity to the heat of the sun, with estimates suggesting that this process began back in June as the comet came within four to five astronomical units (the standard measure of space distance based on Earth’s distance from the sun) from our own particular star. From the size of the coma, Borisov may be losing 2kg of dust and 60kg of water to it every second. And that’s quite a lot of dust and water, especially for what turns out to be so small an object.
Knowing the exact size of this interstellar comet will help astrophysicists to estimate just how many such objects might be populating our solar system and the wider Milky Way. However, the solar system that Borisov claims as its own original home remains a mystery.
2/I Borisov initially entered our solar system from the direction of the constellation of Cassiopeia and is on a huge, elliptical orbit that is barely dented by the gravity of the sun that has every other object in the vicinity firmly in its grasp. This is partly due to Borisov’s sheer speed, which also testifies to its extra-solar origins, currently, at a blistering 32 kilometers per second, nearly twice the speed at which the man-made extra-solar traveler Voyager 1 is cruising at, in a bid to get out into the wider universe.
Most comets come from the freezing outer edges of the solar system, still beholden to the sun’s gravity even at that distance, so interstellar visitors are big news. But there is a chance that this may be 2/I Borisov’s final visit. The comet’s trajectory will take it to within 2au of the sun, a range at which many other comets perish, an outcome partly depending on the size of their nucleus, with some scientists estimating a 10% chance that this may be Borisov’s fate.
It is also one of an extraordinary eight comets to have been discovered by Crimean ‘amateur’ astronomer Gennadiy Borisov, this one spotted first back in August.
But are interstellar objects really more like buses than we think? Have two turned up in just the last two years out of dumb luck or is the trick to seeing comets, like catching buses, all about waiting in the right place for when they come by? Hopefully observing 2/I Borisov will help us determine if this is a sheer fluke, or if there are far more such objects regularly visited the solar system than we had previously realized.
But for now, the best plan is to keep watching the journey of plucky little 2/I Borisov, keep snapping photos and learning what we can of it, and keep our fingers crossed that getting within 2au of our own sun, an alien to this interstellar traveler, will not be the end of it.
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NASA spacecraft nears historic dwarf planet arrival
NASA's Dawn spacecraft has returned new images captured on approach to its historic orbit insertion at the dwarf planet Ceres. Dawn will be the first mission to successfully visit a dwarf planet when it enters orbit around Ceres on Friday, March 6.
"Dawn is about to make history," said Robert Mase, project manager for the Dawn mission at NASA's Jet Propulsion Laboratory in Pasadena, California. "Our team is ready and eager to find out what Ceres has in store for us."
Recent images show numerous craters and unusual bright spots that scientists believe tell how Ceres, the first object discovered in our solar system's asteroid belt, formed and whether its surface is changing. As the spacecraft spirals into closer and closer orbits around the dwarf planet, researchers will be looking for signs that these strange features are changing, which would suggest current geological activity.
"Studying Ceres allows us to do historical research in space, opening a window into the earliest chapter in the history of our solar system," said Jim Green, director of NASA's Planetary Science Division at the agency's Headquarters in Washington. "Data returned from Dawn could contribute significant breakthroughs in our understanding of how the solar system formed."
Dawn began its final approach phase toward Ceres in December. The spacecraft has taken several optical navigation images and made two rotation characterizations, allowing Ceres to be observed through its full nine-hour rotation. Since Jan. 25, Dawn has been delivering the highest-resolution images of Ceres ever captured, and they will continue to improve in quality as the spacecraft approaches.
Sicilian astronomer Father Giuseppe Piazzi spotted Ceres in 1801. As more such objects were found in the same region, they became known as asteroids, or minor planets. Ceres was initially classified as a planet and later called an asteroid. In recognition of its planet-like qualities, Ceres was designated a dwarf planet in 2006, along with Pluto and Eris.
Ceres is named for the Roman goddess of agriculture and harvests. Craters on Ceres will similarly be named for gods and goddesses of agriculture and vegetation from world mythology. Other features will be named for agricultural festivals.
Launched in September 2007, Dawn explored the giant asteroid Vesta for 14 months in 2011 and 2012, capturing detailed images and data about that body. Both Vesta and Ceres orbit the Sun between Mars and Jupiter, in the main asteroid belt. This two-stop tour of our solar system is made possible by Dawn's ion propulsion system, its three ion engines being much more efficient than chemical propulsion.
"Both Vesta and Ceres were on their way to becoming planets, but their development was interrupted by the gravity of Jupiter," said Carol Raymond, deputy project scientist at JPL. "These two bodies are like fossils from the dawn of the solar system, and they shed light on its origins."
Ceres and Vesta have several important differences. Ceres is the most massive body in the asteroid belt, with an average diameter of 590 miles (950 kilometers). Ceres' surface covers about 38 percent of the area of the continental United States. Vesta has an average diameter of 326 miles (525 kilometers), and is the second most massive body in the belt. The asteroid formed earlier than Ceres and is a very dry body. Ceres, in contrast, is estimated to be 25 percent water by mass.
"By studying Vesta and Ceres, we will gain a better understanding of the formation of our solar system, especially the terrestrial planets and most importantly the Earth," said Raymond. "These bodies are samples of the building blocks that have formed Venus, Earth and Mars. Vesta-like bodies are believed to have contributed heavily to the core of our planet, and Ceres-like bodies may have provided our water."
"We would not be able to orbit and explore these two worlds without ion propulsion," Mase said. "Dawn capitalizes on this innovative technology to deliver big science on a small budget."
In addition to the Dawn mission, NASA will launch in 2016 its Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx) spacecraft. This mission will study a large asteroid in unprecedented detail and return samples to Earth.
NASA also places a high priority on tracking and protecting Earth from asteroids. NASA's Near-Earth Object (NEO) Program at the agency's headquarters manages and funds the search, study and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. NASA is pursuing an Asteroid Redirect Mission (ARM), which will identify, redirect and send astronauts to explore an asteroid. Among its many exploration goals, the mission could demonstrate basic planetary defense techniques for asteroid deflection. | 0.87462 | 3.416327 |
Image: Hubble views star nearing its end
This image from the NASA/ESA Hubble Space Telescope shows NGC 5307, a planetary nebula that lies about 10,000 light-years from Earth. It can be seen in the constellation Centaurus (the Centaur), which can be seen primarily in the southern hemisphere.
A planetary nebula is the final stage of a Sun-like star. As such, planetary nebulas allow us a glimpse into the future of our own solar system.
A star like our Sun will, at the end of its life, transform into a red giant. Stars are sustained by the nuclear fusion that occurs in their core, which creates energy.
The nuclear fusion processes constantly try to rip the star apart. Only the gravity of the star prevents this from happening.
At the end of the red giant phase of a star, these forces become unbalanced. Without enough energy created by fusion, the core of the star collapses in on itself, while the surface layers are ejected outward. After that, all that remains of the star is what we see here: glowing outer layers surrounding a white dwarf star, the remnants of the red giant star's core.
This isn't the end of this star's evolution though—those outer layers are still moving and cooling. In just a few thousand years they will have dissipated, and all that will be left to see is the dimly glowing white dwarf. | 0.91545 | 3.401712 |
Here are a couple of views of Neptune as you have probably never seen the planet before. They were captured earlier today by astronomer Mike Brown using a 10-meter (33 ft) telescope at the W. M. Keck observatory on Hawaii.
Neptune is so distant that most amateur astronomers have only ever seen it as a small dot in binoculars – if they have ever seen it at all. Through telescopes it usually appears as a bluish but fairly bland disk which is our view of sunlight refected from the clouds that permanently shroud it.
But the icy world dazzles in orange with some bright features in its atmosphere in the pictures from Mike. That is because he was observing in infrared light from the observatory site 4,145 metres (13,600 ft) above sea level.
One of Mike’s images is a wide-angle view and includes largest moon Triton, which is thought to be a captured Kuiper Belt object which might therefore be much like ex-planet Pluto. Such remote worlds are especially interesting to Mike, a professor at the California Insitute of Technology, whose research centres on the icy bodies out beyond Neptune. His work was largely instrumental in seeing Pluto demoted to the level of dwarf planet in 2006 and so not for nothing does he rejoice in the Twitter name of @plutokiller.
Mike told Skymania News during his observing session: “The funny thing about the images is that they are sort of an unintended by-product of what we’re doing. Our main goal for the night is to try to understand the different regions on Triton – where is the methane, where is the nitrogen, how do the surface frosts vary with season on the moon?
“So most of the night we were collecting spectra rather than pretty pictures. But to set up on Triton we had to image it first, and I just thought it was so spectacular that I should post it.”
Mike explained the dramatic appearance of different features in the photo of Neptune. He said: “The big difference is doing the imaging in the infrared where methane absorbs most of the photons. So the bright places are high clouds where the sunlight reflects off of them before it had a chance to pass through much of the atmosphere. Dark is clear atmosphere full of methane absorption.”
With its inner neighbour Uranus, Neptune is one of the solar system’s ice giants. It was only discovered in 1846 and, since it takes 165 years to circle the Sun, it is completing its first orbit this year since that time.
If you compare the two images of Neptune you can see that the planet has clearly rotated between them. It turns once on its axis in a little over 16 hours.
Observations from Voyager 2 as it flew past in 1989 revealed a dark storm on Neptune plus bright clouds racing at incredible speeds of up to 700 miles (1,100 km) per hour.
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With the arrival of spring, we can step out during the late evening hours (around 11 p.m. local daylight time) and count up to 11 "first magnitude" stars – the brightest in the sky. At no other time of the year can we see this many bright stars at one time. But while this initially might sound impressive, the truth is that seven of these bright twinklers belong not to stars associated with spring, but with the departing stars of winter. Indeed, Orion the Hunter and its bright retinue are slowly departing the scene, dropping progressively lower each evening in the western sky.
Two of the remaining four bright stars actually adorn the warm nights of summer: Vega in the constellation of Lyra, the Lyre that is low in the northeast, and Deneb, marking the tail feathers of Cygnus, the Swan, just coming up above the northeast horizon. [Vernal Equinox 2018! See the 1st Day of Spring from Space]
The final two stars are the lone bright stars of the spring season: Spica in the constellation of Virgo the Virgin, is over toward the southeast part of the sky, and Regulus, which marks the heart of Leo the Lion. The rest of the firmament contains stars that are generally medium to dim in overall brightness. There are, of course, a few conspicuous star patterns, such as the famous Big Dipper that appears upside-down high in the north, and the backward question-mark grouping of stars that outlines the head and mane of Leo, popularly known as the Sickle.
When I give sky shows at New York's Hayden Planetarium, I often tell my audiences that they can always find Leo by first locating the Big Dipper and then imagining that the bowl is filled with water. "Now pretend," I would tell my audience, "that you've drilled a hole in the bottom of the Dipper and you allow all that water to spurt out through that hole. Who would get wet?
It would be Leo, with the water falling on his head, which is where you would find the famous Sickle.
Three dogs but no cats
During the 18th century, some star atlases depicted a cat: Felis, the creation of the French astronomer Joseph Jérôme Le Francais de Lalande. He explained his choice: "I am very fond of cats. I will let this figure scratch on the chart. The starry sky has worried me quite enough in my life, so that now I can have my joke with it." [Constellations of the Night Sky: Famous Star Patterns Explained]
Incidentally, "Felis" means cat in Latin, and I always used to wonder whether the famous cartoon character "Felix the Cat" somehow owes his name to Felis. Felix, however, is derived from the Latin word felicis, which means "happy." So, while the two names sound somewhat alike, they have different meanings.
Ultimately, the International Astronomical Union (IAU) did not take too kindly to Lalande's "joke." Felis did not make the cut when the IAU created the now current "official" listing of 88 constellations in 1930. However, cat lovers can be consoled by the fact that along with Leo, there are two other members of the cat family that are near to each other in the current evening sky, albeit rather faint: Leo Minor, the Little Lion and Lynx.
I'll have more to say about Lynx in a moment.
An unfortunate crustacean
Of the 12 zodiacal constellations, the dimmest is now soaring high in the south: Cancer the Crab. So faint are the stars that comprise this star pattern, we might refer to Cancer as an empty space in the sky. Because it contains no star brighter than 4th magnitude, the crab is difficult, if not impossible, to see under a light-polluted sky.
Cancer is essentially a Greek creation. This creeping creature was sent by Zeus' jealous wife, Juno, to fatally bite Hercules, Zeus' son from his liaison with Alcmene. The crab arrived just as Hercules was battling the multiheaded Hydra, one of his assigned 12 "labors." The crab obeyed Juno's orders, but its bite was no more than a mere annoyance to Hercules, who was much too busy to look where his was stepping. As Hercules backpedaled, he ended up crushing Cancer under his heel.
Juno then placed the hapless little crab in the sky as a reward for his services, but failed to adorn it with any conspicuous stars and thus this unfortunate crustacean has been almost invisible ever since.
Now back to Lynx, one of only two animal constellations (the other being Phoenix) that has identical Latin and English names. With only one 3rd magnitude star, Lynx is similar to Cancer in that it is one of the hardest constellations to find, much less visualize as what it supposedly represents. [Find the Felines: Cats in the Night Sky]
Johannes Hevelius, a Polish astronomer, introduced this wild cat in his star atlas, which was published in 1690. In his star atlas, the allegorical drawing of Lynx depicted his brightest star in the tuft of its tail. And from these drawings it seems that nearby Leo Minor was playfully trying to bite Lynx's tail.
Like Lynx, the Little Lion is quite faint and in his book, "Exploring the Night Sky with Binoculars" (Cambridge University Press, 2000), the late, legendary British astronomer Sir Patrick Moore made reference to Leo Minor's "dubious claims to a separate identity."
Although the telescope was just coming into general use during Hevelius' time, he openly abandoned this relatively new invention. In his star atlas, he tucked a cartoon into the corner of one sky chart showing a cherub holding a card with the Latin phrase: "Optimum nudo oculo," which translated means: "The naked eye is best." In creating Lynx, Hevelius chose a cat-like animal that possesses acute eyesight.
But as we've already noted, Lynx is one of the hardest constellations to visualize. So much so, that even Hevelius himself openly admitted that you would have to have a lynx's eyes to see it!
Thus, I would suspect that in order to provide you with the incentive to go out tonight and search for Lynx will require a lot of "purr-suasion" on my part.
But he's such a faint star pattern, I wouldn't blame you if you put off that task for another night.
Just call it "pro-cat-stination."
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications, and he is also an on-camera meteorologist for Fios1 News in Rye Brook, NY. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com. | 0.825219 | 3.582649 |
We know two facts about our galaxy that are, in isolation, mundane. One is that many stars are part of a two-star system and may orbit each other at distances similar to those of the planets in our own Solar System. The second is that stars that are similar in mass to the Sun will end their fusion-driven existences by expanding into bloated red giants. Put those two facts together and you have an inescapable and intriguing consequence: a lot of stars are going to end up expanding enough to swallow their neighbor.
What happens then can be hard to understand, in part because there are so many potential options. If the companion star is massive enough, the transfer of mass could trigger its explosion. It's also possible that friction could bleed energy from the orbit of the companion star, reducing its orbit until it is merged. Or, because the outer layers of the red giant are so diffuse, it's possible that the cores of the two stars could end up sharing a single envelope, continuing to orbit each other.
While it's easy to know when we've observed an explosion, it's much harder to figure out when we're looking at either of the latter two options. Normally, we'd rely on physical models to tell us what would happen in these cases, but generating a model of these conditions has turned out to be pretty complex. Now, however, some researchers are suggesting that a common-envelope binary star is the best way of explaining an object they've imaged.
An observation-based model
The object that the international team imaged is called HD101584, and it had been imaged previously. The earlier data indicated that it was a binary star system, with a low-mass star and an more luminous companion that had progressed further in its evolution. These images had indicated that the more advanced star had entered either the red giant phase of its existence or an even later era called an asymptotic giant. To get a better handle on what they were looking at, the researchers obtained observing time on the Atacama Large Millimeter Array, or ALMA.
ALMA is a collection of telescopes that operates at wavelengths that are longer than visible. This makes ALMA sensitive to the emissions made by warm dust and allows it to pick out a number of elements in gases, including things like oxygen, nitrogen, and silicon. It's sensitive enough that it can identify when specific isotopes of some elements are present. In addition, a number of simple chemical compounds were also detected. That ability is important for these observations, because older stars have often produced lots of heavier elements, and their relative density can allow gravity to separate out some elements at different depths of the star.
The other thing that ALMA's imaging allows is the determination of red and blue shifts in the material it's imaging. If a cloud of material is in motion relative to the Earth, that motion will impart a Doppler shift in any light it emits. Thus, by picking up these shifts, we can measure when specific chemical elements are moving within a structure.
All of these abilities turned out to be needed, as HD101584 has a complicated structure, with multiple pieces in motion. As expected, the distribution of elements in the area was also uneven, as some elements weren't present in some of the structures identified by the presence of other elements.
To figure this out, the authors combined all the velocity and chemical element data to produce a three-dimensional model of the structure of HD101584. This included information on which structures were moving and where they are going.
Lots of stuff going on
One of the challenges of the model was figuring out just how big all the structures were. The authors considered both the red giant and asymptotic giant branches but found that their data on oxygen isotope ratios was inconsistent with the latter option. This results in estimates where the system is closer to Earth and all of its structures a bit smaller.
In any case, the model indicates that there are at least four different things going on in HD101584. For one, some of the material from the giant star has been captured in a disk that slowly orbits both of the stars at a distance of around 150 times that of the typical Earth-Sun distance. Even farther out, there's a torus of material that's still expanding away from the stars, possibly first ejected when the envelope of the giant star first engulfed its companion.
The evidence for that engulfment comes from the second two structures detected in the ALMA data. One of these is an hourglass-shaped structure of two bubbles extending out from the stars. Embedded in that are jets of rapidly moving material. That material is moving too quickly to have been propelled out by a normal stellar process, or even the gravitational forces generated by two stars in such close proximity.
Instead, the authors argue it must have been ejected as one smaller companion star moved through the envelope of the giant star: "It is difficult to reconcile such high kinetic energies with anything but a common-envelope evolution scenario where gravitational binding energy is released when the companion is captured by, and falls towards, the primary."
Based on the apparent length of the structures and their present velocity, the authors could estimate how long ago they were formed. While these estimates varied based on which structure they were looking at, all of them were less than 2,000 years and some closer to 200. Thus, it seems that the merger of the two stars has happened extremely recently, at least in cosmological terms.
Scanning a number of additional systems with properties similar to those of HD101584 suggests there might be a population of objects at various ages and points in their evolution. Again, that shouldn't be surprising, given the statistics of how high the frequency of close-in binary star systems are. But, if these observations can be confirmed and extended, then it raises the prospect that we could get data from enough systems to build a comprehensive model of the complicated physics behind the evolution of these systems. | 0.894397 | 4.019526 |
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