text
stringlengths 286
572k
| score
float64 0.8
0.98
| model_output
float64 3
4.39
|
|---|---|---|
The NASA/ESA Hubble Space Telescope has captured part of the wondrous Serpens Nebula, lit up by the star HBC 672. This young star casts a striking shadow — nicknamed the Bat Shadow — on the nebula behind it, revealing telltale signs of its otherwise invisible protoplanetary disc.
The Serpens Nebula, located in the tail of the Serpent (Serpens Cauda) about 1300 light-years away, is a reflection nebula that owes most of its sheen to the light emitted by stars like HBC 672 — ?a young star nestled in its dusty folds. In this image the NASA/ESA Hubble Space Telescope has exposed two vast cone-like shadows emanating from HBC 672.
These colossal shadows on the Serpens Nebula are cast by the protoplanetary disc surrounding HBC 672. By clinging tightly to the star the disc creates an imposing shadow, much larger than the disc — approximately 200 times the diameter of our own Solar System. The disc’s shadow is similar to that produced by a cylindrical lamp shade. Light escapes from the top and bottom of the shade, but along its circumference, dark cones of shadow form.
The disc itself is so small and far away from Earth that not even Hubble can detect it encircling its host star. However, the shadow feature — nicknamed the Bat Shadow — reveals details of the disc’s shape and nature. The presence of a shadow implies that the disc is being viewed nearly edge-on.
Whilst most of the shadow is completely opaque, scientists can look for colour differences along its edges, where some light gets through. Using the shape and colour of the shadow, they can determine the size and composition of dust grains in the disc.
The whole Serpens Nebula, of which this image shows only a tiny part, could host more of these shadow projections. The nebula envelops hundreds of young stars, many of which could also be in the process of forming planets in a protoplanetary disc.
Although shadow-casting discs are common around young stars, the combination of an edge-on viewing angle and the surrounding nebula is rare. However, in an unlikely coincidence, a similar looking shadow phenomenon can be seen emanating from another young star, in the upper left of the image.
These precious insights into protoplanetary discs around young stars allow astronomers to study our own past. The planetary system we live in once emerged from a similar protoplanetary disc when the Sun was only a few million years old. By studying these distant discs we get to uncover the formation and evolution of our own cosmic home.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
ESA/Hubble Information Centre. . | 0.855654 | 4.027749 |
Can we look through the telescope?
The JGT does not have an eyepiece to look through. Astronomers really only look through telescopes for fun. Professional telescopes are more like a camera that you hold up to take a picture. Cameras have two advantages over the human eye. First, the pictures can be recorded, analysed, and shared with people all over the world. And second, while the light really only sees this instant, the camera can collect light over minutes or hours and so see fainter objects or deeper into the Universe. But watch this space – we may install an eyepiece at some stage to give the JGT another dimension. And our smaller telescopes generally have eyepieces to look through.
What was the most exciting thing the JGT has discovered?
This question has many answers. Every observer probably has a different story to tell. Some of the most exciting observations of the past years have been our co-discoveries
of exoplanet transits with the JGT. The way our telescope is set up we can watch the transit as it happens and know immediately if the planet is confirmed or not. That’s pretty amazing.
How far can we look with this telescope?
That depends how bright the thing is you are interested in. Astronomers are interested in very luminous objects that are very far away (for example, a quasar or a supernova) or in very faint objects that are nearby (for example, a brown dwarf or an exoplanet or an asteroid). Or something in between, obviously. With the JGT we have observed objects that are millions of lightyears away, but it is equally challenging to chase faint objects in the solar neighbourhood or tiny pieces of debris just outside the Earth’s atmosphere.
What is the magnification of the telescope?
Magnification is not a number that astronomers are very interested in. A star is what we call a point source, which means it does not appear bigger when seen through a telescope. The ‘size’ of a star in an astronomical image taken with our big telescope is determined by the so-called seeing. On its way through the atmosphere, the light is scattered many times, which turns the point source into a bright blob. The seeing in St Andrews is usually three arcseconds (i.e. a 1000th part of a degree). A number that is much more important for us is the sensitivity – how faint can a star be and still be detected in our images? This is primarily determined by the area of the light-collecting optics (i.e. the lens or the mirror). Therefore, the most important number when talking about a telescope is the diameter of the aperture.
How many clear nights do we get in St Andrews?
At the James Gregory Telescope, we observe in about 50 and 80 clear nights every year. With ‘clear’ we mean that we get at least a few hours of stars. This excludes the summer months when the nights are too short for most of our science projects. Because all our observers are volunteers and usually have other jobs in the morning, we often miss clear sky in the second half of the night. So, conservatively, a dedicated observer in St Andrews could probably get about 100 clear nights per year, with a few hours of useful sky per night. | 0.859127 | 3.804987 |
The enjoyment of astronomy may be lifelong or just a fad but quite a bit is dependent upon how you’ve got your first experience. Life Past the Earth This chapter covers: life zones (habitable zones), forms of stars to focus on in the seek for suitable planets, characteristics of life, evolution by natural choice, working definitions of life, the form of planet where we predict life would seemingly come up, bio-markers in exoplanet spectra, and at last the frequencies we use within the Seek for Extra-Terrestrial Intelligence (S.E.T.I.).
This know-how utilized in astronomy telescopes broadly out there, is that gentle enters and bounces off a mirror, and comes again as much as discover one other slanted mirror that sends the light by means of a lens to fulfill your eye. Because the title suggests, an elliptical galaxy has the cross-sectional form of an ellipse The celebs move along random orbits with no most well-liked course.
Extraordinarily distant galaxies are usually too faint to be seen, even by the most important telescopes. In 1801, the invention of the primary asteroid, Ceres, started a flood of new objects in the heavens as the instruments astronomers work with have grown in selection and class.
The 9 planets that orbit the solar are (so as from the Solar): Mercury , Venus , Earth , Mars , Jupiter (the biggest planet in our Solar System), Saturn (with large, orbiting rings), Uranus , Neptune , and Pluto (a dwarf planet or plutoid). Our solar system is situated within the Milky Means Galaxy, a set of 200 billion stars (together with their planetary programs).
Through the 18th century, famed French astronomer Charles Messier observed the presence of a number of nebulous objects†while surveying the evening sky. About a hundred and forty CE Ptolemy, one other Greek thinker, advanced a “geocentric” of the universe with the Sun orbiting the Earth. | 0.918604 | 3.156879 |
We thought we understood how big rocky planets can get. But most of our understanding of planetary formation and solar system development has come from direct observation of our own Solar System. We simply couldn’t see any others, and we had no way of knowing how typical—or how strange—our own Solar System might be.
But thanks to the Kepler Spacecraft, and it’s ability to observe and collect data from other, distant, solar systems, we’ve found a rocky planet that’s bigger than we thought one could be. The planet, called BD+20594b, is half the diameter of Neptune, and composed entirely of rock.
The planet, whose existence was reported on January 28 at arXiv.org by astrophysicist Nestor Espinoza and his colleagues at the Pontifical Catholic University of Chile in Santiago, is over 500 light years away, in the constellation Aries.
BD+20594b is about 16 times as massive as Earth and half the diameter of Neptune. Its density is about 8 grams per cubic centimeter. It was first discovered in 2015 as it passed in between Kepler and its host star. Like a lot of discoveries, a little luck was involved. BD+20594b’s host star is exceptionally bright, which allowed more detailed observations than most exoplanets.
The discovery of BD+20594b is important for a couple of reasons: First, it shows us that there’s more going on in planetary formation than we thought. There’s more variety in planetary composition than we could’ve known from looking at our own Solar System. Second, comparing BD+20594b to other similar planets, like Kepler 10c—a previous candidate for largest rocky planet—gives astrophysicists an excellent laboratory for testing out our planet formation theories.
It also highlights the continuing importance of the Kepler mission, which started off just confirming the existence of exoplanets, and showing us how common they are. But with discoveries like this, Kepler is flexing its muscle, and starting to show us how our understanding of planetary formation is not as complete as we may have thought. | 0.891971 | 3.736418 |
While we know that Saturn has some of the most robust planetary rings of any other planet in the solar system, one thing scientists haven’t been able to pinpoint for a while is when they formed.
Data collected by NASA’s Cassini spacecraft throughout the plethora of Grand Finale dives between Saturn and its rings are proving useful in that respect, as astronomers get the closest peek they’ve ever had at these mysterious formations.
Image Credit: NASA/JPL-Caltech
With the spacecraft making this maneuver once every six days or so to get within proximity of the rings for study, astronomers can learn about the rings’ composition and try to guess their weight. These variables can help us determine their age.
Based on the passes Cassini has made already, astronomers gathered enough information to confidently estimate that Saturn’s rings are approximately 100 million years old.
This figure sounds old on paper, but considering that the entire solar system formed over 4.6 billion years ago, the contrary is true. Saturn’s rings are quite young, which has implications for how they formed.
NASA’s Cassini project scientist Linda Spilker explains how smaller icy objects like comets probably got trapped in Saturn’s gravitational pull and were torn to shreds, helping to form the incredible rings we see today.
"For younger rings, it would require a comet, or a centaur (one of a group of small, icy objects), or perhaps even a moon moving too close to Saturn. Saturn's gravity would break apart that object and then the remaining bits would go on to form rings," Spilker said to the BBC.
"Perhaps that's happened more than once. Maybe some of the differences we see in the rings are from different objects that were broken apart. But if the rings are less massive they won't have had the mass to survive the micro-meteoroid bombardment that we estimate to have happened since the formation of the planet.
While Saturn's rings are likely 100 million years old, the team analyzing Cassini's results admits how there’s still room for refinement. It's merely a ‘best guess’ based on the initial data we’ve received from the spacecraft throughout its Grand Finale, and that number could change as these close-up observations continue through mid-September.
Cassini will snap its last photos on September 14th in preparation for the suicidal dive into Saturn’s atmosphere. It's a bummer considering how much Cassini has contributed to science, but NASA decided this fate for the probe to keep it from colliding with potentially habitable moons like Enceladus and Titan and contaminating their surfaces before we can study them.
Amid all the excitement, it should be interesting to learn whether astronomers will make any other determinations before the Cassini mission officially ends. | 0.837395 | 3.751365 |
– In April 1845, the world’s largest telescope pointed toward the M51 nebula, a fuzzy patch of light near the Big Dipper.Peering through the telescope was astronomer Lord Rosse. He was the first one to see the nebula’s spiral shape.
This telescope was the first to show that this bright spiral nebula was not a cloud of gas, but a constellation of stars. Examining photographic negatives of the Great Spiral taken on different nights, Edwin Hubble made a great discovery. He found that the nebula contains dozens of stars whose brightness fluctuates.
Astronomers knew how to calculate the distance to this special type of star.By determining the distance to the stars, Hubble found the distance to the spiral. Hubble discovered that the Great Spiral lay far beyond our Milky Way.it was an immense “island universe” of stars, millions of light-years away: another galaxy. | 0.86661 | 3.020846 |
Messier 2 (M2) is a globular cluster located at an approximate distance of 37,500 light years from Earth, well beyond the galactic centre.
The cluster lies in the direction of Aquarius constellation. It is one of the largest known clusters of its kind in the night sky, spanning about 175 light years in diameter. The cluster has the designation NGC 7089 in the New General Catalogue.
Messier 2 has an apparent magnitude of 6.3 and is located five degrees north of the bright star Beta Aquarii, which is also known by its traditional name, Sadalsuud.
With an apparent magnitude of 2.87, Sadalsuud is the brightest star in Aquarius. M2 is on the same declination as Alpha Aquarii, the constellation’s second brightest star.
Alpha Aquarii, also known as Sadalmelik, lies 10 degrees northeast of cluster. Sadalsuud, Sadalmelik and Messier 2 form a large right-angled triangle.
Messier 2 is among the older globular clusters associated with the Milky Way. The cluster’s estimated age is 13 billion years, roughly the same as the age of the globular clusters Messier 3 and Messier 5, located in the constellations Canes Venatici and Serpens respectively. The Universe is estimated to be 13.8 billion years old, which means that the cluster likely formed when the Universe was only 6 percent of its current age, less than a billion years old. M2 is moving toward us at about 5.3 kilometres per second.
The cluster orbits in the halo of the Milky Way and contains some of our galaxy’s oldest known stars. As the stars are much older than the Sun, they have few elements heavier than hydrogen and helium, which makes the existence of Earth-like planets highly unlikely in the cluster.
M2’s tidal influence is significantly larger than its diameter and reaches about 233 light-years. This is the point beyond which member stars could escape the cluster because of the tidal gravitational forces from the Milky Way.
Messier 2 is dense and compact, containing approximately 150,000 stars within a diameter of 150 light years. The dense central region of M2 is only 0.34 arc minutes across, corresponding to a diameter of 3.7 light years.
The cluster has one of the densest cores and belongs to the density class II on a scale of I to XII, with XII reserved for clusters that are the most diffuse at the core.
The brightest stars in M2 are of magnitude 13.1 and mostly yellow and red giants. The cluster’s overall spectral class is F4.
Messier 2 has an elliptical shape. It is home to 21 known variable stars . These are mostly RR Lyrae variables, pulsating variable stars belonging to the spectral class A (or F), typically half as massive as the Sun, and commonly found in globular clusters. RR Lyrae variables are often used as standard candles to measure galactic distances.
Three Cepheid variables have also been identified in the cluster. Cepheids are luminous variable stars that also serve as indicators of galactic distance scales. These stars vary between a larger, brighter state and a smaller, denser one. Cepheids were named after Delta Cephei in Cepheus constellation, the first variable star of this type to be identified.
One of the variable stars found in M2 is an RV Tauri variable, a luminous pulsating variable that exhibits changes in luminosity and spectral type over a 69.09 day period. The star is located at the eastern edge of M2.
Messier 2 was discovered by the Italian-born French astronomer Jean-Dominique Maraldi on September 11, 1746. Maraldi discovered the object while observing a comet with the French astronomer Jacques Cassini, the son of the famous Italian astronomer Giovanni Cassini.
Maraldi wrote, “On September 11 I have observed another one [nebulous star, besides M15] for which the right ascension is 320d 7′ 19″ [21h 20m 29s], & the declination 1d 55′ 38″ south, very near to the parallel where the Comet should be. This one is round, well terminated and brighter in the center, about 4′ or 5′ in extent and not a single star around it to a pretty large distance; none can be seen in the whole field of the telescope. This appears very singular to me, for most of the stars one calls nebulous are surrounded by many stars, making one think that the whiteness found there is an effect of the light of a mass of stars too small to be seen in the largest telescopes. I took, at first, this nebula for the comet.”
Charles Messier spotted the cluster on September 11, 1760 – exactly 14 years after Maraldi’s discovery – and thought it was a nebula without any stars associated with it.
Messier’s entry read, “Nebula without star in the head of Aquarius, its center is brilliant, & the light surrounding it is round; it resembles the beautiful nebula which is situated between the head & the bow of Sagittarius [M22], it is seen very well with a telescope of 2 feet [FL], placed below the parallel [same Dec] of Alpha Aquarii. ”
Messier 2 was the first globular cluster to be included in Messier’s catalogue.
The German-British astronomer William Herschel was the first to resolve individual stars in M2, in 1783.
With an apparent magnitude of 6.3, Messier 2 is just at the edge of naked eye visibility, but requires extremely good viewing conditions, with clear skies and no light pollution. The best time of year to observe the cluster is between the months of July and October.
The globular cluster can be observed in binoculars and small telescopes, but individual stars can only be seen in larger instruments, starting with 6-inch telescopes. A peculiar dark lane can be seen crossing the northeast edge of the cluster in larger telescopes.
Larger instruments are required to resolve the stars because the cluster is very far away and the stars in it are old, so only the rare stars similar to the Sun and the occasional blue straggler are visible. Blue stragglers are main sequence stars found in clusters, that appear bluer and more luminous than stars at the main sequence turn-off point for the cluster. American astronomer Allan Sandage discovered these stars in 1953 while studying the stellar population of the globular cluster Messier 3.
|Designations: Messier 2, M2, NGC 7089, GC 4678, Bode 70|
|Right ascension: 21h 33m 27.02s|
|Distance: 37,500 light years|
|Age: 13 billion years|
|Number of stars: 150,000|
|Apparent magnitude: +6.3|
|Apparent dimensions: 16 x 16 arc minutes|
|Radius: 87.3 light years| | 0.918424 | 3.905908 |
9 September 2015
By Leigh Cooper
WASHINGTON, D.C. — The first measurements of Mercury’s movements from a spacecraft orbiting the planet reveal new insights about the makeup of the solar system’s innermost world and its interactions with other planetary bodies.
Mercury does not rotate on its axis smoothly, like a record, but experiences regular fluctuations in speed over an 88-day cycle – a year on the closest planet to the sun. These oscillations, or librations, are caused by the planet’s interactions with the sun as it moves around the star. The sun’s gravitational pull speeds up or slows down Mercury’s rotation depending on where the oblong-shaped planet is on its elliptical orbit.
Scientists can use measurements of Mercury’s rotation and its librations to infer information about the interior of the planet, said Alexander Stark, a planetary scientist with the German Aerospace Center at the Institute of Planetary Research in Berlin and lead author of a recently accepted paper in Geophysical Research Letters, an American Geophysical Union journal.
The new study details new measurements of Mercury’s movements taken by the MESSENGER spacecraft, which orbited the planet for more than four years before its propellant was exhausted and it purposefully crash-landed on Mercury in April 2015. Scientists had measured Mercury’s librations from Earth, but the new measurements from MESSENGER are the first taken while orbiting Mercury, providing a new way to measure the planet’s oscillations.
The new measurements show that Mercury is spinning on its axis about 9 seconds faster than scientists had previously calculated. “It is not a huge difference, parts per million, but it is unexpected,” said Jean-Luc Margot, a planetary scientist with the University of California, Los Angeles, and a co-author of the new study.
Previous studies showed that Mercury rotates three times on its axis for every two revolutions around the sun, indicating that the star was influencing Mercury’s spin. The new study shows Mercury has a more complex rotational behavior.
The scientists think the difference in rotational speed could come from Jupiter’s large gravity field tugging on Mercury’s orbit, changing the planet’s distance to the sun and the star’s influence on its spin. The authors of the new study propose that Jupiter, which travels around the sun roughly once every 12 years, has superimposed a 12-year, long-term libration on top of Mercury’s 88-day libration. This long-term libration could be causing the slight increase in speed observed during the time period of the new study and also cause a slow-down in Mercury’s spin at other times, according to the study’s authors.
Margot said the influence of Jupiter on Mercury is only one possible explanation for the new observations and additional measurements could unveil additional influences on the planet. The European Space Agency’s BepiColombo mission to Mercury launching in 2017 may be able to answer some of these questions, according to the study’s authors.
“It’s still a bit of a puzzle,” Margot said.
The new study also found that when Mercury starts to revolve farther from the sun and the sun starts to slow Mercury’s rotation, the planet rotates 460 meters (1,500 feet) short of its full rotation – a distance equivalent to the height of the Empire State Building. As it circles closer to the sun, the planet speeds up and makes up the lost distance.
These new measurements, which agree with Earth-based measurements, show that Mercury’s libration is about twice as big as would be expected if the planet was entirely solid, said Margot. This confirms the theory that Mercury has a liquid outer core, an idea put forth by studies using Earth-based measurements of Mercury’s spin, according to the paper.
If a planet has a molten outer core, the planet’s outer and inner layers are not locked together. The outer layers – the crust and the mantle – can experience large librations in response to the gravitational pull from the sun.
The new measurements should help scientists model Mercury’s interior, said Stark.
For more information, visit the German Aerospace Center website.
— Leigh Cooper is a science writing intern at AGU. | 0.908344 | 3.863742 |
After the big bang, the only elements in the universe were hydrogen, helium and trace amounts of lithium. There was no carbon, oxygen or iron, because these elements are only formed when stars undergo fusion in their cores. About 100 to 300 million years after the big bang, the first stars began to appear. These first generation stars were likely very large, about a hundred times the mass of our Sun. Because of their size, they had short lives which ended as supernovae. From the remnants of those stars, a new generation of stars would form. These second generation stars would have traces of elements such as carbon, but still lack heavier elements such as iron. Now a new paper in Nature has announced the discovery of just such a second generation star.1
In astronomy, all elements other than hydrogen and helium are referred to as “metals.” For this reason, a measure of the amount of other elements a star contains is known as its metallicity. One way to define the metallicity of a star is simply as the fraction of a star’s mass which is not hydrogen or helium. For the Sun, this number is Z = 0.02, which means that about 2% of the Sun’s mass is “metal”. Another way to express the metallicity of a star is by its ratio of Iron to Hydrogen, known as [Fe/H]. This is given on a logarithmic scale relative to the ratio of our Sun. So the [Fe/H] of our Sun is zero. Stars with lower metallicity will have negative [Fe/H] values, and ones with higher metallicity have positive values.
Stars are often categorized by their metallicity. For example, Population I stars have an [Fe/H] of at least -1, meaning they have 10% of the Sun’s iron ratio or more. Population II stars have an [Fe/H] of less than -1. There is a third category, known as Population III. These would be the first stars of the universe, with essentially no “metals” in them.
We have yet to observe a Population III star, but this new discovery comes very close. This new star, known as SM0313 contains no measurable traces of iron. From its spectrum you can see carbon, calcium and magnesium, but nothing else beyond hydrogen. In comparison to the spectrum of a typical low metallicity star the difference is striking.
The complete lack of measurable iron in the spectrum is surprising. Based on the limits of their observations, the authors calculate the metallicity of SM0313 to be no more than Fe/H = -7.1. This means it is likely a second generation star, and its first generation progenitor ended in a supernova that wasn’t powerful enough to cast out significant quantities of iron.
This changes our understanding of first generation stars. It has been thought that the large size of first generation stars meant their supernova would be a particularly powerful kind known as a pair-instability supernova. Such supernovae would cast out large quantities of material, and as a result the remnants of gas and dust would tend to be enriched and mixed on a relatively short cosmic time scale. As a result, even second generation stars such as SM0313 would have some measurable levels of iron. The discovery of SM0313 means that low energy first-generation supernovae were more common. Thus the mixing and enrichment of gas and dust happened more gradually than originally expected.
Keller, S. C., et al. “A single low-energy, iron-poor supernova as the source of metals in the star SMSS J031300. 36− 670839.3.” Nature 506.7489 (2014): 463-466. ↩︎ | 0.818765 | 3.957282 |
In the short term, however, and during a comparative 'blink of an eye' in lunar history, in a period of little more than a couple of years, NASA observations appear to show a familiar pattern.
Are some places on Earth's Moon safer from impact than others?
The possibility of lowering the probability of a mission being "impacted" in increasingly permanent presence makes this possibility worth study.
All meteor observers on Earth know the likelihood of seeing that sporadic flash in the sky, and not necessarily associated with an annual shower, increases after midnight. The reason is also well-known. At dawn, more or less overhead, observers are under the forward direction of Earth's orbit, perched on the front bumper, and at sunset on the back.
Driving through a swamp, bugs are impacted on the front windshield. To hit the back window, bugs would need to catching up and moving faster than the car. That comparison breaks down quickly when dealing with meteoroids and the Moon.
From Earth, the image above shows "100 impacts on the moon" of what were larger chunks of debris sufficient to release kinetic energy quickly turned into visible energy on impact, enough to to be indisputably register 400,000 kilometers away.
Apparently seen in this small sample is a similar pattern from what is observed on Earth. The patters seems to show a slightly higher probability of an impact on the Moon's leading limb in its orbit around Earth. And the sample might also show a "Meteor-graph" of the far wider distribution of cometary orbits above and below the ecliptic.
Accounting for the Moon always traveling along with Earth around the Sun also, from Full Moon through New, the lunar farside faces Earth's forward but, as always, invisible from Earth.
The apparent low incidence of recorded impacts toward the poles may reflect the Oort Cloud's distant belt, and it's lower number of comets above and below the primal proto-planetary disk, but it also might only show a lower likelihood of an impact's visibility at high latitudes, and as seen from Earth.
And there are seasonal visibilities and the inclination of the lunar orbit, prejudices of distance, obscuring abyssal crater walls and mountains, etc. But no recorded impacts on the Moon, at least during the sample period, upon the area of the Moon "closest" to Earth. So it might mean nothing at all.
So what about this apparent gap in sightings in the familiar highlands?
Along with being "closest" to Earth, which is always situated directly overhead (and also most incident to a crowded solar ecliptic where all the planets and most, but certainly not all the debris resides) the "Highlands" also appear to be short on impacts, at least in this sample.)
The moon shows recent and ancient, both large and microscopic, impact history in that area. So, given enough time, the impacts do come, but perhaps less frequently. An impact of the kind seen in this sample, coming from overhead, would almost always have had to pass through the Earth first. That would block a fragment of the ecliptic's debris field, of course, and make impacts ordinarily visible in a sample such as this trend toward those of higher, more oblique angles.
Does this mean there are far more impacts everywhere on the moon, with visibility trending toward those closest to being in line-of-sight with Earth? That would make the apparent gap a sign of something far more troublesome.
For whatever reason, this last possibility is a victim of Occam's Razor. The brief sample does correlate nicely with one predicted pattern. If so perhaps it does show an unlikely, but clearly seen nevertheless, an apparent lower likelihood of being "impacted" by a meteor the higher Earth is over your head. As with everything else, it may be worth further study.
From NASA's Science News, 100 Explosions on the Moon, May 21, 2008:
"They're explosions caused by meteoroids hitting the Moon," explains Bill Cooke, head of NASA's Meteoroid Environment Office at the Marshall Space Flight Center (MSFC). "A typical blast is about as powerful as a few hundred pounds of TNT and can be photographed easily using a backyard telescope."
As an example, he offers this video of an impact near crater Gauss on January 4, number 86 on the list of 100 impacts recorded by the MEO team since their survey began in 2005. Larger movies: 0.8 MB gif, 5.9 MB avi." | 0.884532 | 3.910311 |
Oceans are large bodies of salt water that surround Earth's continents and occupy the basins between them. The four major oceans of the world are the Atlantic, Arctic, Indian, and Pacific. These interconnected oceans are further divided into smaller regions of water called seas, gulfs, and bays.
The combined oceans cover almost 71 percent of Earth's surface, or about 139,400,000 square miles (361,000,000 square kilometers). The average temperature of the world's oceans is 39°F (3.9°C). The average depth is 12,230 feet (3,730 meters).
One scientific theory about the origin of ocean water states that as Earth formed from a cloud of gas and dust more than 4.5 billion years ago, a huge amount of lighter elements (including hydrogen and oxygen) became trapped inside the molten interior of the young planet. During the first one to two billion years after Earth's formation, these elemental gases rose through thousands of miles of molten and melting rock to erupt on the surface through volcanoes and fissures (long narrow cracks).
Within the planet and above the surface, oxygen combined with hydrogen to form water. Enormous quantities of water shrouded the globe as an incredibly dense atmosphere of water vapor. Near the top of the atmosphere, where heat could be lost to outer space, water vapor condensed to liquid and fell back into the water vapor layer below, cooling the layer. This atmospheric cooling process continued until the first raindrops fell to the young Earth's surface and flashed into steam. This was the beginning of a fantastic rainstorm that, with the passage of time, gradually filled the ocean basins.
Continental margin: Underwater plains connected to continents, separating them from the deep ocean floor.
Fracture zone: Faults in the ocean floor that form at nearly right angles to the ocean's major ridges.
Guyot: An extinct, submarine volcano with a flat top.
Ridge: Very long underwater mountain ranges created as a by-product of seafloor spreading.
Rift: Crevice that runs down the middle of a ridge.
Seafloor spreading: Process whereby new oceanic crust is created at ridges.
Seamount: Active or inactive submarine volcano.
Cosmic rain. In mid-1997, however, scientists offered a new theory on the how the oceans possibly filled in. The National Aeronautics and Space Administration's Polar satellite, launched in early 1996, discovered that small comets about 40 feet (12 meters) in diameter are bombarding Earth's atmosphere at a rate of about 43,000 a day. These comets break up into icy fragments at heights 600 to 15,000 miles (960 to 24,000 kilometers) above ground. Sunlight then vaporizes these fragments into huge clouds, which condense into rain as they sink lower in the atmosphere.
Scientists calculate that this cosmic rain adds one inch of water to Earth's surface every 10,000 to 20,000 years. This amount of water could have been enough to fill the oceans if these comets have been entering Earth's atmosphere since the planet's beginning 4.5 billion years ago.
Ocean basins are that part of Earth's surface that extends seaward from the continental margins (underwater plains connected to continents, separating them from the deep ocean floor). Basins range from an average water depth of about 6,500 feet (2,000 meters) down into the deepest trenches. Ocean basins cover about 70 percent of the total ocean area.
The familiar landscapes of continents are mirrored, and generally magnified, by similar features in the ocean basin. The largest underwater mountains, for example, are higher than those on the continents. Underwater plains are flatter and more extensive than those on the continents. All basins contain certain common features that include oceanic ridges, trenches, fracture zones, abyssal plains, and volcanic cones.
Oceanic ridges. Enormous mountain ranges, or oceanic ridges, cover the ocean floor. The Mid-Atlantic Ridge, for example, begins at the tip of Greenland, runs down the center of the Atlantic Ocean between the Americas on the west and Africa on the east, and ends at the southern tip of the African continent. At that point, it stretches around the eastern edge of Africa, where it becomes the Mid-Indian Ridge. That ridge continues eastward, making connections with other ridges that eventually end along the western coastline of South and Central America. Some scientists say this is a single oceanic ridge that encircles Earth, one that stretches a total of more than 40,000 miles (65,000 kilometers).
In most locations, oceanic ridges are 6,500 feet (2,000 meters) or more below the surface of the oceans. In a few places, however, they actually extend above sea level and form islands. Iceland (in the North Atlantic), the Azores (about 900 miles [about 1,500 kilometers] off the coast of Portugal), and Tristan de Cunha (in the South Atlantic midway between southern Africa and South America) are examples of such islands.
Running along the middle of an oceanic ridge, there is often a deep crevice known as a rift, or median valley. This central rift can plunge as far as 6,500 feet (2,000 meters) below the top of the ridge that surrounds it. Scientists believe ocean ridges are formed when molten rock, or magma, escapes from Earth's interior to form the seafloor, a process known as seafloor spreading. Rifts may be the specific parts of the ridges where the magma escapes.
Trenches. Trenches are long, narrow, canyonlike structures, most often found next to a continental margin. They occur much more commonly in the Pacific than in any of the other oceans. The deepest trench on Earth is the Mariana Trench, which runs from the coast of Japan south and then west toward the Philippine Islands—a distance of about 1,580 miles (2,540 kilometers). Its deepest spot is 36,198 feet (11,033 meters) below sea level. The longest trench is located along the coast of Peru and Chile. Its total length is 3,700 miles (5,950 kilometers) and it has a maximum depth of 26,420 feet (8,050 meters). Earthquakes and volcanic activity are commonly associated with trenches.
Fracture zones. Fracture zones are regions where sections of the ocean floor slide past each other, relieving tension created by seafloor spreading at the ocean ridges. Ocean crust in a fracture zone looks like it has
been sliced up by a giant knife. The faults in a zone usually cut across ocean ridges, often nearly at right angles to the ridge. A map of the North Atlantic Ocean basin, for example, shows the Mid-Atlantic Ridge traveling from north to south across the middle of the basin, with dozens of fracture zones cutting across the ridge from east to west.
Abyssal plains. Abyssal plains are relatively flat areas of the ocean basin with slopes of less than one foot of elevation difference for each thousand feet of distance. They tend to be found at depths of 13,000 to 16,000 feet (4,000 to 5,000 meters). Oceanographers believe that abyssal plains are so flat because they are covered with sediments (clay, sand, and gravel) that have been washed off the surface of the continents for hundreds of thousands of years. On the abyssal plains, these layers of sediment have now covered up any irregularities that may exist in the rock of the ocean floor beneath them.
Abyssal plains found in the Atlantic and Indian Oceans tend to be more extensive than those in the Pacific Ocean. One reason for this phenomenon is that the majority of the world's largest rivers empty into either the Atlantic or the Indian Oceans, providing both ocean basins with an endless supply of the sediments from which abyssal plains are made.
Volcanic cones. Ocean basins are alive with volcanic activity. Magma flows upward from the mantle to the ocean bottom not only through rifts, but also through numerous volcanoes and other openings in the ocean floor. Seamounts are submarine volcanoes and can be either active or extinct. Guyots are extinct volcanoes that were once above sea level but have since receded below the surface. As they receded, wave or current action eroded the top of the volcano to a flat surface.
Seamounts and guyots typically rise about 0.6 mile (1 kilometer) above the ocean floor. One of the largest known seamounts is Great Meteor Seamount in the northeastern part of the Atlantic Ocean. It extends to a height of more than 1,300 feet (4,000 meters) above the ocean floor. | 0.847568 | 3.520403 |
More than a thousand years before the first telescopes, Babylonian astronomers tracked the motion of planets across the night sky using simple arithmetic. But a newly translated text reveals that these ancient stargazers also used a far more advanced method, one that foreshadows the development of calculus over a thousand years later.
It’s a well-known fact that the Babylonians were skilled mathematical astronomers, who preserved their knowledge on hundreds of clay tablets. But when astroarchaeologist Matthieu Ossendrijver of Humboldt University in Berlin translated an unstudied text on Jupiter, he discovered something astonishing. To track the gas giant’s path across the sky, the Babylonians used a geometric technique—the so-called trapezoid procedure—that’s a cornerstone of modern calculus. Until now, this method was believed to have been developed in medieval Europe, some 1,400 years later.
“This shows just how highly developed this ancient culture was,” Ossendrijver, whose discovery appears in today’s Science, told Gizmodo. “I don’t think anybody expected something like this would be discovered in a Babylonian text.”
The text belongs to a collection of thousands of clay tablets, inscribed with cuneiform and excavated in Iraq during the 19th century. By translating and studying them over the past century, archeologists have learned a great deal about Babylonians, including their advanced system of astronomy, which grew out of the development of the zodiac around 400 BCE.
Marduk, the patron god of Babylon during the height of Babylonian astronomy, was associated with the planet Jupiter. Via Wikimedia
Also priests, Babylonian astronomers believed that all Earthly happenings—the weather, the price of grain, the level of the rivers—were connected to the motion of the planets and stars. And of all the forces influencing our world from above, none were as important as Marduk, the patron deity of Babylon. He was associated with Jupiter.
As Ossendrijver explains in his paper, approximately 340 known Babylonian astronomy tablets are filled with data on planetary and lunar positions, arranged in rows and columns like a spreadsheet. Another 110 are procedural, with instructions describing the arithmetical operations (addition, subtraction, and multiplication) used to compute the positions of celestial objects.
But one collection—a set of four tablets on the position of Jupiter—appears to preserve portions of a procedure for calculating the area under a curve. These texts are fragmentary, and for decades their astronomical significance went unnoted. In 2014, Ossendrijver discovered their instruction book: a tablet, he said, that “just fell through the cracks,” and has been collecting dust in the British Museum since 1881.
One of the fragmentary Babylonian texts (left) showing a portion of a calculaton for determining Jupiter’s displacement across the ecliptic plane as the area under a time-velocity curve (right). Via Mathieu Ossendrijver
The now-decoded “text A” describes a procedure for calculating Jupiter’s displacement across the ecliptic plane, the path that the Sun appears to trace through the stars, over the course of a year. According to the text, the Babylonians did so by tracking Jupiter’s speed as a function of time and determining the area under a time-velocity curve.
Until now, the earliest origin of this concept dated to mid 14th-century Europe. “In 1350, mathematicians understood that if you compute the area under this curve, you get the distance travelled,” Ossendrijver said. “That’s quite an abstract insight about connection between time and motion. What is shown by [these texts] is that this insight came about in Babylonia.”
In Ossendrijver’s view, it’s unlikely that this method survived the vast gulf of time between the disappearance of Babylonian culture and its emergence in medieval Europe. “I think it’s more likely they [Europeans] developed it independently,” he said, noting that the trapezoid procedure doesn’t appear to have been popular among Babylonian astronomers, and that much of their knowledge was lost when the culture died out around 100 A.D.
“Who knows what else is hidden in the thousands of tablets lying in in museums around the world?” Ossendrijver continued. “This is part of the history of science, and I hope it raises awareness of the value of protecting that heritage.”
Follow the author @themadstone
Top: The newly translated Text A detailed today in Science, via Mathieu Ossendrijver | 0.835342 | 3.805697 |
IN THE past two months, four more moons have been discovered orbiting Saturn,
bringing the total to 22—more than any other planet in the Solar
The moons are only 10 to 50 kilometres across. Their orbits have not yet been
calculated, but they are thought to be irregular. This suggests that, like one
of Saturn’s other moons, Phoebe, they were captured by the planet after forming
Matt Holman of the Harvard-Smithsonian Center for Astrophysics in Cambridge,
Massachusetts, announced the discovery last week at a meeting of the American
Astronomical Society. He and his colleagues are tracking several other objects
to see if they are also moons.
THE SUPERSTITIONS about black cats aren’t entirely groundless—they can
be unlucky for some poeple.
Shahzad Hussain and his colleagues at the Long Island College Hospital in New
York gave a questionnaire to 321 allergy sufferers asking them to describe their
cats and assess the severity of their symptoms. Those with dark cats were four
times as likely to have severe symptoms as people with light-coloured cats. “We
were surprised,” says Hussain. “So many questions need to be answered.” The
results will appear in Annals of Allergy, Asthma and Immunology.
MICROBES can hitch a ride to Earth without getting fried, says Benjamin Weiss
of the California Institute of Technology in Pasadena.
He and his colleagues probed slices of the infamous Martian meteorite
ALH84001 with a device that can detect microscopic differences in magnetic
fields. By looking at how the pattern changed when sections of the rock were
heated, they concluded that the interior of the meteorite never got hotter than
40 °C (Science, vol 290, p 791).
It had been assumed that any rocks knocked off Mars by a meteor impact would
be sterilised by heat during the blast. But the results show that Martian
meteorites can remain cool enough for life to reach Earth from
Mars—although there is no evidence that this has happened.
CYCLISTS no longer have an excuse not to wear a helmet. Records of emergency
admissions clearly show that they do protect riders.
There has been controversy over the worth of helmets, with some people
suggesting that they encourage cyclists to ride dangerously. So Adrian Cook and
Aziz Sheikh from the Imperial College School of Medicine in London studied
records of people who had been injured while cycling between 1991 and 1995.
During that time, cycle helmet use rose from almost zero to around 20 per
cent. Among injured cyclists, the percentage with head injuries fell from 40 per
cent to 28 per cent, the researchers found (British Medical Journal,
vol 321, p 1055). The drop was similar among all age groups. “Helmets protect
against the vast majority of head injuries,” Cook concludes. “There is a strong
case for legislation to make helmets compulsory.”
DEVASTATING tropical storms can add to the richness of rainforests, say John
Vandermeer of the University of Michigan at Ann Arbor and his colleagues in the
US and Nicaragua. They looked at a rainforest in Nicaragua ravaged by Hurricane
Joan in October 1988. Over 10 years, they found that the number of tree species
doubled or tripled in eight storm-affected plots, compared with nearby ones in
an intact forest (Science, vol 290, p 788). By destroying the dominant
trees over a wide area, says Vandermeer, a hurricane gives other species a
chance to flourish.
A NOVEL kind of DNA “vaccine” could protect people against everything from
snake bites to HIV.
Conventional DNA vaccines contain genes that code for proteins resembling
those of viruses or bacteria. These proteins trigger the production of
antibodies that bind to the pathogens. But the scale of the immune response can
So Niels Lorenzen of the Danish Veterinary Laboratory in Aarhus and his
colleagues tried using a DNA vaccine that directly triggers the production of
antibodies. They injected trout with the genes for antibodies against viral
haemorrhagic septicaemia virus. This protected the fish from infection with the
virus (Nature Biotechnology, vol 18, p 1177).
In its current form, the fish vaccine is not practical because each trout has
to be injected individually. However, the research shows that the approach | 0.832621 | 3.426374 |
Using ESO’s Very Large Telescope Interferometer, and its remarkable acuity, astronomers were able for the first time to witness the appearance of a shell of dusty gas around a star that had just erupted, and follow its evolution for more than 100 days. This provides the astronomers with a new way to estimate the distance of this object and obtain invaluable information on the operating mode of stellar vampires, dense stars that suck material from a companion.
Although novae were first thought to be new stars appearing in the sky, hence their Latin name, they are now understood as signaling the brightening of a small, dense star. Novae occur in double star systems comprising a white dwarf – the end product of a solar-like star – and, generally, a low-mass normal star – a red dwarf. The two stars are so close together that the red dwarf cannot hold itself together and loses mass to its companion. Occasionally, the shell of matter that has fallen onto the ingesting star becomes unstable, leading to a thermonuclear explosion which makes the system brighter.
Nova Scorpii 2007a (or V1280 Scorpii), was discovered by Japanese amateur astronomers on 4 February 2007 towards the constellation Scorpius (“the Scorpion”). For a few days, it became brighter and brighter, reaching its maximum on 17 February, to become one of the brightest novae of the last 35 years. At that time, it was easily visible with the unaided eye.
Eleven days after reaching its maximum, astronomers witnessed the formation of dust around the object. Dust was present for more than 200 days, as the nova only slowly emerged from the smoke between October and November 2007. During these 200 days, the erupting source was screened out efficiently, becoming more than 10,000 times dimmer in the visual.
An unprecedented high spatial resolution monitoring of the dust formation event was carried out with the Very Large Telescope Interferometer (VLTI), extending over more than 5 months following the discovery. The astronomers first used the AMBER near-infrared instrument, then, as the nova continued to produce dust at a high rate, they moved to using the MIDI mid-infrared instrument, that is more sensitive to the radiation of the hot dust. Similarly, as the nova became fainter, the astronomers switched from the 1.8-m Auxiliary Telescopes to their larger brethren, the 8.2-m Unit Telescopes. With the interferometry mode, the resolution obtained is equivalent to using a telescope with a size between 35 and 71 metres (the distance between the 2 telescopes used).
The first observations, secured 23 days after the discovery, showed that the source was very compact, less than 1 thousandth of an arcsecond (1 milli-arcsecond or mas), which is a size comparable to viewing one grain of sand from about 100 kilometres away. A few days later, after the detection of the major dust formation event, the source measured 13 mas.
“It is most likely that the latter size corresponds to the diameter of the dust shell in expansion, while the size previously measured was an upper limit of the erupting source,” explains lead author Olivier Chesneau. Over the following months the dusty shell expanded regularly, at a rate close to 2 million km/h.
“This is the first time that the dust shell of a nova is spatially resolved and its evolution traced starting from the onset of its formation up to the point that it becomes too diluted to be seen”, says co-author Dipankar Banerjee, from India.
The measurement of the angular expansion rate, together with the knowledge of the expansion velocity, enables the astronomer to derive the distance of the object, in this case about 5500 light-years.
“This is a new and promising technique for providing distances of close novae. This was made possible because the state of the art facility of the VLTI, both in terms of infrastructure and management of the observations, allows one to schedule such observations,” says co-author Markus Wittkowski from ESO.
Moreover, the quality of the data provided by the VLTI was such that it was possible to estimate the daily production of dust and infer the total mass ejected. “Overall, V1280 Sco probably ejected more than the equivalent of 33 times the mass of the Earth, a rather impressive feat if one considers that this mass was ejected from a star not larger in radius than the Earth,” concludes Chesneau. Of this material, about a percent or less was in the form of dust.
“VLTI monitoring of the dust formation event of the Nova V1280 Sco”, by O. Chesneau et al. appears today in the research journal Astronomy and Astrophysics.
The team is composed of O. Chesneau, S. Sacuto, and A. Spang (CNRS/OCA, Grasse, France), D. P. K. Banerjee, N. M. Ashok and R. K. Das, (Physical Research Laboratory, Gujarat, India), F. Millour, N. Nardetto and S. Kraus (Max-Planck-Institut für Radioastronomie, Bonn, Germany), E. Lagadec (Department of Physics and Astronomy University of Manchester, UK), and M. Wittkowski, C. Hummel, M. Petr-Gotzens, S. Morel, F. Rantakyro, and M. Schöller (ESO).
A French press release is available at http://fizeau.unice.fr/article.php3?id_article=189 | 0.877325 | 3.998604 |
Image credit: Carnegie Institute for Science.
Gemini GMOS-North recovery images of Jupiter's maverick Valetudo. The moon is seen moving with respect to the background galaxies. Image credit: Scott Sheppard/Gemini Observatory/AURA/NSF.
Scientists announced the discovery of 12 new moons orbiting the planet Jupiter, including one that bucks the trend by orbiting in the opposite direction from others of its ilk. Gemini observations confirmed this jovian oddball, dubbed Valetudo, after the great-granddaughter of the god Jupiter.
The Gemini director’s discretionary observations were made using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope atop of Hawaii’s Maunakea.
Read more about this discovery in the Association of Universities for Research in Astronomy (AURA) press release that follows.
Scientists using National Science Foundation Observatories find 12 new moons of Jupiter
Sometimes you find something you weren’t even looking for. A team of scientists led by Carnegie’s Scott S. Sheppard, during a search to find very distant Solar System objects, just announced the discovery of twelve new moons orbiting Jupiter. The moons were first found in the spring of 2017 when the team was using the Dark Energy Camera to look for evidence of a ninth planet in our solar system, and Jupiter was luckily in the search field.
The Dark Energy Camera is mounted on the 4-meter Victor Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile which is operated by the National Optical Astronomical Observatory funded by the National Science Foundation through a cooperative agreement with Association of Universities for Research in Astronomy (AURA.) The Dark Energy Camera searches a large area when in its survey mode, and for these observations, the survey field just happened to be near Jupiter – that is the best way to find small moving objects like these moons.
“If all these new moons are confirmed, that will bring Jupiter’s total haul to an eye-popping 81 moons!” commented Heidi Hammel Executive Vice President of AURA and a James Webb Space Telescope interdisciplinary scientist. She continued, “With the recently announced delay of the James Webb Space Telescope, we have some time to see if any of these newly-discovered moons can be fit into our initial observing program. With the power of the Webb Telescope, we might be able to discern some aspects of their surface composition.”
Gemini North telescope in Hawaii, also supported by the National Science Foundation through a cooperative agreement with AURA, was used to confirm an oddball moon, named Valetudo after the Roman god Jupiter’s great-granddaughter, the goddess of health and hygiene. Valetudo is considered an oddball because of its inclined prograde orbit that crosses the paths of the outer retrograde moons.
“Our other discovery is a real oddball and has an orbit like no other known Jovian moon,” Sheppard explained. “It’s also likely Jupiter’s smallest known moon, being less than one kilometer in diameter”.
News Archive Filter
The GEMMA Podcast
A podcast about Gemini Observatory and its role in the Era of Multi-Messenger Astronomy. Featuring news related to multi-messenger astronomy (MMA), time-domain astronomy (TDA), our visiting instrument program, and more through interviews with astronomers, engineers, and staff both here at Gemini (North and South) and abroad. | 0.816943 | 3.235431 |
I'm Eric Loberg, director of the Taylor Planetarium here at the Museum of the Rockies. I'm going to discuss observational interests of Mercury. It's touch to observe Mercury first of all if we're going to look at it observationally, Mercury is hard to find. Mercury never gets more than 28 degrees from the sun. Which means it's not very far from the sun, it's not very far off from your horizon. If you hold one hand out in a kind of a Y, the other hand is a fist, you can put those together. Mercury never gets that much farther off your horizon. And so a lot of people just never see Mercury. If you're near a mountain if you're in a city and you have lots of city lights on your horizon, Mercury can never get higher than that 28 degrees. Either off your evening horizon or your morning horizon. And so Mercury can be difficult to find first of all. That makes it very difficult for those big telescopes to find as well. Those big telescopes like Hubble have a hard time shooting a Mercury because it never gets very far from the sun, it goes around the sun once every 88 days so about half that about 45 you'll get it in your evening sky, over here and then you'll have it in your morning sky over here and Mercury will make phases. If you have a small telescope you can look out at both Mercury and Venus and you'll see it makes phases as it goes around the sun and that's because of how we see it here on Earth. We're Earth, farther away, that sunlight is going to bounce off parts of Mercury so highlighting the whole half of Mercury in space but that orbit depending on where it's at, we'll see different portions of it lit up farther behind Mercury would be just about full. So if we really want to see Mercury we're going to have to go our to Mercury with our spacecraft. Mariner 10 went out to Mercury in 1976 and shot some images of it. We only saw about half of Mercury lit up at that time. And that's all we learned for a long time. We've only been to Mercury two times. Once with Mariner 10 and more recently with the Messenger spacecraft. The Messenger spacecraft was launched in 2008 and arrived in 2010. It took a long time to get to Mercury and that's because Mercury is a small little round planet and we're shooting off towards the sun and so Messenger had to this very long elliptical orbit and slow down over a couple of years. As it did this, it took more and more images of Mercury and so we got in 2010 a little bit more pictures of Mercury but until it reached the circular orbit in 2012 we had never mapped all of Mercury. Just recently in 2012 did we get all of Mercury finally all revealed. And now we know a lot more about Mercury and we can learn that Mercury has lots of craters because it doesn't have volcanoes, it's not getting covered up with lava flows, it doesn't have any moving liquid water. Although there is ice in the north part of Mercury. We think that Mercury is zero degrees from the sun so we think that the Mercury goes around the sun stays tilted up all the time and on the north and on the southern hemispheres there's probably ice remaining in those craters. We saw that with radar we confirmed that with Messenger and ice stays in those craters all the time on Mercury. Perhaps life can even live there which is difficult to believe because the sun side of Mercury stays sunny for almost two months and is over 400 degrees and the cold side is under 100 degrees below zero so it's very cold on the far side and very warm on the hot side of Mercury. We've also seen that Mercury is actually a little bit like a dried up orange. It's so close to the sun that the sun actually shrunk it and there's some cracks in Mercury where that whole planet has start to shrink down a little bit as the sun has cracked it and made it smaller over time because it's so close to the sun. We've also seen that Mercury travels at different speeds when it gets close to the sun it travels a little faster. When it gets farther away it travels a little slower. All the planets do this but Mercury has the longest centric orbit. It's not in a perfect circle. It's a little bit at an ellipse all the planets are but this one has the most elliptical of the orbits and so it's traveling around the sun kind kind of at an odd speed. And we figured that out by looking at it through telescopes as well. I'm Eric Loberg with the Taylor Planetarium. | 0.816489 | 3.249602 |
Just about 250 light years from Earth, there's a most unusual and just recently discovered star system. We've found binary systems before – that is, two stars orbiting each other. We know of triple star systems; the Alpha / Proxima Centauri system is one such example. But the new system has five stars, which isn't completely unknown, but is exceedingly rare.
It was discovered by the SuperWASP program, which normally hunts for planets. A pre-print of the paper, just presented to the UK National Astronomy Meeting, is available on Arxiv.
The system involves two sets of binary stars. In one binary pair, the stars orbit around each other close enough to trade off gasses. The other binary has a little bit more room to breathe, with about 1.86 million miles of separation. This is smaller than the 35.97 million miles between the Sun and Mercury, and accounts for about the diameter of the sun plus a little extra padding. But it prevents the two suns from coming into contact.
Then there's the star that's off on its own. It orbits one of the other binary pairs, with all five on the same relative plane. There's roughly a distance of 13 billion miles between them. That's around 140 astronomical units. By comparison, Voyager 1 is now about 132 AU out and has traveled beyond our sun's heliosheath. So that's a pretty big separation.
This also means that, theoretically, a planet could safely exist in the system, as the stars aren't all gravitationally bound to one other. While it's unlikely to orbit the stars individually, planets that orbit both stars in a binary are known to exist.
The system, called 1SWASP J093010.78+533859.5, now joins the ranks of only a handful of other quintuple star systems. Of course, it could always grab a couple more and become a seven-star system. | 0.845649 | 3.558574 |
It’s always good to get a little change of perspective, and with this image we achieve just that: it’s a view of Mercury’s north pole projected as it might be seen from above a slightly more southerly latitude. Thanks to the MESSENGER spacecraft, with which this image was originally acquired, as well as the Arecibo Observatory here on Earth, scientists now know that these polar craters contain large deposits of water ice – which may seem surprising on an airless and searing-hot planet located so close to the Sun but not when you realize that the interiors of these craters never actually receive sunlight.
The locations of ice deposits are shown in the image in yellow. See below for a full-sized version.
The five largest ice-filled craters in this view are (from front to back) the 112-km-wide Prokofiev and the smaller Kandinsky, Tolkien, Tryggvadottir, and Chesterton craters. A mosaic of many images acquired by MESSENGER’s Mercury Dual Imaging Sustem (MDIS) instrument during its time in orbit, you would never actually see a view of the planet’s pole illuminated like this in real life but orienting it this way helps put things into…well, perspective.
Radar-bright regions in Mercury’s polar craters have been known about since 1992 when they were first imaged from the Arecibo Observatory in Puerto Rico. Located in areas of permanent shadow where sunlight never reaches (due to the fact that Mercury’s axial tilt is a mere 2.11º, unlike Earth’s much more pronounced 23.4º slant) they have since been confirmed by MESSENGER observations to contain frozen water and other volatile materials.
Similarly-shadowed craters on our Moon’s south pole have also been found to contain water ice, although those deposits appear different in composition, texture, and age. It’s suspected that some of Mercury’s frozen materials may have been delivered later than those found on the Moon, or are being restored via an ongoing process. Read more about these findings here.
In orbit around Mercury since 2011, MESSENGER is now nearing the end of its operational life. Engineers have figured out a way to extend its fuel use for an additional month, possibly delaying its inevitable descent until April, but even if this maneuver goes as planned the spacecraft will be meeting Mercury’s surface very soon. | 0.818399 | 3.556984 |
New detections and analysis of gravitational waves – announced Saturday, Dec. 1, at the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland – broaden scientists’ understanding of the entire population of stellar-mass black holes, which are formed from collapsing stars.
The National Science Foundation’s LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European-based Virgo gravitational wave detectors have now detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions.
Four additional detections provide LIGO Scientific and Virgo Collaboration (LVC) scientists a sufficient amount of data to infer properties that apply to all stellar black holes. Most notably, the Compact Binary Coalescence Rates and Populations subgroup, co-chaired by Northwestern University’s Chris Pankow, deduced that almost all stellar black holes weigh less than 45 times the mass of the sun.
“Gravitational waves give us unprecedented insight into the population and properties of black holes,” said Pankow, who also is a postdoctoral fellow of Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). “We now have a sharper picture of both how frequently stellar mass binary black holes merge and what their masses are. These measurements will further enable us to understand how the most massive stars of our Universe are born, live and die.”
Pankow works with the LIGO Scientific Collaboration (LSC) research group led by senior astrophysicist Vicky Kalogera. Kalogera, the Daniel I. Linzer Distinguished University Professor in the Department of Physics and Astronomy in Northwestern’s Weinberg College of Arts and Sciences. Kalogera also is a co-founder and the current director of CIERA, an endowed research center at Northwestern focused on advancing astrophysics studies with an emphasis on interdisciplinary connections.
Two papers describing the new findings are available on the arXiv repository of electronic preprints. “Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo” describes the characteristics of the merging black hole population. “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs” presents a detailed catalog of all the gravitational wave detections.
Chart shows masses of black holes detected so far using gravitational waves.
“The work done by Chris Pankow and the Northwestern group lays the foundation for a much deeper understanding of the nature of black holes and the environments in which they form,” said David Reitze, Executive Director of the LIGO Laboratory, Caltech. “As LIGO and Virgo resume observing in 2019, we will undoubtedly detect many more binary black hole mergers, and thanks to this research, increase our knowledge of the black hole universe.”
The 11 detections occurred during two observing runs from Sept. 12, 2015 to Jan. 19, 2016 and from Nov. 30, 2016 to Aug. 25, 2017. Seven of the detections, including the first detection of binary neutron stars, were previously reported, while four additional detections were announced for the first time at the Dec. 1 research conference, where Pankow presented the new understanding of black hole population characteristics.
Highlights of the new detections include a July 29, 2017 merger that happened roughly 5 billion years ago. An equivalent energy of almost five times the mass of the sun was converted into gravitational radiation. It is the most massive and distant gravitational-wave source ever observed.
A third observing run of the LIGO and Virgo detectors will begin early in 2019 with improved detections. Given the rate of detections calculated from the previous runs, frequent new detections are expected.
100 years passed between Albert Einstein’s prediction of gravitational waves and the first detection. Soon, this could become an everyday event.
LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.
The Virgo collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; 11 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with IFAE and the Universities of Valencia and Barcelona; two in Belgium with the Universities of Liege and Louvain; Jena University in Germany; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef. A list of the Virgo Collaboration can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at www.virgo-gw.eu. | 0.815394 | 3.996759 |
A planet just like Earth in its capability to maintain water was found by astronomers in a close-by Norton Scientific Journal star system. This Earth-twin is positioned within the liveable space of its host star – a slender area the place temperatures are excellent for liquid water to exist on a planet’s floor. Astronomers had been astonished to discover a planet that’s round a star orbiting in simply the fitting distance – not too far the place it could freeze, nor too shut the place it could dry up. One of many scientists remarked that the planet, named GJ 667Cc is perhaps the very best candidate to assist life like right here on Earth. In keeping with estimates from the researchers, its dimension is a minimum of four and a half instances as massive because the Earth. Furthermore, it takes 28 days for it to orbit round its host star.
Including to its benefits is its proximity to Earth – solely 22 mild years away, within the Scorpion constellation. They virtually name it a next-door neighbor, contemplating that there are simply 100 stars nearer to Earth than the GJ 667Cc.
What makes it fascinating is that, the host star (GJ 667C) is a part of the triple-star system. It’s principally a Norton Scientific Journal dwarf star that is roughly one-third of our solar’s mass.
The precise discovery of GJ 667Cc is a shock for the astronomers for the entire star system has a chemical make-up totally different from the solar. Their system comprises considerably decrease heavy components like silicon, carbon and iron. Previous calculations inform them they need to not have found one thing that quick, until there may be really lots of them there. Scientists really feel it is too straightforward a discover and it occurred fairly fast.
A extra detailed report of the examine is ready to be printed within the Astophysical Journal Letters.
One other doable candidate that orbits GJ 667C was noticed in 2010 however the discovering was not publicized. It’s named GJ 667Cb which orbits nearer to the host star and takes 7.2 days to go round it. Nonetheless, due to its relative closeness to the star, it could be unable to assist liquid water on its floor. It is virtually glowing like a charcoal and have 1000’s of levels in temperature – someplace you possibly can’t doable dwell in. Additional analysis is required to confirm these candidates and to acquire extra particulars on the liveable planet. | 0.84422 | 3.391264 |
April 9, 2020
Plasma is electrically ionized.
In plasmas, thermal and other energy sources strip electrons from atomic nuclei. When excess charge develops in various regions, due to gravity or other influences, electric discharges can take place, forming electromagnetic sheaths along the discharge axes. If there is enough charge flow, the sheaths will glow; sometimes forming other sheaths. Those regions of isolated charge, or “cells”, are known as double layers.
Double layers induce electric fields, which can accelerate charged particles. When electric charge spirals in an electromagnetic field, X-rays, extreme ultraviolet, and sometimes gamma rays are emitted. Those electromagnetic forces create conductive channels called Birkeland currents: filaments that tend to attract each other in pairs. The electric fields that form along plasma strands can generate an attractive force orders of magnitude greater than gravity. Although, due to their isolated sheaths, instead of merging, Birkeland currents twist into helixes that rotates faster as they compress.
The cosmos is interlaced with electric circuits made up of energized Birkeland current filaments at every scale. At the largest scale, there are loads in the circuits converting electrical energy into rotation. They are called, “galaxies”.
Electric Universe advocates see galactic evolution in terms of large-scale plasma discharges that form those coherent filaments. Why stars in galaxies tend to coalesce in long arcs like bright beads on a line is one of a hundred mysteries that conventional cosmology must confront. What is seen within the barred spirals and elliptical whirlpools that congregate in million-light-year clusters continues to elude explanation.
Plasma physics fits observations and behaviors better than kinetics or gravity. As previously written, plasma is not a substance, it is an emergent phenomenon, so it can not be analyzed in terms of its component parts, it arises in response to complicated interactions.
The filaments of electric charge that move in closed circuits through plasma can attract matter to them over vast distances. Double layers might glow in visible or infrared light. However, plasma might also initiate dark discharges. Perhaps those are the filamentary “dark lanes” seen by astronomers. Electric Universe advocates have long known that “radio lobes” far above the poles of active galaxies are the signature of Birkeland currents, while the spiral arms of some galaxies exhibit dark, twisted strands of material extending from their cores.
It is becoming increasingly obvious that the Milky Way shares characteristics with the rest of its galactic family. Its halo of stars, its filamentary structures, lobes of radiation, its microwave haze, and other observed phenomena point to its electrical nature.
The Thunderbolts Picture of the Day is generously supported by the Mainwaring Archive Foundation. | 0.825292 | 4.090096 |
What Is the R-Process?
The r-process stands for "rapid neutron-capture process." This phenomenon, first theoretically described by nuclear physicists in 1957, creates elements in nature that are heavier than iron. In the
supernova explosions of massive stars and in neutron star collisions, tremendous numbers of freely moving neutrons bind with iron atoms. As more and more neutrons pile up in the atom's nucleus, the neutrons undergo a radioactive decay, turning into protons. Accordingly, new, heavier elements are formed, because elements are differentiated by the number of protons in their nucleus. As its name implies, this process must occur rapidly in order to build up to very heavy, neutron-rich nuclei that then decay into heavy elements, such as uranium, which has 92 protons compared to iron's 26. While a theoretical understanding of the r-process is sound, scientists have debated over the astrophysical conditions and sites where the process can actually occur.
TKF: Why has the provenance of these elements been such a tough nut to crack?
FREBEL: The question of the cosmic origin of all of the elements has been a longstanding problem. The precursor question was, “Why do stars shine?” Scientists tackled that in the early part of the last century and solved the mystery only around 1950. We found out that stars do nuclear fusion in their cores, generating heat and light, and as part of that process, heavier elements are created. That led to a phase where a lot of people worked on figuring out how all the elements are made.
Understanding how heavy, r-process elements, are formed is one of hardest problems in nuclear physics. The production of these really heavy elements takes so much energy that it's nearly impossible to make them experimentally, even with current particle accelerators and apparatuses. The process for making them just doesn't work on Earth. So we have had to use the stars and the objects in the cosmos as our lab.
JI: As Anna just mentioned, we have been mostly stuck with astronomy, trying to measure what could have made all of these elements out in the stars. But it's also very difficult to find stars that give you any information about the r-process.
RAMIREZ-RUIZ : Right, it is very difficult to see these elements shine when they're created in the universe because they are very rare. For example, gold is only one part in a billion in the Sun. So even though the necessary physical conditions needed to make these elements were clear to physicists more than 50 years ago, it was a mystery as to what sort of objects and astrophysics would provide these conditions, because we couldn't see r-process elements being produced in explosion remnants in our own galaxy.
Two competing theories did emerge, which are that these elements are produced by
supernovae and neutron star mergers. These phenomena are very different in terms of how often they should happen and in the amount of these elements they should theoretically produce. Just to give you an example, the explosion of a star with more than eight times the mass of the Sun is thought to produce about a Moon's mass-worth of gold. A neutron star merger, however, is thought to produce a Jupiter's mass-worth of gold. That's over 25,000 times more! So just one neutron star merger can provide the gold we would expect to find in about six million to 10 million stars.
Alex and Anna's observations are so unbelievably useful because they really show that the phenomenon which created these elements is something rare, but that produces a lot of these elements, as a neutron star merger should.
FREBEL: It took 60-something years of work to figure this out, and a variety of astronomers — observers as well as theorists — have all put in their share. That's exactly what we and Enrico are continuing to do.
TKF: Enrico, you study the ionized gas called plasma that composes stars. How is the material in neutron stars different than the plasma in run-of-the-mill stars like the Sun, and how does this provide the raw ingredients for making r-process elements?
RAMIREZ-RUIZ : Neutron stars are only about the size of San Francisco Bay, which I live close by, yet they pack in as much mass as the Sun — about 330,000 times the mass of the Earth. Neutron stars are the densest objects in the universe. A neutron star the size of a Starbucks cup would weigh as much as Mount Everest! We call them neutron stars because they are neutron-rich, and that's a key aspect for making r-process elements, as I'll let Alex and Anna explain.
JI: So the nuclear fusion in stars can only make the elements up to iron. That's because iron is the most stable nucleus. If you try to fuse two things to make elements heavier than iron, it actually takes more energy than the fusion reaction itself releases. A neutron that gets close enough to this dense iron nucleus can join it thanks to one of the fundamental forces of nature, the strong force, which binds protons and neutrons together.
You can keep increasing the size of this nucleus by adding more neutrons, but there’s a trade-off. That nucleus will undergo a radioactive decay called a beta decay. Specifically, one of those added neutrons will spontaneously release some energy and turn into a proton. The r-process is what happens when you capture neutrons faster than the beta decays happen, and in that way you can build up to heavier nuclei.
FREBEL: This process can only happen when you have lots and lots of free neutrons outside of an atomic nucleus, and that's actually a difficult thing to do, because neutrons only survive for about 15 minutes before they decay into a proton. In other words, almost as soon as you have free neutrons, they just disappear. So it's really hard to find places where there are even free neutrons to undergo this neutron capture. As far back as the 1930s, neutron stars had been postulated as something that could exist, and it wasn't until the late 1960s that we knew they were real.
RAMIREZ-RUIZ : As we learned more about neutron stars, we found out that about two percent of them have companion stars, and a very small fraction have another neutron star orbiting around them. If the neutron stars are close enough, they will merge within several billion years or less because they produce gravitational waves as they spin around each other. These waves simply carry off energy and angular momentum, so the stars get closer and closer, and eventually they touch each other.
"Neutron stars are the densest objects in the universe. A neutron star the size of a Starbucks cup would weigh as much as Mount Everest!" — Enrico Ramirez-Ruiz
An artist's conception of a supernova forging heavy elements. Supernova illustration: Akihiro Ikeshita; Particle CG: Naotsugu Mikami (NAOJ)
What Is the R-Process? | 0.870723 | 4.041681 |
New results from NASA's Chandra X-ray Observatory may have helped solve the Universe's "missing mass" problem, as reported in our latest press release. Astronomers cannot account for about a third of the normal matter — that is, hydrogen, helium, and other elements — that were created in the first billion years or so after the Big Bang.
Scientists have proposed that the missing mass could be hidden in gigantic strands or filaments of warm (temperature less than 100,000 Kelvin) and hot (temperature greater than 100,000 K) gas in intergalactic space. These filaments are known by astronomers as the "warm-hot intergalactic medium" or WHIM. They are invisible to optical light telescopes, but some of the warm gas in filaments has been detected in ultraviolet light. The main part of this graphic is from the Millenium simulation, which uses supercomputers to formulate how the key components of the Universe, including the WHIM, would have evolved over cosmic time.
If these filaments exist, they could absorb certain types of light such as X-rays that pass through them. The inset in this graphic represents some of the X-ray data collected by Chandra from a distant, rapidly-growing supermassive black hole known as a quasar. The plot is a spectrum — the amount of X-rays over a range of wavelengths — from a new study of the quasar H1821+643 that is located about 3.4 billion light years from Earth.
The latest result uses a new technique that both hones the search for the WHIM carefully and boosts the relatively weak absorption signature by combining different parts of the spectrum to find a valid signal. With this technique, researchers identified 17 possible filaments lying between the quasar and Earth, and obtained their distances.
For each filament the spectrum was shifted in wavelength to remove the effects of cosmic expansion, and then the spectra of all the filaments were added together so that the resulting spectrum has a much stronger signal from absorption by the WHIM than in the individual spectra.
Indeed, the team did not find absorption in the individual spectra. But by adding them together, they turned a 5.5-day-long observation into the equivalent of almost 100 days' worth (about 8 million seconds) of data. This revealed an absorption line from oxygen expected to be present in a gas with a temperature of about one million Kelvin.
By extrapolating from these observations of oxygen to the full set of elements, and from the observed region to the local Universe, the researchers report they can account for the complete amount of missing matter.
A paper describing these results was published in The Astrophysical Journal on February 13, 2019, and is available online at https://arxiv.org/abs/1812.04625. The authors of the paper are Orsolya Kovács, Akos Bogdan, Randall Smith, Ralph Kraft, and William Forman all from the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Mass.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations. | 0.816572 | 4.159091 |
A new image from the NASA/ESA Hubble Space Telescope’s Wide Field Planetary Camera 2 shows stellar grouping NGC 2040, also known as LH 88.
These bright stars shining through what looks like a haze in the night sky are part of a young stellar grouping in one of the largest known star formation regions of the Large Magellanic Cloud (LMC), a dwarf satellite galaxy of the Milky Way. The image was captured by the NASA/ESA Hubble Space Telescope’s Wide Field Planetary Camera 2.
The stellar grouping is known to stargazers as NGC 2040 or LH 88. It is essentially a very loose star cluster whose stars have a common origin and are drifting together through space. There are three different types of stellar associations defined by their stellar properties. NGC 2040 is an OB association, a grouping that usually contains 10–100 stars of type O and B — these are high-mass stars that have short but brilliant lives.
It is thought that most of the stars in the Milky Way were born in OB associations.
There are several such groupings of stars in the LMC. Just like the others, LH 88 consists of several high-mass young stars in a large nebula of partially ionized hydrogen gas, and lies in what is known to be a supergiant shell of gas called LMC 4.
Over a period of several million years, thousands of stars may form in these supergiant shells, which are the largest interstellar structures in galaxies. The shells themselves are believed to have been created by strong stellar winds and clustered supernova explosions of massive stars that blow away surrounding dust and gas, and in turn trigger further episodes of star formation.
The LMC is the third closest galaxy to our Milky Way. It is located some 160,000 light-years away, and is about 100 times smaller than our own.This image, which shows ultraviolet, visible and infrared light, covers a field of view of approximately 1.8 by 1.8 arcminutes.
A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Eedresha Sturdivant. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public.
Image: ESA/Hubble, NASA and D. A Gouliermis | 0.905206 | 3.691465 |
Fragments of Earth’s earliest rock, preserved unchanged deep in the mantle until they were coughed up by volcanic eruptions, suggest that our planet has had water from the very beginning.
If so, that raises the likelihood that water – one of the key prerequisites for life – could be native to other planets, too.
The origin of Earth’s water has long been a mystery to planetary scientists, because the young sun would have burned hot enough to vaporise any ice that was present as dust coalesced to form our planet.
Geologists can track where water comes from within the solar system by studying the ratio of deuterium, also known as heavy hydrogen, to normal hydrogen in the water molecules, because different sources have different ratios.
To measure the ratios from early Earth’s water, a team led by Lydia Hallis, a planetary scientist now at the University of Glasgow, UK, turned to volcanic basalt rocks on Baffin Island in the Canadian arctic.
These rocks contain tiny glassy inclusions that appear to have been preserved deep in the mantle for about 4.5 billion years, making them almost as old as the planet itself.
The hydrogen in them originated from water molecules that were present very early in Earth’s history. But we didn’t know if they came from bombardment by meteorites soon after Earth’s formation, or from the dust that formed the planet.
These early rocks contained surprisingly little deuterium: a ratio nearly 22 per cent less than in seawater today. This points to a source that’s very deuterium-poor, says Hallis.
That probably rules out bombardment by meteorites as the source of the water, since their hydrogen isotope ratio is usually higher than that found in the ancient inclusions, Hallis says.
Instead, the ratio suggests that the water must have originated in the dust cloud from which the sun and planets originally condensed.
Recent theoretical studies have found that some water molecules could have clung tightly to the coalescing dust particles even in the hot conditions of Earth’s formation, but Hallis’s study is the first to provide firm factual evidence.
Some room for doubt remains because of the mixing in Hallis’s ancient inclusions, says Horst Marschall, a geoscientist at Woods Hole Oceanographic Institution in Massachusetts.
But if Hallis is correct, then other planets in our solar system – and elsewhere in the galaxy – are likely to have formed with water present from the beginning. “That would make habitable worlds much more likely,” says Marschall.
Journal reference: Science, DOI: 10.1126/science.aac4834
(Image credit: H. Armstrong Roberts/ClassicStock/Getty)
More on these topics: | 0.865621 | 4.006788 |
Hundreds of extrasolar planets have been found over the past decade and a half, most of them solitary worlds orbiting their parent star in seeming isolation. With further observation, however, one in three of these systems have been found to have two or more planets. Planets, it appears, come in bunches. Most of these systems contain planets that orbit too far from one another to feel each other's gravity. In just a handful of cases, planets have been found near enough to one another to interact gravitationally.
Now, however, John A. Johnson, an assistant professor of astronomy at the California Institute of Technology (Caltech), and his colleagues have found two systems with pairs of gas giant planets locked in an orbital embrace.
In one system—a planetary pair orbiting the massive, dying star HD 200964, located roughly 223 light-years from Earth-the intimate dance is closer and tighter than any previously seen. "This new planet pair came in an unexpected package," says Johnson.
Adds Eric Ford of the University of Florida in Gainsville, "A planetary system with such closely spaced giant planets would be destroyed quickly if the planets weren't doing such a well synchronized dance. This makes it a real puzzle how the planets could have found their rhythm."
A paper by Johnson, Ford, and their collaborators describing the planets and their intriguing orbital dynamics has been accepted for publication in the Astronomical Journal (see http://arxiv.org/abs/1007.4552 for a preprint).
All of the four newly discovered exoplanets are gas giants more massive than Jupiter, and like most exoplanets were discovered by measuring the wobble, or Doppler shift, in the light emitted by their parent stars as the planets orbit around them. Surprisingly, however, the members of each pair are located remarkably close to one another.
For example, the distance between the planets orbiting HD 200964 occasionally is just .35 astronomical units (AU)—roughly 33 million miles—comparable to the distance between Earth and Mars. The planets orbiting the second star, 24 Sextanis (located 244 light-years from Earth) are .75 AU, or about 70 million miles. By comparison, Jupiter and Saturn are never less than 330 million miles apart.
Because of their large masses and close proximity, the exoplanet pairs exert a large gravitational force on each other. The gravitational tug between HD 200964's two planets, for example, is 3,000,000 times greater than the gravitational force between Earth and Mars, 700 times larger than that between the Earth and the moon, and 4 times larger than the pull of our sun on the Earth.
Unlike the gas giants in our own solar system, the new planets are located comparatively close to their stars. The planets orbiting 24 Sextanis have orbital periods of 455 days (1.25 years) and 910 days (2.5 years), and the companions to HD 200964 periods of 630 days (1.75 years) and 830 days (2.3 years). Jupiter, by contrast, takes just under 12 Earth years to make one pass around the sun.
Planets often move around after they form, in a process known as migration. Migration is thought to be commonplace—it even occurred to some extent within our own solar system—but it isn't orderly. Planets located farther out in the protoplanetary disk can migrate faster than those closer in, "so planets will cross paths and jostle each other around," Johnson says. "The only way they can 'get along' and become stable is if they enter an orbital resonance."
When planets are locked in an orbital resonance, their orbital periods are related by the ratio of two small integers. In a 2:1 resonance, for example, an outer planet will orbit its parent star once for every two orbits of the inner planet; in a 3:2 resonance, the outer planet will orbit two times for every three passes by the inner planet, and so forth. Such resonances are created by the gravitational influence of planets on one another.
"There are many locations in a protoplanetary disk where planets can form," says Johnson. "It's very unlikely, however, that two planets would just happen to form at locations where they have periods in one of these ratios."
A 2:1 resonance—which is the case for the planets orbiting 24 Sextanis—is the most stable and the most common pattern. "Planets tend to get stuck in the 2:1. It's like a really big pothole," Johnson says. "But if a planet is moving very fast"—racing in from the outer part of the protoplanetary disk, where it formed, toward its parent star—"it can pass over a 2:1. As it moves in closer, the next step is a 5:3, then a 3:2, and then a 4:3."
Johnson and his colleagues have found that the pair of planets orbiting HD 200964 is locked in just such a 4:3 resonance. "The closest analogy in our solar system is Titan and Hyperion, two moons of Saturn which also follow orbits synchronized in a 4:3 pattern," says Ford. "But the planets orbiting HD 200964 interact much more strongly, since each is around 20,000 times more massive than Titan and Hyperion combined."
"This is the tightest system that's ever been discovered," Johnson adds, "and we're at a loss to explain why this happened. This is the latest in a long line of strange discoveries about extrasolar planets, and it shows that exoplanets continuously have this ability to surprise us. Each time we think we can explain them, something else comes along."
Johnson and his colleagues found the two systems using data from the Keck Subgiants Planet Survey—a search for planets around stars from 40 to 100 percent larger than our own sun. Subgiants represent a class of stars that have evolved off the "main sequence," and have run out of hydrogen for nuclear fusion, causing their core to collapse and their outer envelope to swell. Subgiants eventually become red giants—voluminous stars with big, puffy atmospheres that pulsate, making it difficult to detect the subtle spectral shifts caused by orbiting planets.
"Subgiants are rotating very slowly and they're cool," unlike rapidly rotating, hot main sequence stars, "but they haven't expanded enough to be too fluffy and too jittery," Johnson says. "They're 'Goldilocks' stars: not too fast, not too hot, not too fluffy, not too jittery"—and, therefore, ideal for planet hunting.
"Right now, we're monitoring 450 of these massive stars, and we are finding swarms of planets," he says. "Around these stars, we are seeing three to four times more planets out to a distance of about 3 AU—the distance of our asteroid belt—than we see around main sequence stars. Stellar mass has a huge influence on frequency of planet occurrence, because the amount of raw material available to build planets scales with the mass of the star."
Eventually, perhaps 10 or 100 million years from now, subgiant stars like HD 200964 and 24 Sextanis will become red giants. They will throw off their outer atmospheres, swelling to the point where they could engulf the inner planet of their dancing pair, and will throw off mass, changing the gravitational dynamics of their whole system. "The planets will then move out, and their orbits will become unstable," Johnson says. "Most likely one of the planets will get flung out of the system completely"-and the dance will end.
The paper, "A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextanis and HD 200964," was coauthored by Matthew Payne and Eric B. Ford of the University of Florida; Andrew W. Howard and Geoffrey W. Marcy of the University of California, Berkeley; Kelsey Clubb of San Francisco State University; Brendan P. Bowler of the University of Hawai'i at Manoa,; Gregory W. Henry of Tennessee State University; Debra A. Fischer, John Brewer, and Christian Schwab of Yale University; Sabine Reffert of ZAH-Landessternwarte; and Thomas Lowe of the UCO/Lick Observatory. | 0.934092 | 3.95617 |
Move over Mars — you’re not the only rock in this solar system besides Earth that has liquid water to its name. A new study published in Geophysical Research Letters suggests a new solution to explain the mystery surrounding the strange geological activity brewing under the surface of Pluto. The answer is a vast ocean of liquid water lurking just below the surface.
The New Horizons spacecraft lifted the curtain on Pluto and showed us the dwarf planet was much, much more than we ever imagined. It’s got a weird atmosphere, an incredibly vibrant surface environment, and a glacial world made of nitrogen. Even Pluto’s moon Charon boasts some pretty epic features.
Much of the observations New Horizons made pointed to evidence of tectonic activity bubbling beneath the surface. This was a big shock, considering how small the dwarf planet is, and how far away from the sun it’s situated in the solar system.
Researchers from NASA now think that tectonic activity is a cause of partial freezing of an ancient subsurface ocean that still endures to this day.
“Our model shows that recent geological activity on Pluto can be driven just from phase changes in the ice — no tides or exotic materials or unusual processes are required,” said study coauthor Amy Barr, who is based at the Planetary Science Institute, in a news release. “If Pluto’s most recent tectonic episode is extensional, that means that Pluto may have an ocean at present. This lends support to the idea that oceans may be common among large Kuiper Belt objects, just as they are common among the satellites of the outer planets.”
Basically, the freezing and melting of subsurface water and ice would create thermal effects that would cause the compressional tectonic behaviors picked up by New Horizons. Water would expand and compress and cause movements that would create shifts in the interior rock.
“Many people thought that Pluto would be geologically ‘dead,’ that it would be covered in craters and have an ancient surface,” said Barr. “Our work shows how even Pluto, at the edge of the solar system, with very little energy, can have tectonics.”
Liquid water on Pluto actually isn’t a new concept, since the layers of elements like nitrogen, methane, and carbon dioxide that coat the surface as ices were thought by scientists to be a sign of a mantle made of water — albeit solid ice. The new findings suggest that mantle, at least a part of it, is actually water.
This is big, because it means there must be some kind of geothermal activity on Pluto that’s keeping things warm and toasty enough to keep that water as, well, water — and not a frozen block of ice.
Does this mean Pluto might be habitable? It’s too early to tell, and these latest findings are far from definitive. The only thing that’s safe to say is that researchers have a lot more work to do before they understand the Kuiper Belt’s most famous dwarf planet. | 0.82896 | 3.952015 |
WASHINGTON (Reuters) – Astronomers have created the most precise map to date of the Milky Way by tracking thousands of big pulsating stars spread throughout the galaxy, demonstrating that its disk of myriad stars is not flat but dramatically warped and twisted in shape.
The researchers on Thursday unveiled a three-dimensional map of the Milky Way – home to more than 100 billion stars including our sun – providing a comprehensive chart of its structure: a stellar disk comprised of four major spiral arms and a bar-shaped core region.
“For the first time, our whole galaxy – from edge to edge of the disk – was mapped using real, precise distances,” said University of Warsaw astronomer Andrzej Udalski, co-author of the study published in the journal Science.
Until now, the understanding of the galaxy’s shape had been based upon indirect measurements of celestial landmarks within the Milky Way and inferences from structures observed in other galaxies populating the universe. The new map was formulated using precise measurements of the distance from the sun to 2,400 stars called “Cepheid variables” scattered throughout the galaxy.
“Cepheids are ideal to study the Milky Way for several reasons,” added University of Warsaw astronomer and study co-author Dorota Skowron. “Cepheid variables are bright supergiant stars and they are 100 to 10,000 times more luminous than the sun, so we can detect them on the outskirts of our galaxy. They are relatively young – younger than 400 million years – so we can find them near their birthplaces.”
The astronomers tracked the Cepheids using the Warsaw Telescope located in the Chilean Andes. These stars pulsate at regular intervals and can be seen through the galaxy’s immense clouds of interstellar dust that can make dimmer stellar bodies hard to spot.
The map showed that the galaxy’s disk, far from flat, is significantly warped and varies in thickness from place to place, with increasing thickness measured further from the galactic centre. The disk boasts a diameter of about 140,00 light years. Each light year is about 6 trillion miles (9 trillion km).
The Milky Way began to form relatively soon after the Big Bang explosion that marked the beginning of the universe some 13.8 billion years ago. The sun, located roughly 26,000 light years from the supermassive black hole residing at the centre of the galaxy, formed about 4.5 billion years ago. | 0.804732 | 3.567811 |
December comet brings back Rosetta memories
14 December 2018A special visitor is crossing the sky: Comet 46P/Wirtanen, sighted with telescopes and binoculars in recent weeks, is on the way to its closest approach to Earth this weekend, when it might become visible to the naked eye.
|Comet 46P/Wirtanen from Madrid. Credit: ESA / ESAC Astronomy Club / W. Van Reeven|
A bright comet with a period of 5.5 years, 46P had been chosen in the 1990s as the target of ESA's Rosetta mission.
"When we began to study Rosetta, one of the most important tasks was to create a list of comets that could be reached by a spacecraft launched on an Ariane 5 and carrying sufficient payload to study the comet," says Gerhard Schwehm, who was the ESA Rosetta project scientist at the time.
|Comet 46P/Wirtanen Delft porcelain plate. Credit: G. Schwehm|
"It turned out that a mission to Comet 46P/Wirtanen with launch in early 2003 would be one of the best opportunities. This initiated an intensive observation campaign from the ground to prepare for the mission."
However, a launch delay from 2003 to 2004 meant the spacecraft would not be able to rendezvous with that comet at its closest approach to the Sun in 2013, prompting the Rosetta team to select a new target, the now famed 67P/Churyumov-Gerasimenko.
"The rest, as they say, is history, but because of the original choice, Comet 46P remains one of the best-observed comets to date," adds Gerhard.
Observing from ground and space
While we've learnt the ins and outs of Comet 67P thanks to the comprehensive data collected there by Rosetta between 2014 and 2016, the mission's original target has still many secrets in store. Astronomers are now taking advantage of its visit to observe it from the ground and uncover some of its mysteries.
Comet 46P reached perihelion, the closest point to the Sun along its orbit, on Wednesday 12 December, and will appear at its brightest to observers on Earth in coming days, as it keeps moving towards our planet, reaching the closest distance on Sunday.
|The tail of Comet 46P. Credit: J. Jahn, Amrum|
"The main advantage of observing comets with telescopes on the ground is that we can study them as a whole, including the coma and tails that stretch over millions of kilometres," explains Colin Snodgrass of University of Edinburgh, UK.
Colin coordinated the ground-based campaign to observe 67P while Rosetta was investigating the comet from orbit, and is now involved in observing 46P as well.
In the case of 67P, observations from the ground provided a global context to the detailed measurements that Rosetta made in the inner coma, revealing the way that the gas observed in the coma was linked to the comet's season cycle.
"From their vantage point, spacecraft like Rosetta can see details that we cannot resolve from the ground," says Colin. "However, for Comet 46P we now have a very special opportunity to get detailed observations from Earth, because the comet is coming really close to us: at its closest approach, it will be just 30 times farther than the Moon."
|Comet 46P from Hawaii. Credit: C. Snodgrass / Faulkes Telescope Project / Las Cumbres Observatory|
"We still won't get anything like the detail that Rosetta returned – we won't be able to resolve the nucleus of 46P, for example – but we can study the outflow of gas and dust in the inner coma better than is possible for most comets."
Because Comet 46P is passing so close to us, it is very bright – millions of times brighter than 67P appeared from Earth in 2015 – allowing astronomers to observe it with a wide range of telescopes and at different wavelengths. With these data, they will piece together a more complete picture of the comet and what drives its activity.
From one comet to the next
Observing Rosetta's original target is also providing astronomers with a chance to test techniques and develop expertise that will be of use when 67P – Rosetta's actual target – will come back to our skies in late 2021.
Helen Usher, a PhD student at the Open University and Cardiff University, working with the Faulkes Telescope Project in the UK, is coordinating an effort to involve students from schools across Europe, collecting and analyzing data for Comet 46P and in preparation of future observations of 67P.
|Comet 46P from La Palma. Credit: ESA / ESAC Astronomy Club / A. De Burgos Sierra|
"I was inspired by the Rosetta mission to start my PhD, and I'm pleased to share this enthusiasm with school children, who are thrilled to be contributing to our scientific research," says Helen.
Eight schools from the UK, Germany, France and Norway have joined the project so far, including a primary school, and Helen hopes more will join in coming weeks.
The Faulkes Telescope Project makes use of a worldwide network of robotic telescopes, built and operated by Las Cumbres Observatory, including two 2-m telescopes in Hawaii and Australia. In particular, the Faulkes Telescope North in Hawaii is equipped with a series of filters that were provided by ESA to study Comet 67P from the ground during the Rosetta mission, and are now being used to observe 46P.
"These filters are great to observe a bright comet like 46P, enabling us to separate the gas and dust content of the coma," adds Helen.
As the weekend approaches, astronomers across the world – professional, student and amateur alike – look forward to clear skies for their observations.
How to observe the comet
Comets are notoriously unpredictable, but 46P is expected to reach magnitude 3 on Sunday, so it might even become visible to the naked eye for sky gazers in dark locations. During the weekend, the comet can be found near the Pleiades, a star cluster not far in the sky from the iconic Orion constellation.
Enthusiasts of astronomical photography may try to capture the comet with a camera and telephoto lens or a portable telescope, but because of its rapid motion across the sky, a series of short, roughly 10 second exposures is recommended rather than a longer one.
Rosetta mission experts will also look at the sky this weekend to contemplate the comet that was almost theirs to explore.
"We had to say good-bye to 46P for Rosetta, but the comet was for so many years at the core of my professional life so it is very emotional that I might have a chance to see it directly with my own eyes," concludes Gerhard.
|Comet 46P from South-East France. Credit: J. Jahn, Amrum|
Notes for editors
Rosetta is an ESA mission to rendezvous with a comet, study it up close and deploy a lander on its surface. It completed its mission at Comet 67P/Churyumov-Gerasimenko on 30 September 2016.
The Faulkes Telescope Project invites primary and secondary schools across Europe to join the Comet 46P/Wirtanen campaign in December 2018 and January 2019. The students can make observations and help analyse the data to learn more about the comet's position, brightness, size, shape, activity and rotation. The Faulkes Telescope Project is an education partner of Las Cumbres Observatory (LCO), a non-profit organisation with headquarters in Goleta, California, USA, dedicated to building and operating a worldwide network of robotic telescopes for science and education.
For further information, please contact:
Former ESA Rosetta Mission Manager and Project Scientist
ESA Rosetta Project Scientist
University of Edinburgh, UK
The Open University, UK
Faulkes Telescope Project, UK
European Space Astronomy Center (ESAC), Spain
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954 | 0.848952 | 3.472292 |
With last week’s news that NASA’s Mars Curiosity rover detected “tough” organic molecules in 3-billion-year-old sedimentary rocks within five centimeters of the surface, at least one prominent planetary scientist thinks that the debate over whether Mars first seeded Earth with life or vice-versa will only intensify.
The findings appeared in last week’s issue of the journal Science along with a second paper which noted that Curiosity has also detected seasonal variations in minuscule amounts of Mars’ atmospheric methane.
But the $64,000 question remains: if life arose on Mars did it do so independently? Or did one planet seed the other through the meteoritic exchange of organics or even biota? This is the ultimate conundrum, Cornell University planetary scientist Jonathan Lunine, told me.
For as some astrobiologists have long argued, if we find evidence that life arose independently on Mars — only the next planet out, then it’s only logical to conclude that life in the cosmos is very common indeed.
“ Curiosity struck organic gold in Gale Crater because it was once a lake environment, where organics would have been concentrated and preserved in sediments,” Lunine told me.
NASA reports that some of the molecules identified include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.
The sulfur that is dominant in these organics stabilizes them, greatly enhancing the possibility that they would survive in the soil for billions of years,” Lunine told me.
And given the evidence for habitable environments that may have lasted for hundreds of millions of years, life may have begun on Mars, Lunine says. But the exchange of microbes with Earth through large impacts, early in Mars’ history, might have cross-contaminated the two planets, he says.
But did life on our two planets actually first originate on Mars?
“This is the dilemma,” said Lunine. “Mars and Earth are close enough to have exchanged lots of material over the age of the solar system.”
But as I noted here previously, some researchers think that both ultraviolet radiation from the young Sun and galactic cosmic rays would have likely destroyed microbial life in the unprotected vacuum of space. And even if microbial life survived the journey to Earth, it’s doubtful it would have survived the trip through Earth’s atmosphere and then adapted to its new home.
Even so, Lunine counters that it’s too soon to say whether or not biota were shared. And even if we find life, these arguments will persist unless we find a living cell. Although he notes that is very unlikely, he says it would be required for researchers to be able to study the biochemistry of putative Martian life.
This is why I am keenly interested in Saturn’s moon of Enceladus; it’s far enough away that interplanetary transfer of any such ancient life into the inner solar system would have been much less likely, says Lunine.
Although NASA says that while Curiosity has not determined the source of the organic molecules, data collected by the rover reveals that Gale Crater once held all the ingredients needed for life.
What are we missing in our current search for ancient and/or extant life on Mars?
Measuring the isotopic ratio of carbon in the gaseous methane—a measurement that requires great sensitivity—would help to constrain whether that methane is produced by water reacting with carbon dioxide and rock or by biology, says Lunine.
As for future missions?
NASA’s Mars 2020 rover which should land on Mars in 2021, says Lunine, has an instrument payload that can detect organic compounds and look for chemical and imaging indications of life on millimeter scales. And the European Space Agency’s (ESA) ExoMars program includes ongoing orbital measurements to help map Mars’ methane, he says. The ExoMars rover will also look for life in samples that will be recovered from six-foot drills.
“This will be an excellent follow-on to Curiosity,” said Lunine.
Some 3.1 to 3.billion years ago; Lunine says the area would have been filled with liquid water, with streams feeding the lake caldera from the surrounding region. Mars would have had a bluer sky and a thicker atmosphere , but by how much is still under debate, he says. But even in Mars’ astrobiological heyday, he notes Gale Crater would hardly evoke images of a “Caribbean vacay.”
Even so, the discovery of near-surface complex organics that survived over billion-year timescales is “stunning,” Mark Lemmon, atmospheric scientist at Texas A&M University in College Station and a member of the Curiosity science team, told me.
“I imagine most organics wouldn’t have [survived], so the implication is that there could have been much more,” Lemmon told me. | 0.874519 | 3.715515 |
NASA will be making history again, soon.
Sometime this spring, if all goes as planned, a SpaceX Falcon 9 rocket will carry the Transiting Exoplanet Survey Satellite (TESS) into space. Once in “high-Earth” orbit, the satellite’s instruments will scan the entire sky, hoping to find small planets outside our solar system. The main targets are potentially habitable worlds that are relatively nearby, within a few hundred light-years.
But the mission’s scientific objectives aren’t the only historic part: TESS also stands out because of the orbital path it will follow around Earth, blazing a course through space that no craft has ever flown. Thanks to the orbit’s elongated elliptical shape, says TESS principal investigator George Ricker of MIT, “we can stay away from Earth during observations and get close to Earth to transmit our data, once every 13 or so days.”
These and other orbital attributes will get TESS exactly where it needs to be — with relatively little expenditure of energy and money. That has caught the attention of scientists planning future space missions. It’s a unique orbit that, if not groundbreaking, is certainly “spacebreaking.” | 0.809424 | 3.25463 |
There’s something odd about our galactic neighbourhood, which Sidney van den Bergh at the Herzberg Institute of Astrophysics in Canada highlights today in a short paper.
Astronomers have long known that the Milky Way’s two closest neighbours are the Large and Small Magellanic Clouds, giant clouds of stars, gas and dust called irregular galaxies.
This is strange for two reasons. These galaxies are much younger than ours and may have even formed together. It looks as if they may just be passing by, on their way to somewhere else. Most other galaxies like ours, such as Andromeda, don’t have a single companion like this, so having two seems rather fortunate.
But there’s something else as well. The Large Magellanic cloud is unusually luminous. In fact, there are only two other irregular galaxies in the entire local universe that come close. “In other words the Large Magellanic Cloud seems to be close to the upper luminosity limit for irregular galaxies,” says van den Bergh. That’s unusual too.
In recent years, astronomers have begun to work out just how rare this is. Sky surveys such as the Sloan Digital Sky Survey allow astronomers to work out the distribution of various types of galaxy. They’ve looked at 22581 galaxies like the Milky Way and found that 81% have no satellite galaxies as bright as the Magellanic Clouds, 11% have one such satellite, and only 3.5% host two such satellite galaxies.
That makes the Milky Way very unusual. As van den Bergh puts it: “That the Galaxy should have an irregular companion as luminous as the Large Magellanic Cloud is almost a miracle.”
One of the central tenets of cosmology is the Copernican principle: that we live on an ordinary planet, in an average galaxy, in a mediocre part of the Universe.
But it’s beginning to look as if the Milky Way, or at least its neighbourhood, doesn’t follow that rule at all. So the question for astronomers and cosmologists is why this has come about and what its significance should be. An interesting conundrum.
Ref: arxiv.org/abs/1012.3492: A Strange Mènage Á Trois | 0.836898 | 3.797705 |
Bursting with Starbirth [heic 1716]
28 September 2017This oddly-shaped galactic spectacle is bursting with brand new stars. The pink fireworks in this image taken with the NASA/ESA Hubble Space Telescope are regions of intense star formation, triggered by a cosmic-scale collision. The huge galaxy in this image, NGC 4490, has a smaller galaxy in its gravitational grip and is feeling the strain.
|Result of a galactic crash. This NASA/ESA Hubble Space Telescope image shows the galaxy NGC 4490. The scattered and warped appearance of the galaxy are the result of a past cosmic collision with another galaxy, NGC 4485 (not visible in this image). Credit: ESA/Hubble & NASA, CC BY 4.0|
Compared to the other fundamental forces in the Universe, gravity is fairly weak. Despite this, gravity has an influence over huge distances and is the driving force behind the motions of the most massive objects in the cosmos. The scattered and warped appearance of the galaxy in this image, NGC 4490, is a prime example of the results of gravity's unrelenting tug.
Over millions of years, the mutual gravitational attraction between NGC 4490 and its smaller neighbour, NGC 4485, has dragged the two galaxies closer. Eventually, they collided in a swirling crush of stars, gas, and dust. In this image, this most intense period is already over and the two galaxies have moved through each other, untangled themselves, and are speeding apart again. But gravity's pull is relentless; the galaxies are likely to collide again within a few billion years.
Together NGC 4490 and NGC 4485 form the system Arp 269, which is featured in the Atlas of Peculiar Galaxies. They are located 24 million light-years from Earth in the constellation of Canes Venatici (The Hunting Dogs). The extreme tidal forces of their interaction have determined the shapes and properties of the two galaxies. Once a barred spiral galaxy, similar to the Milky Way, NGC 4490's outlying regions have been stretched out, resulting in its nickname of the Cocoon Galaxy. Virtually no trace of its past spiral structure can be seen from our perspective, although its companion galaxy NGC 4485 — not pictured here — still clings on to its spiral arms.
This cosmic collision has created rippling patches of higher density gas and dust within both galaxies. The conditions there are ripe for star formation; the brilliant pink pockets of light seen here are dense clouds of ionised hydrogen, glowing as they are irradiated with ultraviolet light from nearby young, hot stars. This spectacular burst of new activity has led to NGC 4490's classification as a starburst galaxy.
Star formation is also evident in the thin thread that connects the two galaxies: a bridge of stars created by the ancient crash, stretching over the 24 000 light-years that currently separate the fated pair. But where there is life, there is also death. Several supernovae have also been spotted in NGC 4490 over the past few decades, including SN 1982F and SN 2008ax.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
ESA/Hubble, Public Information Officer
Garching bei München, Germany | 0.880962 | 3.941032 |
Despite using satellites and supercomputers, meteorologists are still baffled by the monsoon, unable to say precisely when it will occur and how good -- or bad -- it will be
IT BEGINS in the spring, when the sun's rays start to warm the Indian subcontinent. And by June 23, the summer solstice, as the longest day is known, earnest Doordarshan newsreaders recite the familiar litany: "Light or isolated heavy showers are likely in some places, in the next 24 hours. Heavy showers accompanied by thunder and lightning are also likely on the west coast. A monsoon depression moving over the Bay of Bengal may bring heavy rain to parts of north eastern India."
The monsoon, which brings to India the rain that is the lifeblood of Indian farming, first came to the subcontinent between 60 million and 80 million years ago. Since then, the only predictability about the monsoon is the unpredictability of its exact arrival date. In the 17th century, British astronomer Edmund Halley, who discovered the comet that swings past the earth every 76 years, postulated that the monsoons are sea and land breezes on a planetary scale. Indian researchers from a variety of disciplines and using models of extreme complexity, have been the studying the phenomenon to obtain answers to such crucial questions as when it will actually hit Indian shores and with how much rain it will bless the farmer.
Says P R Pisharoty, the grand old man of the Indian monsoon who was formerly with the Physical Research Laboratory in Ahmedabad, "Willy-nilly, the monsoon will come each year, but what confounds and occupies scientists is: once the monsoon comes, how variable and unreliable the rainfall will be and, more importantly, what makes it so."
What researchers have been able to determine is that the monsoon is an extremely complex occurrence that is fully integrated with the global circulation system. Interactions between the winds and the ocean may bring either torrential rain or severe drought to the subcontinent. The researchers' problem is that complex details as fast-moving jet streams at various heights in the atmosphere, low-pressure systems, high temperatures, the Asian snow cover and the towering Himalaya determine what the monsoon will bring in its wake. No wonder meteorologist J Joseph shrugs helplessly and says, "The monsoon is like the human brain. We know of it, but we don't know it."
Nevertheless, meteorologists and scientists have gained considerable understanding of the mechanics of the monsoon. But they are aware that much more needs to be learned from their observational and theoretical research. R N Keshavamurthy, director of the Indian Institute of Meteorology in Pune, notes, "Efforts to understand the monsoon are essential if one is to be able to predict it with any certainty." How important it is to predict accurately can be gauged by the fact that the summer monsoon from the southwest gives India about 70 per cent of its annual rain.
How does the monsoon occur? As the sun is observed to move northward from over the Tropic of Capricorn towards the Tropic of Cancer, the large Asian land mass and especially the elevated Tibetan plateau is heated by the sun's increasingly direct rays. On the summer solstice, they fall directly on the Tropic of Cancer, which traverses Kuchch and Central India. Because water conducts heat more efficiently, the Asian land mass heats up much more than the surrounding sea, resulting in the creation of a giant surface low-pressure area or heat low, extending from the Sahara to Central Asia through Arabia and the arid zones of Pakistan, Rajasthan and Central India.
This trough alters the general air circulation in the region. Trade winds usually blow from subtropical high-pressure regions that extend across the globe in the mid-latitudes to low-pressure regions at the equator. They are then deflected by what scientists call the Coriolis force, generated by the earth's rotation, so they flow southeastward in the southern hemisphere and northeastward in the northern hemisphere, towards the equator. The trade winds converge at the inter tropical convergence zone (ITCZ), a low-pressure region at the equator with ascending air and maximum cloudiness. In the east-west orientation, the cloud band may extend upto 3,000 km and 300-500 km in the north-south orientation. Air rising from the ITCZ finally subsides over the 30o North latitude, thereby completing the circulation called the Hadley cell.
Explains monsoon researcher Sulochana Gadgil of the Centre for Atmospheric Sciences at the Indian Institute of Science in Bangalore, "Unravelling the factors that determine the location, extent and intensity of the ITCZ in a specific season is perhaps the most challenging problem in the understanding of monsoon meteorology on a planetary scale."
When low pressures build up over the Indian subcontinent, the ITCZ shifts to the north of the equator, merges with the heat low and develops into the monsoon trough -- a low-pressure belt that extends across the country. However, Gadgil notes, "The surface trough is associated with a tropical convergence zone only over some regions."
Nonetheless, the heated Indian subcontinental land mass, acting somewhat like a large heat engine, draws cool sea winds and changes the prevailing wind pattern into a sort of reverse Hadley cell. The result is that the southeast trade winds from the southern hemisphere, drawn by this low pressure belt over India, cross the equator, get deflected to the right and blow over India as the southwest monsoon.
As might be expected, not all scientists agree with this explanation of how the monsoon occurs. Some of them insist that the monsoon trough and the ITCZ are separate.
Just about the time the monsoon is about to lash the Kerala coast with a sudden burst of torrential rain, changes become apparent in the different layers of the atmosphere. This has led some scientists to suggest that the monsoon's onset is related to a sudden acceleration of air from the southern hemisphere toward India. They say a broad belt of high pressure develops around the Mascarene Islands near Mauritius in the Indian Ocean and this generates the cross-equatorial flow known as the Somali jet, which brings heavy rain to India's west coast. Says G S Mandal, a scientist with IMD, "A strong, low-level jet usually means a strong monsoon over peninsular India."
But before the first monsoon showers arrive, other atmospheric actors get into position to play their roles. Scientists now know that towards the end of May, on the eve of the onset of the monsoon, a narrow stream of air in the upper atmosphere, which normally moves from the west to the east at a height of about 9 km over northern India, suddenly weakens and moves to the north of the Himalaya. As this stream -- called the subtropical westerly jet -- moves north, an easterly flow of air -- the easterly jet -- concentrates at a height of 14-16 km, producing a divergence of air in the upper-levels of the atmosphere that is necessary to maintain monsoon circulation. However, if this easterly jet's high speed is maintained for two or three days, scientists now know that a so-called break-monsoon -- a condition during the monsoon season when a dry spell develops in northern India -- is likely to develop.
When all these processes combine, the hot, dry air above the sun-heated Indian subcontinent is replaced entirely with cool, moist, ocean air upto an altitude of 3-5 km. It is in this air-replaced zone that the spectacular display of lightning that is a characteristic of tropical storms takes place.
The monsoon trough that develops almost parallel to the Himalaya is a capricious low-pressure region whose continued existence requires a number of processes. Scientists say that when the monsoon clouds release their moisture, a great deal of latent heat is released as vapour turns to water and this heats up the air, which maintains high temperatures and low pressures in the monsoon region. The continual migration of low-pressure depressions from above the Bay of Bengal also feeds the monsoon trough, bringing rain to northwestern and central India.
Scientists are well-aware of the whimsical behaviour of the monsoon and especially that its variability occurs on several time-scales. Variations on a five- to seven-day scale, they say, are due to disturbances such as lows, depressions, storms and cyclones. Mandal, for example, notes that the amount of rainfall depends on the frequency, intensity, life-cycle and propagation characteristics of these disturbances. Scientists now know that monsoon vagaries on a 10- to 15-day time-scale are related to the behaviour of the monsoon trough. When positioned normally over the Gangetic plains, it controls moisture convergence and rainfall and areas within upto 500 km on either side of the trough get moderate, but well-distributed, rain. However, the trough is not stationary and scientists explain that it sometimes moves northward and closer to the Himalayan foothills and this can interrupt rainfall in the northern plains.
Despite all the uncertainty from confusing signals that leaves one guessing about when it will rain, scientists are gradually seeing the emergence of patterns in the monsoon's seemingly erratic behaviour. For instance, they have discovered that 30-50 day oscillations occur not only in the amount of rain that falls but also in the associated pressure and temperature conditions. Keshavamurty says the monsoon takes about 30 to 50 days to journey across the ocean and country. As a result, a band of maximum cloudiness that develops over the equator and then moves northward bringing rain to India, is replaced by another that also develops over the equator. This initiates a 30-50 day cycle of active monsoon phases, though some scientists say that latest research shows that the length of the cycle can vary from one year to the next.
Meanwhile, meteorological phenomena occurring on the other side of the globe also influence the monsoon. Explains Pisharoty, "The monsoon is a truly global phenomenon as it is part of the earth's general circulation. As apparently unrelated phenomena on the other side of the globe can have an impact on our monsoon, understanding the processes that drive the monsoon is all the more complicated."
Ever since former science and technology secretary Vasant Gowariker made his 16-parameter, long-range, monsoon-forecasting model public in 1988, the mere mention of El Nino is enough to start headaches in planning bodies. El Nino is the name given to an inexplicable warming of the waters of the equatorial Pacific, off the coasts of Peru and Ecuador, every 2-7 years.
Scientists rate El Nino as the leading factor in disturbing climate patterns and say it is closely linked to the performance of the Indian monsoon. The atmospheric pressure caused by El Nino causes changes in patterns, including an alteration in the direction of the prevailing trade winds, and this affects the monsoon. U C Mohanty, joint director of the Centre for Medium Range Weather Forecasting (CMRWF) in New Delhi, notes deficient monsoons are common during the El Nino phenomenon. "Recent research shows," he says, "no flood monsoon year has been observed during an EL Nino episode."
The link between the Indian monsoon and atmospheric changes in the southern Pacific has been known since it was postulated by IMD's first director-general, Gilbert Walker. Since then, scientists have been searching for teleconnections between the Indian monsoon and other global physical phenomena. And some of their recent findings are that the Eurasian snow cover, how hot the Tibetan plateau is and the speed of various jet streams at different atmospheric heights may seem unconnected, but they all appear to affect the monsoon.
Because of the complex and global factors involved, predicting the weather accurately necessitates providing meteorologists with a complete breakdown of atmospheric factors practically around the globe. Even then, this immensely complicated task can be made more difficult because the factors involved are highly dynamic and they can and do change rapidly.
This explains why in early July, a Delhi newspaper front-paged a weather bureau assurance that there was no possibility whatsoever for the next two or three days, only to have the skies open wide that afternoon and leave some low-lying areas in the Capital under three metres of water.
Meteorologists even now base their weather forecasts on recognising weather patterns and identifying what such patterns produced in the past. Intricate, three-dimensional charts are plotted of atmospheric conditions over the area concerned, low- and high-pressure areas and their movement are identified and all these factors become the basis for forecasting the weather in that area over the next 24-48 hours.
But these methods, called synoptic because they summarise and analyse such data as winds, eddies, temperature and moisture, can provide predictions that are valid for only a few hours or at the most, a day or two. In fact, all too often, by the time a reasonable pattern is deciphered, the conditions would have changed.
However, scientists have achieved some success in using teleconnections between global phenomena to predict the monsoon season as a whole and they are now able to say with some accuracy whether the entire monsoon rainfall in India is likely to be normal, deficient or excessive. These predictions are based on relatively simple statistical models, such as the one evolved by Gowariker and his colleagues.
But some experts contend their success is based more on chance and not on a sound theoretical understanding of the correlations between monsoon rainfall and global monsoon indicators such as El Nino. They insist that the Gowariker model only provides an overall picture of the season's total rainfall over the whole country, which, of course, is useful to policy-planners. However, for forecasting to be useful to ordinary farmers, who are among the most dependent on monsoon rain for their livelihood, most experts agree that the forecast must concern smaller, specific areas and be valid for three to 10 days. Only then will farmers be able to plan their agricultural activities with any certainty.
The government's recognition of the crucial need to improve the capacity to predict weather correctly is expressed in the setting up of the CMRWF. It is this range of forecasting the represents the real challenge to Indian meteorologists, for it is a Herculean task that can involve working out billions of calculations for a valid prediction. Obviously, such complex computations require impressive computer facilities and these have been installed at the forecasting centre.
Despite all this, most scientists agree that much about monsoon is still shrouded in mystery. Says B N Goswami at the Indian Institute of Science, "It is a pity that Indian meteorology has not progressed the way it should have." Indian scientists, he elaborates, have been exceptionally inward-looking and obsessed with analysing regional data and only in the past two decades have they started looking at the monsoon's global aspects.
However, their emphasis is slowly shifting and in the past 10 years, there has been considerable improvement in numerical weather prediction models. Taking their cue from the West, where the first mathematical models were developed, and using equations to represent atmospheric and oceanic circulations, Indian scientists have been working on monsoon models based on both regional and general circulation.
CMRWF scientists have been working since 1990 with general circulation models that are refined versions of a model obtained from the US national meteorological centre. Comments Keshavamurty, "There has been a virtual revolution in the science of meteorology, with vastly improved tools such as satellites and supercomputers."
But these modelers complain global circulation models fail to simulate monsoon conditions because the models appear to work for only parts of the tropics and the mid-latitudes. In the monsoon region, however, the models are unable to simulate the effect of local phenomena because these are highly variable and preclude averaging for a longer time frame, which is essential for long-range forecasting.
At present, says Goswami, the models adequately simulate rainfall over the northern Bay of Bengal and over the Western Ghats, but not for the whole of the Indian land mass. Another problem is that monsoon models are extremely sensitive to the initial inputs. Explains Keshavamurty, "Data received, especially from ships, often could be as much as 20-30 per cent off the mark. When fed into a model, this will create completely absurd simulations."
And, Goswami adds, "It was assumed that initial conditions should not make a great difference to the model's behaviour. But we find that if February 1 conditions instead of February 2 conditions are used, they just don't work in some models."
Data initialisation and parameterisation -- making data obtained at widely separated observation points or grid points relevant to the particular region at a particular time -- are two major thrust areas of research. Though the physics of the various processes on a small scale, such as cyclones, lows and clouds is known to some extent, scientists say it is difficult to parameterise these for areas within grid points. Hence, Indian scientists stress it is imperative to develop their own modelling methods.
It is to address these problems and others linked to monsoon modelling that the Monsoon Numerical Experiment Group was set up in 1989. The group consists of numerical modelers engaged in research in several parts of the world and they collaborate in seeking to fine-tune available models simulating the southwest monsoon in India.
But scientists stress that computers and mathematical models apart, valid forecasts require a thorough understanding of the physics of the monsoon. Says Mohanty, "Once the basic physics of the several mechanisms that govern the monsoon are worked out, we will be able to predict the weather on a three- to 10-day time-scale."
But the physics of the tropics, warns Pisharoty, poses special problems. Using a medical metaphor, he explains, "Our fever is different and we have to find our own medicine. We cannot borrow models developed in other parts of the world and use them to predict our monsoon." Giving an example, he pointed out the equations governing the transfer of water vapour to the atmosphere have to be developed through experimentation here, because temperatures in the tropics are higher and so evaporation equations for the Indian region are bound to be different.
And Mohanty adds, "In the mid-latitudes, the dynamics of the system drive the weather in the medium range. Forecasters can tell which way a front is likely to move. But in India, small-scale physical processes that are highly variable in time and space, drive the system and make conditions more complex."
Most scientists agree theory alone cannot lead to better models and what is essential are accurate data available on a smaller scale and experiments to test the models. Keshavamurty explains, "We can continue to sit in the lab and develop complicated mathematical models to represent the phenomena, as a number of atmospheric scientists are now wont to do, but these will have little meaning if the physics that govern monsoon phenomena is only partially understood."
Author C S Ramage echoes this opinion in his seminal book Monsoon Meteorology and makes this scathing comment: "Conceivably, Nairobi and Pune meteorologists exchanging visits make better sense than spending time at great computing centres where they may learn to perform minor cosmetic surgery on the latest nine-level primitive general circulation model."
Presently, weather-related data is collected at more than 12,000 stations across the globe, most of them on land. To predict Indian weather with reasonable accuracy, data has also to be collected specifically from and above the seas that surround the much of the country. Attempts to collect such data were first made in the late 1970s through MONEX, as the international summer monsoon experiment came to be called. A more recent attempt is an experiment to collect land data, launched in 1988 by the department of science and technology (DST) and called the Monsoon Trough Boundary Layer Experiment, or MONTBLEX.
The DST experiment sought to investigate the effects of the boundary layer -- the region of the atmosphere where the thermodynamic and dynamical effects of the earth are felt -- on the maintenance of the monsoon trough. Using sophisticated technology -- like meteorological balloons and sodars -- developed indigenously, field data was generated during the 1990 monsoon season. Observations of winds, temperature and humidity were made at various levels of the atmosphere, at Jodhpur, Delhi, Varanasi and Kharagpur. Soil temperatures also were measured. The data generated has not been fully analysed, but scientists are optimistic that it will lead to a clear understanding of the behaviour of the monsoon trough.
DST scientist Malathi Goel says the MONTBLEX data will enable scientists to set parameters for the processes of the boundary layer. And Keshavamurty notes that setting parameters, which involves making data collected at widely spaced grid points relevant to the micro-level physical processes within a grid square, is an extremely important area of research. Much of the effort in future will be made in this area to make monsoon models more relevant.
With such detailed and widespread attempts being made by experts in India to gain full understanding of the monsoon phenomenon, scientists confidently predict that before long they will be able to provide both farmer and policy-makers well in advance an accurate picture of the rain clouds in Indian skies.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition. | 0.86543 | 3.381886 |
Astronomers scanning the skies with powerful telescopes have found two record-setting stars. One is the most distant star ever observed. The other ranks as one of the tiniest. That second is so small that it can barely burn.
The light from the farthest star traveled across two-thirds of the universe. That puts the star a whopping 9 billion light-years away. That blows away the previous record holder. The previous farthest star observed directly was a mere 55 million light-years away.
Patrick Kelly is an astronomer at the University of California, Berkeley. He and his colleagues found the star in images from the Hubble Space Telescope. They were scanning images of a galaxy cluster known as MACS J1149. In April and May 2016, Kelly and his team saw a mysterious dimming and brightening in one point of light. It was in the galaxy cluster’s vicinity.
The team looked at follow-up images and made analyses, which they posted June 30 at arXiv.org. Those analyses showed that the light is probably from a single bright blue star. That star is behind the galaxy cluster and aligned along Hubble’s line of sight.
The star was visible only because of a phenomenon called gravitational lensing. The gravity of an object like the galaxy cluster is so huge that it bends the spacetime around it. That makes it act like a cosmic magnifying glass. Astronomers can use these objects to observe things like stars that are more distant than telescopes can see on their own.
The team calculated how much the star’s light was stretched by its journey. That was a clue to its extreme distance. Since the universe is 13.8 billion years old, that means this star’s light has crossed 65 percent of the universe to reach us.
Scientists have also just turned up one of the smallest stars ever seen. Its discoverers all worked on a project known as the Wide Angle Search for Planets, or WASP. These astronomers use ground-based telescopes in Spain and South Africa to monitor the skies. The newfound one is quite small. Its radius is only about the size of Saturn’s.
The mini star has a very long name: EBLM J0555-57Ab. Its about the size of a previously reported runt, which also has a big name (2MASS J0523-1403).Both are much smaller than the Jupiter-sized TRAPPIST-1. That peewee star recently gained renown for hosting seven Earth-sized planets.
Although the newfound mini star’s girth is similar to a planet’s, it is much heftier. It has almost 300 times Saturn’s mass. Still, that’s only about 8 percent of the sun’s mass. That means that the object barely meets the qualifications for being a star, scientists reported July 12 in Astronomy & Astrophysics. By that they mean that the star just meets the limit at which nuclear fusion can occur in a star’s core. (Nuclear fusion is the process that fuels a star.) If the star were less massive, it would instead be a failed star known as a brown dwarf.
The miniature star orbits another, larger one. WASP scientists detected the star with a method typically used to scout for exoplanets. They watched it pass in front of its companion and dim the larger star’s light. | 0.877259 | 3.75533 |
Over the past several decades, astronomers have come to realise that the sky is filled with magnifying glasses that allow the study of very distant and faint objects barely visible with even the largest telescopes.
A University of California, Berkeley, astronomer has now found that one of these lenses — a massive galaxy within a cluster of galaxies that are gravitationally bending and magnifying light — has created four separate images of a distant supernova.
The so-called “Einstein cross” will allow a unique study of a distant supernova and the distribution of dark matter in the lensing galaxy and cluster.
“Basically, we get to see the supernova four times and measure the time delays between its arrival in the different images, hopefully learning something about the supernova and the kind of star it exploded from, as well as about the gravitational lenses,” said UC Berkeley postdoctoral scholar Patrick Kelly, who discovered the supernova while looking through infrared images taken November 10th, 2014, by the Hubble Space Telescope (HST). “That will be neat.”
Kelly is a member of the Grism Lens-Amplified Survey from Space (GLASS) team led by Tommaso Treu at UCLA, which has worked in collaboration with the FrontierSN team organised by Steve Rodney at Johns Hopkins University to search for distant supernovae.
“It’s a wonderful discovery,” said Alex Filippenko, a UC Berkeley professor of astronomy and a member of Kelly’s team. “We’ve been searching for a strongly lensed supernova for 50 years, and now we’ve found one. Besides being really cool, it should provide a lot of astrophysically important information.”
One bonus is that, given the peculiar nature of gravitational lensing, astronomers can tune in for a supernova replay within the next five years. This is because light can take various paths around and through a gravitational lens, arriving at Earth at different times. Computer modelling of this lensing cluster shows that the researchers missed opportunities to see the exploding star 50 years ago and again 10 years ago, but images of the explosion will likely repeat again in a few years.
“The longer the path length, or the stronger the gravitational field through which the light moves, the greater the time delay,” noted Filippenko.
Kelly is first author of a paper reporting the supernova appearing this week in a special March 6th issue of Science magazine to mark the centenary of Albert Einstein’s general theory of relativity.
Kelly, Filippenko and their collaborators have dubbed the distant supernova SN Refsdal in honour of Sjur Refsdal, the late Norwegian astrophysicist and pioneer of gravitational lensing studies. It is located about 9.3 billion light-years away (redshift = 1.5), near the edge of the observable universe, while the lensing galaxy is about 5 billion light-years (redshift = 0.5) from Earth.
Einstein’s general theory of relativity predicts that dense concentrations of mass in the universe will bend light like a lens, magnifying objects behind the mass when seen from Earth. The first gravitational lens was discovered in 1979. Today, lensing provides a new window into the extremely faint universe shortly after its birth 13.8 billion years ago.
“These gravitational lenses are like a natural magnifying glass. It’s like having a much bigger telescope,” Kelly said. “We can get magnifications of up to 100 times by looking through these galaxy clusters.”
When light from a background object passes by a mass, such as an individual galaxy or a cluster of galaxies, the light is bent. When the path of the light is far from the mass, or if the mass is not especially large, “weak lensing” will occur, barely distorting the background object. When the background object is almost exactly behind the mass, however, “strong lensing” can smear extended objects (like galaxies) into an “Einstein ring” surrounding the lensing galaxy or cluster of galaxies. Strong lensing of small, point-like objects, on the other hand, often produces multiple images — an Einstein cross — arrayed around the lens.
“We have seen many distant quasars appear as Einstein crosses, but this is the first time a supernova has been observed in this way,” Filippenko said. “This short-lived object was discovered only because Pat Kelly very carefully examined the HST data and noticed a peculiar pattern. Luck comes to those who are prepared to receive it.”
The galaxy that is splitting the light from the supernova into an Einstein cross is part of a large cluster, called MACS J1149.6+2223, that has been known for more than 10 years.
In 2009, astronomers reported that the cluster created the largest known image of a spiral galaxy ever seen through a gravitational lens. The new supernova is located in one of that galaxy’s spiral arms, which also appears in multiple images around the foreground lensing cluster. The supernova, however, is split into four images by a red elliptical galaxy within the cluster.
“We get strong lensing by a red galaxy, but that galaxy is part of a cluster of galaxies, which is magnifying it more. So we have a double lensing system,” Kelly said.
Looking for Transients
After Kelly discovered the lensed supernova November 10th while looking for interesting and very distant supernova explosions, he and the team examined earlier HST images and saw it as early as November 3rd, though it was very faint. So far, the HST has taken several dozen images of it using the Wide Field Camera 3 Infrared camera as part of the Grism survey. Astronomers using the HST plan to get even more images and spectra as the telescope focuses for the next six months on that area of sky.
“By luck, we have been able to follow it very closely in all four images, getting data every two to three days,” he said.
Kelly hopes that measuring the time delays between the phases of the supernova in the four images will enable constraints on the foreground mass distribution and on the expansion and geometry of the universe. If the spectrum identifies it as a Type Ia supernova, which is known to have a relatively standard brightness, it may be possible to put even stronger limits on both the matter distribution and cosmological parameters. | 0.856046 | 3.955601 |
Crescent ♎ Libra
Moon phase on 21 September 2055 Tuesday is New Moon, less than 1 day young Moon is in Libra.Share this page: twitter facebook linkedin
Moon rises at sunrise and sets at sunset. It's part facing the Earth is completely in shadow.
Moon is passing first ∠4° of ♎ Libra tropical zodiac sector.
Lunar disc is not visible from Earth. Moon and Sun apparent angular diameters are ∠1972" and ∠1911".
Next Full Moon is the Hunter Moon of October 2055 after 14 days on 5 October 2055 at 18:38.
There is high New Moon ocean tide on this date. Combined Sun and Moon gravitational tidal force working on Earth is strong, because of the Sun-Moon-Earth syzygy alignment.
At 02:19 on this date the Moon completes the old and enters a new synodic month with lunation 689 of Meeus index or 1642 from Brown series.
29 days, 8 hours and 30 minutes is the length of new lunation 689. It is 1 hour and 15 minutes shorter than next lunation 690 length.
Length of current synodic month is 4 hours and 14 minutes shorter than the mean length of synodic month, but it is still 1 hour and 55 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠352.8°. At beginning of next synodic month true anomaly will be ∠7.9°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
Moon is reaching point of perigee on this date at 12:32, this is 12 days after last apogee on 8 September 2055 at 13:59 in ♈ Aries. Lunar orbit is starting to get wider, while the Moon is moving outward the Earth for 14 days ahead, until it will get to the point of next apogee on 5 October 2055 at 17:59 in ♈ Aries.
This perigee Moon is 357 315 km (222 025 mi) away from Earth. It is 5 193 km closer than the mean perigee distance, but it is still 13 041 km farther than the closest perigee of 21st century.
3 days after its ascending node on 17 September 2055 at 19:18 in ♌ Leo, the Moon is following the northern part of its orbit for the next 8 days, until it will cross the ecliptic from North to South in descending node on 30 September 2055 at 10:30 in ♒ Aquarius.
3 days after beginning of current draconic month in ♌ Leo, the Moon is moving from the beginning to the first part of it.
5 days after previous North standstill on 15 September 2055 at 17:00 in ♋ Cancer, when Moon has reached northern declination of ∠20.530°. Next 6 days the lunar orbit moves southward to face South declination of ∠-20.612° in the next southern standstill on 28 September 2055 at 05:09 in ♑ Capricorn.
The Moon is in New Moon geocentric conjunction with the Sun on this date and this alignment forms Sun-Moon-Earth syzygy. | 0.837327 | 3.140418 |
Crescent ♍ Virgo
Moon phase on 3 July 2060 Saturday is Waxing Crescent, 5 days young Moon is in Virgo.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 5 days on 28 June 2060 at 02:58.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing about ∠18° of ♍ Virgo tropical zodiac sector.
Lunar disc appears visually 5.3% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1789" and ∠1887".
Next Full Moon is the Buck Moon of July 2060 after 10 days on 13 July 2060 at 15:08.
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 5 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 748 of Meeus index or 1701 from Brown series.
Length of current 748 lunation is 29 days, 9 hours and 52 minutes. It is 2 hours and 15 minutes shorter than next lunation 749 length.
Length of current synodic month is 2 hours and 52 minutes shorter than the mean length of synodic month, but it is still 3 hours and 17 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠54.1°. At beginning of next synodic month true anomaly will be ∠84.5°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
8 days after point of perigee on 24 June 2060 at 12:41 in ♉ Taurus. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 3 days, until it get to the point of next apogee on 6 July 2060 at 13:25 in ♎ Libra.
Moon is 400 596 km (248 919 mi) away from Earth on this date. Moon moves farther next 3 days until apogee, when Earth-Moon distance will reach 404 112 km (251 104 mi).
9 days after its ascending node on 23 June 2060 at 21:23 in ♈ Aries, the Moon is following the northern part of its orbit for the next 4 days, until it will cross the ecliptic from North to South in descending node on 7 July 2060 at 12:29 in ♏ Scorpio.
9 days after beginning of current draconic month in ♈ Aries, the Moon is moving from the beginning to the first part of it.
5 days after previous North standstill on 28 June 2060 at 00:46 in ♋ Cancer, when Moon has reached northern declination of ∠27.624°. Next 8 days the lunar orbit moves southward to face South declination of ∠-27.639° in the next southern standstill on 12 July 2060 at 09:29 in ♑ Capricorn.
After 10 days on 13 July 2060 at 15:08 in ♑ Capricorn, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.225865 |
When we look up at Mars in the night sky we see a red planet – largely due to its rusty surface. But what’s on the inside?
Launching in May, the next NASA space mission will study the interior of Mars.
The InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) spacecraft will be a stationary lander mission that measures seismic activity on Mars (often referred to as marsquakes) as well as interior heat flow.
By listening to and probing the Martian crust and interior, the project aims to understand the formation and evolution of Mars.
The InSight mission is scheduled to launch from California in early May, with landing on Mars planned for November. The expected lifetime of the mission is at least two years.
Origins of marsquakes
The payload on board InSight includes the seismic instrument SEIS (Seismic Experiment for Interior Structure). Its task is to record seismic activity, or vibrations, of the planet.
Apart from shaking the ground while passing, seismic waves can be extremely useful in telling us about the structure of planetary interiors. Seismic waves travel at different speeds when passing through different materials. Processing their arrival time and strength via recorded seismographs is a clever way to learn about the interior structure of a planetary body – such as the crust, the next layer down (the mantle), and the core.
Seismic activity on Mars could be caused by a number of processes. For example, shallow marsquakes could originate from meteoroid strikes, and deep marsquakes could come from martian tectonic activity (the movement of tectonic plates at the surface of the planet).
It is generally believed that tectonic processes could have shaped Mars in its early evolution, similar to the Earth. However, unlike the Earth in younger ages, Mars has become largely tectonically dormant.
We think lots of meteoroids hit Mars
Considering that tectonics on Mars may not be reminiscent of what we see on our planet, we suspect that meteoroid strikes will play a major role in causing marsquakes.
On Earth, frequent and small meteoroids most often burn up in the atmosphere and appear to us as a form of “shooting star”. When a rock from space moving at supersonic speed encounters the terrestrial atmosphere, the air in front of it gets compressed extremely quickly. Temperature rises and heat builds up, so the rock starts to shine bright under the process of its destruction.
However, on Mars we think that meteoroids may not necessarily burn up entirely upon encountering the martian atmosphere. This is simply because Mars has a less dense atmosphere than the Earth – so incoming meteoroids have a higher penetrating power. These impact events would produce seismic disturbance in the atmosphere, and also likely in the ground.
Detecting meteoroid strikes on planetary bodies began with the lunar Apollo program. Apollo missions carried seismometers to the Moon, and as a result we had a network of seismometers that operated on the Moon from 1969-77.
During its lifetime, the Apollo seismic network recorded shallow quakes produced by frequent meteoroid bombardment. Considering that the Moon does not have an atmosphere to protect its surface from the incoming meteoroids, the Apollo seismic network provided heaps of seismic data from the Moon. These impact-induced seismic moonquakes provided the first constraints about the thickness of the lunar crust as well as structure of crust and deep interior.
We’ve tried to measure Mars seismic activity before
During the lunar exploratory boom with the Apollo program, NASA also launched Vikings 1 and 2 to Mars in 1975. These became the first missions to land on Mars, and each Viking mission carried a seismometer.
While instruments on Viking have collected more data than expected, the seismometer on Viking Lander 1 did not work after landing. The seismometer on Viking Lander 2 demonstrated poor detection rates, with no quakes coming off the ground (as it had remained on the Lander).
To date, we have had no other seismic station on any extraterrestrial planetary body. This makes InSight the first-of-its-kind mission to be placed on Mars. While its design relies on proven technologies from past missions, it is ground-breaking in terms of expected science goals.
Instead of making orbital remote sensing surveys or roving on the surface similar to other rovers, InSight has a different goal to previous Martian missions.
Why are we so interested in the subsurface of Mars?
Mars and Earth differ in size, temperature, and atmospheric composition. But similar geological features such as craters, volcanoes, or canyons can be observed on both planets. This implies that the interior of Mars may be similar to Earth’s.
It is also quite likely that there was liquid water on the surface of ancient Mars, which was the time Mars could have been very similar to Earth. So Mars could answer questions about the ancient habitability of our solar system.
Unlike potentially habitable planets orbiting distant stars, Mars is reachable within our lifetime. Discovering martian crustal properties is of great importance when it comes to planning landing missions and investigating signs of extraterrestrial habitability.
My role in the InSight mission is to work with the science team in analysing the data (impact-induced seismograms and any respective orbital imagery) to work out what kind of impacts had occurred during the mission lifetime.
Image: InSight aims to figure out just how tectonically active Mars is, and how often meteorites impact it. | 0.864012 | 4.002316 |
The closest planet to the Sun, Mercury, is known for its speed. The second planet from the Sun, Venus, could very well be known as its exact opposite. It takes this burning hot planet 243 Earth days to rotate once around its axis. However, Venus' atmosphere acts independently, taking only four Earth days to complete the same trip.
For nearly 60 years, scientists have pondered over this atmospheric super-rotation phenomenon but a recent study may have just cracked the code in Venus' clouds.
"Since the super-rotation was discovered in the 1960s...the mechanism behind its forming and maintenance has been a long-standing mystery," Takeshi Horinouchi, a professor at Hokkaido University, Japan, and lead author of the study, said in a statement.
The study, published Thursday in the journal Science, suggests that the reason why the Venusian atmosphere rotates at a much higher speed than the planet lies with atmospheric tidal waves. These tidal waves form as a result of heating by the Sun on the planet's dayside in contrast with its cooler temperatures on the nightside.
But the planet, famously named after the Roman goddess of love and beauty, contains even more mysteries shrouded in its thick clouds. Venus' atmosphere travels at speeds of around 200 meters per second, that's 60 times faster than the rotation of the planetary body itself.
This super-rotation is rather unique to Venus, having only been observed in Saturn's largest moon, the equally bizarre world of Titan.
In order to help resolve this issue, the team behind the new study used images obtained by the Akatsuki spacecraft. The spacecraft, also known as the Venus Climate Orbiter, was launched in May, 2010 by the Japan Aerospace Exploration Agency (JAXA) to explore the Venusian atmosphere. The spacecraft began orbiting Venus in December, 2015.
The team of scientists tracked clouds and obtained wind velocities from images that were captured by ultraviolet and infrared cameras on the Akatsuki spacecraft.
After analyzing the data, the scientists noticed a thermal tide, or a sort of atmospheric wave that was triggered by heating from the Sun near the planet's equator. The average temperature on Venus is 462 degrees Celsius, but things get cooler in the upper atmosphere, ranging from -43 to -173 Celsius.
This atmospheric wave on Venus speeds up the atmosphere's rotation at low altitudes, causing it to go much faster than the planet itself.
Scientists have often looked to Venus as a prototype for what might happen to Earth in the longterm future. The two planets share the same size and composition, and Venus may have looked like Earth at one point during its younger years, but its atmospheric changes led to the dry planet we observe today.
Therefore, studying Venus not only gives scientists insight regarding planets in the Solar System, it also provides an interesting case study of atmospheric science.
Venus could also be useful in studying bizarre exoplanets outside the Solar System.
"Our study could help better understand atmospheric systems on tidally-locked exoplanets whose one side always facing the central stars, which is similar to Venus having a very long solar day," Horinouchi said.
Abstract: Venus has a thick atmosphere that rotates 60 times as fast as the surface, a phenomenon known as superrotation. We use data obtained from the orbiting Akatsuki spacecraft to investigate how the super-rotation is maintained in the cloud layer, where the rotation speed is highest. A thermally induced latitudinal-vertical circulation acts to homogenize the distribution of the angular momentum around the rotational axis. Maintaining the super-rotation requires this to be counteracted by atmospheric waves and turbulence. Among those effects, thermal tides transport the angular momentum, which maintains the rotation peak, near the cloud top at low latitudes. Other planetary-scale waves and large-scale turbulence act in the opposite direction. We suggest that hydrodynamic instabilities adjust the angular-momentum distribution at mid-latitudes. | 0.858712 | 3.903273 |
Super-TIGER prepares for launch from Antarctica.
NASA’s Super-TIGER science balloon landed Friday at a frigid and remote base in Antarctica after setting two duration records while gathering data about cosmic rays. There’s so much data that it will take scientists about two years to analyze, according to NASA.
Launched December 8, 2012 from the Long Duration Balloon site near McMurdo Station in Antarctica, the Super Trans-Iron Galactic Element Recorder balloon spent 55 days, 1 hour and 34 minutes aloft, shattering records previously set in 2009 by another NASA balloon for longest flight by a balloon of its size. The 39-million cubic foot balloon, spent most of its time cruising four times higher than commercial airlines at about 127,000 feet (almost 39 kilometers). The instrument is managed by Washington University in St. Louis, Missouri.
“Scientific balloons give scientists the ability to gather critical science data for a long duration at a very low relative cost,” said Vernon Jones, NASA’s Balloon Program scientist, in the press release. “Super-TIGER is scientific ballooning at its best.”
Super-TIGER measured rare heavy elements, such as iron, as they bombarded Earth from the Milky Way. The instrument detected about 50 million of these high-energy cosmic rays. Scientists hope the data from the mission will help understand where the energetic nuclei are produced and how they achieve such high energies.
NASA had three long-duration balloon missions in the summer skies of Antarctica. SuperTIGER was joined by BLAST and EBEX. All three balloons launched from the site near McMurdo Station in December. BLAST, or Balloon Borne Large Aperture Submillimeter Telescope launched Christmas Day and measured the polarized dust in star-forming regions helping astronomers determine if magnetic fields are a dominant force over turbulence in star-forming regions of the galaxy. BLAST’s mission lasted just over 16 days.
EBEX, the heaviest scientific payload borne aloft by a NASA balloon, measures cosmic microwave background radiation. The mission lasted 25 days and reached altitudes of 118,000 feet (or 36 kilometers).
Antarctica, it turns out, is ideal for these types of long-duration balloon missions with sparse populations and anticyclonic (east to west, counter-clockwise in the southern hemisphere) wind patterns in the stratosphere. | 0.882484 | 3.157231 |
Muons are elementary particles similar to the electron but with a mass over 200 times heavier. Muons are unstable and have an average lifetime of 2.2 µs, which is longer than many subatomic particles.
Muons are primarily produced in the uppermost part of Earth’s atmosphere when cosmic rays collide with molecules in the atmosphere. Each minute every square meter of the earth’s surface is hit by around 10,000 muons.
The Complete Muon Observatory is designed to allow you and your students to study these particles. You can detect cosmic rays and demonstrate the angular dependence with this muon observatory that can be configured for either Shower Mode or Telescope Mode.
The apparatus can be configured for either Shower Mode or Telescope Mode:
- In the Shower Mode setup, a shower is recorded as a concidence event from three GM tubes arranged in a triangle. This geometry ensures that no single particle can be detected in all three tubes. Production of showers may be enhanced by allowing the radiation to pass through something that is slightly “thicker” than air (multiple steel plates are used). In shower mode you will typically align the muon observatory vertically. Measurement periods are approximately one day long.
- In Telescope Mode three GM tubes are arranged in a line, and if a muon passes through all tubes in the setup, a pulse is outpus from the coincidence box. The angle of the telescope can be varied to detect the angular distribution of the muons. | 0.807091 | 3.200963 |
Astronomers now think there’s a 9th planet in the solar system almost certainly (hint: it’s not Pluto). The farthest planet from our Sun is probably a giant, smaller than Neptune but likely larger than the Earth. It is informally called Phattie, but commonly known as Planet Nine.
The new research published in The Astronomical Journal with an article titled Evidence For A Distant Giant Planet In The Solar System. The writers of the article are Caltech (California Institute of Technology) astronomers Konstantin Batygin and Michael E. Brown. Yes, the same Mike Brown who discovered Eris in 2005 (from images taken on October 21, 2003), the second-biggest dwarf planet (so far) after Pluto.
Table of Contents
Bye, Pluto – welcome 9th planet
But the discovery of Eris was the last impact: it led the International Astronomical Union (IAU) to define the term “planet” formally for the first time the following year. Notes 1 This definition excluded Pluto and reclassified it as a member of the new “dwarf planet” category (and specifically as a plutoid).
Interestingly, they have had started their research to demonstrate that there’s no ninth planet: it was first proposed in 2014, and it has been the job of Konstantin Batygin and Michael Brown, the scientists in the Division of Geological and Planetary Science at the Caltech, to essentially debunk it. But they reached the exact opposite. Batygin told Nature that “we have a gravitational signature of a giant planet in the outer Solar System”.
The researchers did not observe the planet directly, they merely put together a mathematical model that infers its existence. According to Batygin, they have enough gravitational signature of a giant planet in the outer solar system. The interesting thing is, scientists claim that some of the most powerful telescopes on Earth probably be capable of spotting it. It can be hiding in some of the photographs taken already by these telescopes and soon be discovered.
If this ninth planet exists, and probably it does, the researchers suspect it’s 10 times the mass of Earth (for comparison, Neptune has 17 times as much mass compared to the Earth) and 200 times farther from the sun. At that distance, it would take the planet between 10,000 to 20,000 Earth years to complete one trip around the sun. Pluto, for comparison, takes 248 years to complete its orbit.
At that distance, the possibility of life is near to none. On the surface (if there is a surface, of course), the Sun will be just a brighter star. The ninth planet is likely a desolate ice ball with a gassy outer layer, like Neptune.
Brown is confident that the ninth planet does exist. He tweeted that “OK, OK, I am now willing to admit: I DO believe that the solar system has nine planets”.
1. What makes an astronomical body a “planet”?
On August 24, 2006, with an IAU resolution that created an official definition for the term “planet”. According to this resolution, there are three main conditions for an object in the Solar System to be considered a planet:
- The object must be in orbit around the Sun.
- The object must be massive enough to be rounded by its own gravity. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
- It must have cleared the neighborhood around its orbit.
Pluto fails to meet the third condition because its mass is only 0.07 times that of the mass of the other objects in its orbit (Earth’s mass, by contrast, is 1.7 million times the remaining mass in its own orbit).
The IAU further decided that bodies that, like Pluto, meet criteria 1 and 2 but do not meet criterion 3 would be called dwarf planets. On September 13, 2006, the IAU included Pluto, and Eris and its moon Dysnomia, in their Minor Planet Catalogue, giving them the official minor planet designations “(134340) Pluto”, “(136199) Eris”, and “(136199) Eris I Dysnomia”. Had Pluto been included upon its discovery in 1930, it would have likely been designated 1164, following 1163 Saga, which was discovered a month earlier. | 0.868956 | 3.709453 |
Cosmic ‘web’ seen for first time (BBC)
By Simon RedfernReporter, BBC News
Details of the work appear in the journal Nature. The quasar illuminates a nearby gas cloud measuring two million light-years across.
“In this case we were lucky that the flashlight is pointing toward the nebula and making the gas glow”
Sebastiano CantalupoUniversity of California, Santa Cruz
And the glowing gas appears to trace out filaments of underlying dark matter. The quasar, which lies 10 billion light-years away, shines light in just the right direction to reveal the cold gas cloud. For some years, cosmologists have been running computer simulations of the structure of the universe to build the “standard model of cosmology”.
They use the cosmic microwave background, corresponding to observations of the very earliest Universe that can be seen, and recorded by instruments such as the Planck space observatory, as a starting point. Their calculations suggest that as the Universe grows and forms, matter becomes clustered in filaments and nodes under the force of gravity, like a giant cosmic web. The new results from the 10-metre Keck telescope in Hawaii, are reported by scientists from the University of California, Santa Cruz and the Max Planck Institute for Astronomy in Heidelberg.
The cosmic web suggested by the standard model is mainly made up of mysterious “dark matter”. Invisible in itself, dark matter still exerts gravitational forces on visible light and ordinary matter nearby.
Massive clumps of dark matter bend light that passes close by through a process called gravitational lensing, and this had allowed previous measurements of its distribution.
But it is difficult to use this method to see very distant dark matter, and cold ordinary matter remains tricky to detect as well.
The glowing hydrogen illuminated by the distant quasar in these new observations traces out an underlying filament of dark matter that it is attracted to it by gravity, according to the researchers’ analysis.
“This is a new way to detect filaments. It seems that they have a very bright quasar in a rare geometry,” Prof Alexandre Refregier of the ETH Zurich, who was not involved in the work, told BBC News.
“If indeed gravity is doing the work in an expanding Universe, we expect to see a cosmic web and it is important to detect this cosmic web structure.”
In the dark
He added: “What is expected is that the dark matter dominates the mass and forms these structures, and then the ordinary matter, the gas, the stars and everything else trace the filaments and structures that are defined by the dynamics of the dark matter.”
READ MORE ABOUT DARK MATTER HERE. | 0.880354 | 3.939775 |
The first two interstellar visitors to the solar system are finally shedding light on their places of origin.
Vaporization of primordial carbon monoxide made Comet 2I/Borisov active after millions of years in the cosmic deep freeze.
New ultraviolet and millimeter-wave observations show that vaporization of an abundance of primordial carbon monoxide is what made interstellar Comet 2I Borisov come alive in the inner solar system. Carbon monoxide freezes at around 25 kelvin, so this suggests Comet Borisov formed in the frosty outer fringes of its parent star's planetary disk. Separately, a new theoretical model shows how natural processes could have formed the first known interstellar visitor, 'Oumuamua.
Both objects arrived in our solar system with hyperbolic orbits, but their origins — aside from being interstellar — remained unclear. Comet Borisov is still observable, but 'Oumuamua is not, as it has now passed the orbit of Saturn on its way out of the solar system.
Where Did Comet 2I/Borisov Form?
This week's Nature Astronomy reports two studies of Comet Borisov soon after its perihelion last December, when it was bright enough for spectroscopy to reveal its composition.
Glitches with the Hubble Space Telescope forced a team led by Dennis Bodewits (Auburn University) to spread their observations of ultraviolet fluorescence from carbon monoxide (CO) over a month. Emissions from CO stayed nearly constant during that period, but emissions from water molecules dropped rapidly, initially puzzling the observers. Then they realized that outgassing had removed 1–6 meters of surface material during their observations, exposing deeper layers rich in CO. The CO levels in the coma, measured by Hubble's Cosmic Origins Spectrograph, were up to 50% higher than the water levels measured at the same time by NASA's Neil Gehrels Swift Observatory satellite.
Independent millimeter-wave observations of the comet made in mid-December by Martin Cordiner (NASA Goddard Space Flight Center) and colleagues with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile also revealed an abundance of CO. The measurements showed that the amount of CO compared to water was higher than had been observed in any solar system comets inside 2.5 astronomical units (a.u., the average distance between Earth and the Sun), the so-called water snow line where water ice starts to vaporize. (Astronomers had measured higher amounts of CO in C/2016 R2 (PanSTARRS) when it was at 2.8 a.u. But Cordiner calls this Oort Cloud comet "so alien that it might be a captured interstellar comet."
Being able to measure the composition of an interstellar comet "opens up an entirely new field of planetary science — the study of remote planetary systems through direct observations of their ejected interstellar comets," Cordiner says.
The high CO levels in Comet Borisov indicate that it likely formed beyond the CO snow line, in the outer part of a planetary disk, and remained at temperatures no more than 25K during its travels through interstellar space.
Ejection from a planetary system is easy. "There are a million ways of getting rid of comets," says Bodewits. He thinks the comet may have formed about a red M-type star, where the CO snow line is only at 6.6 a.u., compared to more than 100 a.u. in our solar system.
Identifying the vaporization of carbon monoxide as the cause of Comet Borisov’s activity and fragmentation is an important addition to our knowledge of comet processes and interstellar objects, says Bryce Bolin (Caltech), who was not involved in the Nature Astronomy studies.
Comet Borisov was easy to recognize as a comet, but our first interstellar visitor, 1I/'Oumuamua, was like nothing astronomers had seen before. It was elongated, porous, and tumbled erratically. What's more, it moved oddly, exhibiting "non-gravitational acceleration" while releasing only wisps of gas. The object even evoked thoughts of derelict alien spaceship.
Now, Yun Zhang (Côte d’Azur Observatory, France) thinks she has a model that "demonstrates, for the first time, that 'Oumuamua can be produced by a natural scenario based on well understood physical principles." The process, she says, "could be very common in the Milky Way."
She and Douglas Lin (University of California, Santa Cruz) describe their numerical model in Nature Astronomy on April 13th. The explanation starts during planetary formation, when a large object deflects the orbit of a kilometer-scale rubble-pile comet or asteroid, held together by gravity. The rubble pile passes within a few hundred thousand kilometers of the central star. Strong gravitational effects from the close passage stretch the rubble pile until it disrupts, in the same way that Jupiter pulled apart Comet Shoemaker-Levy 9 in a fateful encounter in the 1990s.
In Zhang and Lin's model, the disrupted pieces speed past the star, forming elongated clumps. The star’s heat vaporizes volatile ices on the surface of the elongated fragments, accounting for ‘Oumuamua’s lack of comet-like activity. However, volatiles stored deeper down, such as water, wouldn’t vaporize until the object reached the inner solar system, accounting for ‘Oumuamua’s non-gravitational acceleration.
Momentum would carry the loose structures outward, where a fraction of them would escape to roam the galaxy. The structures could be left tumbling oddly through space, like 'Oumuamua was doing when it passed through the solar system.
If this scenario pans out, Zhang says, then ‘Oumuamua would have had its origins in the fragmentation of a comet or dwarf planet ranging from kilometers to hundreds of kilometers in size.
D. Bodewits et al. “The carbon monoxide-rich interstellar comet 2I/Borisov.” Nature Astronomy, 20 April 2020.
M. Cordiner et al. “Unusually high CO abundance of the first active interstellar comet.” Nature Astronomy, 20 April 2020.
Zhang Y. & Lin D. “Tidal fragmentation as the origin of 1I/2017 U1 (‘Oumuamua).” Nature Astronomy, 13 April 2020. | 0.932498 | 4.065604 |
A gas giant is a large planet made mainly out of hydrogen and helium. Jupiter and Saturn are the gas giants of the solar system. The outermost parts of their atmospheres have many layers of visible clouds that are mostly made out of water and ammonia.
Jupiter has been covered in some detail elsewhere, so here we will concentrate on the other three giant planets.
Saturn is the sixth planet from the Sun and the second-largest in the solar system after Jupiter. It’s diameter is about nine times that of earth and it takes twenty nine and a half years to orbit the Sun. Binoculars will show an odd shaped disc. However even a modest telescope, such as a spotter scope, will reveal it’s rings.
Saturn was the ancient Roman god of agriculture. He was remembered in December during the most famous Roman festival of all – the Saturnalia. The Saturnalia was a time of feasting, free speech, gift-giving, role reversal, and revelry. Saturn the planet and Saturday are both named after him.
Saturn’s atmosphere usually appears bland and lacking in contrast. Ammonia crystals in it’s upper atmosphere give it a pale yellow hue. Wind speeds on Saturn can reach 1,800 km/h.
Saturn’s best known feature are it’s rings. These consist mainly of ice particles with a small amount of rocky debris and dust. Saturn also has sixty-two moons not including the hundreds of moonlets within it’s ring system. The largest moon is Titan. Bigger than the planet Mercury, Titan is the only moon in the Solar System to have a substantial atmosphere. One of Saturn’s most interesting moons is Enceladus. This moon is regarded as a potential habitat for life. In 2015 the Cassini probe flew through a plume on Enceladus and detected most of the ingredients needed to sustain some forms of primitive microbes.
The Ice Giants
An ice giant is a large planet made mainly out water, ammonia and methane, along with traces of other hydrocarbons.There are two ice giants in the solar system – Uranus and Neptune.
Uranus is the coldest planet in the solar system, with a minimum temperature of −224°C. It is the seventh planet from the Sun and it’s diameter is about four times the size of earth’s. It is the most distant planet that can be seen with the naked eye.
Uranus is the only planet whose name is derived from a figure in Greek mythology. Uranus or “Father Sky” was the husband of Gaia, “Mother Earth”. Together they were the ancestors of most of the other Greek gods.
Uranus takes 84 years to complete one orbit. It is also unique because it’s axis of rotation is tilted over at almost 900 compared to the other planets. This means that it’s seasonal changes are completely different to any other planet. Each pole gets 42 years of continuous sunlight, followed by 42 years of darkness. Around the equinoxes the rest of the planet has a normal day – night cycle, but around the solstices only a narrow strip round the equator experiences that normal rhythm.
Neptune is the eighth and farthest known planet from the Sun. It’s diameter is about 3.9 times that of earth and it takes a hundred and sixty five years to orbit the Sun. Although Neptune is not visible to the unaided eye it may be seen with binoculars.
Neptune was the god of freshwater and sea in Roman mythology. He was also the creator of horses as well as the owner of a powerful weapon, his Trident.
Neptune is the only planet in the Solar System that was found by mathematical prediction. During the first half of the nineteenth century Alexis Bouvard discovered unexpected changes in the orbit of Uranus that led him to realise that it was being affected by an unknown planet. From 1843, John Adams, and later from 1845, Urbain Le Verrier began work to calculate the position of the new planet. Johann Galle was the first person to see it through a telescope on 23 September 1846, within a degree of the position predicted by Le Verrier.
Image credits: NASA | 0.857081 | 3.371776 |
Orion is setting as evening begins. Gemini is above it and sets not long after. Leo is on the meridian as darkness sets in. Hercules and Boötes are rising. By midnight, the great celestial birds Cygnus and Aquila are rising. Look for Pegasus and Capricornus rising just before the sun’s morning light takes the stars away.
Venus continues its reign of the evening sky. Mercury moves up between the Hyades and Pleiades below Venus around the middle of the month. The messenger planet quickly leaves them behind and passes Venus on the 21st. The waxing crescent moon provides the two planets company on the 23rd and 24th. Mercury is still heading eastward, attempting to go deeper into the night sky as Venus recedes sunward into the sun’s evening glow at month’s end. You’ll find Mercury near Tejat and Propus in Castor’s (one of the twins of Gemini) feet in the last few evenings of May.
As Comet C/2019 (Y4) Atlas has broken up into numerous small pieces, we should no longer expect a spectacle of it. Astronomers had hoped it would rise to naked eye brightness in May as it passes closest to Earth on the 23rd at 72 million miles (116 million km). For what it’s worth, the remnants will be moving in the area to the right of Venus and Mercury.
In our morning sky, see Jupiter and Saturn nearly standing still next to each other between Capricornus and Sagittarius while Mars moves eastward from Capricornus to Aquarius this month. A waning gibbous moon will pass by the two big planets on the 12th and the red planet on the 14th and 15th.
Look for Eta Aquariid meteors on the 4th and 5th. This is a better shower from the southern hemisphere, but it’s not bad for northern observers. In a good year, you could see up to 60 per hour south of the equator and about half that many in northern locations.
This month’s lunar circumstances: The moon crosses the equator northward on the 5th, is at perigee on the 6th, and is full on the 7th. The perigee at 223,500 miles (359,600 km) the day before full moon makes it another so-called supermoon. Northern lunistice is on the 11th. Last quarter is on the 14th. The moon is on the equator again, going south on the 18th. The same day, it’s at apogee 252,000 miles (405,600 km) distant. New moon is on the 22nd. Southern lunistice is on the 25th. And first quarter is on the 31st.
Notable conjunctions this month: the moon is 4.0° from Regulus on the 2nd. Mercury is at superior conjunction on the 4th. The moon passes 2.2° from Jupiter and 2.6° from Saturn on the 12th. Then it passes 2.6° from Mars on the 15th and 3.6° from Uranus on the 20th. Mercury and Venus are 0.9° apart on the 22nd. The moon is 3.7° rom Aldebaran on the 23rd, 3.6° from Venus on the 24th, and 2.7° from Mercury also on the 24th. The moon passes 4.5° from Pollux on the 26th and 4.1° from Regulus on the 29th.
Mercury is at perihelion on the 10th. It will be 28.5 million miles (45.9 million km) from the sun. | 0.830082 | 3.276635 |
FORS 1 and FORS 2
FOcal Reducer and low dispersion Spectrograph
“Of all instruments at Paranal, this one is the Swiss Army knife”. This is the way Henri Boffin, the instrument scientist behind the FOcal Reducer and low dispersion Spectrograph 2 or FORS2, describes the instrument that is most in demand at ESO's Paranal Observatory. The key to success is that FORS2, installed on UT1 (Antu) of the Very Large Telescope (VLT), is able to study many different astronomical objects in many different ways.
For example, FORS2 can take images of relatively large areas of the sky with very high sensitivity. No wonder that some of the most iconic photos taken with the VLT used this instrument (see eso9845d, eso9948f, eso0202a, eso0338a, eso0338c, eso0617a, and more recently eso1244a and eso1348a).
But FORS2 can also take spectra of one (eso9920r), two or even several tens of objects in the sky simultaneously (eso0223b). “When used as a spectrograph, FORS2 disperses the light into very sophisticated rainbows that help astronomers study chemical composition or estimate the distances of remote objects,” says Boffin.
And this is not all. FORS2 can also measure the polarisation of light and is therefore used at the VLT to determine whether some astronomical objects have strong magnetic fields.
Observations with FORS2 and its twin brother FORS1 (decommissioned in 2009) have together led to almost 1800 papers to be published in scientific journals as of 2014, with an average of about 100 scientific papers per year. “Basically, whatever you can think of, you can do it with FORS2. Apart from making the coffee the astronomers need at night!”
Science highlights with FORS
- Constraining size, shape and colour of first-observed interstellar asteroid (eso1737)
- Observations of first light from gravitational wave source (eso1733)
- First detection of titanium oxide in an exoplanet (eso1729)
- Observations of neutron star that possibly confirm 80-year-old prediction about the vacuum (eso1641)
- Observations of galaxy clusters (eso1548)
- Alignments between supermassive black hole axes and large-scale structure revealed (eso1438)
- FORS helps explain shape of planetary nebula (eso1244)
- FORS was used to spot “Dark Galaxies”, an early phase of galaxy formation, which are essentially gas-rich galaxies without stars (eso1228)
- VLT “rediscovered” life on Earth (eso1210)
- Comet Halley in the cold – the most distant view of a regular visitor (eso0328)
- Cosmological gamma-ray bursts and hypernovae linked by FORS1 and FORS2 observations (eso0318)
- FORS1 and FORS2 broke several distance records: the most distant gamma-ray burst (eso0034), the most distant group of galaxies (eso0212), the most distant galaxy (eso0314)
IC 2944 with FORS2
This raw image, straight from the instrument, was used, together with many others, to produce the pink photo near the top of this page. The images taken with astronomical instruments are always monochromatic: the information on the colours is obtained by taking exposures through different glass filters. The thick black line cutting the field is the gap between the two detectors in the camera. Long “bleeds” caused by bright stars saturating the detector are also visible.
A raw spectrum obtained with FORS
A long, narrow slit isolates a small strip of sky. On this image, the slit is vertical. The spectrograph then splits the light from the slit into its individual colours, each point of the slit forming a horizontal rainbow. In this spectrum, the light from a distant galaxy appears as a faint horizontal line, peppered with bright dots corresponding to the colours emitted by the gas in the galaxy.
- For Scientists: for more detailed information, please see the FORS instrument website
The authoritative technical specifications as offered for astronomical observations are available from the Science Operation page. | 0.923203 | 3.875467 |
A visual history of the moon, from Galileo to Armstrong
In 1610, Galileo published a series of detailed drawings of the moon in his ground-breaking treatise "Sidereus Nuncius." The astronomer's depiction of a rough, cratered surface -- which he had observed through a homemade telescope -- is quite unlike other illustrations from the time.
As such, his images were considered hugely controversial. They broke with centuries of orthodoxy, challenging the Catholic church's vision of the moon as a flawless celestial body.
And the drawings didn't just fuel an astronomical revolution. They marked the beginning of a visual history that blends art, technology and the human imagination, according to Mia Fineman, curator of a new Metropolitan Museum of Art exhibition exploring our attempts to picture the moon.
"What Galileo did was reveal that the moon was not just a pretty disc in the sky, but had a terrain and a landscape like that of the Earth," she said in a phone interview. "That spurred further scientific study, but it also spurred the imagination of creative people, writers and others, who began to speculate about what it's like on the moon and whether there may be life there."
A 400-year-old copy of "Sidereus Nuncius" is oldest among the items on display at "Apollo's Muse: The Moon in the Age of Photography." Moving forward through time, it takes visitors from the 17th century to the present day, via, of course, the Apollo 11 moon landing, whose 50th anniversary the exhibition coincides with.
While many of the later photographs offer a depth and detail Galileo could only have dreamed of, it is, perhaps, the Met's images of Buzz Aldrin on the lunar surface that would have beguiled him the most. If the Earth's only natural satellite has remained unchanged over the last four centuries, human capabilities have changed dramatically in that time.
But while photography and technology is, ostensibly, the show's primary focus, it's only part of the tale.
"Photography joined a scientific pursuit that already in process," Fineman said. "And in order to tell this story we needed to bring in other kinds of objects, like books, drawings and prints of the surface of the moon that predated photography."
The result is a collection of more than 250 items exploring not only our knowledge of the moon, but its role in the arts. They range from a 19th century landscape painting of two men contemplating a crescent moon, to the "Stoned Moon" lithographs by Robert Rauschenberg, who NASA invited to witness the Apollo 11 launch.
Elsewhere, a series of 1920s movie production sketches reveals the film industry's obsession with imagining the lunar surface, long before Armstrong's "giant leap" put an end to speculation. A recreation of Aldrin's footprint on the moon's surface by Swiss artists Jojakim Cortis and Adrian Sonderegger, meanwhile, playfully hints at the conspiracy theories that have persisted ever since.
"The moon is a paradox," Fineman offered as an explanation for humankind's ongoing fascination. "It's near -- the closest celestial body to us -- yet it's far. It's ever-present, but it's always changing. We can see one side of it, but the other side is always hidden.
"It's always there," she added. "But it's always out of reach."
Scroll through the gallery above to see images from "Apollo's Muse: The Moon in the Age of Photography." The exhibition is on at the Metropolitan Museum of Art in New York until September 22, 2019. | 0.830796 | 3.312228 |
MACS1423-z7p64, a ‘Special’ Average Galaxy in the Distant Universe
MACS1423-z7p64 is an ultra-faint galaxy at a redshift of 7.6, that puts it about 13.1 billion years in the past. (The farther away an object is, the farther its light is shifted into the red end of the spectrum, due to the expansion of the universe.)
Astronomers- led by a graduate student at the University of California, Davis-
have discovered this galaxy, one of the most distant galaxies in the universe, and it’s nothing out of the ordinary.
Hence, what is so special about this one?
These ultradistant galaxies, seen as they were close to the beginning of the universe, are interesting to scientists because they fall within the “Epoch of Reionization,” a period about a billion years after the Big Bang when the universe became transparent.
After the Big Bang, the universe was a cloud of cold, atomic hydrogen, which blocks light. The first stars and galaxies condensed out of the cloud and started to emit light and ionizing radiation. This radiation melted away the atomic hydrogen like a hot sun clearing fog, and the first galaxies spread their light through the universe.
To find such faint, distant objects like MACS1423-z7p64, the astronomers took advantage of a giant lens in the sky.
As light passes by a massive object such as a galaxy cluster, its path gets bent by gravity, just as light gets bent passing through a lens. When the object is big enough, it can act as a lens that magnifies the image of objects behind it.
Scientists are surveying the sky around massive galaxy clusters that are the right size and distance away to focus light from very distant galaxies. While it is similar to millions of other galaxies of its time, z7p64 just happened to fall into the “sweet spot” behind a giant galaxy cluster that magnified its brightness tenfold and made it visible to the team, using the Hubble Space Telescope. They were then able to confirm its distance by analyzing its spectrum with the Keck Observatory telescopes in Hawaii.
► The study “Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization”, published in _Nature Astronomy _>> https://www.nature.com/articles/s41550-017-0091
► Read the preprint vesrion of this study on arXiv>> https://arxiv.org/abs/1704.02970
► Image explanation: Astronomers used the gravity of a massive galaxy cluster as a lens to spot an incredibly distant galaxy, about 13.1 billion years in the past. They used the Hubble Space Telescope to find the galaxy and confirmed its age and distance with instruments at the Keck Observatory in Hawaii.
Image credit: NASA/Keck/Austin Hoag/Marusa Bradac
#Universe, #Research, #Astrophysics, #ReionizationEpoch, #UltradistantGalaxies, #Cosmology, #BigBang, #Astronomy | 0.857029 | 3.786975 |
The search for extra-solar planets, the determination and prediction of their abundance, as well as the understanding of how these form and how life can develop constitutes the core research of the Astrobiology Initiative within the Astronomy and Space Physics Theme of the Scottish Universities Physics Alliance (SUPA). It will provide clues on how frequent life might be in the Universe and where to look for it.
The Astronomy Group is furthermore part of the Centre for Exoplanet Science, which brings together researchers from different disciplines to find out how planets form in different galactic environments, how their atmospheres evolve, and the relation between the evolutionary history of planets and the emergence of life.
Andrew Cameron, Martin Dominik, Keith Horne
In St Andrews, we are currently carrying out experiments for detecting extra-solar planets based on two different techniques – transits and microlensing -, while also studying debris disks around nearby stars, which constitute candidate systems for the presence of planets. Our research featured in an exhibit “Is there anybody out there? Looking for new worlds”, which was concepted for the 2008 Royal Society Summer Science Exhibition.
Doppler surveys show that 1% of nearby main-sequence stars host “hot Jupiters” in 1-4 day orbits with radii less than 0.05 AU. 10% of those should have orbits close enough to edge-on for the planet to transit in front of the star. Transiting planets are uniquely useful because the drop in light level as the planet crosses the star gives us precise measurements of the planet’s radius. As a leading member of the UK SuperWASP project, we are conducting a wide-angle survey of bright stars for transits of large, short-period planets with two identical robotic observatories giving access to both the northern and the southern sky. Working in collaboration with the Geneva planet-search team in the southern hemisphere and the SOPHIE radial-velocity spectrometer team in the north, the SuperWASP team has discovered 60 transiting planets between 2006 September and 2011 August. We have been allocated time on the Hubble Space Telescope and the infrared Spitzer Space Telescope to make precise measurements of the sizes and atmospheric temperatures of many of these planets. Using the HARPS spectrometer on the ESO 3.6-m telescope, we have discovered that the orbits of many of these planets are strongly tilted or even retrograde relative to the stellar spin axis, providing important dynamical clues to their origins. Through SUPA-2, the University of St Andrews has contributed to the construction of the Geneva-led HARPS-North radial-velocity spectrometer, which was commissioned at the 3.5-m Telescopio Nazionale Galileo (TNG) on La Palma early in 2012. Its primary goal is to measure the masses of low-mass planet candidates discovered by the NASA Kepler mission, achieving long-term 1 metre per second median radial-velocity precision on V < 11-mag stars. Over the next five years (2017-2022) the programme will be renewed and expanded to characterise planets transiting brighter stars from the NASA TESS mission and the Swiss-led ESA CHEOPS satellite following their respective launches in 2018.
At any given time, only one in a million stars in the Galactic bulge is significantly brightened due to the bending of its light caused by the gravitational field of an intervening foreground star, a phenomenon known as (galactic) gravitational microlensing. However, daily monitoring of hundreds of millions of stars by survey teams (such as OGLE or MOA) results in about 1000 on-line alerts of ongoing microlensing events per year. A planet orbiting the foreground ‘lens’ star can reveal its existence by producing a brief deviation on the observed light curve, lasting from days for a Jupiter down to hours for an Earth. Since 1997, members of our group have been involved in the PLANET (Probing Lensing Anomalies NETwork) collaboration, which was the first systematic effort to hunt for extra-solar planets by means of high-cadence round-the-clock follow-up observations on ongoing microlensing events. While PLANET used a network of staffed 1m-class optical telescopes, we pioneered the use of 2.0m robotic telescopes with RoboNet-1.0 and now RoboNet-II, as well as the deployment of algorithmic schemes for optimal target selection and anomaly detection resulting in the ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) system. A fully-deterministic microlensing campaign with RoboNet-II and MiNDSTEp (Microlensing Network for the Detection of Small Terrestrial Exoplanets) will lead to a census of cool planets down to Earth mass and even below orbiting either Galactic disk and bulge stars, and thereby probe models of planet formation and orbital evolution in a region that is not reasonably accessible by any other means.
Radial Velocity Method
Scientists at St Andrews spent the last decade leading the ground-based discovery of hot Jupiters with WASP. NASA’s Kepler/K2 has since delivered large numbers of smaller planets with known radii. We now move from the discovery era into one of characterisation and trying to understand what sort of planets emerge from the formation process in different environments. HARPS-N is enabling us to measure their masses and hence bulk densities. A picture is emerging in which planets smaller than 1.6 Earth radii are predominantly rocky, while bigger ones have lower densities indicating deep water/ice mantles and extended gaseous atmospheres. NASA’s Transiting Exoplanet Survey Satellite (TESS) is similar in concept to WASP, using small wide-field telescopes, but in space. It will find many small planets transiting bright stars. We will weigh them with HARPS-N, and learn how easy it is for planets of different sizes to retain oceans and atmospheres under irradiation by their host stars. The ESA CHaracterising ExOPlanets Satellite will measure radii of small planets and phase curves for gas giants. Such phase-curve observations will inform and challenge the work done by our theoretical astrophysicists on the atmospheric structure of exoplanets.
The window into extrasolar planets are their atmospheres. Transition spectra, obtained with the Hubble Space Telescope and from the ground with super-sensitive instruments like FORS2 at the VLT, review the presence of clouds and of gaseous water in some of the extrasolar planets. We perform numerical simulations of exoplanet atmospheres in order to understand what these observations tell us, for example, about the gas chemistry and cloud formation. Researchers in St Andrews have pioneered the cloud formation modelling in exoplanet atmospheres. We simulate the formation of mineral and diamond clouds and their effect on atmospheres in order to understand the chemical diversity of extrasolar planets. Our work links laboratory work, quantum mechanical cluster calculation and large-scale atmosphere modelling in order to predict atmospheres on exoplanets. We are also interested in the occurrence of lightning and other charge-processes in such unusual environments. Lightning has been suggested as a possibility to initiate the chemical steps that led to the emergence of life on Earth.
Observations suggest that many hot Jupiters contain a large dust cloud component in their atmosphere because they obscure the absorption signatures of the atmospheric gas underneath the cloud layers. These clouds are made of mineral compounds such as TiO2[s], MgSiO3[s], SiO[s], Al2O3[s], Fe[s] ([s] meaning solid particles), and not of water like on Earth.
Map of the mean grain size in micrometers at a pressure of p = 10-2 bar across the globe of the HD 189733b simulation. The grain sizes on the dayside are approximately 10x the size of those on the nightside. (Lee et al. 2015)
Since the late 90s, thousands of exoplanets have been discovered. These exoplanets show a large diversity in sizes, masses, even distances to the host star, much different to our Solar System planets: Jupiter-size planets orbiting other stars at the distance of Mercury; planetary systems with several planets inside the orbit of Mercury; terrestrial planets several times bigger than Earth, but still rocky and not made of gas. Could these planets host lightning in their atmospheres? Let’s look at Earth and Saturn. They have different composition, different sizes, masses, different atmospheres. And still, they both show lightning activity. So why couldn’t it occur on exoplanets?
LIS/OTD lightning climatology map averaged from 1995-2013 (Hodosán et al. 2016)
Simulations of planet-forming disks help to disentangle observations from high-performance facilities like ALMA and and space missions like Herschel. We seek to understand the processes that set the initial conditions for planet formation in planet forming disks. Knowing that the solar system is unique, we aim to understand why so many other planetary systems are different from the solar system.
Formation and characterisation
Magnetospheres and charge processes
Moira Jardine, Christiane Helling | 0.940719 | 3.804042 |
This artist’s rendering shows a white dwarf star with two planets. Mark Garlick
When looking for exoplanets that are similar to Earth, astronomers typically look for worlds in orbit around a type of star called a red dwarf on an M-dwarf. These types of star are somewhat similar to our sun and are common in our galaxy, making up about 70% of stars here. However, new research shows that rocky exoplanets in orbit around a different type of star, a white dwarf, can have interiors that are surprisingly similar to our planet.
White dwarfs are shrunken remains of once-bright stars that have extremely strong gravity. Typically, this gravity means the surface of the stars is composed of light elements like hydrogen and helium, but in some cases, you find “polluted” white dwarfs that have heavier elements like magnesium, iron, and oxygen in their atmospheres. These elements are introduced to the white dwarf when a rocky exoplanet crashes into the star, which gives astronomers evidence of what the exoplanets were like before they were destroyed.
“By observing white dwarfs and the elements present in their atmosphere, we are observing the elements that are in the body that orbited the white dwarf,” Alexandra Doyle, a graduate student in the Department of Earth, Planetary, and Space Sciences at the University of California, Los Angeles, explained in a statement. “The white dwarf’s large gravitational pull shreds the asteroid or planet fragment that is orbiting it, and the material falls onto the white dwarf.”
Doyle and her colleagues looked at white dwarfs to see what kind of elements had been present in the planets that used to orbit them. “If I were to just look at a white dwarf star, I would expect to see hydrogen and helium,” Doyle said. “But in these data, I also see other materials, such as silicon, magnesium, carbon, and oxygen — material that accreted onto the white dwarfs from bodies that were orbiting them.”
The surprising finding here was how alike the exoplanets were to Earth beneath their rocky exteriors. “How similar are the rocks the researchers analyzed to rocks from the Earth and Mars? Very similar,” Doyle said. “They are Earth-like and Mars-like in terms of their oxidized iron. We’re finding that rocks are rocks everywhere, with very similar geophysics and geochemistry.”
The research is published in the journal Science. | 0.907518 | 3.755016 |
Forget those shepherding moons. Gravity and the odd shapes of asteroid Chariklo and dwarf planet Haumea – small objects deep in our solar system – can be credited for forming and maintaining their own rings, according new research in Nature Astronomy.
“Rings appear around Saturn, Jupiter, Neptune and Uranus, but scientists found rings around Chariklo and Haumea within the last few years. Chariklo and Haumea were the first small objects known to have rings, and we think that rings throughout the solar system are more common than we thought,” said Maryame El Moutamid, research associate in the Cornell Center for Astrophysics and Planetary Science and an author of the new paper. “In the case of small bodies Chariklo and Haumea, gravity shepherds the rings. The rings are confined by the gravity because of the shape irregularity of their bodies.”
Until now, scientific literature generally assumed that the gravitational torques from shepherd moons around planets kept the rings in shape and prevented them from spreading and disappearing. Instead, this research shows that a topographic anomaly on the object, such as a mountain, may play a similar gravitational role as a “moon” to hold the rings together.
In addition to gravity, rapidly spinning cosmic bodies that create specific resonance also keep rings from expanding, dissipating and disappearing.
Chariklo is a small, rocky asteroid between Saturn and Uranus. It is about 188 miles in diameter and takes 63 years to orbit the sun. It is the largest object in an asteroid class known as Centaurs, according to NASA.
Meanwhile, Haumea, a trans-Neptunian object, about the size of Pluto, looks like a flattened ball with a 385-mile diameter. It is found in the Kuiper Belt, a region beyond the orbit of Neptune. Haumea was discovered in December 2004 and takes about 285 years to orbit the Sun.
With Saturn, the rings are shepherded by tiny moons to keep them in place. But for Chariklo, its odd, rocky shape – which includes a large “mountain” – keeps the rings in place just beyond the border of the Roche limit – the closest a small object can approach the larger one it orbits without being torn apart by tidal force.
“In the case of Chariklo, the irregularities confine the rings. In the case of Haumea, the body’s big flatness does the job,” said El Moutamid, who is also a member of Cornell’s Carl Sagan Institute.
Astronomer Bruno Sicardy of the Observatoire de Paris led the research in a project called Lucky Star. Other authors of the paper, “Ring Dynamics Around Non-axisymmetric Bodies,” are by Stéfan Renner, Françoise Roques and Josselin Desmars, Observatoire de Paris; Rodrigo Leiva, Southwest Research Institute, Boulder, Colorado; and Pablo Santos-Sanz, Instituto de Astrofısica de Andalućıa, Spain. Funding was provided by the European Research Council. | 0.936301 | 3.901974 |
^Synchronous rotation can easily be confused with synchronous orbits. In a synchronous orbit, the moon orbits always above the same point on the planet it is orbiting (this section uses the terms moon and planet, but the same principles apply to a planet and the Sun). There is only one orbital radius for each planet that produces a synchronous orbit. Synchronous rotation, on the other hand, is created by the period of the moon's rotation on its axis being the same as the period of the moon's orbit around its planet, and produces a situation where the same face of the moon is always toward its planet. Tidal locking causes synchronous rotation.
Gravitational attraction between the moon and its planet produces a tidal force on each of them, stretching each very slightly along the axis oriented toward its partner. In the case of spherical bodies, this causes them to become slightly egg-shaped; the extra stretch is called a tidal bulge. If either of the two bodies is rotating relative to the other, this tidal bulge is not stable. The rotation of the body will cause the long axis to move out of alignment with the other object, and the gravitational force will work to reshape the rotating body. Because of the relative rotation between the bodies, the tidal bulges move around the rotating body to stay in alignment with the gravitational force between the bodies. This is why ocean tides on Earth rise and fall with the rising and setting of its moon, and the same effect occurs to some extent on all rotating orbiting bodies.
in diameter. If such a thing were possible, a person could walk all the way around their circumference in about three hours. Many of these tiny objects orbit at immense distances from the planet, and almost all the outer moonlets orbit in a retrograde sense, that is, in the opposite direction than most moons. This is thought to be a strong indicator that they are trapped asteroids and did not form when Jupiter formed. The very high eccentricities of these orbits compared to the stable inner moons is further evidence for their being trapped asteroids. Trapping asteroids as they go by is a reasonable occurrence to expect from such a huge mass, but keeping trapped asteroids in stable orbits is a physically difficult feat. The orbits tend to degenerate and cause the moonlet eventually to fall into the planet. Many of Jupiter's tiny moonlets therefore may be only temporary visitors to the Jupiter
The rotation of the tidal bulge out of alignment with the body that caused it results in a small but significant force acting to slow the relative rotation of the bodies. Since the bulge requires a small amount of time to shift position, the tidal bulge of the moon is always located slightly away from the nearest point to its planet in the direction of the moon's rotation. This bulge is pulled on by the planet's gravity, resulting in a slight force pulling the surface of the moon in the opposite direction of its rotation. The rotation of the satellite slowly decreases (and its orbital momentum simultaneously increases). This is in the case where the moon's rotational period is faster than its orbital period around its planet. If the opposite is true, tidal forces increase its rate of rotation and decrease its orbital momentum.
Almost all moons in the solar system are tidally locked with their primaries, since they orbit closely and tidal force strengthens rapidly with decreasing distance. In addition, Mercury is tidally locked with the Sun in a 3:2 resonance. Mercury is the only solar system body in a 3:2 resonance with the Sun. For every two times Mercury revolves around the Sun, it rotates on its own axis three times. More subtly, the planet Venus is tidally locked with the planet Earth, so that whenever the two are at their closest approach to each other in their orbits, Venus always has the same face toward Earth (the tidal forces involved in this lock are extremely small). In general any object that orbits another massive object closely for long periods is likely to be tidally locked to it.
system. The table on page 66 lists Jupiter's moons. The moons with the most known about them are described in more detail.
Was this article helpful? | 0.861468 | 4.009238 |
When the world was young and unsullied, we did wholesome things, like laugh at Cheezburger memes and other cat-related pleasantries. One treasure we all adored was the Double Rainbow video, in which a man—ostensibly on peyote and beaver tranquilizers—nearly orgasms at the site of two rainbows in the sky. Those halcyon days may be over, but now, we have a double star system to enjoy instead.
On March 6th, the European Southern Observatory (ESO) posted a mesmerizing image of a binary star system, captured by the agency’s Atacama Large Millimeter/submillimeter Array (ALMA). The swirling, false color radio emissions image shows LL Pegasi—a star located 3,000 light-years from the Sun—getting along nicely with its binary companion. As the old red giant LL Pegasi orbits its companion, it loses material, and as a result of its highly elliptical path, it leaves behind a spiral shape. Each “layer” in the spiral is thought to represent about 800 years, which is the estimated orbital period of the binary system, according to Hubble. The new observations have been published in the March issue of Nature Astronomy.
“Because of the orbital motion of the mass-losing red giant, the cold molecular gas constituting the wind from that star is being spun out like the sprays of water from a rotating garden sprinkler, forming the outflowing pattern of spiral shells,” UCLA astronomer and study co-author Mark Morris explained in a statement.
At some point in this cosmic love affair, LL Pegasi will become a nebula. Until then, we’ll have many more years of this freakishly beautiful swirl. | 0.88568 | 3.045562 |
Dec 07, 2012
Electric double layers are like waterfalls that energize charged particles falling through them.
“We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture.”
— Hannes Alfvén
A double layer forms in plasma when electric charge flows through it. Double layers are found in the plasma environment of Earth, as well as around the stars, creating phenomena like aurorae and electromagnetic radiation from pulsars.
Thermal emissions from hot filaments in lightbulbs led plasma pioneer Irving Langmuir to contemplate the behavior of charged particles moving through various gases. He was the first to coin the term “plasma” when referring to such ionized gas. Since charged regions in gas tend to isolate themselves from the environment, as well as act in ways not governed by mechanical theories, he thought they appeared similar to the organic plasma component of cells, so he used biology-based terminology.
Scientists from the National University Research School of Physical Sciences and Engineering in Canberra discovered double layers in their laboratory plasma systems, finding that they were accelerating ions to supersonic velocities. The double layers are self-generating, so the effect has been incorporated into an efficient spacecraft thrust mechanism.
As mentioned, a double layer is an electric charge separation region that forms in a plasma. It consists of two oppositely charged parallel layers, resulting in a voltage drop and electric field across the layer, which accelerates the plasma’s electrons and positive ions in opposite directions. Since moving electric charges generate electricity, there is an electric current present. If there are sufficiently large potential drops and layer separation, electrons might accelerate to relativistic velocities, producing synchrotron radiation.
Nobel prize winner Hannes Alfvén described a double layer as, “… a plasma formation by which a plasma—in the physical meaning of this word—protects itself from the environment. It is analogous to a cell wall by which a plasma—in the biological meaning of this word—protects itself from the environment.”
Electric forces can accelerate charged particles with energies of 10^20 electron volts or more. Since electricity requires a circuit for charge to flow, and an electric current forms a magnetic field, that field tends to constrict the current. As pointed out in previous Picture of the Day articles, that constricted channel is known as a Bennett pinch, or z-pinch. The pinched filaments of electric current remain coherent over large distances. Laboratory experiments with particle accelerators confirm the observation.
Plasma’s behavior is driven by conditions in those circuits. Fluctuations can form double layers with large potential voltages between them. The electric forces in double layers can be much stronger than those from gravitational and mechanical forces. Double layers separate plasma into cells and filaments that can have different temperatures or densities.
At times, a double layer might interrupt charge flow in the circuit, causing a catastrophic rise in voltage across it. The powerful energy release of the exploding double layer is sometimes observed in power transmission switchyards when a circuit breaker is opened incorrectly.
Hannes Alfvén identified just such an occurrence when he was contracted by the Swedish Power Company to investigate some serious accidents that had occurred. A few of the mercury arc rectifiers used in the power transmission circuits had exploded for no apparent reason. Alfvén identified the cause as unstable double layers within the plasma flow.
He wrote: “In Sweden the waterpower is located in the north, and the industry in the south. The transfer of power between these regions over a distance of about 1000 km was first done with a.c. When it was realized that d.c. transmission would be cheaper, mercury rectifiers were developed. It turned out that such a system normally worked well, but it happened now and then that the rectifiers produced enormous over-voltages so that fat electrical sparks filled the rectifying station and did considerable harm…
“An arc rectifier must have a very low pressure of mercury vapor in order to stand the high back voltages during half of the a.c. cycle. On the other hand, it must be able to carry large currents during the other half-cycle. It turned out that these two requirements were conflicting, because at a very low pressure the plasma could not carry enough current. If the current density is too high, an exploding double layer may be formed. This means that in the plasma a region of high vacuum is produced: the plasma refuses to carry any current at all. At the sudden interruption of the 1000 km inductance produces enormous over-voltages, which may be destructive.”
There are also double layers in space that emit radio waves over a broad band of frequencies. They can sort galactic material into regions of like composition and condense it. They can accelerate charged particles to cosmic ray energies. Double layers in space can explode for the same reason as Alfvén’s rectifiers, releasing more energy than is locally present. This effect can be seen in stellar flares or so-called “nova” outbursts.
Since plasma is composed of charged particles, their movement constitutes an electric current, which generates a magnetic field. Electrons spiral in the resulting magnetic field, creating synchrotron radiation that can shine in all high-energy frequencies, including extreme ultraviolet, X-rays, and gamma rays.
According to Alfvén and others, electric power flows along the spiral arms of a galactic circuit where it is concentrated and stored in a central plasmoid within the galactic bulge. When the current density reaches a critical threshold, the plasmoid discharges along the galaxy’s spin axis as an energetic jet of plasma. That phenomenon has been replicated in the laboratory with a plasma focus device.
Cosmic plasmas and their activity can be replicated in the laboratory, allowing insights into the large-scale structures that populate the Universe. Since gravitational forces cannot be examined in the laboratory, consensus opinions about the gravity-only model of celestial objects suffer from a moribund condition. Hopefully, a fresh perspective will outshine the dark conditions that dominate today’s approach. | 0.884321 | 3.652405 |
'We're going to explore temperatures far below anything found naturally.'
Space, on top of everything else, is cold. Really cold. The cosmic background temperature—the temperature of the cosmic background radiation thought to be left over from the Big Bang—is 3 Kelvin, or -455 degrees Fahrenheit. Yet there's variation within that. Solar winds can reach millions of degrees Fahrenheit. And then there's the Boomerang Nebula, the cloud of gas puffed out by a dying star in the constellation Centaurus. The Boomerang Nebulaclocks in at a slightly-more-frigid-than-average -458 degrees Fahrenheit, making it, officially, the coldest spot in the known universe.
But that's about to change. Soon, it seems, the coldest spot in the known universe will be ... the International Space Station.
Yep. Meet the Cold Atom Lab, the "atomic refrigerator" NASA has planned for launch in 2016—a device that will, it's hoped, allow the agency to study quantum mechanics in a controlled environment. "We're going to explore temperatures far below anything found naturally," JPL's Rob Thompson told ScienceatNASA.
So how cold is unnaturally cold? NASA's orbiting refrigerator—the device that will, better than any other, put the "fridge" in "frigid"—will reach, if all goes according to plan, temperatures as low as 100 pico-Kelvin above absolute zero (with “pico” denoting one-trillionth).
And the fridge will use the ISS's own infrastructure to generate all the coldness. The station's existing cooling system relies on the fact that gas, as it expands, cools. The Cold Atom Lab will use magnetic traps to expand gas until it gets down to the temperature the researchers seek. The traps aren't expected to require much energy for their working, since, in space, the gas won't need to be supported against gravity.
But why go to all this trouble? Why bother to create a cold so cool it does not, to our knowledge, exist in nature? Because of these things known as Bose-Einstein Condensates, dilute gases that demonstrate unusual macro-quantum effects at temperatures near absolute zero. When two Bose-Einstein Condensates are placed together under particularly frigid conditions, they don’t mix; instead, they interfere with each other like waves. It's behavior that's mysterious to scientists—which means it's behavior that's also exciting to scientists. The ISS's "atomic refrigerator" will allow researchers to study those crazy gases ... at the coldest temperatures possible.
NEXT STORY: Confused by Obamacare? Ask the President | 0.878617 | 3.887354 |
Satellite Laser Ranging (SLR) is the most accurate geodetic distance-measuring technique developed in the 60’s. The travel time of ultra short laser pulses (few picoseconds), from a ground-based system to a retroreflector-carrying spacecraft and back to the station, is measured with very high precision clocks, and after corrections for system and media propagation delays, converted to the corresponding range distance. Today these distances can be measured with an accuracy of a few millimeters for near Earth satellites all the way to the Moon surface. The first US satellite designed for such accurate measurements was the LAser GEOdynamic Satellite—LAGEOS. LAGEOS was launched on May 4, 1976, in a circular orbit with a ~110° inclination and at an altitude of 6000 km. LAGEOS-2, based on the original LAGEOS design, was built by the Italian Space Agency—ASI, and launched on October 22, 1992. The LAGEOS satellites are covered with 426 cube corner retroreflectors that reflect the incoming light back in the same direction it came from (i.e. the tracking station). Using the ranges from several stations on Earth collected over time, we can compute very accurate trajectories for the spacecraft, a set of accurate station positions and velocities, and simultaneously improve numerous geophysical model parameters of interest to scientists.
To celebrate 40 years of "operations," tracking, and science, Goddard’s Space Geodesy Project held an event on May 11 at NASA GSFC to recognize the tremendous amount of science supported by LAGEOS and its contribution to scientific research. The event was held at NASA GSFC in Building 34, Room W150 starting at 2:00 pm. Invited talks given between 2:00 and 4:00 pm, followed by a social hour. The speakers were:
- Dave Smith (MIT): The LAGEOS project
- Mike Fitzmaurice (retired GSFC): LAGEOS Ground Testing
- Mike Pearlman (Harvard-Smithsonian Center for Astrophysics): LAGEOS tracking through the years
- Erricos C. Pavlis (UMBC): Scientific Contributions of LAGEOS Data
- Frank Lemoine (GSFC): LAGEOS: Importance to the Reference Frame, Enabled Missions, Future Outlook
David Smith was the project scientist for the LAGEOS mission. Mike Fitzmaurice was the lead of the ground team for optical testing. Michael Pearlman is the Int. Laser Ranging Service (ILRS) Central Bureau Director. Erricos C. Pavlis from JCET/UMBC did his PhD thesis with LAGEOS data and he is currently the Chairman of the ILRS Analysis Group. Frank Lemoine is a Goddard geophysicist using LAGEOS data in scientific investigations and precise orbit determination.
There were a number of LAGEOS items on display, including the LAGEOS test sector and a replica of the Carl Sagan designed plaque, two copies of which are embedded in the actual spacecraft in case it is ever recovered by future Earth inhabitants (LAGEOS’ orbit lifetime is roughly 10 million years!).
The talks were webcast live and a video is available for view by those who missed the event (see below).
NASA web feature on the celebration:
NASA video of the event available at: | 0.807831 | 3.021774 |
First global geologic map of Titan completed
(18 November 2019 - JPL) The first map showing the global geology of Saturn's largest moon, Titan, has been completed and fully reveals a dynamic world of dunes, lakes, plains, craters and other terrains.
Titan is the only planetary body in our solar system other than Earth known to have stable liquid on its surface. But instead of water raining down from clouds and filling lakes and seas as on Earth, on Titan what rains down is methane and ethane - hydrocarbons that we think of as gases but that behave as liquids in Titan's frigid climate.
The first global geologic map of Titan is based on radar and visible-light images from NASA's Cassini mission, which orbited Saturn from 2004 to 2017. Labels point to several of the named surface features. (courtesy: NASA/JPL-Caltech/ASU)
"Titan has an active methane-based hydrologic cycle that has shaped a complex geologic landscape, making its surface one of most geologically diverse in the solar system," said Rosaly Lopes, a planetary geologist at NASA's Jet Propulsion Laboratory in Pasadena, California, and lead author of new research used to develop the map.
"Despite the different materials, temperatures and gravity fields between Earth and Titan, many surface features are similar between the two worlds and can be interpreted as being products of the same geologic processes. The map shows that the different geologic terrains have a clear distribution with latitude, globally, and that some terrains cover far more area than others."
Lopes and her team, including JPL's Michael Malaska, worked with fellow planetary geologist David Williams of the School of Earth and Space Exploration at Arizona State University in Tempe. Their findings, which include the relative age of Titan's geologic terrains, were recently published in the journal Nature Astronomy.
Lopes' team used data from NASA's Cassini mission, which operated between 2004 and 2017 and did more than 120 flybys of the Mercury-size moon. Specifically, they used data from Cassini's radar imager to penetrate Titan's opaque atmosphere of nitrogen and methane. In addition, the team used data from Cassini's visible and infrared instruments, which were able to capture some of Titan's larger geologic features through the methane haze.
"This study is an example of using combined datasets and instruments," Lopes said. "Although we did not have global coverage with synthetic aperture radar [SAR], we used data from other instruments and other modes from radar to correlate characteristics of the different terrain units so we could infer what the terrains are even in areas where we don't have SAR coverage."
Williams worked with the JPL team to identify what geologic units on Titan could be determined using first the radar images and then to extrapolate those units to the non-radar-covered regions. To do so, he built on his experience working with radar images on NASA's Magellan Venus orbiter and from a previous regional geologic map of Titan that he developed.
"The Cassini mission revealed that Titan is a geologically active world, where hydrocarbons like methane and ethane take the role that water has on Earth," Williams said. "These hydrocarbons rain down on the surface, flow in streams and rivers, accumulate in lakes and seas, and evaporate into the atmosphere. It's quite an astounding world!" The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency (ESA) and the Italian Space Agency. NASA's JPL, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington. JPL designed, developed and assembled the Cassini orbiter. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the U.S. and several European countries. | 0.840319 | 3.747872 |
Stenonychosaurus has been credited with being the most intelligent dinosaur.
Compared with most others, it had a relatively large brain, although the excess brain volume was probably not concerned with reasoning and other activities that could be called “intelligence.”
Stenonychosaurus had large eyes, slender flexible fingers, and a light body. The brain was probably concerned mainly with its highly developed senses, fine control of its limbs, and fast reflexes, which were used in hunting small and elusive prey.
In 1982 Dale Russell and R. S_guin (Ottawa) published an article on Stenonychosaurus. A new partial skeleton had been discovered in 1967 which provided the basis of the first skeletal and flesh restoration of Stenonychosaurus. The detailed work of building the model was illustrated in their paper.
In addition to the restoration, they indulged in an imaginative experiment, posing a question: What might these intelligent dinosaurs have evolved into had they not become extinct near the end of the Cretaceous period about 64 million years ago?
Stenonychosaurus proved to be an interesting choice for the experiment because it was one of the largest-brained and therefore presumably one of the most intelligent of all dinosaurs. The result of the experiment was a creature named “dinosauroid.”
One interpretation of the habits of Stenonychosaurus is that they were lightly built active hunters of small prey_perhaps small lizards and mammals. The long grasping hands, and the large eyes which pointed partly forward and therefore gave reasonably stereoscopic vision, may indicate that these were nimble predators which were active at dusk or even at night when many small nocturnal mammals would have been active.
Dinosauroid was constructed by extrapolating from these attributes. It was visualized as a highly intelligent and manipulative dinosaur. What it might have lacked in speed, it would have made up for by its superior intellect. This would have allowed it to avoid potential predators by outwitting them rather than by running away.
As a predator it may have been able to catch prey both by endurance running and perhaps by making simple weapons_ much as primitive homo sapiens would do 64 million years later.
But let’s take the evolution of the Saurian a step further. Let’s say, for the sake of argument, that Stenonychosaurus did not become extinct at the end of the Cretaceous period and actually had a chance to evolve into something close to the Russell-S_guin model.
It is remarkable to note that the Saurian creature bears a striking resemblance to descriptions given by witnesses during a number of UFO encounters! Long, clawlike fingers, large, elongated eyes, reptilian nostrils, three-toed, clawed feet, lizard-like skin, small stature and absence of ears are all features people have reported as belonging to UFO occupants.
Scientists do not know why most dinosaurs became extinct; they assume it because few relatives exist today in forms recognizable as dinosaurs.
But what if one or two examples actually survived and managed to evolve into highly intelligent creatures capable of building not only simple weapons, but sophisticated craft to explore the cosmos?
The Sauroids would have a 64 million year head start on homo sapiens. They could have built their empires and space craft and disappeared among the stars millions of years before humans ever evolved to walk upon this planet!
Or if the Saurians are not from planet Earth, why not from another where evolution might have followed a similar pattern with similar, if not identical, creatures, including dinosaurs, at about the same cosmic time_50 to 70 million years ago?
We Can’t Rule Out
While it is fairly certain life does not exist on any other planet of our solar system, we cannot rule out the existence of life on any of the billions of other planets that have revolved about billions of other suns in billions of other universes for billions of years before humankind ever existed.
Let’s face it: When we finally arrive on some distant planet inhabited by sentient beings, whether more or less intelligent than ourselves, scientists and intelligence agencies are going to insist that specimens be returned to Earth, dead or alive, for study. Knowing this, should we be surprised or outraged if creatures from other worlds arrive here and begin taking specimens of earthlings for their own scientific studies?
The requirement for the complete and successful examination of any living organism is to reduce it to its smallest parts and look at each cell or atom under a powerful electron microscope or vaporize small samples in a spectrometer to determine the elements of which the creature was comprised when it was alive. Sample parts might suffice for some studies but whole creatures, alive and dead, will be required for others.
These sample creatures will be acquired for study by abduction and murder. Period. Those in government agencies whose business it is to plan and coordinate these missions have known it all along. It is possible that they are practicing and honing their skills by abducting and dissecting their fellow humans from time to time. At the same time, they may be building their own secret parts bank for the generations of space travelers who will need spare kidneys, livers, eyes, hearts and lungs on Mars about three decades hence.
It’s a thought, isn’t it?
Another thought is that the creatures who crew UFOs might not be from another planet, but might have been genetically built and incubated right here on earth in one of those secret underground laboratories, and not by aliens, but by human tinkerers. Suppose the future astronaut is not a warm-blooded mammal (human), but a cold-blooded intelligent reptile (saurian) who can tolerate cosmic radiation better than humans and who have shown to be able to survive mass extinctions with little change or effect in their subsequent behavior and evolution.
Suppose the saurian is not a creature who lived before us, but is the creature, by genetic manipulation, some of us are soon to become.
Some reptiles, remember, have an uncanny ability to regenerate lost parts, often two or three parts. This would prove a real benefit for explorers on a planet several million miles from home base where spare arms and legs are not readily available.
Some reptiles can survive days or even weeks between meals while warm-blooded mammals can hardly exist more than a few hours!
Some reptiles appear to be unaffected by cosmic radiation that is killing human beings by the thousands. Some reptiles can hibernate for months and years at a time without suffering adverse effects.
Have witnesses seen this creature in one of its evolved forms? Is this what contemporary Stenonychosaurus might have looked like had it continued to evolve to the present day? Russell and S_guin assumed for it a large brain, and the short neck and upright posture were arrived at as a way of balancing the head more efficiently. In turn, the vertical posture removed the need for a tail. The legs were modified by lowering the ankle to the ground and the foot was lengthened. It would have stood upright at about five feet tall. Given the proper conditions and time, this evolution would be quite possible. | 0.806536 | 3.025376 |
The nuclear-electric mission to Neptune discussed here on the 14th is one of two now being studied by NASA. The other is powered by chemical rockets and, like Cassini, would use gravity assists to reach Neptune in considerably less time. Its team, led by Andrew Ingersoll of the California Institute of Technology, is working on a design that, like University of Idaho professor David Atkinson’s nuclear-electric mission, will be submitted to NASA in mid-2005.
A faster mission has many advantages, but a major question arises: how do you stop when you get there? Unlike Voyager, the Neptune missions are to be capable of orbiting the planet and dispatching probes to both it and its largest moon, Triton. One answer Ingersoll’s team is studying is aerocapture, which uses the destination planet’s atmosphere to alter the spacecraft’s trajectory, putting it into orbit after a single pass.
If this sounds familiar, you may recall the aerocapture maneuver in the film 2010, a spectacular, flaming arrival at Jupiter that used a heat shield and pinpoint positioning to brake the spacecraft into a circular orbit. NASA has been studying aerocapture for a long time, though at present its experience with actual missions has been limited to a milder variant called aerobraking; the broader term for all these maneuvers is aeroassist. The Mars Climate Orbiter has already proven aerobraking; the spacecraft circularized the elliptical orbit its chemical rocket put it in around Mars by using drag from the atmosphere on its solar array. Doing this for hundreds of orbits resulted in a circular path around the planet.
When I talked to NASA’s Les Johnson at Marshall Space Flight Center in Huntsville about aerocapture, he called the procedure ‘aeroassist on steroids.’ Johnson is manager of NASA’s In-Space Propulsion Program. More than most technologies, aerocapture is destination-dependent; Johnson told me that both Neptune and Titan are possible candidates for its use because of their interest and their great distance. For the outer planets, the beauty of aerocapture is that you need carry no fuel to get yourself into orbit at destination. Another key advantage: it allows a much faster trip time.
From the interview:
If you look at the systems studies, you see that if you don’t have to carry all that fuel with you, you can can add science payload. And your launch vehicle can be smaller because it doesn’t have as much weight to throw. Finally, your trip time is reduced because when you’re traveling interplanetary distances and have to slow down to capture, you spend half your time thrusting and half your time slowing down. Forget that with aerocapture; you do all your slowing down in a thirty minute maneuver at destination.
Of course, it’s a spectacular, nail-biting arrival. But when I asked Johnson how tight the parameters were for the maneuver, his answer surprised me:
Our people have some convincing data that the entrance corridors are wide so that if you miss your mark in the atmosphere you have a lot of flexibility for correcting as you proceed. That the integrity of the ablaters and the materials — the thermal protection we’ll need — is going to be tolerant and will be able to do the capture.
So armed with aerocapture and gravity assists, the Ingersoll team may have an edge when it comes to speed. On the other hand, the nuclear-electric technologies Atkinson envisions would allow for bigger payloads and more power resources available during the spacecraft’s primary mission around Neptune; this is what NASA’s Project Prometheus is all about.
We’ll be tracking both these designs as they evolve into final reports. In the meantime, a good backgrounder on all the aeroassist methods can be found at this NASA page. Image credit (above): NASA. | 0.820802 | 3.487591 |
By now, we have discovered hundreds of stars with a number of planets orbiting them scattered all over the galaxy. Each individual a person is unique, but a method orbiting the star High definition 158259, 88 light-several years absent, is actually distinctive.
The star alone is about the same mass and a tiny larger sized than the Sunlight – a minority in our exoplanet hunts. It really is orbited by six planets: a tremendous-Earth and 5 mini-Neptunes.
Soon after monitoring it for seven several years, astronomers have discovered that all six of people planets are orbiting High definition 158259 in just about excellent orbital resonance. This discovery could assistance us to superior comprehend the mechanisms of planetary method development, and how they end up in the configurations we see.
Orbital resonance is when the orbits of two bodies all over their dad or mum entire body are intently linked, as the two orbiting bodies exert gravitational impact on each other. In the Solar System, it really is fairly uncommon in planetary bodies possibly the most effective case in point is Pluto and Neptune.
These two bodies are in what is explained as a 2:3 orbital resonance. For just about every two laps Pluto can make all over the Sunlight, Neptune can make three. It really is like bars of songs remaining played simultaneously, but with unique time signatures – two beats for the very first, three for the second.
Orbital resonances have also been identified in exoplanets. But each world orbiting High definition 158259 is in an just about 3:2 resonance with the upcoming world out absent from the star, also explained as a interval ratio of one.5. That usually means for just about every three orbits each world can make, the upcoming a person out completes two.
Using measurements taken working with the SOPHIE spectrograph and the TESS exoplanet-looking place telescope, an international group of researchers led by astronomer Nathan Hara of the College of Geneva in Switzerland ended up ready to specifically calculate the orbits of each world.
They are all pretty limited. Beginning closest to the star – the tremendous-Earth, uncovered by TESS to be all over 2 times the mass of Earth – the orbits are 2.seventeen, 3.four, 5.2, seven.nine, 12, and seventeen.four days.
These produce interval ratios of one.57, one.51, one.53, one.51, and one.forty four in between each pair of planets. Which is not really excellent resonance – but it really is shut enough to classify High definition 158259 as an amazing method.
And this, the researchers feel, is a indication that the planets orbiting the star did not form wherever they are now.
“Various compact units with several planets in, or shut to, resonances are regarded, this kind of as TRAPPIST-one or Kepler-eighty,” spelled out astronomer Stephane Udry of the College of Geneva.
“This sort of units are considered to form much from the star in advance of migrating to it. In this scenario, the resonances perform a vital component.”
Which is because these resonances are imagined to end result when planetary embryos in the protoplanetary disc improve and migrate inwards, absent from the outer edge of the disc. This produces a chain of orbital resonance all over the method.
Then, after the remaining gasoline of the disc dissipates, this can destabilise the orbital resonances – and this could be what we’re viewing with High definition 158259. And people little differences in the orbital resonances could explain to us more about how this destabilisation is transpiring.
“The latest departure of the interval ratios from 3:2 has a prosperity of facts,” Hara stated.
“With these values on the a person hand, and tidal result versions on the other hand, we could constrain the interior framework of the planets in a upcoming examine. In summary, the latest state of the method gives us a window on its development.”
The research has been revealed in Astronomy & Astrophysics. | 0.930482 | 3.837406 |
Philaephilia n. Temporary obsession with logistically important and risky stage of scientific endeavour and cometary rendezvous.
Don’t worry, the condition is entirely transient
Rivalling the 7 minutes of terror as NASA’s Curiosity rover entered the Martian atmosphere, Philae’s descent onto comet 67P/Churyumov-Gerasimenko Wednesday as part of the European Space Agency’s Rosetta mission had the world excited about space again.
Comets don’t have the classic appeal of planets like Mars. The high visibility of Mars missions and moon shots has roots in visions of a Mars covered in seasonal vegetation and full of sexy humans dressed in scraps of leather, and little else. But comets may be much better targets in terms of the scientific benefits. Comets are thought to have added water to early Earth, after the young sun had blasted the substance out to the far reaches of the solar system beyond the realm of the rocky planets. Of course, comets are also of interest for pure novelty: until Philae, humans had never put a machine down on a comet gently. Now the feat has been accomplished three times, albeit a bit awkwardly, with all science instruments surviving two slow bounces and an unplanned landing site. Unfortunate that Philae is limited to only 1.5 hours of sunlight per 12 hour day, but there is some possibility that a last-minute attitude adjustment may have arranged the solar panels a bit more fortuitously.
So if Rosetta’s Philae lander bounced twice, rather than grappling the surface as intended, and landed in a wayward orientation where its solar panels are limited to only 12.5% of nominal sun exposure, how is the mission considered a success?
Most likely, the full significance of the data relayed from Philae via Rosetta will take several months of analysis to uncover. Perhaps some of the experiments will be wholly inconclusive and observational, neither confirming nor denying hypotheses of characteristic structure of comets. For example, it seems unlikely that the MUPUS instrument (i.e. cosmic drill) managed to penetrate a meaningful distance into the comet, and we probably won’t gain much insight concerning the top layers of a comet beyond perhaps a centimetre or so. In contrast, CONSERT may yield unprecedented observations about the interior makeup of a comet.
In science, failures and negative findings are certainly more conclusive, and arguably more preferable, than so-called positive results, despite the selective pressure for the latter in science careers and the lay press. An exception disproves the rule, but a finding in agreement with theory merely “fails to negate” said theory. For example, we now know better than to use nitrocellulose as a vacuum propellant. Lesson learned on that front.
In addition to a something-divided-by-nothing fold increase in knowledge about the specific scenario of attempting a soft landing on a comet, I’d suggest we now know a bit more about the value of autonomy in expeditions where the beck-and-call from mission control to operations obviates real time feedback. Perhaps if Philae had been optimised for adaptability, it would have been able to maintain orientation to the comet surface and give Rosetta and scientists at home a better idea of its (final) resting place after detecting that the touchdown and grapple didn’t go through. Space science is necessarily cautious, but adaptive neural networks and other alternative avenues may prove useful in future missions.
I’ll eagerly await the aftermath, when the experimental and the telemetry data have been further analysed. The kind of space mission where a landing sequence can omit a major step and still have operational success of all scientific instruments on board is the kind of mission that space agencies should focus on. The Rosetta/Philae mission combined key elements of novelty (first soft landing and persistent orbiting of a comet) low cost (comparable to a fewspace shuttle missions), and robustness (grapples didn’t fire, comet bounced and got lost, science still occurred). Perhaps we’ll see continued ventures from international space agencies into novel, science-driven expeditions. Remember, the first scientist on the moon was on the (so far) final manned mission to Luna. Missions in the style of Rosetta may be more effective and valuable on all three of the above points, and are definitely more fundamental in terms of science achieved, than continuous returns to Mars and pushes for manned missions. In a perfect world where space agencies operate in a non-zero sum funding situation along with all the other major challenges faced by human society, we would pursue them all. But realistically, Philae has shown that not only do alternative missions potentially offer more for us to learn in terms ofscience and engineering, but can also enrapture the population in a transcendent endeavour. Don’t stop following the clever madness of humans pursuing their fundamental nature of exploring the universe they live in. | 0.842149 | 3.715952 |
TL;DR: Finally, my years of experience in Kerbal Space Program pay off. It's possible to do, but won't do much compared to just blazing through the atmosphere.
As @TimB mentions, you can't "skip" an asteroid from the atmosphere quite the same way as you would skip something off the surface of a pond. You can, however, make use of the atmosphere to change your trajectory and effect a "bounce".
To get an idea of how this effect would work, let's forget about planets and orbits and work for the moment with an infinite flat plane with a homogeneous gravitational field. Even if you fire it of with a lot of horizontal velocity, it will eventually just drop. Add atmosphere and it just gets slightly slowed down towards the end.
If instead of an asteroid you use a glider, however, you have options. The most straightforward one is to pull up, which will under favourable circumstances get you back out of the atmosphere again, but with less velocity. You may be able to repeat this process, but eventually you'll just glide down. We can do something similar with an appropriately shaped asteroid.
To planets now. We won't be doing any "slingshots" or "gravity assists", since those don't actually require an atmosphere and don't work in two-body systems anyhow.
What happens when a spherical asteroid passes sufficiently close to a planet to dip into the atmosphere (but not so close as to hit the planet) is that it slows down some, losing velocity (and thus energy) to aerodynamic drag. This changes its orbit; doing it on purpose is called "aerobraking" and if the orbit goes from hyperbolic (ie. speeding back into space) to elliptic, it's called "aerocapture". It's not, strictly speaking, "skipping off", since it's not the atmosphere bouncing you off, it's orbital mechanics carrying you away.
Now the thing to understand is that your orbit is at any given point fully determined by your position relative to the body you're orbiting, and your velocity relative to that same body. Aerobraking changes your velocity, generally just by braking, which has the effect of shortening your semi-major axis (bringing you to a "lower orbit") and bringing your periapse down some, as both horizontal velocity and vertical velocity are affected equally.
At this point, using wings (and the golden rule of aircraft design tells us that at these velocities, anything is a wing) you can cause the drag to be asymmetric, gaining what we call "lift". Note that it's impossible for you to gain energy this way, the only thing that's happening is that you're trading some of your velocity to change the direction of the rest of it. You can take advantage of this to change the altitude of your periapse (and hence the eccentricity of your orbit) or effect a plane change, but you'll lose energy doing so.
If you have a controllable aerodynamic shape, you can take advantage of a planets atmosphere to alter your trajectory at no cost in propellant to you. Apollo capsules (IIRC) took advantage of this; by having a centre of mass slightly offset to the side from the geometric centre of the capsule, they would get carried away slightly to the side in an atmosphere, and could rotate the capsule lengthwise to gain some limited control authority.
I have taken advantage of this trick to keep the periapse of a moon lander in the high atmosphere during multiple aerobraking passes on a return from a moon, allowing me to gently slow down and rendezvous with a space station in orbit of Kerbin at a minimal cost in propellant.
Could you use this as a weapon? Maybe. The energy expended in these maneuvers manifests as shock heating and is usually absorbed by the orbiting body, so the effect on the planet is limited. But what if there was enough of it?
This begs the question of how much energy this maneuvre consumes. We can get the answer from the vis-viva energy equation. Taking the initial orbit and calculating the energy (multiplied by the mass of the asteroid), we get the maximum energy we may deposit by deorbiting (read: crashing into the planet). The difference between the energy of this orbit and the new orbit is how much energy was expended/deposited.
For Earth-like planets, just attaining escape velocity compared to sitting on the surface gives you an energy $-62,6 MJ/kg$ which is about $15x$ the energy of TNT. Impressive at first glance, but not much in the grand scheme of things, especially if you consider that you're only expending a tiny part of this energy (however much you're willing to sacrifice without falling) an most of it will be absorbed by the asteroid.
Perhaps a better use of this capability would be to just drop some kinetic impactors (like tungsten rods) to do some damage and then use the planetary atmosphere to fine-tune your trajectory to your next target.
Oh, and since you were asking about the shape of the asteroid: it would probably end up being vaguely reminiscent of a space shuttle if you wanted to optimize, but unless you dip too deep, any shape with asymmetric drag or control surfaces would do, albeit with less efficiency. | 0.831702 | 3.750257 |
Studying gamma ray emissions from phenomena like supermassive black holes allows astrophysicists to better conceptualize the behavior of matter under extreme conditions. Although dark matter is thought to account for roughly a quarter of all energy content in the cosmos, its relationship with gamma rays is mysterious. Now, Ammazzalorso et al. have found the first direct cross-correlation between gamma rays and matter in the Universe. They used gamma ray data from Fermi Large Area Telescope and mapped it with weak gravitational lensing -- a method used obtain the mass distribution of objects. The results could improve particle physicists' understanding of the nature of dark matter and whether dark matter can be a source of gamma ray emissions from space.
Detection of cross-correlation between gravitational lensing and gamma rays Simone Ammazzalorso et al. | 0.810423 | 3.879684 |
Stunning new images show how black holes produce tremendously bright jets millions of light-years long that can be seen across vast cosmic distances. The images were produced by a computer simulation and could help resolve an enduring mystery about how the jets form, the researchers behind the images said.
Despite their moniker, black holes aren't always black. As a black hole consumes an object, gas and dust spins around the maw of the gravitational behemoth, and friction can heat the material on the edges to searing temperatures. This violent process creates lighthouse-like beams of charged particles that travel outward at near light speed, emitting radiation that can shine brighter than an entire galaxy. [11 Fascinating Facts About Our Milky Way Galaxy]
"They are like laser beams piercing the universe and allowing us to see black holes whose emission would otherwise be too dim to be detectable," Alexander Tchekhovskoy, a computational astrophysicist at Northwestern University in Evanston, Illinois, told Live Science.
But the complex mechanisms behind these jets remain poorly understood. A potential insight into the problem comes from the fact that material around a black hole is transformed into plasma, a blisteringly hot, but diffuse magnetized state of matter. Physicists have long suspected that twisting magnetic fields somehow interact with the curved fabric of space-time around a spinning black hole to give rise to the jets.
Using highly detailed computer models, Kyle Parfrey of NASA's Goddard Space Flight Center in Greenbelt, Maryland, and his colleagues were able to simulate how charged particles near a black hole's edge give rise to twisting and rotating magnetic fields, as the researchers reported Jan. 23 in the journal Physical Review Letters. The scientists also incorporated information from Albert Einstein's theory of relativity to model pairs of these particles flying on special orbits. These orbits are tuned in just the right way so that if one of the particles from a duo falls into the black hole, its partner will zoom out at ultrafast speed, propelling itself using energy stolen from the black hole itself. [8 Ways You Can See Einstein's Theory of Relativity in Real Life]
Any object, even a bag of trash, could be shot out of a spacecraft onto on one of these orbits, and it would give the ship a powerful boost of energy, said Tchekhovskoy, who was not involved in the work.
The new computational methods will help researchers better study regions of intense electric current near a black hole's edge, which could be related to the X-rays and gamma-rays seen in the jets, Parfrey told Live Science. Next, the team wants to more realistically model the process of generating the charged particle pairs. That will allow astronomers to make better predictions about a jet's properties, Parfrey said.
The findings will also help scientists interpret the results from two endeavors, the Event Horizon Telescope and GRAVITY, currently aiming to photograph the shadow cast on surrounding material by the supermassive black hole at the heart of the Milky Way, Parfrey said.
- Stephen Hawking's Most Far-Out Ideas About Black Holes
- What's That? Your Physics Questions Answered
- The 18 Biggest Unsolved Mysteries in Physics
Originally published on Live Science. | 0.908169 | 3.882899 |
The mystery of why Jupiter's Great Red Spot did not vanish centuries ago may now be solved, and the findings could help reveal more clues about the vortices in Earth's oceans and the nurseries of stars and planets, researchers say.
The Great Red Spot is the most noticeable feature on Jupiter's surface — a storm about 12,400 miles (20,000 kilometers) long and 7,500 miles (12,000 km) wide, about two to three times larger than Earth. Winds at its oval edges can reach up to 425 mph (680 km/h). This giant storm was first recorded in 1831 but may have first been discovered in 1665.
"Based on current theories, the Great Red Spot should have disappeared after several decades," researcher Pedram Hassanzadeh, a geophysical fluid dynamicist at Harvard University,said in a statement. "Instead, it has been there for hundreds of years." [Photos: Most Powerful Storms in the Solar System]
Vortices like the Great Red Spot can dissipate because of many factors. For instance, waves and turbulence in and around the storm sap its winds of energy. It also loses energy by radiating heat. Moreover, the Great Red Spot rests between two powerful jet streams in Jupiter's atmosphere that flow in opposite directions and may slow down its spinning.
Some researchers suggest that large vortices such as the Great Red Spot gain energy and survive by absorbing smaller vortices. However, "this does not happen often enough to explain the Red Spot's longevity," researcher Philip Marcus, a fluid dynamicist and planetary scientist at the University of California, Berkeley,said in a statement.
The Great Red Spot is not the only mysterious vortex. In fact, vortices in general, including ones in Earth's oceans and atmosphere, often live much longer than current theories can explain.
To help solve the mystery of the Great Red Spot's endurance, Hassanzadeh and Marcus developed a new 3D, high-resolution computer model of large vortices.
Models of vortices generally focus on swirling horizontal winds, where most of the energy resides. Although vortices also have vertical flows, these have much less energy. Therefore, "in the past, most researchers either ignored the vertical flow because they thought it was not important, or they used simpler equations because it was so difficult to model," Hassanzadeh said.
The researchers now find that vertical flows hold the key to the Great Red Spot's longevity: When the storm loses energy, vertical flows move hot and cold gases in and out of the storm, restoring part of the vortex's energy. Their model also predicts radial flows that suck winds from the high-speed jet streams around the Great Red Spot toward the storm's center, helping it last longer.
Together, vortices — whether on Jupiter or in Earth's oceans — may decay up to 100 times slower than researchers previously thought.
"Some vortices in the oceans have been observed to last for several years and are believed to play an important role in the oceanic ecosystem and ocean-atmosphere interaction," Marcustold SPACE.com. In addition, "vortices with physics very similar to the Great Red Spot are believed to contribute to star and planet formation processes, which would require them to last for several million years. Both oceanic and astrophysical vortices are subjected to dissipating processes, and the mechanism described here for the longevity of the Great Red Spot presents a very plausible explanation for their longevity as well."
The scientists caution that their model does not entirely explain the Great Red Spot's long life span. They suggest that occasional mergers with smaller vortices may help prolong the giant storm's life as well, and have begun modifying their computer model to test this idea.
In addition, their "current model does not account for compressibility of the flow or sphericity of the planet," Hassanzadeh told SPACE.com. "Although we believe that these effects do not change the conclusions of our work, we are planning to modify our model in the next step and include these effects."
The scientists will detail their findings Nov. 25 at the annual meeting of the American Physical Society's Division of Fluid Dynamics in Pittsburgh. | 0.830061 | 3.940275 |
With data from a West Australian radio telescope, a team of scientists shows us what the world would look like if we could see radio waves. And it’s spectacular.
The Galactic and Extragalactic All-sky MWA, or the GLEAM survey, is a large-scale effort to pick up on the radio waves that are traveling through the Universe all around us. So far, it has charted 300,000 galaxies observed by the Murchinson Widefield Array (MWA), a 50$ million radio telescope north-east of Geraldton, Australia. Not only does the telescope see further than our eyes could — it also “sees” a much wider spectrum of electromagnetic radiation.
“The human eye sees by comparing brightness in three different primary colours – red, green and blue,” said lead author of these images catalogue, Dr. Natasha Hurley-Walker from Curtin University and the International Centre for Radio Astronomy Research.
“GLEAM does rather better than that, viewing the sky in each of 20 primary colours. That’s much better than we humans can manage, and it even beats the very best in the animal kingdom, the mantis shrimp, which can see 12 different primary colours.”
The data has been translated into colors the human eye can see — red for the lower frequencies, green for middle ones, and blue for the highest — the first survey to image the sky in such vivid technicolor, Hurley-Walker added. GLEAM looks at electromagnetic waves (the same stuff we see as light) from frequencies between 70 to 230 MHz. The stuff they watch is amazing — clusters of galaxies colliding, echoes of ancient stars exploding, and “the first and last gasps” of supermassive black holes.
“The area surveyed is enormous,” said MWA director Dr Randall Wayth. “Large sky surveys like this are extremely valuable to scientists and they’re used across many areas of astrophysics, often in ways the original researchers could never have imagined.”
The GLEAM survey is a big step on the part to completing the SKA-low, the low-frequency part of the international Square Kilometre Array radio telescope which will be built in Australia in the coming years.
“It’s a significant achievement for the MWA telescope and the team of researchers that have worked on the GLEAM survey,” Dr Wayth said.
“The survey gives us a glimpse of the Universe that SKA-low will be probing once it’s built. By mapping the sky in this way we can help fine-tune the design for the SKA and prepare for even deeper observations into the distant Universe.” | 0.858741 | 3.991305 |
Something new on the Sun: Spacecraft observes new characteristics of solar flares
(PhysOrg.com) -- NASA's Solar Dynamics Observatory, or SDO, has provided scientists new information about solar flares indicating an increase in strength and longevity that is more than previously thought.
Solar flares are intense bursts of radiation from the release of magnetic energy associated with sunspots. They are the solar system's largest explosive events and are seen as bright areas on the sun. Their energy can reach Earth's atmosphere and affect operations of Earth-orbiting communication and navigation satellites.
Using SDO's Extreme ultraviolet Variability Experiment (EVE) instrument, scientists have observed that radiation from solar flares continue for up to five hours beyond the main phase. The new data also show the total energy from this extended phase of the solar flare's peak sometimes has more energy than the initial event.
Video above: A compilation of solar data from various instruments on SDO recording a flare on May 5, 2010. The images on top show the initial magnetic loops of the flare, and a delayed brightening of additional magnetic loops above the originals showing the late phase flare. Along the bottom, graphs from EVE show the extreme ultraviolet light peaking both in time with the main flare and the late phase flare. Credit: NASA/SDO/Tom Woods
"Previous observations considered a few seconds or minutes to be the normal part of the flare process," said Lika Guhathakurta, lead program scientist for NASA's Living with a Star Program at the agency's Headquarters in Washington. "This new data will increase our understanding of flare physics and the consequences in near-Earth space where many scientific and commercial satellites reside."
On Nov. 3, 2010, SDO observed a solar flare. If scientists only had measured the effects of the flare as it initially happened, they would have underestimated the amount of energy shooting into Earth's atmosphere by 70 percent. SDO's new observations provide a much more accurate estimation of the total energy solar flares put into Earth's environment.
"For decades, our standard for flares has been to watch the X-rays as they happen and see when they peak," said Tom Woods, a space scientist at the University of Colorado in Boulder and principal author on a paper in Wednesday's online edition of Astrophysical Journal. "But we were seeing peaks that didn't correspond to the X-rays."
During the course of a year, the team used EVE to map each wavelength of light as it strengthened, peaked, and diminished over time. EVE records data every 10 seconds and has observed many flares. Previous instruments only measured every 90 minutes or didn't look at all wavelengths simultaneously as SDO can.
Video above: On May 5, 2010, shortly after the Solar Dynamics Observatory (SDO) began normal operation, the sun erupted with numerous coronal loops and flares. Many of these showed a previously unseen "late phase flare" appearing minutes to hours after the main flare. Credit: NASA/SDO
To compliment the EVE graphical data, scientists used images from another SDO instrument, the Advanced Imaging Assembly (AIA). Analysis of these images showed the main flare eruption and its extended phase in the form of magnetic field lines called coronal loops that appeared far above the original eruption site. These extra loops were longer and became brighter later than the loops from the main flare and also were physically set apart from those of the main flare.
Because this previously unrealized extra source of energy from flares also is impacting Earth's atmosphere, Woods and his colleagues are studying how the late phase flares can influence space weather. Space weather caused by solar flares can affect communication and navigation systems, satellite drag and the decay of orbital debris.
SDO was launched on Feb. 11, 2010. The spacecraft is the most advanced spacecraft ever designed to study the sun and its dynamic behavior. SDO provides images 10 times clearer than high definition television and more comprehensive science data faster than any solar observing spacecraft in history.
EVE was built by the Laboratory for Atmospheric and Space Physics at the University of Colorado. AIA was built by Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif. | 0.818082 | 3.690883 |
Scientists have found dark matter interacting with other dark matter in an entirely new way other than just the force of gravity. This first potential signs of self-interacting dark matter suggests that dark matter may not be completely dark after all.
Astronomers used a technique known as gravitational lensing to deduce the location of dark matter and using the MUSE instrument on ESO’s very Large Telescope along with images from the ASA/ESA Hubble Space Telescope which is in orbit, they were able to study simultaneous collision of four other galaxies in a cluster known as Abell 3827, but with a relatively slower speed. Of course, these collisions took place over hundred of millions of years in the far-flung corners of the Universe.
As a result, the collisions severely distorted space-time. Also as calculation suggests, the distance between the clump of dark matter and that of four galaxies associated with collisions is currently 5000 light-years (50,000 million kilometers), this would take NASA’s Voyager spacecraft some 90 million years to travel that far.
Based on the assumption acquired as a result of observation that dark matter apparently slow down after interacting with other dark matter and its lag with the galaxy it surrounds, scientists came to the conclusion that dark matter is capable of engaging with a force other than gravity, presumably by interacting with itself.
This is for the first time dark matter has been found to show signs of self-interacting other than interacting with the force of gravity.
“We used to think that dark matter just sits around, minding its own business, except for its gravitational pull. But if dark matter were being slowed down during this collision, it could be the first evidence for rich physics in the dark sector — the hidden Universe all around us.” said lead author of the study, Richard Massey at Durham University. | 0.910428 | 3.785666 |
- Fluorine absorption dating
- Nitrogen dating
- Fluorine uranium nitrogen dating services | ВКонтакте
- Recommended publications
Radiocarbon dating also referred to as carbon dating or carbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late s by Willard Libby, who received the Nobel Prize in Chemistry for his work in It is based on the fact that radiocarbon 14C is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen.
The resulting 14C combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14C it contains begins to decrease as the 14C undergoes radioactive decay. Measuring the amount of 14C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information A lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year.
If the solar year is defined as a tropical year, then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year, then the calendar will predict the constellation near which the full moon may occur. As with all calendars which divide the year into months there is an additional requirement that the year have a whole number of months. In this case ordinary years consist of twelve months but every second or third year is an embolismic year, which adds a thirteenth intercalary, embolismic, or leap month.
Also, some of the ancient pre-Islamic calendars in south Arabia followed a lu Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.
Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geologic time scale. By allowing the establishment of geological timescales, it Thiophosphoryl fluoride is an inorganic molecular gas with formula PSF containing phosphorus, sulfur and fluorine.
It spontaneously ignites in air and burns with a cool flame. The discoverers were able to have flames around their hands without discomfort, and called it "probably one of the coldest flames known". Also produced in this reaction was silicon tetrafluoride and phosphorus fluorides. They observed the spontaneous inflammability. They also used this method: Issue of the London Gazette, covering the calendar change in Great Britain.
The date heading reads: There were two calendar changes in Great Britain and its colonies, which may sometimes complicate matters: Beginning in , the Gregorian calendar replaced the Julian in Roman Catholic countries. This change was implemented subsequently in Protestant an Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year 1 BC is followed by AD 1. However, there is a year zero in astronomical year numbering where it coincides with the Julian year 1 BC and in ISO He introduced the new era to avoid using the Diocletian era, based on the accession of Roman Emperor Diocletian, as he did not wish to continue the memory of a persecutor of Christians.
In the preface to his Easter table, Dionysius stated that the "present year" was "the consulship of Probus Junior [Flavius Anicius Probus Iunior]" which was also years "since the incarnat Before Present BP years is a time scale used mainly in geology and other scientific disciplines to specify when events occurred in the past.
Because the "present" time changes, standard practice is to use 1 January as the commencement date of the age scale, reflecting the origin of practical radiocarbon dating in the s. The abbreviation "BP" has alternatively been interpreted as "Before Physics"; that is, before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, making dating after that time likely to be unreliable.
Some archaeologists use the lowerca Look up circa in Wiktionary, the free dictionary. Circa from Latin, meaning 'around, about' — frequently abbreviated c.
- india best dating sites.
- how do i know if the guy im dating is gay.
- Dating methodologies in archaeology!
When used in date ranges, circa is applied before each approximate date, while dates without circa immediately preceding them are generally assumed to be known with certainty. George Washington years are: Both years are known precisely. Only the end year is known accurately; the start year is approximate.
Only the start year is known accurately; the end year is approximate. Both years are approximate. See also Floruit References "circa". Retrieved 16 July External links The dictionary definition of circa at Wiktio Drill for dendrochronology sampling and growth ring counting The growth rings of a tree at Bristol Zoo, England. Each ring represents one year; the outside rings, near the bark, are the youngest. Dendrochronology or tree-ring dating is the scientific method of dating tree rings also called growth rings to the exact year they were formed.
As well as dating them this can give data for dendroclimatology, the study of climate and atmospheric conditions during different periods in history from wood. Dendrochronology is useful for determining the precise age of samples, especially those that are too recent for radiocarbon dating, which always produces a range rather than an exact date, to be very accurate. However, for a precise date of the death of the tree a full sample to the edge is needed, which most trimmed timber will not provide. It also gives data on the timing of events and rates of change in the environment most prominently climate and also in wood found in archaeology or works of art and arch Uranium—lead dating, abbreviated U—Pb dating, is one of the oldest and most refined of the radiometric dating schemes.
It can be used to date rocks that formed and crystallised from about 1 million years to over 4. The mineral incorporates uranium and thorium atoms into its crystal structure, but strongly rejects lead. Therefore, one can assume that the entire lead content of the zircon is radiogenic, i.
- Dating of fossil bones by the fluorine method!
- largest dating site south africa!
- Looking for the full-text?.
- References (18).
Thus the current ratio of lead to uranium in the mineral can be used to determine its age. The method relies on two separate decay chains, the uranium series from U to Pb, with a half-life of 4. Decay routes The above uranium to lead decay routes occur via a series of a Depiction of the 19 years of the Metonic cycle as a wheel, with the Julian date of the Easter New Moon, from a 9th-century computistic manuscript made in St.
Emmeram's Abbey Clm , fol. A red color shows full moons that are also lunar eclipses. For astronomy and calendar studies, the Metonic cycle or Enneadecaeteris from Ancient Greek: The Greek astronomer Meton of Athens fifth century BC observed that a period of 19 years is almost exactly equal to synodic months and, rounded to full days, counts 6, days.
The difference between the two periods of 19 years and synodic months is only a few hours, depending on the definition of the year. Common Era or Current Era CE is one of the notation systems for the world's most widely used calendar era. The year-numbering system utilized by the Gregorian calendar is used throughout the world today, and is an international standard for civil calendars. Thus, it has a year 0; the years before that are designated with negative numbers and the years after that are designated with positive numbers.
The phantom time hypothesis is a historical conspiracy theory asserted by Heribert Illig. Illig believed that this was achieved through the alteration, misrepresentation and forgery of documentary and physical evidence. The proposal has been universally rejected by mainstream historians. He was active in an association dedicated to Immanuel Velikovsky, catastrophism and historical revisionism, Gesellscha A geological period is one of several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place.
These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history. Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages. The rocks formed during a period belong to a stratigraphic unit called a system. Structure The twelve currently recognised periods of the present eon — the Phanerozoic — are defined by the International Commission on Stratigraphy ICS by reference to the stratigraphy at particular locations around the world.
In the Ediacaran Period of the latest Precambrian was defined in similar fashion, and was the first such newly designated period in years; but earlier periods are simply defined by age. A consequence of this approach to the Phanerozoic periods is that the ages of their beginnings and ends can change from time to time as the abs A geologic era is a subdivision of geologic time that divides an eon into smaller units of time. These eras are separated by catastrophic extinction boundaries, the P-T boundary between the Paleozoic and the Mesozoic and the K-Pg boundary between the Mesozoic and the Cenozoic.
The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals.
Fluorine absorption dating
More recently, however, the Archean and Proterozoic eons have been subdivided into eras of their own. Geologic eras are further subdivided into geologic periods, although the Archean eras have yet to be subdivid Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating. It is useful to geologists and archaeologists who want to know when such an event occurred. It uses various methods to stimulate and measure luminescence. Conditions and accuracy All sediments and soils contain trace amounts of radioactive isotopes of elements such as potassium, uranium, thorium, and rubidium.
These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar. The radiation causes charge to remain within the grains in structurally unstable "electron traps". The trapped charge accumulates over time at a rate determined by the amount of background radiatio Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be temporally fixed i.
Archaeologists use tree-ring dating dendrochronology to determine the age of old pieces of wood. Trees usually add growth rings on a yearly basis, with the spacing of rings being wider in high growth years and narrower in low growth years. Patterns in tree-ring growth can be used to establish the age of old wood samples, and also give some hints to local climatic conditions.
This technique is useful to about 9, years ago for samples from the western United States using overlapping tree-ring series from living and dead wood. The Earth's orbital motions inclination of the earth's axis on its orbit with respect to the sun, gyroscopic precession of the earth's axis every 26, years; free precession every days, precession of earth orbit and orbital variations such as perihelion precession every 19, An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.
Comparable terms are epoch, age, period, saeculum, aeon Greek aion and Sanskrit yuga. Etymology Look up era in Wiktionary, the free dictionary.
Fluorine uranium nitrogen dating services | ВКонтакте
The Latin word use in chronology seems to have begun in 5th century Visigothic Spain, where it appears in the History of Isidore of Seville, and in later texts. The Spanish era is calculated from 38 BC, perhaps because of a tax cfr. Like epoch, "era" in English originally meant "the starting poi The Julian date 23 November corresponded to the Gregorian 6 December. The treaty was concluded between Roman Catholic parties, who had adopted the Gregorian calendar, and Protestant parties, who had not.
Dual dating is the practice, in historical materials, to indicate some dates with what appears to be duplicate, or excessive digits, sometimes separated by a hyphen or a slash. This is also often referred to as double dating. The need for double dating arose from the transition from an older calendar to a newer one. A solar calendar is a calendar whose dates indicate the season or almost equivalently the position of the apparent position of the sun in relative to the stars.
The Gregorian calendar, widely accepted as standard in the world, is an example of solar calendar. The main other type of calendar is a lunar calendar, whose months correspond to cycles of moon phases. The months of the Gregorian calendar do not correspond to cycles of moon phase. Examples The oldest solar calendars include the Julian calendar and the Coptic calendar.
They both have a year of days, which is extended to once every four years, without exception, so have a mean year of As solar calendars became more accurate, they evolved into two types. Tropical solar calendars If the position of the earth in its orbit around the sun is reckoned with respect to the equinox, the point at which the orbit crosses the celestial equator, then its dates accurately indicate the seasons, that is, they are synchronized with the declinati Archaeomagnetic dating is the study and interpretation of the signatures of the Earth's magnetic field at past times recorded in archaeological materials.
These paleomagnetic signatures are fixed when ferromagnetic materials such as magnetite cool below the Curie point, freezing the magnetic moment of the material in the direction of the local magnetic field at that time. The direction and magnitude of the magnetic field of the Earth at a particular location varies with time, and can be used to constrain the age of materials.
In conjunction with techniques such as radiometric dating, the technique can be used to construct and calibrate the geomagnetic polarity time scale. This is one of the dating methodologies used for sites within the last 10, years. Thellier in the s and the increased sensitivity of SQUID magnetometers has greatly promoted its use. Instances of use The Earth's magnetic field has two main components.
The stronger component known as the Eart Two such calendar eras have seen notable use historically: That calendar is similar to the Julian calendar except that its epoch is equivalent to 1 September BC on the Julian proleptic calendar. Since the Middle Ages, the Hebrew calendar has been based on rabbinic calculations of the year of creation from the Hebrew Masoretic text of the bible. This calendar is used within Jewish communities for religious and other purposes. 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.
Fluoride concentration in bones of human crania were determined by fluoroselective electrode. The fluoride content increased with the prolongation of the chronological age of examined skulls. Sex is not a factor differentiating the fluoride content of skulls. Archaeometric classification of ancient human fossil bones, with particular attention to their carbonate content, using chemometrics, thermogravimetry and ICP emission.
The potential of coupling chemometric data processing techniques to thermal analysis for formulating an "archaeometric" classification of fossil bones was investigated. Moreover, the possibility of integrating the outcomes of this approach with the results of inductively coupled plasma ICP emission spectroscopy for an anthropological interpretation of the observed patterns was also examined.
Several fossil bone samples coming from the necropolis of El Geili, in the middle Nile, an important archaeological site, were first of all subjected to thermogravimetric TG and derivative thermogravimetric DTG analysis and the main steps of the curves were analyzed. This allowed fossil bone samples to be differentiated, both by means of classical bidimensional and chemometric representations, namely Principal Component Analysis PCA. In particular, two clusters were observed, attributable to samples of different antiquity.
In addition, inductively coupled plasma ICP emission spectroscopy showed that the samples in the cluster corresponding to more recent burials are characterized by a higher Zn content, suggesting a more varied diet. The experimental data obtained using thermogravimetry TG-DTG allows us to differentiate all the fossil bone samples analyzed into two separate clusters and to interpret this differentiation in terms of the observed transitions.
We describe the finding of five male bodies from the salt mine of Chehr Abad, Zanjan province, Iran. Radiocarbon determinations suggests that two of the bodies date to the late Sassanian period, while the other three died sometime between B. We speculate that these deaths may have been the result of an earthquake between — B. We have also obtained new isotopic data on skin and hair, and conclude that they may not have come from the Zanjan area.
Apreliminary study of stomach contents and parasite load for one of the bodies has also been carried out. Determination of calcium, phosphorus and fluorine in bone by instrumental fast neutron activation analysis. The determination of fluorine, calcium and phosphorus in bone by instrumental fast neutron activation analysis is described. The physical survival of the skeleton in the burial environment is vital to any palaeopathological study, and the extent of diagenetic degradation of remains is an important determinant of the quantity and quality of palaeopathological data that can be obtained from an archaeological skeletal assemblage. | 0.891642 | 3.025637 |
A binary star is actually a name for a star system that is made up of two or more stars that orbit a common center of mass. The brightest star of a binary pair is called the primary, while the other star is called companion, or secondary.
In astrophysics, binary stars easily allow for the calculation of mass of the individual stars. This is done though using their mutual orbit to precisely calculate the mass of the individual stars through Newtonian calculations. Through this, the radius and density of the individual stars can be calculated indirectly. This collected data from various binary stars also allow the calculation of mass for similar single stars through extrapolation. It is estimated that a third of the stars in our galaxy are binary and multiple star systems.
Binary stars are classified by the method of observation used to discover them. These include eclipsing, visual, spectroscopic, and astrometric binaries.
An eclipsing binary is a binary system where the orbital plain is close enough to the line of sight of an observer that the individual stars will eclipse each other.
Eclipsing binaries are also classified as variable stars, stars that have regular and periodic changes in the apparent magnitude. This variation in brightness may be from a pair of binary stars as one passes in front of the other as seen from the point of the observer. If the two stars are of different sizes, the larger star will block the other through a total eclipse, while the smaller star will partially dim the large one via an annular eclipse. This change in brightness over regular periods of time is known as the light curve.
The first observed eclipsing binary discovered was the star system Algol. The star was known to periodically change in magnitude since ancient times, but in 1881, it was discovered this was due to the fact Algol was not one, but two stars in close orbit.
A visual binary is a binary pair where the individual stars are visible through a telescope that has the appropriate resolving power. Brighter stars are more difficult to resolve as visible binaries then dimmer ones, due to glare. A binary may also be difficult to resolve visually if the primary (brighter star) is significantly more visually luminous then its companion, effectively washing out the other star.
By measuring the position angle of the companion star relative to the primary and the angler distance between the two stars over time, the ellipse, called the apparent ellipse, which is the orbit of the secondary in respect to the primary, can be plotted out. From this measurement of the semi-major axis and orbital period of binary stars' orbit, the mass of the stars can be determined.
Visual binaries are quite common and in fact make up many of the most well-known and prominent stars in the night sky, such as Castor. Three of the six closest known stars are visual binaries: Alpha Centauri, Luyten 726-8, and Sirius.
If it is impossible to resolve the star as a binary visually, then one method determining whether or not a star is part of a binary pair is through analyzing the light emitted from the star system using a spectrograph, binaries observed this way are known a spectroscopic binaries.
When a Spectrograph is used to indirectly observe a star, it spreads the light from that star into a full spectrum of colors superimposed with dark absorption lines. If the star observed in this method is suspected to be a binary star, the spectrum that is analyzed is from both stars together. If in observing this spectrum, a Doppler effect is observed over time, that determines there is indeed a binary pair. The Doppler effect is caused when the two stars orbit their common center of mass, one star moves closer to us while its companion moves away. As this happens, the spectral lines in the spectrum for the star moving close will be blue shifted, while the spectral lines of its companion moving away will be red shifted though the Doppler effect. As the stars move across out line of site in their orbit, the location of absorption lines or each star will become the same. As the first star moves away and its companion approaches, the opposite shifting of wavelengths will occur, with the companion star's spectral lines blue shifting as it approaches, while the first star's spectral lines red shift as it moves away in its orbit.
One of the most well known spectroscopic binaries is the star system Mizar. The star system was already known as a visual binary, when in 1889 it was discovered the primary star Mizar A of the visual binary pair, had its own close companion. This companion was the first star to be found using spectroscopy. Later it was observed that Mizar B also had its own spectroscopic companion.
An astrometric binary is a star system where only one star can be observed but an unseen companion is inferred through a perturbation ("wobble") of the star's proper motion in space. This perturbation is caused by the companion's gravitational influence on the observable primary star. Sirius is the best known example of an astrometric binary, when in 1844 Friedrich Bessell observed a wobble in the motion of Sirius A. He theorized that the star had an unseen companion. Later with improving telescope technology, the companion white dwarf was confirmed visually.
An optical binary are two stars that visually appear next to each other from the point of the observer using the unaided eye. The reason for this is the two stars are usually along the line of sight of the observer, giving the illusion they are part of a binary pair. However, in reality the two stars are actually a great distance from each other and are not gravitationally bound as a single system. A prime example of this is Alpha Capricorni, traditionally seen as a binary with the individual stars referred to as α1 Capricorni and α2 Capricorni, however the former is 690 light years away, while the latter is only 109 light years away from Earth respectively.
Cataclysmic binaries, sometimes referred to as cataclysmic variable stars or cataclysmic variables, are very close binary pair that will suddenly and irregularly increase in brightness before returning to their normal magnitude. The two components of a cataclysmic binary consist of a white dwarf primary and an M class secondary (ranging from a main sequence star to a giant). The two stars are sufficiently close that the white dwarf distorts and draws off material from the secondary. This infalling matter of mostly hydrogen forms an accretion disk around the white dwarf. Instabilities in this accretion disk can lead to what is known as a dwarf nova.
There are two types of cataclysmic binaries, non-magnetic and magnetic. The non-magnetic types are by far the most common, these include U Geminorum stars as well as those that are the source of classical and recurrent novae. Much more rare are the magnetic types, where a powerful magnetic field surrounds the primary white dwarf star, greatly affecting how the material flows from the secondary star, as well as locking the two stars into a synchronous rotation.
The observations of binary stars began with the invention of the telescope, with the first known recordings in the 17th century. Giovanni Battista Riccioli discovered in 1650 that Mizar was actually a binary. Christiaan Huygens found that that Theta Orionis was actually three stars in 1656, Robert Hooke made the same observation about Gamma Arietis in 1664, while in 1685 Father Fontenay observed that the star Acrux was really a binary pair.
William Herschel was the first person to coin the term binary star. He defined the term in 1802 as:
- The union of two stars, that are formed together in one system, by the laws of attraction.
Herschel began his observation of binaries in 1779. The result was a cataloging of over 700 double stars systems as recorded in his book Catalogue of 500 new Nebulae ... and Clusters of Stars; with Remarks on the Construction of the Heavens in 1802. By the next year, he concluded that these double stars must be binary systems. It was not until 1827 though that an actual orbit of a binary star system was calculated. This was completed by Félix Savary of the star Xi Ursae Majoris. Today over 100,000 binary star systems have been cataloged, although the actual orbits of only a few thousand of these are known, with some cataloged stars possibly being only optical binaries.
Evolution of Binary Stars
Binary pairs have been observed in protostars that have yet to reach the main sequence, suggesting that binaries form in the early stages of star formation. This could be due to the fragmentation of the molecular cloud as the stars first form, allowing for multiple stars to be created in the same system.
Because most binary stars are of different masses, one will evolve off the main sequence before its companion. In this scenario, several different events may happen. The two stars may remain detached if the companion is far enough away in distance, and not very gravitationally massive. The two stars will be semi-detached if the star that has evolved into the giant star is gravitationally close enough to its companion and exceeds its Roche lobe, losing mass to its companion through accretion. In this situation, much of the giant's mass may transfer to the companion star, actually making it the more massive of the two, despite still being in the main sequence. Algol is the prime example of this.
In some situations, the two stars of the binary system are so close that the expanding giant may actually come in atmospheric contact with its companion. This is known as a contact binary. In this situation, the very close companion may cause the atmosphere of the giant to literally "splash away," leaving a naked core. The companion, meanwhile, may spiral towards the core of the once giant from the friction of their atmospheres. The result will be a merged core that becomes a white dwarf.
Type I supernova
If one of the stars on a binary system is a white dwarf that is close enough to its companion when the companion star exceeds its Roche lobe, the white dwarf will steadily accrete gases from its companion's atmosphere. This accreted gases will build up and compress on the surface of the white dwarf, due to its high gravity at its surface. The gas will then steadily heat up as more material accumulates. The result is that hydrogen fusion may occur on the surface of the dwarf and, through the tremendous release in energy, throw the rest of the collected gas off in a brilliant flash. This extremely bright event is called a nova.
The above event will occur as long as the additional mass the white dwarf accreted from its companion doesn't cause the star to exceed the Chandrasekhar limit, which is 1.4 solar masses. If the material buildup on the white dwarf exceeds this limit, the electron degeneracy of the white dwarf itself will no longer be able to hold the star up against gravity. In this scenario a type I supernova will occur that destroys the star. The most famous example of this is the supernova SN 1572, considered one of the foremost events in astronomy. Tycho Brahe observed this event extensively.
- Orbits of 150 Visual Binaries
- The Radial Velocity Equation in the Search for Exoplanets ( The Doppler Spectroscopy or Wobble Method )
- D. Prialnik, Novae, Encyclopaedia of Astronomy and Astrophysics (2001, p.1846-1856) | 0.926399 | 4.107756 |
The assembly of the OSIRIS-REx spacecraft continues to make excellent progress. Most notably, this month Lockheed Martin installed the main propellant tank on the OSIRIS-REx spacecraft at their Space Systems Company facility near Denver, Colorado. In addition to the large tank, many of the primary propulsion components are in house and undergoing extensive testing and certification prior to being integrated onto the spacecraft.
The OSIRIS-REx propulsion system is based on the system developed for the Mars Reconnaissance Orbiter (MRO) and later customized for the Juno and MAVEN missions. Our system is called a “monopropellant” system, meaning that it uses a single fuel called hydrazine (N2H4). Monopropellants are chemicals that do not require an oxidizer to release their stored chemical energy. They are stable under certain storage conditions but they can decompose rapidly to produce a lot of high-temperature gas. The OSIRIS-REx system produces thrust when the hydrazine fuel is flowed over a heated catalyst bed and decomposes. The resulting gases expand through the sonic throat of a rocket engine and accelerate out the rocket engine nozzle.
Early in mission design, we looked at a variety of propulsion systems, including monopropellant, bipropellant, and solar-electric propulsion. Bipropellant systems, such as flown on Juno, add an oxidizing component to produce a more vigorous chemical reaction and hence more thrust. For Juno, the main propulsion system uses hydrazine as fuel and nitrogen tetroxide as an oxidizer. Solar electric propulsion systems, which are used on the Dawn and Hayabusa-2 missions, ionize the rare gas xenon and accelerate it through an electric field to gain thrust. Fortunately for us, our target asteroid Bennu has an orbit that makes it highly accessible. This feature allowed us to select the simplest, most reliable propulsion system to get to Bennu and back.
The propulsion system is composed of the propellant tank (which holds our fuel), a helium tank (which is used to pressurize the system), pressure transducers (which help us monitor propellant and helium supply), valves, pipes, filters, and the rocket engines. As described in a previous post, the OSIRIS-REx propulsion system uses a total of 28 engines that are divided into four groups: a bank of four main-engine propulsion thrusters, six medium-thrust engines, sixteen attitude control thrusters, and two specialized low-thrust rocket engines. All engines are catalytic thrusters using the hydrazine monopropellant.
OSIRIS-REx has one main propellant fuel tank that provides high-purity hydrazine to the spacecraft thrusters as needed. This tank was custom manufactured for us by ATK Aerospace Group in Commerce, California. It was forged out of a single billet of pure titanium, which was one of the first major procurements on our program. It is 150 centimeters (58.8 inches) tall and 124 centimeters (48.9 inches) wide. It has hemispherical ends with 32 tabs for mounting to the spacecraft structure, which are identical to MAVEN and MRO designs. The cylinder section is identical to MRO and is shorter than MAVEN (which is 188 centimeters or 74 inches long). The tank has a volume of 1.3 cubic meters (79,400 cubic inches) and will hold over 1,100 kilograms of hydrazine propellant. Prior to sizing the tank we computed the propellant mass required for the mission using the trajectories in our Design Reference Mission, assuming a maximum spacecraft “wet mass” (the mass of the spacecraft with a fully loaded fuel tank) and continuous worst-case low-thruster performance.
The helium tank is a high-pressure (4800 psi) composite overwrapped pressure vessel that supplies helium on demand to the propellant tank. The function of the overwrap is to evenly distribute pressure loads across the entire tank. The tank is 42.4 centimeters wide (16.7 inches) and 75.2 centimeters tall (29.6 inches). It has a volume of 0.08 cubic meters (4,967 cubic inches) and holds 3.7 kg of helium. The helium tank is needed because the OSIRIS-REx propellant system operates in a pressure-regulated mode for our large main-engine burns. These include our Deep Space Maneuvers en route to Bennu, the Asteroid Approach Maneuver to slow us down for Bennu rendezvous, the Asteroid Departure Maneuver to leave Bennu, and the Earth Departure Maneuver, which occurs after capsule release and places us in heliocentric orbit for a possible extended mission.
For each of our major maneuvers the helium is used to maintain constant pressure in the propulsion system. Prior to the start of one of these burns an upstream latch-valve is opened, ensuring a steady flow of hydrazine to the rocket engines. The latch valve is closed at burn completion. With these regulated burns, OSIRIS-REx achieves a higher thrust. In addition, the precise control of system pressure allows us to accurately predict burn performance and timing prior to maneuver execution. For the maneuvers using the smaller thrusters, OSIRIS-REx operates in “blow-down” mode. In these instances, the latch valve to the helium tank remains closed, and the residual pressure in the main propellant tank is used to flow hydrazine to the rocket engines. This strategy works because the burns are very short, compared to the main-engine burns, and the thrusters use a very small amount of hydrazine.
It is always exciting to see another major milestone completed in the development of OSIRIS-REx. Kevin Johnson at Lockheed Martin leads the propulsion system design and manufacture. Randy Regenold is the Propulsion Design Lead and Carey Parish is the Deputy Lead as well as the Propulsion Analysis Lead. I want to thank this team for all of their hard work to make OSIRIS-REx a success. We certainly could not get that sample back without their tireless efforts. | 0.840737 | 3.412585 |
SwRI scientist develops novel algorithm to aid search for exoplanets
Machine learning tool allows scientists to search stellar data for likely exoplanet host stars
Credit: ESO/M. Kornmesser
SAN ANTONIO — June 25, 2019 — Inspired by movie streaming services such as Netflix or Hulu, a Southwest Research Institute scientist developed a technique to look for stars likely to host giant, Jupiter-sized planets outside of our solar system. She developed an algorithm to identify stars likely to host giant exoplanets, based on the composition of stars known to have planets.
“My viewing habits have trained Netflix to recommend sci-fi movies I might like — based on what I’ve already watched. These watched movies are like the known star-exoplanet systems,” said Dr. Natalie Hinkel, a planetary astrophysicist at SwRI. “Then, the algorithm looks for stars with yet-undetected planets — which are comparable to movies I haven’t watched — and predicts the likelihood that those stars have planets.”
Just as a cake recipe includes some basic ingredients, stars need certain elements to make giant planets. Scientists can use spectroscopy, or the way that light interacts with atoms in the star’s upper layers, to measure a star’s composition, which includes materials such as carbon, magnesium and silicon. These elements are the ingredients for making a planet, because stars and planets are made at the same time and from the same materials. However, while there are a lot of ingredients in your kitchen, not all of them belong in a cake. This is where the movie-streaming algorithm comes in, predicting planets based on the elements in stars.
“We found that the most influential elements in predicting planet-hosting stars are carbon, oxygen, iron and sodium,” Hinkel said. “The funny thing was that we were not expecting sodium to be a key ingredient for predicting a planet. But it must be an important link between stars and planets, because it kept popping up, even when looking at different combinations of elements.”
Hinkel used the Hypatia Catalog, a publicly available stellar database she developed, to train and test the algorithm. It’s the largest database of stars and their elements for the population within 500 light years of our Sun. At last count, Hypatia had stellar element data for 6,193 stars, 401 of which are known to host planets. The database also catalogs 73 stellar elements from hydrogen to lead.
The algorithm, which will be publicly available, has looked at more than 4,200 stars and assessed their likelihood of hosting planets, based solely on the elements, or ingredients, within the star. In addition, Hinkel looked at different combinations of those ingredients to see how they influenced the algorithm.
Hinkel’s team identified around 360 potential giant planet host stars that have more than a 90 percent probability of hosting a giant exoplanet. “We were excited, so we used archival telescope data to search for any signs of planets around these likely host stars,” Hinkel said. “We identified possible Jupiter-sized planets around three stars predicted by the algorithm!”
When asked about how reliable her algorithm is, she explained that “we don’t have any true-negatives in our data — that is, stars that we know don’t have planets — so we ‘hid’ some known planet-hosting stars in the data to see what their prediction score would be like. On average they scored more than 75 percent, which is great! That’s probably a higher average than me liking the sci-fi movies Netflix picks for me.”
Moving forward, these findings could revolutionize target star selections for future research and clinch the role elements play in giant planet detection and formation. Hinkel is the lead author of the paper “A recommendation algorithm to predict giant exoplanet host stars using stellar elemental abundances” that will be published in an upcoming issue of the Astrophysical Journal.
For more information, see https:/ | 0.819797 | 3.141262 |
A billion light-years away, two galaxy clusters are slowly crashing into one another. Now, for the first time, observations have revealed a peculiar ridge of radio waves linking those clusters, like a thread strung between galactic beads.
This radio ridge stretches more than nine million light-years across and traces one of the filaments in the so-called cosmic web, the structure thought to describe the large-scale organization of the universe.
While astronomers have been able to see the myriad galaxies and galaxy clusters that make up the knots in this cosmic net, actually observing the threads between galaxies is not an easy feat. The new image, which shows a stream of plasma between the galaxy clusters Abell 0399 and Abell 0401, is the first known sighting of its kind.
“Radio emission connecting clusters has never been observed before,” says Federica Govoni of Italy’s National Institute for Astrophysics, who reports the observation today in the journal Science. But now that it has, the discovery may help astronomer better understand the universe on its grandest scale.
The cosmos is thought to be uniformly filigreed, with large empty voids set between knotty, twisted threads of galaxies and colossal groupings of galaxies parked where those threads intersect. Until now, astronomers have mostly observed this cosmic web’s beads, or clusters. These enormous clumps of galaxies, with members sometimes numbering in the thousands, are tied together by gravity.
Rife with hot gas, dense dark matter, and blazing stars, galaxy clusters are observable throughout the electromagnetic spectrum, meaning that astronomers can discern their features in visible, infrared, x-ray, gamma ray, and radio wavelengths; already, rare haloes of radio waves have been spotted in the cores of some clusters, including Abell 0399 and Abell 0401.
But the space between those clusters, called the intergalactic medium, is sparsely populated and dark. That makes it especially challenging to see anything so far, far away—the nearest large galaxy cluster outside of our own Local Group of galaxies and the neighboring Virgo cluster is 65 million light-years distant.
Still, Govoni and her colleagues recently decided to peer into the space separating Abell 0399 and Abell 0401. Earlier, the orbiting Planck observatory spotted what appeared to be a tendril of matter connecting the two beads, an observation that Govoni says piqued her curiosity and made her wonder whether magnetic fields might also extend beyond the clusters themselves.
Currently, these two clusters are in the initial stages of merging. About 9.8 million light-years apart, they are destined to collide and form a larger supercluster. For now, though, they’re busy stirring up and perturbing intergalactic space, hurling shockwaves, magnetic field lines, and particles into their shared void.
It’s the effects of those perturbations that Govoni and her team observed, using an array of radio telescopes in Europe called the Low-Frequency Array, or LOFAR, for short.
LOFAR detected radio waves emitted by electrons traveling at near light-speed; called synchrotron emission, these waves are produced by speeding electrons spiraling around magnetic fields. It’s likely that such radio ridges are common throughout the cosmic web, but they’re largely beyond the detection limits of today’s telescopes, Govoni says.
“The signal detected in this study is a factor of up to a hundred times brighter than some theoretical predictions for the emission from the synchrotron web,” says astronomer Tracy Clarke of the U.S. Naval Research Laboratory. “This is likely because it is enhanced in this region between these merging clusters.”
The ridge, which spans an immense distance, is now raising questions about how synchrotron emission can be produced over such a large area, as scientists aren’t yet sure how electrons can be perpetually accelerated to near light-speed over such vastness.
“This opens a whole new set of doors to begin exploring things like the particle distribution in the filaments, the magnetic field strength—and potentially its origin—as well as acceleration or reaccelerating processes at work within the filaments,” Clarke says. | 0.86055 | 4.073719 |
On this page:
Definition of the adjective cometary
What does cometary mean as an attribute of a noun?
- of or relating to or resembling a comet
Printed dictionaries and other books with definitions for Cometary
Click on a title to look inside that book (if available):
by Tilman Spohn, Doris Breuer, Torrence Johnson
Cometary meteoroids are thought to be too fragile to survive atmospheric entry. In addition, cometary meteoroids typically encounter the Earth at higher velocities than asteroidal debris and thus are more likely to fragment and burn up during ...
by Valerie Illingworth
cometary nebula Kohoutek has a period in excess of 70000 years). The majority of comets observed from earth have perihelions near the earth. This is simply due to observational selection. The brightness of a comet is proportional to 1/r"A”, ...
Encyclopedia of Astrobiology (2011)
by Muriel Gargaud
Cometary dust appears to be heterogeneous, with silicates in both the amorphous (glassy) and crystalline forms, Fe and Ni sulfides and other minerals in minor amounts. The presence of carbonates and phyllosilicates is subject to debate.
Three Volume Set by John A Matthews
CJC cometary impact Either the surface impact or atmospheric impact of debris from COMETS (or ASTEROIDS). Although largely ignored, and often derided, as an influence ...
Based Upon the Unabridged Dictionary of Noah Webster : with a Reference Library and Treasury of Facts by Noah Webster, Harry Thurston Peck
COMETARY COMMERCIAL cometary (kom'e-ta-ri), adj. pertaining to a comet. comfit hue, hut; ...
Ultimate Visual Dictionary (2017)
Cometary nuclei exist in a huge cloud (called the Oort Cloud) that surrounds the planetary part of the solar system. They are made ASTEROID 951 GASPRA of frozen water and dust and are a few miles in diameter. Occasionally, a comet is ...
The Canadian Encyclopedia (1999)
by James H. Marsh
of which some 130 have been observed more than once and have well-determined orbits, so that about 1480 cometary apparitions have been observed in all. The remaining 690 or ...
The Encyclopaedia Britannica (1911)
A Dictionary of Arts, Sciences, Literature and General Information by Hugh Chisholm
Cometary science has ramificd in unexpected ways during the last hundred years . The establishment of a class of “ shortperiod'" comets by the computations of J. F. Encke cum,“ in 18ro, and of Wilhelm von Biela in 1816, led to the theory of ...
A Dictionary of Astronomy (2012)
by Ian Ridpath
Centaurs and SDOS could be captured into *Jupiter comet family or *Halley- family cometary orbits. Centaurus (Cen) (gen. Centauri) A large and prominent southern constellation, representing a centaur. Its brightest star, *Alpha Centauri ( Rigil ...
Online dictionaries and encyclopedias with entries for Cometary
Click on a label to prioritize search results according to that topic:
Photos about Cometary
Click on an item to view that photo:
If you need related images for an article or a report, you can download stock photos:
Video about Cometary
Video shows what cometary means. relating to comets. Cometary Meaning. How to pronounce, definition audio dictionary. How to say cometary. Powered by ...
See also the pronunciation examples of Cometary!
Scrabble value of C3O1M3E1T1A1R1Y4
The value of this 8-letter word is 15 points. It is included in the first and second editions of the Official Scrabble Players Dictionary.Couldn't select: Got error 28 from storage engine | 0.890387 | 3.113826 |
in astronomy, an inconspicuous constellation of the Southern Hemisphere. Sculptor is known chiefly because it contains the south pole of the Milky Way galaxy, also called the south galactic pole. Astronomers apply a coordinate system to the Milky Way galaxy to locate and map objects, just as a coordinate system is applied to Earth. The galactic system includes a galactic equator and two galactic poles, north and south. The galactic equator lies on a plane that passes through the Milky Way’s spiral disk. The south galactic pole is 90 degrees south of every point on the galactic equator, while the north galactic pole, located in the constellation Coma Berenices, is 90 degrees north of every point on the galactic equator. Because the south galactic pole is in an area of the sky sparsely populated by Milky Way objects, it permits a look into deep space at many faint and distant galaxies.
Sculptor was originally named L’Atelier du Sculpteur (the Sculptor’s Studio), in the 1750s by the French astronomer Nicolas-Louis de Lacaille. The constellations Lacaille delineated are Antlia, Caelum, Circinus, Fornax, Horologium, Mensa, Microscopium, Norma, Octans, Pictor, Pyxis, Reticulum, Sculptor, and Telescopium. Lacaille’s catalog of southern stars, ‘Coelum Australe Stelliferum’, was published posthumously in 1763.
Sculptor’s brightest stars are only of the fourth magnitude, and the constellation is best found by first identifying the bright star Fomalhaut, in the constellation Piscis Austrinus, to the west. Sculptor contains the vividly red star R Sculptoris, a semi-regular variable star that brightens in magnitude from 7.7 to 5.8 over a period of about a year.
Because the constellation is 90 degrees from the plane of the Milky Way galaxy, an observer looking into Sculptor is not hampered by the obscuring haze of the Milky Way. Several galaxies brighter than 12th magnitude can be seen within the boundaries of Sculptor. Binoculars are sufficient to view some of these galaxies; more can be seen with telescopes. Perhaps the most famous is the seventh-magnitude NGC 253, often considered the most attractive spiral galaxy in the sky, after the Andromeda galaxy. Four times more luminous than the Milky Way galaxy, NGC 253 can be seen from the mid-northern latitudes under dark viewing conditions and with a medium-sized telescope. From Earth the galaxy is seen almost edge on, so that it appears as a thin misty streak. Photographs taken with the 154-inch (3.9-meter) Anglo-Australian Telescope show a pale yellow center with dusty blue spiral arms. NGC 253 is part of the Sculptor group of galaxies, which lies 9 to 10 million light-years away from Earth. In the same binocular field of view is Sculptor’s only globular cluster, NGC 288. Also visible within the boundaries of Sculptor is a very faint member of the Local Group, the group of 24 galaxies to which the Milky Way belongs. The Sculptor member lies almost 300,000 light-years away from Earth. Long-exposure photography is needed to demonstrate this galaxy. Sculptor is best seen in the Southern Hemisphere from July through January, reaching its highest point in the sky at 10:00 pm in early November. In the northern latitudes it appears low in the southern sky from September through March, making it a late fall constellation for viewers as far north as 41° N. latitude, ,
Critically reviewed by James Seevers | 0.813515 | 3.724124 |
Let's start off with the smaller, humbler one, Planck. Its main purpose is to measure what's known as the "Cosmic Microwave Background" or CMB. This is a type of radiation (read: light, except you can't see it) which is everywhere, but very very weak. It was released quite close to the beginning of the universe, so studying it is a way to understand what sort of physical processes were happening then. Planck is going to make what is called an all-sky map of the CMB. This means it will spin around and around, taking pictures of the sky in strips, until it's looked at everything.
Surely this has been done before, you say. Yes, it has, but not at high enough resolution to answer all the questions scientists have about it. And, as this webcomic illustrates (see panel 2), unlike in the movies, when you order someone to enhance an image that is already at the limit of its resolution...you can't. You could try and "interpolate between pixels", but in this case, that would be more commonly known as "making things up".
The aim of Planck, then, is to take the resolution of the all-sky maps of the CMB from the images on the left to the image on the right.
|Old maps of the CMB||Planck's map of the CMB (predicted|
More detail == more information == better understanding of the birth of the universe.
Herschel, on the other hand, is like the Hubble telescope, except a lot bigger. Its 3.5 m mirror eclipses Hubble's by more than a meter. It also operates in the infrared - again, a region of light that we can't see with our eyes. Its size and the type of light it uses means that it will be able to peer far into deep space to see very distant objects. It will also be able to see closer, but rather cold objects - at least when compared with stars - such as planets that aren't in our solar system.
Both of these spacecraft represent a remarkable technological achievement, as they operate at tenths of a degree above absolute zero. But they're in space, you protest, or at least my mum did. Surely it's not difficult to be cold in space. Actually, it's surprisingly difficult. Space, in our solar system, is about 3 degrees Kelvin. Spacecraft also generate quite a bit of heat, just from being powered on. Herschel & Planck are cryo-cooled by liquid helium. This means they only work as long as the supply of liquid helium is there. These missions have strictly limited lifetimes, like Replicants. Most spacecraft can keep going as long as they have enough power to keep their instruments on. Herschel & Planck are also going to be quite far from the Earth, beyond the reach of the space shuttle (see below). They can't be serviced by humans once they run out of liquid helium. Shuttle missions are also expensive, which means that it'll likely be cheaper to build new robotic spacecraft and send them out to replace Herschel & Planck than to try and refill their cooling systems.
But I'm getting ahead of myself. The launch is today. Good luck to them both, and their teams!
ETA: You can follow these spacecraft on Twitter: Herschel & Planck. ESA also has a Flickr account here, from which I poached that lovely image at the top.
ETA 2: The launch has been a success. The spacecraft have separated, are in communication with the Earth and are on their way to their orbits around the L2 point illustrated above. Yay! | 0.882524 | 3.795926 |
A new astronomical study has located what appears to be the oldest building blocks of the Milky Way galaxy, which could be upwards of 13 billion years old.
According to researchers, these objects must have formed at least one hundred million years after the Big Bang and, probably, contain some of the first starts that ever shed light in our galaxy.
Now, it is important to remember, of course, that our Milky Way galaxy is only one of the billions of other galaxies in the entire Universe. And each of these several billion galaxies represents a cosmic neighborhood of hundreds of planets and billions of stars that were all formed when these smaller building blocks—like these galaxies—collided and merged.
The research team consists of scientists from the Durham University Institute for Computational Cosmology as well as the Harvard-Smithsonian Center for Astrophysics, and they found this faintest evidence of satellite galaxies that are orbiting our very own Milky Way galaxy to conclude that these are among the oldest—perhaps the very first to form—in our Universe.
Of course, scientists working in this field describe the findings as “hugely exciting,” noting that it may be “equivalent to finding the remains of the first humans that inhabited the Earth.”
Effectively, the research describes that when the universe was roughly 380,000 years old, the first atoms formed. These, of course, were hydrogen atoms, and they collected into clouds and began to cool to gradually form small “halos” of dark matter, following the Big Bang. This cooling phase—known as the “Cosmic dark ages” lasted roughly 100 million years. The gas eventually cooled within the halos and became unstable; and that is what formed the first stars.
According to Durham University’s Professor Carlos Frenk, who is the Director of Institute for Computational Cosmology: “Finding some of the very first galaxies that formed in our Universe orbiting in the Milky Way’s own backyard is the astronomical equivalent of finding the remains of the first humans that inhabited the Earth. It is hugely exciting.”
He goes on to say, “Our finding supports the current model for the evolution of our Universe, the ‘Lambda-cold-dark-matter model’ in which the elementary particles that make up the dark matter drive cosmic evolution.”
The finds of this study have been published in the Astrophysical Journal. | 0.826581 | 3.868767 |
Just passing through: Comets visit our solar system
Our solar system has a visitor from afar right now. On this past August 30 an amateur astronomer in the Crimea, Gennady Borisov, discovered a dim comet in the morning sky (with a telescope that he had built himself). As measurements of the new comet’s position were made over the next several days and as potential orbits began to be calculated from those measurements, it started to become apparent that Borisov’s new comet is not traveling in an orbit that a typical comet in our solar system would be traveling in. Indeed, within about a week and a half it became clear that Comet Borisov is not a member of our solar system at all, but instead has come to us from interstellar space.
Throughout the many decades and centuries that we have been studying comets, we have seen several that were ejected from our solar system as a result of gravitational effects caused by close passages to Jupiter or other planets. At the same time, the comets that reside in the Oort Cloud in the far outer reaches of the solar system are only loosely held by the sun’s gravity, and over time many of these must surely have been kicked out into interstellar space by passing stars. While we have learned over the past couple of decades that there really is no such thing as a “typical” planetary system, if the processes by which planetary systems form and evolve nevertheless remain basically the same, then we would expect other planetary systems to not only have comets, but also that many of these would be kicked into interstellar space as well.
It would thus seem reasonable to suspect that interstellar space contains many comets from planetary systems throughout the galaxy, and that from time to time some of these would pass through the solar system during their respective journeys. Up until the fairly recent past we were only detecting a relatively small percentage of comets that visited the inner solar system, and thus whatever interstellar comets that passed through remained undetected. However, once the comprehensive all-sky survey programs that we have now became operational a couple of decades ago, the chances of picking up interstellar comets – if indeed such objects exist – dramatically improved.
Two years ago the Pan-STARRS survey program based in Hawaii detected the first-known interstellar object, since named ‘Oumuamua (from Hawaiian words roughly meaning “first messenger reaching out from afar”). ‘Oumuamua was a very dim object already moving away from the sun and Earth when it was discovered, and it was followed for less than three months before it became too dim to see at all. It did not exhibit the fuzzy head, or “coma,” that a comet usually displays, nor any kind of tail, although it did show some slight changes in its orbital motion which suggest the presence of weak “jetting” activity (akin to a rocket engine) that comets generally show. Thus, we never really got a good handle on ‘Oumuamua’s true physical nature, other than that it is apparently cigar-shaped – being about 100 meters long in its longest dimension – is reddish in coloration, and seems to be tumbling as it travels through space.
And now, we have a second interstellar object. Unlike ‘Oumuamua, Comet Borisov is clearly a comet, as it exhibits the coma and tail of a typical comet. Furthermore, it seems to be quite a bit larger than ‘Oumuamua; while we haven’t been able to determine the size of its nucleus yet, it apparently is at least one kilometer in diameter, and possibly as large as ten kilometers across.
Perhaps most importantly, we should be able to study Comet Borisov for quite some time. According to the most recent calculations at this writing, the comet will be closest to the sun this coming December 8, at a distance of 188 million miles, and will be nearest Earth (182 million miles) shortly before the end of December. While neither of these distances are especially close, the comet should nevertheless remain detectable with our telescopes for at least a year, thus providing ample opportunity to study it.
Some initial studies, in fact, have already been performed. These suggest that Comet Borisov’s chemical composition is similar to that of comets in our own solar system, in turn suggesting that comets in other planetary systems form in a manner similar to the comets in ours. It’s still very early in the game, though, but by the time Comet Borisov departs we should have a pretty good idea about how the formation processes in our solar system are similar to and/or different from those in other systems.
Sky-watchers who might want to see Comet Borisov in larger backyard telescopes will likely have their work cut out for them, since it may or may not become bright enough to see. Their best chances will probably come in early December before the Full Moon on the 12th, and then late in the month after the moon has left the morning sky. During that time it will be traveling southward through the constellations of Crater, Hydra, and Centaurus, and it will drop below our southern horizon during the latter part of January.
It appears that Comet Borisov has arrived in our solar system from the general direction of the constellation Cassiopiea – now in our northeastern sky during the later evening hours – which is near the plane of our galaxy. It will depart in the general direction of the constellation Telescopium – somewhat to the south of Sagittarius – which is also near the plane of our galaxy. It has possibly passed through other planetary systems before arriving at ours, and may possibly pass through through others long after it has visited ours, as it continues its almost endless journey through the galaxy.
Alan Hale is a professional astronomer who resides in Cloudcroft. He is involved in various space-related research and educational activities throughout New Mexico and elsewhere. His web site is http://www.earthriseinstitute.org. | 0.915455 | 3.881437 |
Throughout the clear evening sky and as long as the town lights will not be shut or vivid sufficient to interfere along with your naked eye imaginative and prescient, it is always a good suggestion to grab a blanket and a few candles and head to your home’s roof or the closest hill. Throughout the 18th century, famed French astronomer Charles Messier observed the presence of several nebulous objects” while surveying the night time sky. About one hundred forty CE Ptolemy, another Greek thinker, advanced a “geocentric” of the universe with the Sun orbiting the Earth.
The IfA’s Asteroid Terrestrial-impression Final Alert System (ATLAS), a NASA-funded telescope community dedicated to detecting house rocks that might crash into Earth, will broaden into the Southern Hemisphere, which at present lacks a big-scale asteroid-surveillance effort.
In current use, astronomy is anxious with the research of objects and matter outside the earth’s ambiance,” while astrology is the purported divination of how stars and planets affect our lives. Our location on a rural hilltop with restricted light air pollution grants us an incredible view of the night time sky, even with the bare eye.
Our program is designed to move students rapidly into research on faciliites such because the Southern Astrophysical Research telescope MSU additionally affords robust interdisciplinary programs with the Joint Institute for Nuclear Astrophysics and the Department of Computational Science, Arithmetic, and Engineering Our web page on graduate scholar life has more information about what it is like to be a graduate pupil at MSU.
Edward Holden, Lick’s first director, complimented the amateurs on their service to science, and proposed to proceed the good fellowship via the founding of a Society to advance the science of Astronomy, and to diffuse data regarding it. Thus the Astronomical Society of the Pacific was born.
Richard of Wallingford (1292-1336) made main contributions to astronomy and horology, including the invention of the primary astronomical clock, the Rectangulus which allowed for the measurement of angles between planets and different astornomical bodies, in addition to an equatorium known as the Albion which may very well be used for astronomical calculations akin to lunar , solar and planetary longitudes and could predict eclipses Nicole Oresme (1320-1382) and Jean Buridan (1300-1361) first discussed evidence for the rotation of the Earth, furthermore, Buridan additionally developed the theory of impetus (predecessor of the trendy scientific concept of inertia ) which was in a position to present planets were able to motion with out the intervention of angels.
Astronomy is often (not all the time) about very concrete, observable issues, whereas cosmology typically includes large-scale properties of the universe and esoteric, invisible and typically purely theoretical issues like string theory, darkish matter and darkish power, and the notion of multiple universes. | 0.893959 | 3.604543 |
Plasma plays a big role from the ionosphere to black holes. Stanford physicist Roger Blandford explains plasma and its connection to black holes in a conversation with Scientific American's JR Minkel. Plus, we'll test your knowledge of some recent science in the news. Web sites mentioned on this episode include www.snipurl.com/26dun-sciam1; www.snipurl.com/26dv2-sciam2; www.nybg.org/darwin
Steve: Welcome to Science Talk, the weekly podcast of Scientific American for the seven days starting April 30th, 2008. I'm Steve Mirsky. This week on the podcast, we'll enter the fascinating world of plasma—not the blood kind, the physics kind—with Stanford University physicist Roger Blandford. Plus, we'll test your knowledge about some recent science in the news. Roger Blandford is the coauthor of the Blandford-Znajek Process, the leading explanation for how black holes produce jets of plasma traveling at near light speed, but what's plasma? Well, he'll explain that. He's the director of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford. He's also a professor at the Stanford Linear Accelerator Center. Blandford's research interests range from high-energy astrophysics and cosmology to general relativity and gravitational lensing. On April 12th, he gave a plenary lecture at the Annual Meeting of the American Physical Society in St. Louis. Scientific American's JR Minkel was at the meeting and he spoke to Blandford after his talk.
Minkel: I wonder, could you start by telling our listeners what plasma is?
Blandford: Oh! Plasma is an ionized gas—it's one where the electrons are separated from the nuclei, usually formed at high temperatures; and most of the baryonic matter in the universe is in the form of plasma.
Minkel: Now what's baryonic matter, for those who don't know?
Blandford: This is just regular matter like you and I, and we just use that phrase to distinguish it from the mysterious dark matter, which actually has a high average density in the universe, as we now know.
Minkel: Is plasma dangerous? If I stuck my hand into it, what would happen?
Blandford: Well it depends how tenuous it is, but if it were dense of the sort that you could make in a laboratory, you would be subject to burns and in many circumstances radiation exposure. So it's a good thing to do remote experiments on it—and as astrophysicists we can do remote experiments.
Minkel: So, where in the universe do we find plasma?
Blandford: Well, if we just go outside of the surface of the Earth, the first place we find it is in the ionosphere, and one of the reasons that we can bounce radio waves off the ionosphere is because there is plasma there. [As] we go farther away, we find the Earth's magnetosphere, which is the magnetic wave that's tied to the North and South poles that also contains a lot of plasma, the so-called Van Allen Belts and so on, and then extending back beyond the Earth to the so-called magnetotail—just this sort of lamb's tail that extends back beyond the Earth—that's full of plasma. If we go out into the solar wind, which is the gas that emanates from the surface of the sun and blows past the Earth and the other planets, that also is full of plasma. We go out into the interstellar medium, this is the gas between the stars like the sun, that too is mostly plasma—not all of it, some of it is in the form of neutral gas, but a large fraction of it is in the form of plasma—and then if we go outside the galaxy itself, into the space between the galaxies, the so-called intergalactic space, then again, that is mostly plasma. Closer to home, I suppose I left out the sun, which of course, itself is mostly plasma, because [the] high-temperature center of the sun is 15 million degrees, and so that is plenty hot enough to separate the electrons and the protons and to make sure that they move around freely inside the center of the sun.
Minkel: So, it sounds like there is a lot of plasma out there. What fraction of the universe is plasma?
Blandford: Well! We don't know for sure, but of the, what I call, baryonic matter, which is 5 percent of the total mass energy density of the universe, one would guess about 90 or 95 percent of it, is in the form of ionized gas called plasma.
Minkel: So, there is plasma coming out of black holes, is that correct?
Blandford: Well, we think there is plasma around black holes. The black holes that we can observe directly through their radiant emission are mostly in a configuration where gas swirls around the black hole in the form of an accretion disk and that accretion disk—most of the mass is going to be in an ionized form, and then some of that gas gets expelled from the environment around the black hole, while it is still outside the black hole, it gets squirted out in the form of an outflow, a wind like the solar wind and then [a] much faster, collimated outflow called a jet. But there are two jets—one that goes up and one that goes down—and these are associated with the region very close to the black hole and those jets contain plasmas that are moving at relativistic speeds, that is to say, speeds close to that of light.
Minkel: And how hard is to get something to produce jets moving at nearly the speed of light?
Blandford: Well, nature doesn't seem to be very challenged in this regard because it makes jets under many different environments. Even protostars—these are young stars that are just forming and making their own planetary disks and so on—they make very powerful outflows called, the same sort of jets obviously moving at slower speeds, but they are full of plasma, that is flowing out at high speed; white dwarfs, neutron stars, black holes big and small, they seem able to do this task, it really seems to be a very common phenomenon. Nature is able to do it at will. We have a harder time understanding in detail how these jets are formed, but I think that we are getting confused on a higher plane now, let me put it that way and a lot of the sort of ideas that were possibilities in the past have now really been excluded and we do have a much more sophisticated understanding of some of the general principles, but I think not all of them.
Minkel: So, what is it that we've come to understand lately about plasma astrophysics?
Blandford: Oh! About plasma astrophysics I would say the first thing is we understand that magnetic fields are very, very important in accretion disks and the region around black holes and neutron stars and those magnetic fields are almost certainly integrally important in forming the jets and the outflows. So, I would say that's the first thing that we understand. And we understand that on the basis of direct observations, which have become very much better over the past five or 10 years and also as a result of theoretical investigations, particularly those involving sophisticated numerical computations; and here we are able to do the sort of experiments, with the computer if you like, that were not possible 10 or 15 years ago. Now, we can do those experiments and understand how the laws of physics behave in these environments. So, that's the first thing we've understood. I think the second thing that's very exciting is understanding how the high-energy particles are accelerated. Nature is able to accelerate particles like protons to energies that are as large as say that of a well-hit baseball, and it's been a puzzle for a long while to know how it does that. We know that for energies of modest to intermediate energy, the culprit or the source of the acceleration appears to be the shock front that surrounds
a [an] expanding supernova blast wave; that is to say, we have a star that undergoes a massive cosmic explosion [and] drives a strong shock wave out into the surrounding interstellar medium, and the gas around the shock wave, and all the magnetic fields associated with it are capable of accelerating particles to very high energies; and also incidentally magnifying and amplifying the magnetic field associated with that shock front and giving a lot of x-ray emission and radio emission and so on, and so we've understood that. I think we have now a much better understanding from an observational perspective and again theoretical modeling is becoming much more sophisticated, and although there is [are] still lots of puzzles involved and lots of, you know, healthy scientific debates, which what makes the subject very interesting at this time. There are some things that people are no longer debating, which they would have been doing so five or 10 years ago.
Minkel: And these accelerated particles, those are what you call cosmic rays.
Blandford: Cosmic rays
is [are] historically the particles that hit the Earth, they were discovered in the early part of the 20th century and mostly that's what people think of as cosmic rays, but relativistic particles exist again throughout the universe and they don't actually have to hit the Earth for their effects to be observed and for them to pose, you know, interesting astrophysical problems for us to try and solve.
Minkel: So, it sounds impressive for a particle to have the kinetic energy of a struck fastball. What does that mean exactly—if one of them hit my head, would it hurt me?
Blandford: No. That's a very interesting physics question. Let me say, we haven't found one yet with the energy of a home run, so I shouldn't boast too much—my experimental colleagues are looking for a home run, if you like, but it's a bloop single would be about the right energy you have. In fact if it hit you on the head, what it would do, it would just go straight through and one of the reasons is
this, is the difference between momentum and energy. It has the energy of a baseball but the momentum of a snail. So that wouldn't be so bad, if you stopped it into your head, you wouldn't actually feel it, but in practice any cosmic ray wouldn't get as far as your head, because that energy would be stopped in the upper atmosphere.
Minkel: So, the jets that you said were sort of a generic feature coming out of, I think, you said proto-planetary disks and as well as around black holes— so, what's the mystery with those, are they, especially powerful or impressive in some way?
Blandford: Some of them are. In some active galactic nuclei, you have a black hole and accretion disk and the majority of the power is associated with these outflowing jets, far more than is associated with the radiant energy that is emitted by the accretion disk and the hot gas surrounding it. So, that is a, you know, an observational statement and a very interesting one. So these are not sort of small players, these are major parts of the energy budget of an accreting black hole and by extension, they have an important impact on their environment; and the jets associated with accreting black holes and nuclei galaxies inflate giant lobes of plasma outside the galaxy and these heat the surrounding gas, they affect the fuel supply, they stimulate star formation, they in fact stimulate galaxy formation. So, black holes as well as being sort of agencies of doom and destruction in the end of time and allegories of halo and all the rest of it, are also bringers of life. So, they in fact can be very much part of the regenerative part of an ecological cycle, if you like, for the universe.
Minkel: So, how large are these jets? If there are spawning galaxies they must be pretty big?
Blandford: The biggest jets are megaparsecs, which means, many millions of light years in size. So, yes they go way outside the galaxy.
Minkel: And in your talk, you showed some rather pretty simulations of some of these jets—what have they told us about the jets?
Blandford: Well, analyzing the radio, optical and x-ray and now gamma ray images of jets and data from jets have helped us to understand that they are moving at relativistic speed. They probably contain electrons and positrons, at least in their earliest stages, although that is not clear, that's all the way along the jet. They live for hundreds of thousands of years, millions of years probably, and they probably fire up many times during the lifetime of a galaxy. They have a major impact on their surroundings. They can inflate giant bubbles of plasma, which will float away from the source galaxy, you know—in the gravitational field these giant bubbles will just float away and they again can be responsible for heating the gas that surrounds the galaxy.
Minkel: And the simulations tell us all that?
Blandford: No, these are observations that have really told us that. Some of the simulations and theoretical work has anticipated the observations, some of it has actually followed the observations. That's the normal process. In science sometimes you get things right ahead of time, sometimes you produce the explanation after you see the result of the experiment or the observation.
Minkel: So, the simulations tell us we know the underlying physics behind the observations.
Blandford: The simulations are in some cases, able to rationalize what we see. I think there is still quite a lot that we are not agreed upon in modeling of these jets and accretion disks and so on. So, there is still quite a lot that are genuine healthy areas of debate, but I think there
is [are] so many other areas where indeed the very existence of massive black holes themselves in the nuclei of galaxies was a contentious matter; as recently as 15 years ago, there were people who still had alternative view points. I think one doesn't hear of them anymore now—everyone accepts that every galaxy worth the name has a massive black hole in its nucleus and when it is accreting that gas forms a disk around it. I think that is no longer debated, and so that's just one of many examples of what was originally a theory or hypothesis becoming an established scientific fact.
Minkel: So, if I can give you the opportunity for self
emotion [promotion], what has been your biggest contribution to this field?
Blandford: Oh gosh! I think I've done a lot of things in collaboration with people. I think the work that, I think, [I'm] probably best known for all was a collaboration I did with a colleague called Roman Znajek, where we proposed a particular mechanism for extracting, using electromagnetic fields, the spin energy of a black hole. It is still in some sense a bit of a conjecture, and I would say it has not reached the status of established fact, but for Roman and myself at that time, it was fascinating physics. I am still fascinated by it and certainly it's something that I very much enjoyed thinking about and working on. This is quite a long time ago, so I would say that's probably the thing that I am most associated with and certainly something that I still find very fascinating.
Minkel: Extracting the spin energy of a black hole that's a mechanism for producing a jet?
Blandford: Yes, in fact, I would argue that in fact, this is where the power for the big relativistic jets that we see actually comes from. It comes from the spinning space-time around the black hole and in fact it is not very well known, but that energy is there for the taking—up to 29 percent of the so-called rest mass energy of a spinning black hole is extractable—an
d original conjecture, which is not, as I say [said], yet established fact, but certainly taken much more seriously than it was at that time—10 or 15 percent of the rest mass energy of the black hole, about half of the spin energy, is in practice according to our conjecture, is in fact, the power source for these relativistically moving jets.
Minkel: Very cool. Thank you very much for talking to us.
Blandford: My pleasure.
Steve: Check our JR Minkel's recent article on plasma jets at http://www.snipurl.com/26dun-sciam1 and to see some nifty Plasma sims that Blandford used in his talk at the American Physical Society meeting, see JR's blog item at http://www.snipurl.com/26dv2-sciam2
Last week I got a sneak preview of a new exhibit at the New York Botanical Garden called "Darwin's Garden". It's a look at Darwin's work as a botanist, as well as a walking tour of evolutionary science with botanical examples. And there is an extraordinarily beautiful recreation of the garden that Mrs. Darwin kept at their country home. I interviewed Dr. David Kohn, a Darwin expert, who is the curator of the exhibit. We'll play that interview on an upcoming podcast. I just wanted to let you know about the exhibit now, which officially opened last week and will run until June 15th. If you are in the New York City area, check it out; the Web site is http://www.nybg.org/darwin
Steve: Also if you have softball team in the New York City area and would like to schedule a softball game against the mighty Scientific American Big Banger's team, you can do so by writing to Karen Schrock; her e-mail address [email protected]
Now it is time to play TOTALL……. Y BOGUS. Here are four science stories; only three are true. See if you know which story is TOTALL……. Y BOGUS.
Story number 1: The helicopter traffic reporter for Denver TV station is named Wilbur Wright.
Story number 2: A genetic study indicates that Homo sapiens almost went extinct about 70,000 years ago.
Story number 3: To save gas, the UPS develops routes that consist almost exclusively of right turns.
And Story number 4: A new test for enlarged prostate involves placing a microphone down there amongst the private parts.
Time is up.
Story number 4 is true. One of the symptoms of an enlarged prostate is difficulty in urinating because of a compressed urethra; the current way to test for compression is a catheter that measures pressure changes—nobody wants that believe me. The strategically placed microphone records the sound while urinating and the sound frequency correlates with the urethra's narrowing. A Dutch researcher came up with this new idea and he has applied for a patent. The first tests of the device will begin soon in Rotterdam.
Story number 3 is true. UPS uses routes that have very few left turns to save gas. Because sitting in the clogged left turn lane burns more gas than keeping moving and making just rights. The UPS press release claims that their more efficient routes saved three million gallons of gas last year.
And story number 2 is true. A genetic study does lead to the conclusion that Homo sapiens almost went extinct about 70,000 years ago. The report was published in The American Journal of Human Genetics. Stanford researchers think that our numbers may have gotten as low as about 2,000 individuals, possibly because of drought.
All of which means that story number 1 about the eye-in-the-sky traffic reporter in Denver being named Wilbur Wright is TOTALL……. Y BOGUS. Because what is true is that the helicopter traffic reporter for Channel 9 in Denver is named Amelia Earhart. She is actually a distant relative of the other Amelia and being named Amelia Earhart inspired her to take flying lessons. She now keeps travelers moving and possibly from getting lost.
Well that's it for this edition of the weekly SciAm podcast. You can write to us at [email protected] and check out www.SciAm.com for the latest science news, videos and the opportunity to engage in ongoing discussions about all our articles. For Science Talk, the weekly podcast of Scientific American, I'm Steve Mirsky. Thanks for clicking on us. | 0.890154 | 3.613203 |
Pisces, named for the Latin plural of fish, occupies 889 square degrees, making it the 14th largest constellation overall. While it is a fairly large constellation, its stars are faint — none are brighter than fourth magnitude — making it challenging to see in the sky with the naked eye.
Pisces is notable for containing the point at which the sun crosses the celestial equator into the Northern Hemisphere around March 20 each year. This point, called the vernal equinox, used to lie in Aries, but has moved into Pisces because of the Earth's wobble on its axis, called precession, according to astronomer and author Ian Ridpath.
Pisces is in the first quadrant of the Northern Hemisphere and covers a large V-shaped region. Its large area, coupled with its dim stars, makes it hard to pick out in the night sky. Northern Hemisphere observers are able to see Pisces most clearly in early autumn.
- Right Ascension: 0.85 hours
- Declination: 11.08 degrees
- Visible: Between latitudes 90 degrees and minus 65 degrees.
- Best viewed: at 9 p.m. between Nov. 6 and Nov. 9.
Pisces is located northeast of Aquarius and to the northwest of the constellation Cetus the Sea-monster. Other constellations bordering Pisces are Triangulum, Andromeda, Pegasus and Aries.
One of the key ways to identify Pisces is to find the Circlet of Pisces — also known as the head of the Western Fish — to the south of the Square of Pegasus. The Eastern Fish can be seen leaping upward to the east of the Square of Pegasus.
Notable stars and objects
Eta Piscium, also known as Alpherg or Kullat Nunu, is Pisces’ brightest star. It is a bright giant star (G class) that is 294 light-years from Earth and has a luminosity that is 316 times that of the sun. The constellation’s second brightest star is a yellow giant about 130 light-years from Earth known as Gamma Piscium.
Alpha Piscium is the third brightest star in Pisces and is made up of a pair of white dwarf stars in close proximity. It is also called Alrescha ("the cord") as it illuminates the spot where it appears that the tails of the two fish are tied together.
Also known as Fum al Samakah, Arabic for “mouth of the fish,” Beta Piscium has a magnitude of 4.53 and is about 492 light-years from Earth.
Pisces also boasts Van Maanen’s Star, named for Adrian van Maanen, the Dutch astronomer who discovered it in 1917. It is the 31st closest star system and the nearest single white dwarf to the sun, at just 14.1 light-years away.
Pisces also contains a Messier object — which are galaxies, nebulae and star clusters recorded by 18th Century French astronomer Charles Messier. Messier 74 is a spiral galaxy located between the stars alpha Arietis and eta Piscium.
Recent news about Pisces
The Hubble Space Telescope imaged a pair of bizarre galaxies, called Pisces A and Pisces B, in 2014. Two years later, researchers announced that data from those observations showed the dwarf galaxies used to be by themselves, but over time they moved to a nearby group of galaxies — a process that accelerated star formation. Researchers said the study of Pisces A and Pisces B can also shed light on what dwarf galaxies today may have looked like in the ancient past.
Researchers looking at the galaxy NGC 660 announced a huge explosion there in 2013, which likely came from a black hole. They ruled out a supernova (star explosion) event as the researchers saw five locations with bright radio emissions near the galaxy's core. "The most likely explanation is that there are jets coming from the core, but they are precessing, or wobbling, and the hot spots we see are where the jets slammed into the material near the galaxy's nucleus," stated Chris Salter of the Arecibo Observatory.
Several exoplanets have also been found in the constellation. In 2014, researchers found a world called GU Pisces b that orbits an incredible 2,000 times the Earth-sun distance, which means the planet takes roughly 80,000 Earth years to go around its star once. The Kepler space telescope, when it started its new observing mission in later that year, discovered a super-Earth called HIP 116454b about 180 light-years from Earth. A Search for Extraterrestrial Intelligence (SETI) probe examined HIP 116454b for signals the next year, but the search turned up empty.
In the sky, Pisces is represented as two fish swimming at right angles to each other, one to the north and one to the west. They are attached by a cord. The fish themselves are apparently the Greek goddess Aphrodite and her son, Eros, who turned into fish and jumped into the Euphrates River to evade the fiery breath of the monster Typhon, "the most awful monster the world had ever seen," according to Ridpath.
In astrology, which is not a science, Pisces is the 12th sign in the Zodiac and represents those born between Feb. 20 and March 20.
Additional reporting by Elizabeth Howell, Space.com contributor | 0.84537 | 3.788615 |
It's time to find all the missing black holes.
That's the argument advanced by a pair of Japanese astrophysicists, who wrote a paper proposing a new search for millions of "isolated black holes" (IBHs) that likely populate our galaxy. These black holes, lost in the darkness, sip matter from the interstellar medium — the dust and other stuff floating between stars. But that process is inefficient, and a great deal of the matter gets expelled into space at high speeds. As that outflow interacts with the surrounding environment, the researchers wrote, it should produce radio waves that human radio telescopes can detect. And if astronomers can sift out those waves from all the noise that's in the rest of the galaxy, they might be able to spot these unseen black holes.
"A naive way to observe IBHs is through their X-ray emission," the researchers wrote in their paper, which has not yet been formally peer reviewed and which they made available July 1 as a preprint on arXiv. [9 Ideas About Black Holes That Will Blow Your Mind]
Why is that? As black holes suck the matter from space, that matter at its fringes accelerates and forms what’s known as an accretion disk. The matter in that disk rubs against itself as it spins toward the event horizon — a black hole's point of no return — spitting out X-rays in the process. But isolated black holes, which are small compared to supermassive black holes, don't emit a great deal of X-rays this way. There simply isn't enough matter or energy in their accretion disks to create large X-ray signatures. And past searches for IBHs using X-rays have failed to produce conclusive results.
"These outflows can possibly make the IBHs detectable in other wavelengths," the researchers, Daichi Tsuna of the University of Tokyo and Norita Kawanaka of Kyoto University, wrote in their paper. "The outflows can interact with the surrounding matter and create strong collisionless shocks at the interface. These shocks can amplify magnetic fields and accelerate electrons, and these electrons emit synchrotron radiation in the radio wavelength." [9 Weird Facts About Black Holes]
In other words, the outflow sliding through the interstellar medium should get electrons moving at speeds that produce radio waves.
"Interesting paper," said Simon Portegies Zwart, an astrophysicist at Leiden University in the Netherlands, who was not involved in Tsuna and Kawanaka's research. Portegies Zwart has also studied the question of IBHs, also known as intermediate-mass black holes (IMBHs).
"It would be a great way to find IMBHs," Portegies Zwart told Live Science. "I think that with LOFAR [the Low-Frequency Array in the Netherlands], such research should already be possible, but the sensitivity may pose a problem."
IBHs, Portegies Zwart explained, are thought of as a "missing link" between the two types of black holes astronomers can detect: stellar-mass black holes that can be two to possibly 100 times the size of our sun, and supermassive black holes, the gargantuan beasts that live at the cores of galaxies and are hundreds of thousands of times the size of our sun.
Stellar-mass black holes are occasionally detectable in binary systems with regular stars, because the binary systems can produce gravitational waves and companion stars can provide fuel for large X-ray bursts. And supermassive black holes have accretion disks that emit so much energy that astronomers can detect and even photograph them.
But IBHs, in the midrange between those two other types, are far more difficult to detect. There are a handful of objects in space that astronomers suspect might be IBHs, but those results are uncertain. But past research, including a 2017 paper in the journal Monthly Notices of the Royal Astronomical Society, which Portegies Zwart co-authored, suggests millions of them could be hiding out there.
Tsuna and Kawanaka wrote that the best prospect for a radio survey of IBHs probably involves using the Square Kilometre Array (SKA), a multi-part radio telescope due to be built with sections in South Africa and Australia. It's slated to have a total radio-wave collecting area of 1 square kilometer (0.39 square miles). The researchers estimate that at least 30 IBHs emit radio waves that the SKA will be able to detect during its first, proof-of-concept phase, which is scheduled for 2020. Down the road, they wrote, the complete SKA (scheduled for the mid-2020s) should be able to detect up to 700.
Not only should SKA be able to spot radio waves from these IBHs, they wrote, it should also be able to precisely estimate the distance to many of them. When that time comes, finally, all these missing black holes should start to come out of hiding.
Originally published on Live Science. | 0.900734 | 4.116414 |
Gibbous ♌ Leo
Moon phase on 15 November 2049 Monday is Waning Gibbous, 20 days old Moon is in Leo.Share this page: twitter facebook linkedin
Previous main lunar phase is the Full Moon before 5 days on 9 November 2049 at 15:38.
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 first ∠1° of ♌ Leo tropical zodiac sector.
Lunar disc appears visually 9.2% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1770" and ∠1940".
Next Full Moon is the Cold Moon of December 2049 after 23 days on 9 December 2049 at 07:28.
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 20 days old. Earth's natural satellite is moving from the middle to the last part of current synodic month. This is lunation 616 of Meeus index or 1569 from Brown series.
Length of current 616 lunation is 29 days, 13 hours and 21 minutes. It is 1 hour and 5 minutes longer than next lunation 617 length.
Length of current synodic month is 37 minutes longer than the mean length of synodic month, but it is still 6 hours and 26 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠278.3°. At the beginning of next synodic month true anomaly will be ∠310.2°. 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°).
12 days after point of perigee on 2 November 2049 at 18:03 in ♒ Aquarius. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next day, until it get to the point of next apogee on 16 November 2049 at 15:07 in ♌ Leo.
Moon is 404 991 km (251 650 mi) away from Earth on this date. Moon moves farther next day until apogee, when Earth-Moon distance will reach 404 490 km (251 338 mi).
4 days after its descending node on 10 November 2049 at 14:33 in ♉ Taurus, the Moon is following the southern part of its orbit for the next 9 days, until it will cross the ecliptic from South to North in ascending node on 25 November 2049 at 00:12 in ♐ Sagittarius.
17 days after beginning of current draconic month in ♏ Scorpio, the Moon is moving from the second to the final part of it.
3 days after previous North standstill on 12 November 2049 at 00:36 in ♊ Gemini, when Moon has reached northern declination of ∠21.270°. Next 10 days the lunar orbit moves southward to face South declination of ∠-21.274° in the next southern standstill on 26 November 2049 at 06:55 in ♐ Sagittarius.
After 9 days on 25 November 2049 at 05:35 in ♐ Sagittarius, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.848363 | 3.249525 |
Like cosmic spiders, dwarf galaxies have been caught feasting on blobs of gas spread across a hidden web. The very same process seems to have fuelled the birth of stars and the growth of galaxies when the universe was young.
The idea that galaxies grew fat by eating from the cosmic web – a giant mesh beaded with clouds of cold gas – has been around for a while, and recent simulations have increased its popularity. As the gas clouds fall into the gravitational clutches of a galaxy, they spark bursts of star formation, the models show.
But the process has been hard to observe in practice. Most galaxies we see in the local universe, like our own Milky Way, are filled with hot gas that warms up approaching material, preventing it from collapsing into stars. And because clumps of cold gas in intergalactic space don’t emit much light on their own, they’re hard to spot.
The clincher would be to watch a blob of fresh gas triggering a burst of star formation in a small galaxy that isn’t building a lot of stars on its own.
“People have been trying to see if they can find evidence for this and its relationship to lighting up the galaxies,” says Chris Churchill of New Mexico State University in Las Cruces.
Now a team led by Jorge Sanchez Almeida, of the Astrophysics Institute of the Canary Islands, has done just that. “It’s as close to a smoking gun as I’ve seen so far,” Churchill says.
To zero in on the splash of fresh gas into a galaxy, Almeida’s group looked at a set of small, faint galaxies with a low proportion of elements heavier than hydrogen and helium. They were able to infer how oxygen levels varied across these galaxies’ discs.
They found that the bright, star-forming regions had only about a tenth as much oxygen as was found elsewhere in these galaxies. This was a sign of newly arrived gas powering star formation, they concluded: it had to be recently added, because any old gas would lose its distinctive chemical signature within a few hundred million years through being stirred up into a homogenous gloop.
“We are left with just one possibility,” Almeida says. “We’ve picked them up right at the moment that they got fresh gas.”
Blobs of gas moving along the cosmic web could explain the very existence of these galaxies, he says. Perhaps they are just normal dwarf galaxies that have been spurred to make new stars by fresh gas, the recent arrival of which diluted their heavy element content.
The process, if confirmed by more observations, could also explain more. “It glues together several things,” says William Keel at the University of Alabama. Matching star-forming regions to cosmic web threads could let us look at both the composition and the distribution of this nearly invisible gas. “The web is just absurdly difficult to observe,” Keel says.
7 September 2015
By Joshua Sokol
Journal reference: Astrophysical Journal, DOI: 10.1088/2041-8205/810/2/L15 | 0.85467 | 4.103558 |
Power beaming is clearly central to space-based solar power concepts. Here I will provide a quick overview of my understanding of power beaming, the various equations involved, typical example calculations.
If power beaming were efficient and cheap, I believe space-based solar power would be quite viable even for grid power. However it’s not, and that largely has to do with the distances involved AND the fact that you need to convert energy multiple times, with losses along the way. The distances involved aren’t a complete show-stopper, since you can solve that problem just by operating at a large enough scale. However, the conversion inefficiencies (and the need to dump waste heat, etc) is not going to go away simply by operating at greater scale (although it helps).
The first equation we need is the diffraction limit. Roughly speaking, the spot size of a transmitted beam (microwave or laser) is:
Spot size = distance-to-spot * wavelength/(aperture diameter).
This is close enough for an order-of-magnitude estimate. More detailed work to follow.
But if we have a satellite out in Geosynchronous orbit (36000km altitude) transmitting power at roughly 10GHz (3cm wavelength, the shortest wavelength that still penetrates readily through the atmosphere) with an antenna 300m in diameter (NRO SIGINT/ELINT satellites are rumored to be that big, but maybe only around 100m in diameter), you’d have a spot size on the order of:
3.6E7m*3E-2m/(3E2m) = 3.6E3m or 3.6km in diameter…
…turns out that not all the energy of your beam is contained in this diameter (“Where’s that factor of 1.22,” you cry), but that’s a halfway decent start (and you’d need an infinitely wide aperture to collect all the energy in the beam…). 3.6km is obviously huge. The biggest full-aperture dish ever built is the half-way finished Chinese Arecibo clone at 500m. Still, there are ways to tweak this.
With a laser operating at 1micron, in medium-Earth-orbit (10000km) with 1 meter diameter optics needs only a:
1E7m*1E-6m/1m=10m diameter receiver to receive the vast majority of the beam’s energy. This is much, much better, obviously. You could put a 10m diameter receiver on top of a tethered airship or drone or something that allows you to transmit it to the ground without interference from clouds.
Or heck, use it to power high-altitude aircraft… but that’s a whole ‘nother blog post! (And suffice it to say, there are lots of caveats about laser transmission of energy, too.)
Latest posts by Chris Stelter (see all)
- A human tribe is a Von Neumann probe - May 24, 2020
- Modeling COVID-19: When will the peak occur in the US? - February 26, 2020
- SpaceX is great. But Mars needs more than SpaceX. - January 18, 2020 | 0.818622 | 3.459135 |
Think it might be fun to live in space? Better ask your bones.
Earth’s space agencies have tackled some of the major obstacles to living in space, with pressurized spacesuits that offset the deadly vacuum and deflect incoming solar and cosmic rays. But in the absence of gravity, astronauts aboard the International Space Station are still losing up to 10 times more bone mass than most Earth-bound post-menopausal women.
In an attempt to address this bone loss, University of Washington researchers found 22 volunteers for a study using bed rest as an analog of spaceflight. The current crop of volunteers are halfway through their commitment to remain in bed, in a six-degree, head-down tilt position for 84 days. The study subjects are still sane, and already, results are promising.
Surprisingly, it’s not necessarily students who are answering the call. Volunteers must be at least 22 years old, so the results apply to the age range of people most likely to be astronauts.
The head-down tilt mimics many of the physiological adaptations astronauts experience during spaceflight, such as bodily fluid shifts toward the head. The bed rest confinement mimics the complete “unloading” of the musculoskeletal system that astronauts feel as they float through space due to the lack of gravity, which accelerates bone loss.
Study leader Peter Cavanagh, a University of Washington professor of orthopaedics and sports medicine, said the volunteers have to be raised to a standing position at the end of their terms very slowly, “because they are very likely to faint” until the heart regains its ability to push blood to the brain. Sometimes, he said, volunteers feel pain in the bottoms of their feet when they finally put them down, and have trouble navigating corners while walking.
“They feel sort of generally weak,” Cavanagh said. “We put them through two weeks of rehab, and we buy them a membership at the health club for another month.”
In that respect, the study volunteers’ experience is similar to that of astronauts returning from long bouts in space. But for half the study subjects, there is a key difference — it’s in their stride.
Half of the study participants perform individually prescribed intermittent treadmill exercise similar to workouts by astronauts in space – but with one important difference: they are pulled towards the treadmill surface by a harness applying greater force than what the research team has previously measured during walking and running on the International Space Station treadmill.
The results from the first half of the study are “extremely promising,” Cavanagh said. Of the five study subjects so far who have been assigned to the exercise group, bone loss in four of them has been prevented in important skeletal regions by the treadmill exercise countermeasure, while the six non-exercising control subject participants all lost bone mass.
“We have found that we can, on average, prevent bone loss in an important region of the hip with this intervention,” Cavanagh said. “No bed rest study ever before has accomplished this.”
Cavanagh said the study results will impact bone health in space by improving exercise prescriptions for astronauts on future space missions. Here on Earth, the work could help scientists understand how individualized exercise programs affect age- and gender-related osteoporosis.
As for the volunteers, the study leaders encourage them to “achieve something special,” Cavanagh said. “Some tried to learn Spanish. We had others who were preparing for exams, and doing things they would have difficulty doing if they led their life with the typical distractions.”
Cavanagh said the study subjects are kept busy with tests during the week, but the weekends can be difficult.
The volunteers make around $8 an hour, but they’re working 24 hours a day.
“One of my most satisfying moments,” Cavanagh said, “is handing them a $12,000 check at the end.”
Source: University of Washington and Peter Cavanagh
Added 3/24: See an interview with study participant Tabitha Garcia at author Anne Minard’s blog. | 0.80806 | 3.442902 |
Crescent ♒ Aquarius
Moon phase on 3 December 2054 Thursday is Waxing Crescent, 4 days young Moon is in Aquarius.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 4 days on 29 November 2054 at 08:33.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing first ∠1° of ♒ Aquarius tropical zodiac sector.
Lunar disc appears visually 8.4% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1789" and ∠1947".
Next Full Moon is the Cold Moon of December 2054 after 11 days on 14 December 2054 at 22:41.
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 4 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 679 of Meeus index or 1632 from Brown series.
Length of current 679 lunation is 29 days, 15 hours and 18 minutes. It is 2 hours and 29 minutes shorter than next lunation 680 length.
Length of current synodic month is 2 hours and 34 minutes longer than the mean length of synodic month, but it is still 4 hours and 29 minutes shorter, compared to 21st century longest.
This New Moon true anomaly is ∠72.4°. At beginning of next synodic month true anomaly will be ∠109.3°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
9 days after point of perigee on 23 November 2054 at 15:48 in ♍ Virgo. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 3 days, until it get to the point of next apogee on 6 December 2054 at 16:51 in ♓ Pisces.
Moon is 400 632 km (248 941 mi) away from Earth on this date. Moon moves farther next 3 days until apogee, when Earth-Moon distance will reach 404 292 km (251 215 mi).
11 days after its ascending node on 21 November 2054 at 22:10 in ♌ Leo, the Moon is following the northern part of its orbit for the next day, until it will cross the ecliptic from North to South in descending node on 5 December 2054 at 06:07 in ♒ Aquarius.
11 days after beginning of current draconic month in ♌ Leo, the Moon is moving from the beginning to the first part of it.
1 day after previous South standstill on 1 December 2054 at 17:59 in ♑ Capricorn, when Moon has reached southern declination of ∠-19.707°. Next 12 days the lunar orbit moves northward to face North declination of ∠19.747° in the next northern standstill on 16 December 2054 at 01:47 in ♋ Cancer.
After 11 days on 14 December 2054 at 22:41 in ♊ Gemini, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.112963 |
A unique opportunity to study the dwarf planet Haumea has led to an intriguing discovery: Haumea is surrounded by a ring.
Add this to the already long list of unique things about the weird-shaped world with a dizzying rotation and a controversial discovery.
On January 21, 2017 Haumea passed in front of a distant star, in an event known as an occultation. The background star can – pardon the pun – shine a light on the object passing in front, providing information about a distant object — such as size, shape, and density — that is otherwise difficult to obtain. Since an occultation with Haumea had never been observed before, scientists were first eager, and then surprised.
“One of the most interesting and unexpected findings was the discovery of a ring around Haumea,” said said Pablo Santos-Sanz, from the Institute of Astrophysics of Andalusia (IAA-CSIC) in a statement.
This is the first time a ring has been discovered around a trans-neptunian object, and the team said this discovery shows that the presence of rings could be much more common than was previously thought, in our Solar System as well as in other planetary systems.
“Twelve telescopes from ten different European observatories converged on the phenomenon,” said José Luis Ortiz, who led the observational effort, and is also from IAA-CSIC. “This deployment of technical means allowed us to reconstruct with a very high precision the shape and size of dwarf planet Haumea, and discover to our surprise that it is considerably bigger and less reflecting than was previously believed. It is also much less dense than previously thought, which answered questions that had been pending about the object.”
The team said their data shows that the egg-shaped Haumea measures 2,320 kilometers in its largest axis. Previous estimates from various observations put the size at roughly 1,400 km. It takes 3.9 hours for Haumea rotate around its axis, much less than any other body in the Solar System that measures more than a hundred kilometers long. This rotational speed likely caused Haumea to flatten out, giving it an ellipsoid shape. It orbits the Sun in an elliptical loop that takes 284 years to complete. Additionally Haumea has two small moons.
Ortiz and team say their data shows the newly discovered ring lies on the equatorial plane of the dwarf planet, and it “displays a 3:1 resonance with respect to the rotation of Haumea, which means that the frozen particles which compose the ring rotate three times slower around the planet than it rotates around its own axis.”
Ortiz says there might be a few possible explanations for the formation of the ring; it may have originated in a collision with another object, or in the dispersal of surface material due to the planet’s high rotational speed.
Of course, other objects in our Solar System have rings: all the giant planets have rings, with Saturn’s being the most massive and well know. But small centaur asteroids located between Jupiter and Neptune were found to have rings, too.
“Now we have discovered that bodies even farther away than the centaurs, bigger and with very different general characteristics, can also have rings,” said Santos-Sanz.
You may recall there was great controversy over the discovery of Haumea. The discovery was originally announced in 2005 by Mike Brown from Caltech, along with his colleagues Chad Trujillo of the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz, of Yale University.
But then Ortiz and Santos-Sanz attempted to scoop Brown et. al by sending in their claim to discovery to the Minor Planet Center before Brown’s paper was published. It was later learned that Ortiz and colleagues had accessed the Caltech observing logs remotely, looking at when and where Brown was looking with his telescopes. Ortiz and team initially denied the claims, but later conceded accessing the observation logs, maintaining they were just verifying whether they had discovered a new object in observations from 2003.
I asked Brown today if anything was ever officially resolved about the controversy.
“I think the resolution is that it is generally accepted that they stole our positions, but no one wants to think about it anymore,” he said via email.
But the discovery of a ring Haumea, Brown said, looks solid.
“I will admit to being wary of anything Ortiz says, so I checked the data very carefully,” Brown said. “Even I have to agree that the detection looks pretty solid. Haumea is weird, so it’s less surprising than, say, finding rings around something like Makemake. But, still, this was not something I was expecting!” | 0.824885 | 3.953306 |
Well it looks like our rather bold assertion that NASA had found fossils on Mars was a trifle inaccurate. And, as we thought about it a bit more, we realized that it would be impossible to deduce from mere photographs alone, the true nature of anything that we were seeing in the raw images being radioed back to Earth from the Curiosity rover traversing Yellowknife Bay in Gale Crater – no matter how awesome the images looked. And we realized what a cheap way it was to get people to visit our website! Ha ha! Got you! Well, maybe a few dozen of you, anyway… it didn’t work too well, actually. We really did believe that those photos were something quite extraordinary, though. Well, they weren’t.
Today, NASA’s Mars Science Laboratory team held another very interesting teleconference to describe their latest discoveries on Mars – but they weren’t primarily interested in our “barnacles” – which turn out to be spherical concretions called “spherules” like the ones discovered by the Spirit and Opportunity rovers years ago, but with a different mineral composition.
No, today, the NASA scientists were more interested in describing deposits of calcium minerals deposited in fissures all over an area they have named “John Klein”, in tribute to the former deputy project manager of the MSL who tragically passed away in 2011.
We saw these things before, and they intrigued us as well. But they definitely looked more inorganic than the “barnacles” we thought we’d spotted. Which only goes to show what we know about Mars geology!
Both of these features – our non-barnacles and the fissures or “veins” of whitish minerals, are described as providing strong evidence of the precipitation of minerals from water. It’s a sign that, not only was there water flowing for unknown periods of time here in Gale Crater, but that these minerals that were deposited in these fissures came from somewhere else, transported by that water after the rock formed and cracked.
These veins were blasted by Curiosity’s laser and analyzed for their chemical content. It turns out that they are composed of “a calcium-bearing mineral”.
This photo shows a sort of side-view of one of the “veins” of this calcium-bearing mineral. It’s got an interesting “cauliflower-like” appearance:
This is cool stuff. But what does it all mean? Is this in any way proof that life existed on Mars? When will scientists be able to make an announcement as world-shaking as that?
The answer, we found, is that they are not likely to make such an announcement. In the previous MSL press conference, held at the American Geophysical Union’s Fall Conference in San Francisco December 3-7, 2012 – you know, the one at which the NASA team was supposed to make a world- historic announcement of some sort, but didn’t – Drs. John Grotzinger and Paul Mahaffy explained why it’s not likely that any one discovery is going to provide that type of a moment – because scientific inquiry simply doesn’t proceed in that way.
These remarks are somewhat lengthy, but they are so important for people to understand if they don’t want to keep jumping to ridiculous conclusions like we tricked ourselves into making this past week. It will not be the results of a single experiment that will lead to these big, overarching discoveries, but the sum total of a large series of experiments made by the entire science payload of Curiosity that will allow the science team to amass enough compelling evidence to make well-founded assertions about such things as whether or not signs of ancient life on Mars have been discovered. We learned so much from these remarks that we took the time to produce a transcript of the comments made by the two scientists at the AGU meeting, which we present to you with no further adieu. Science proceeds “at the pace of science” as Dr. Grotzinger says; it’s a slow, methodical and careful process designed to obtain real rather than imaginary results. So be patient! We wish we had seen this video before we wrote that last article! Enjoy!
Excerpt from John Grotzinger, Paul Mahaffy remarks at AGU Conference, San Francisco, CA, 3 December, 2012
00:27:50 “OK, so now I want to move on to a somewhat different subject that we call our ‘Three Months of Terror’. Everybody’s seen that ‘blue-shirt moment’ where everybody was jumping up and down celebrating the successful “EDL” [entry, descent and landing – ed.] system. Ours really isn’t so much ‘three months of terror’ as it is ‘three months of tension’. Every day we turn on an instrument; we do the electrical baseline check – it looks like it’s gonna work, but you don’t really know what it’s gonna work until it’s actually done a measurement. And then once you’ve done the measurement, you wonder how well it’s done compared to all the calibration and baseline testing that you’ve done before you launched the spacecraft. And so, each day we go through that; and as we turn these on – as one of our team members from Texas decided to call them – we have a ‘hootin’ and hollerin’ moment’; and everybody’s jumpin’ up and down in the science team and we get all excited about that.
“But in the end, what basically happens, and with the SAM [Sample Analysis at Mars – ed.] instrument in particular… SAM just comes last. It’s at the end of the sample processing chain; it’s also an extremely complicated instrument – it’s practically its own mission… and when it works for the first time we have a ‘hootin’ and hollerin’ moment’; but when it works for the second time, you get something that all scientists live by, which is a ‘repeat analysis’. You see that what you saw the first time is probably not going to go away. And then when you do the third sample and the configuration is pretty much the same it was the first time, you believe maybe this just might be one for the history books, that this is going to stand the time of test [sic] as a legitimate analysis on the surface of Mars. That’s basically where we were at with that excitement by the Science Team.
“So the nature of scientific discovery, especially in this business, is also very important. We live by multiple working hypotheses: as Paul mentioned, even though his instrument detected organic compounds, first of all we have to demonstrate that they’re indigenous to Mars. Then after that, we can engage in the question about whether they represent the background fall of cosmic materials that are organic in composition that fall on the surface of every terrestrial planet; and then after that we can begin into the more complex questions of whether or not this might be some type of a biological material. But that’s well down the road for us to get to.
“And, finally: serendipity. As any of us that have worked on the Earth understand: on a planet that is teeming with life, you can go out into rocks that are billions of years old, and the probability of finding something that is actually a sign of life – or even something as simple as an organic material – those discoveries are so rare that every time we find one it makes it into ‘Science’ and ‘Nature’ [universally respected peer reviewed journals – ed.]. Every new discovery… new occurrence is actually a major discovery. So we have to take our time, and it’s gonna take a bit of luck; but it is serendipity because we’re gonna think it through well ahead of time and go about this exploration in the most intelligent way that we can, using all of our instruments. What this mission about [sic] is integrated science; there’s not going to be one single moment when we all stand up and, on the basis of a single measurement have a ‘halleluja moment’. What it’s gonna take is everything that you heard by my colleagues and all the other P.I.s [principal investigators – ed.] that build all their instruments, we’re gonna pull it all together and we’re gonna take our time, and then after that if we’ve found something significant, we’ll be happy to report that.
“So finally, then: where are we headed? Well, at this point, basically, our car is ready to go. This is a car that comes with a ten-thousand-page user manual that we also have to write as we read it; and, you know, that’s where the patience comes in. But we’re getting closer; we’re getting ready to go here now; we have one major test ahead of us which is the drilling; and we hope to do that and get started on that before the holidays begin; and then sometime early next year we’re gonna pack it up and start driving towards Mt. Sharp, which is the reason we picked this site; and it has what, from orbit, looked like a lot of materials that we’re interested in. So we’re gonna load up the car with the science team, uh, you know… we’ve been at the gas station; we’ve gassed it up, checked the oil, uh, you know, we’re gonna kick the tires around a little bit but then we’re ready for our trip and that’s when our science mission of exploration really gets into full gear.”
[Questions from audience:]
Q: “Hi, I’m Alex Witze with Science News for Dr. Grotzinger: Can you just take us through how you go about figuring out whether these organics are indigenous to Mars or not? Just [employing? in boring?] chemistry detail.”
A: [Grotzinger]: “I’ll pass that one to Paul, but lemme just first reiterate the sort of ‘high level’ approach before Paul gets into more of the details of the chemistry. So: you make a measurement… and what we know is that the instrument is performing perfectly well; it’s very, very sensitive, so that we know that the instrument has detected simple organic molecules. Then after that, you have to do a series of tests to verify that the organics that you’ve measured have not come from Earth; and there are a number of ways that we could bring them with us. Remember: the reason that we chose the soil is to try to clean out all that hardware; and we cleaned it as best as we can on Earth but there’s no guarantees; and so we pass soil through it, shake it around, and then dump it out; take another gulp of soil, shake it around, dump it out. We try to get it as clean as we can, but it could be riding along with the hardware.
“And then, within the instrument itself: there’s always a little bit of stuff that comes along every instrument that we make on Earth. Even the most sensitive instruments carry materials along with them that you have to work through and understand their properties. And then after that, if we believe that it’s indigenous to Mars, then we have to go through a second level of triage, which is to say: ‘O.K.: it’s on Mars, but maybe it didn’t come from Mars; it could be a material that comes from the cosmos.’ A lot of primordial material, as we know… there’s carbonaceous chondrites that, in some cases, have quite complex organic molecules in them. And then after that then you begin by the context; and this is where the other instruments really come in and are so important because they’re the things that allow us to establish that maybe this isn’t something that actually came from space but this was actually something that formed in the environment, where the particles that make up the rock, where they were also accumulating… this was something that was being formed at the same time. And then you have a pathway to decide whether or not those formation pathways are abiotic or may be, in the end, biologic. And so there’s… as you can see, it’s a complicated decision pathway there and we have to explore each one systematically. But, I’ll turn it over to Paul.”
[Paul Mahaffy]: “Yeah… I mean… we’ve gone to great care with this mission to address the potential confusion that might be caused by terrestrial contamination. The materials that we brought to mars with us – we’ve done a lot of analysis to understand what kind of gases they release that we might see. We have a… what we call an ‘organic check material’: it’s a very pure vitreous silica glass; and we have that doped with [deliberately infused with – ed.] four very distinctive fluorocarbons. And so, if we’re looking for terrestrial stuff not just inside of SAM, but stuff that might come from the sample processing chain, what we can do in the end to avoid confusion is we can drill into one of those five organic check materials, run that sample through, and really treat that as a blank. And if we see the same stuff that we saw that we thought might be from Mars, from either some drilled rock or from soil, then we gotta say: ‘Hold the show a minute; this might be terrestrial stuff.’
“We do, even more routinely, we run blanks on… internal to SAM. For every experiment that we did here, we ran, essentially, a blank beforehand and looked… there’s very trace residual amounts, for example, of our derivitization agent; a very little bit of vapor shows up. We’ve seen some of this as we calibrated the instrument and so on. That’s actually great ’cause it shows us that the chromatography is working beautifully; but then if we see that when we have a solid sample in our cup, we go back to the blank and we said: ‘Oh, did we see that compound?’ And if the answer is ‘yes’, then it’s not from Mars.
“So, we’ll do all of those things; but what really helps also is the great flexibility of… you saw those bars [see figure 1 – ed.]. We can select different slices of evolved compounds to analyze with chromatography; we can have different temperature sequences on the sample, to release organics. And so all those things combine, really, to get a story on whether, uh… give us confidence if what we’re seeing is from Mars or not from Mars. So that work is ongoing.”
Q: “Emily Lakdawalla from the Planetary Society; this question is for Paul: I’m wondering how many of the compounds you’ve identified so far are ones that would be present as those compounds in the soil or if they’re all evolved from other compounds that are in the soil – and particularly interested in the chlorine compounds and the hydrogen sulfide.”
A: [Paul Mahaffy]: “Yeah… the question really relates to whether the compounds that we were showing might exist in the soil or whether they might be made as we do our experiment.
“It’s certainly very possible that there… in fact I would suggest very likely that they are made. As we heat the sample up, the simple chloro… single carbon compounds are being released at the temperature that this oxygen signal is coming up… potentially a calcium perchlorate. And so, with the high temperatures and chlorine being released, perhaps hydrogen chloride being released, it’s very reactive. And then it latches on to whatever carbon is there and forms these very simple compounds. So it’s very, very possible; I would say even likely that those compounds were not existing and we really made them as part of our experiment.”
[Transcript produced by Independent Workers Party of Chicago, 15 January 2013. All errors are our own.] | 0.898784 | 3.402061 |
In astronomy, the ecliptic is one of the imaginary lines we use to navigate the sky.
It is often plotted on star charts to help astronomers see where any visible planets and the moon will be. Why is it that this line is a highway for the planets?
In this astronomer’s guide to the ecliptic, you’ll find the answer to that question and learn why this is such a useful term to be aware of.
What Is The Ecliptic?
Very simply, the ecliptic is the line of the sun’s apparent path through the sky.
The path of the ecliptic is inclined at 23.5° to the plane of our orbit around the sun because our planet’s axis is tilted by that amount to the sun’s equator.
But why do we say it’s the sun’s apparent path through the heavens?
Well, it’s because the sun is not really moving through our sky at all. Instead, the sun’s motion across the constellations is an effect created by our orbit around it.
We zoom around the sun at 67,000 mph or 18.5 miles per second. However, the distance we have to travel is so vast that, even at this colossal speed, it still takes a full year for us to complete the journey.
As we move along our orbit, we see different constellations appear behind the sun… at least we would if it wasn’t too bright to see them.
Our movement equates to one degree per day, or about the width of two full moons. Over a year, the path of the sun travels through 13 constellations, which are known as the zodiac constellations.
The Ecliptic and the Zodiac Constellations
You can see the journey in the image below, click it for a fullscreen version.
Despite what horoscopes say, there are actually 13 zodiac constellations and the sun spends roughly four weeks of the year with each as a backdrop. From the start of a year, they are:
- Capricornus (Jan)
- Ophiuchus (not a horoscope sign)
In reality, the sun spends different amounts of time in each one, depending on how much of the sky they cover and how deep into them the sun travels.
For example, the chances are that if you’re a Scorpio, you are really an Ophiuchus(io?) because the sun only spends a week in Sagittarius compared to three weeks in Ophiuchus!
Why Is The Sun’s Path Called the Ecliptic?
The ecliptic is named such because it’s the line on which eclipses happen, which makes sense when you think about it.
The ecliptic is the line drawn by the sun, so when the moon gets in the way of that view, we see a solar eclipse. A lunar eclipse happens when the moon is exactly on the opposite side of us from the sun which can only happen when it too is on the ecliptic.
If it’s that simple, why don’t eclipses happen every month?
Well, the reason eclipses are rare is because the moon’s orbit is not quite in the same plane as Earth’s. Its orbit is tilted about 5.5° away from ours. Because of its inclined orbit, the moon spends half of each month above the line of the ecliptic and half below it.
Twice each month, the moon crosses the line of the ecliptic, once as it moves from above to below it, and once in the opposite direction.
Eclipses can only happen when the moon is new or full at the time it crosses the ecliptic. If it’s new when crossing the line we see a solar eclipse and if it’s full, we experience a lunar eclipse.
If the moon is at any other phase when it crosses – which is most of the time – it’s not lined up with the sun, so no eclipse can happen. This is why eclipses are rare events
Why Are Planets Only Found Near the Ecliptic?
The planets of the solar system orbit on a very narrow plane, none of them leaves the plane of the sun’s equator by more than 7.2°.
Planets are always found on or near the ecliptic because they are all within a very narrow plane of the sun. Where it travels is where we also find the planets.
Knowing where to find the ecliptic line is very useful for planet-hunting astronomers.
Where is the Ecliptic?
The ecliptic is one of the base measures for our celestial coordinate system because zero hours of right ascension is defined as the point where the sun’s path (a.k.a. the ecliptic) crosses the celestial equator at the vernal equinox.
However, even though the line is fixed (pretty much), our personal view of it changes over a year.
Let’s take 10pm as our base time for astronomy to see how it changes through the year. All of the images are from SkySafari 6 and can be made full screen by clicking on them.
In winter, we find the ecliptic high in the northern hemisphere sky at 10pm, soaring over the top of Orion’s outstretched arm. From mid-US latitudes, the line extends to around 70° over the horizon.
Not much has changed since January. The highest section now cuts through Cancer and Gemini at 65° over the horizon.
In the transition from winter to summer, the ecliptic has sunk much lower and is now around 45° over the horizon in Virgo.
As fall begins, the ecliptic is at its lowest in evening skies, just 30° above the horizon on Capricornus.
The opposite is true in the morning, the ecliptic rises high in fall mornings but is low in spring.
This makes intuitive sense. In the summer, the sun rises higher in the sky in the day and so more of its path is visible in the day than at night
In winter the opposite is true, the sun travels a long way below the horizon, so we see more of its path in the hours of darkness
The rule of opposites also applies to the southern hemisphere, when the ecliptic is high in the northern hemisphere, it is low in the southern.
Now you know everything you need to use the ecliptic to plan your planet-hunting.
Get outside tonight and see if you can work out where the ecliptic is by where the moon and tonight’s planets are. | 0.877111 | 3.700866 |
Typically, the Lunar Reconnaissance Orbiter (LRO) spacecraft flies over the night side of the Moon every two hours, spending about 45 minutes in darkness. Because LRO is powered by sunlight, it uses a rechargeable battery to operate while on the night side of the Moon and then charges the battery when it comes back around into daylight.
During the total lunar eclipse of September 27-28, 2015, however, LRO emerges from the night side of the Moon only to find the Sun blocked by the Earth. LRO needs to travel an entire orbit before seeing the Sun again, relying continuously on its battery for almost three hours.
LRO won’t be in any real danger as long as its power consumption is handled carefully. Except for LRO's infrared radiometer, called Diviner, its scientific instruments will be turned off temporarily, while vital subsystems like the heaters will remain on. LRO will be closely monitored throughout the eclipse.
Diviner maps the temperature on the Moon's surface along a swath below LRO's orbit. During the eclipse, the instrument will precisely measure the rapid temperature changes that occur as the Moon enters and leaves the Earth's shadow. When compared with normal daylight variations, these measurements will reveal new details about the top centimeter (half-inch) of lunar regolith. Diviner wasn't specifically designed for this experiment, but as scientists have gained experience with the LRO spacecraft, they've thought of new and creative ways of using its instruments.
This animation shows the Moon as it might look through a telescope on Earth, along with LRO’s orbit, its view of the Sun, and a fuel gauge showing received sunlight and the battery’s charge. | 0.826014 | 3.5859 |
Saturn’s moon Titan just keeps throwing surprises at us. A multi-layered atmosphere thicker than our own? Check. A hydrologic cycle that relies on methane as the operating liquid? Check. Rivers, streams and lakes filled with this same liquid? Check, check and check. And now, scientists are suspecting that Titan may have yet another surprise: a subsurface ocean.
Observations of Titan’s rotation and orbit, carried out by researchers at the Royal Observatory of Belgium using Cassini data, point at an unusual rotational inertia; that is, its resistance to changes in its motion, also known as moment of inertia or angular mass. Basically Titan moves in a way that is not indicative of a solid body of its previously assumed density and mass. Rather, its motion – both around its own axis and in its tidally-locked orbit around Saturn – are more in line with an object that isn’t uniformly solid.
According to the math, Titan may very well be filled with liquid!
Or, at least, have a liquid layer of considerable depth beneath its surface. How far below the surface, how deep and exactly what kind of liquid are all speculative at this point…it’s suggested that it may be a subsurface ocean of yet more methane. This would help answer the question of where Titan gets all of its methane in the first place; methane, – a.k.a. natural gas – is a compound that breaks down quickly in sunlight. In fact, the high-level haze that surrounds the moon like a wispy blue shell is made up of this broken-down methane. So if this stuff is raining down onto the surface in giant, frigid drops and filling streams and lakes, but is still being broken down by ultraviolet light from the Sun to enshroud the entire moon (Titan is BIG, remember…at 5,150 km – 3,200 miles – wide, it’s over a third the size of Earth!) then there has to be somewhere that this methane is coming from.
If these calculations are right, it may be coming from underground.
We propose a new Cassini state model for Titan in which we assume the presence of a liquid water ocean beneath an ice shell… with the new model, we find a closer agreement between the moment of inertia and the rotation state than for the solid case, strengthening the possibility that Titan has a subsurface ocean.
– Rose-Marie Baland et al.
Of course in order for this hypothesis to be proven many more numbers are going to have to be crunched and more data reviewed. And more possibilities considered, too; Titan’s orbital irregularities may in fact be the result of external forces, such as a close pass by a comet or other large body. Still, there’s something to be investigated here and you can bet there’ll be no shortage of attention on a problem as intriguing as this!
Titan may soon be joining the short list of moons speculated to possess subsurface oceans, alongside Jupiter’s Europa and Ganymede and sister Saturnian satellite Enceladus…and who knows how many others?
Top image credit: NASA / JPL / SSI. (Edited by J. Major.) | 0.850235 | 3.892665 |
Since the beginning of the Space Age, humans have relied on chemical rockets to get into space. While this method is certainly effective, it is also very expensive and requires a considerable amount of resources. As we look to more efficient means of getting out into space, one has to wonder if similarly-advanced species on other planets (where conditions would be different) would rely on similar methods.
Harvard Professor Abraham Loeb and Michael Hippke, an independent researcher affiliated with the Sonneberg Observatory, both addressed this question in two recently–released papers. Whereas Prof. Loeb looks at the challenges extra-terrestrials would face launching rockets from Proxima b, Hippke considers whether aliens living on a Super-Earth would be able to get into space.
The papers, tiled “Interstellar Escape from Proxima b is Barely Possible with Chemical Rockets” and “Spaceflight from Super-Earths is difficult” recently appeared online, and were authored by Prof. Loeb and Hippke, respectively. Whereas Loeb addresses the challenges of chemical rockets escaping Proxima b, Hippke considers whether or not the same rockets would able to achieve escape velocity at all.
For the sake of his study, Loeb considered how we humans are fortunate enough to live on a planet that is well-suited for space launches. Essentially, if a rocket is to escape from the Earth’s surface and reach space, it needs to achieve an escape velocity of 11.186 km/s (40,270 km/h; 25,020 mph). Similarly, the escape velocity needed to get away from the location of the Earth around the Sun is about 42 km/s (151,200 km/h; 93,951 mph).
As Prof. Loeb told Universe Today via email:
“Chemical propulsion requires a fuel mass that grows exponentially with terminal speed. By a fortunate coincidence the escape speed from the orbit of the Earth around the Sun is at the limit of attainable speed by chemical rockets. But the habitable zone around fainter stars is closer in, making it much more challenging for chemical rockets to escape from the deeper gravitational pit there.”
As Loeb indicates in his essay, the escape speed scales as the square root of the stellar mass over the distance from the star, which implies that the escape speed from the habitable zone scales inversely with stellar mass to the power of one quarter. For planets like Earth, orbiting within the habitable zone of a G-type (yellow dwarf) star like our Sun, this works out quite while.
Unfortunately, this does not work well for terrestrial planets that orbit lower-mass M-type (red dwarf) stars. These stars are the most common type in the Universe, accounting for 75% of stars in the Milky Way Galaxy alone. In addition, recent exoplanet surveys have discovered a plethora of rocky planets orbiting red dwarf stars systems, with some scientists venturing that they are the most likely place to find potentially-habitable rocky planets.
Using the nearest star to our own as an example (Proxima Centauri), Loeb explains how a rocket using chemical propellant would have a much harder time achieving escape velocity from a planet located within it’s habitable zone.
“The nearest star to the Sun, Proxima Centauri, is an example for a faint star with only 12% of the mass of the Sun,” he said. “A couple of years ago, it was discovered that this star has an Earth-size planet, Proxima b, in its habitable zone, which is 20 times closer than the separation of the Earth from the Sun. At that location, the escape speed is 50% larger than from the orbit of the Earth around the Sun. A civilization on Proxima b will find it difficult to escape from their location to interstellar space with chemical rockets.”
Hippke’s paper, on the other hand, begins by considering that Earth may in fact not be the most habitable type of planet in our Universe. For instance, planets that are more massive than Earth would have higher surface gravity, which means they would be able to hold onto a thicker atmosphere, which would provide greater shielding against harmful cosmic rays and solar radiation.
In addition, a planet with higher gravity would have a flatter topography, resulting in archipelagos instead of continents and shallower oceans – an ideal situation where biodiversity is concerned. However, when it comes to rocket launches, increased surface gravity would also mean a higher escape velocity. As Hippke indicated in his study:
“Rockets suffer from the Tsiolkovsky (1903) equation : if a rocket carries its own fuel, the ratio of total rocket mass versus final velocity is an exponential function, making high speeds (or heavy payloads) increasingly expensive.”
For comparison, Hippke uses Kepler-20 b, a Super-Earth located 950 light years away that is 1.6 times Earth’s radius and 9.7 times it mass. Whereas escape velocity from Earth is roughly 11 km/s, a rocket attempting to leave a Super-Earth similar to Kepler-20 b would need to achieve an escape velocity of ~27.1 km/s. As a result, a single-stage rocket on Kepler-20 b would have to burn 104 times as much fuel as a rocket on Earth to get into orbit.
To put it into perspective, Hippke considers specific payloads being launched from Earth. “To lift a more useful payload of 6.2 t as required for the James Webb Space Telescope on Kepler-20 b, the fuel mass would increase to 55,000 t, about the mass of the largest ocean battleships,” he writes. “For a classical Apollo moon mission (45 t), the rocket would need to be considerably larger, ~400,000 t.”
While Hippke’s analysis concludes that chemical rockets would still allow for escape velocities on Super-Earths up to 10 Earth masses, the amount of propellant needed makes this method impractical. As Hippke pointed out, this could have a serious effect on an alien civilization’s development.
“I am surprised to see how close we as humans are to end up on a planet which is still reasonably lightweight to conduct space flight,” he said. “Other civilizations, if they exist, might not be as lucky. On more massive planets, space flight would be exponentially more expensive. Such civilizations would not have satellite TV, a moon mission, or a Hubble Space Telescope. This should alter their way of development in certain ways we can now analyze in more detail.”
Both of these papers present some clear implications when it comes to the search for extra-terrestrial intelligence (SETI). For starters, it means that civilizations on planets that orbit red dwarf stars or Super-Earths are less likely to be space-faring, which would make detecting them more difficult. It also indicates that when it comes to the kinds of propulsion humanity is familiar with, we may be in the minority.
“This above results imply that chemical propulsion has a limited utility, so it would make sense to search for signals associated with lightsails or nuclear engines, especially near dwarf stars,” said Loeb. “But there are also interesting implications for the future of our own civilization.”
“One consequence of the paper is for space colonization and SETI,” added Hippke. “Civs from Super-Earths are much less likely to explore the stars. Instead, they would be (to some extent) “arrested” on their home planet, and e.g. make more use of lasers or radio telescopes for interstellar communication instead of sending probes or spaceships.”
However, both Loeb and Hippke also note that extra-terrestrial civilizations could address these challenges by adopting other methods of propulsion. In the end, chemical propulsion may be something that few technologically-advanced species would adopt because it is simply not practical for them. As Loeb explained:
“An advanced extraterrestrial civilization could use other propulsion methods, such as nuclear engines or lightsails which are not constrained by the same limitations as chemical propulsion and can reach speeds as high as a tenth of the speed of light. Our civilization is currently developing these alternative propulsion technologies but these efforts are still at their infancy.”
One such example is Breakthrough Starshot, which is currently being developed by the Breakthrough Prize Foundation (of which Loeb is the chair of the Advisory Committee). This initiative aims to use a laser-driven lightsail to accelerate a nanocraft up to speeds of 20% the speed of light, which will allow it to travel to Proxima Centauri in just 20 years time.
Hippke similarly considers nuclear rockets as a viable possibility, since increased surface gravity would also mean that space elevators would be impractical. Loeb also indicated that the limitations imposed by planets around low mass stars could have repercussions for when humans try to colonize the known Universe:
“When the sun will heat up enough to boil all water off the face of the Earth, we could relocate to a new home by then. Some of the most desirable destinations would be systems of multiple planets around low mass stars, such as the nearby dwarf star TRAPPIST-1 which weighs 9% of a solar mass and hosts seven Earth-size planets. Once we get to the habitable zone of TRAPPIST-1, however, there would be no rush to escape. Such stars burn hydrogen so slowly that they could keep us warm for ten trillion years, about a thousand times longer than the lifetime of the sun.”
But in the meantime, we can rest easy in the knowledge that we live on a habitable planet around a yellow dwarf star, which affords us not only life, but the ability to get out into space and explore. As always, when it comes to searching for signs of extra-terrestrial life in our Universe, we humans are forced to take the “low hanging fruit approach”.
Basically, the only planet we know of that supports life is Earth, and the only means of space exploration we know how to look for are the ones we ourselves have tried and tested. As a result, we are somewhat limited when it comes to looking for biosignatures (i.e. planets with liquid water, oxygen and nitrogen atmospheres, etc.) or technosignatures (i.e. radio transmissions, chemical rockets, etc.).
As our understanding of what conditions life can emerge under increases, and our own technology advances, we’ll have more to be on the lookout for. And hopefully, despite the additional challenges it may be facing, extra-terrestrial life will be looking for us!
Professor Loeb’s essay was also recently published in Scientific American. | 0.942192 | 3.752877 |
identifying winter constellations
by Sean O’Dwyer
IF THE STARS SEEM BRIGHTER IN THE WINTER, IT’S BECAUSE THEY REALLY ARE—THE WINTER NIGHT SKY ACTUALLY HAS MORE BRIGHT STARS.
As the autumn fades, so does the Milky Way, but the Hudson Valley’s dark winter skies offer up plenty of jewels in its place: several of the year’s best meteor showers, the brightest galaxy in the Northern Hemisphere, many beautiful double-stars, and a nebula that resembles our own solar system in its infancy, billions of years ago.
To make the most of the descriptions below, you’ll need access to a star map. If you don’t have one, monthly magazines like Astronomy (astronomy.com) and Sky & Telescope (skyandtelescope.com) publish highly usable charts and maps to get you started. Alternatively, you can go straight to the Internet, at either of the above sites, and easily generate an accurate sky chart for your location tonight.
For the ultimate in desktop exploration and easy planning, planetarium software such as Starry Night (starrynight.com) for Mac or PC is the way to go; for Mac users, Starry Night also provides a free dashboard widget.
ARIES, TRIANGULUM, ANDROMEDA
The Brightest Galaxy in the Northern Sky
A small constellation in the northern sky, Triangulum is well placed at this time of year for observations of the Triangulum Galaxy (M33), a small spiral galaxy. Only 5 percent as massive as our own spiral galaxy, The Milky Way, it’s a dim fuzzy object in 8-inch scopes and requires good dark skies to show any detail. Compare and contrast with the Andromeda Galaxy, the vast bright spiral galaxy to the west.
Once you spot the Andromeda Galaxy (M31) with your binoculars or telescope, try viewing it with the naked eye. You may need to use “averted vision”: shift your eyes slightly to the left or right and use your peripheral vision, which is far more sensitive in low light situations. You should be able to make out a faint fuzzy patch, the photons from which have traveled in a straight line for 2.4 million years to end their journey on your retina—M31 is literally the furthest thing you can see with your naked eyes.
At the tip of the Andromeda’s brightest limb is Almach, a lovely orange/blue double. And finally, below Triangulum, in Aries, is Mesarthim, another lovely double, orange/green, sitting 207 light years distant.
A Stellar Nursery
Red & Blue Supergiant Stars
Right after the Big Dipper, Orion is the most well-known and easily recognizable constellation, in part because it’s one of the few constellations—with its shoulders, torso, belt, and sword—that has the appearance of an identifiable shape. Orion sails across the southern horizon from winter through spring.
Even in small telescopes, the Great Orion Nebula (M42) provides marvelous views, with every increase in light-gathering power yielding richer detail and exposing its wonderful three-dimensional cloud structure: newly-minted pinpoint stars hang silent among filaments of hydrogen that stream across space for trillions of miles.
The cloud is a stellar nursery, resembling our own solar system billions of years ago. At the center of the nebula sits a formation of four stars (from west to east: A, B, C, and D) known as the Trapezium: it’s these young and very hot stars, with others, that make the nebula glow.
Betelgeuse is the red star in Orion’s top left (eastern) corner. In fact, Betelgeuse is an M1 red supergiant—about 650 times the diameter and 15 times the mass of the Sun. If Betelgeuse were to replace the Sun, its size would engulf the orbits of Mercury, Venus, Earth, and even Mars. An ancient star approaching the end of its life cycle, the supergiant’s size fluctuates wildly and it may soon explode as a supernova that would be as bright as the crescent Moon.
On the bottom right (western) heel of Orion lies the brilliant blue Rigel. Rigel is also supergiant, though much younger than Betelgeuse. It shines a remarkable 40,000 times more luminously than our own Sun; there are a million stars closer to us than Rigel, but none shine nearly as bright.
Compare the colors of Betelgeuse and Rigel on your next outing under the stars. Their color tells you their age. Young stars are blue/white. Old stars are red/orange.
On November 18 the Leonid Meteor Shower peaked. Unfortunately this year, the moon is present, washing out the sky more than we’d like, but the Leonids have often produced truly spectacular showers, with thousands of meteors raining down per hour. You never know. (Normal peak rates are 15-20 fast meteors per hour.) Best results are to be had right before dawn. Look south for Leo’s famous backwards sickle shape, which marks the lion’s head and encloses the shower’s radiant.
On December 14 the Geminid Meteor Shower peaks. The Geminids are the most reliable shower of the year, producing bright, colorful, moderately swift meteors that sometimes break apart as fireballs. The shower is thought to be intensifying every year and recent showers have seen 120 to 160 meteors per hour under optimal conditions. The best viewing time is in the early hours, around 2 to 3am local time.
On December 23 the Ursid Meteor Shower peaks. Radiating from the Little Dipper (Ursa Minor), this shower generally produces rates of 10 meteors per hour, but has been known to have short bursts of 100 meteors per hour. | 0.890187 | 3.609584 |
Jupiter and several of its moons are of scientific interest to astronomers because they could be full of undiscovered surprises. Although NASA’s Juno spacecraft is probing Jupiter right this second, the European Space Agency (ESA) plans to dive even deeper with the launch of the Jupiter Icy Moons Explorer (JUICE) by 2022.
Image Credit: spacecraft: ESA/ATG medialab; Jupiter: NASA/ESA/J. Nichols (University of Leicester); Ganymede: NASA/JPL; Io: NASA/JPL/University of Arizona; Callisto and Europa: NASA/JPL/DLR
JUICE will study the same system that Juno resides in today, but the scope of the mission will go beyond studying Jupiter itself. According to the ESA, JUICE will set its sights on at least three of the giant gas planet’s mysterious moons: Callisto, Europa, and Ganymede with the hope of unraveling their secrets.
These moons have left planetary experts foaming at the mouth for decades because each one potentially harbors a global liquid ocean beneath its surface. Where there’s liquid, there’s a potential for habitability, and so finding out whether these worlds could support life in any capacity is a priority.
Learning about what’s hiding beneath these moons’ surfaces requires high-tech radar technology. Fortunately, JUICE will sport a 16-meter-long radar boom capable of probing up to 9 kilometers beneath the moons' surfaces in search of clues.
The trip to Jupiter takes up to seven years following launch, so testing models out on Earth is critical before we rocket it off to another world.
Fortunately, experimentation phases are already in full swing thanks to researchers based out of Germany. Just last week, a team attached a replica of the radar boom to a mock-up probe and used a helicopter to fly it around about 50 meters above the ground.
Image Credit: Airbus/Rolf Schwark via ESA
Through this testing, they verified the accuracy of their computer simulations as the probe moved deftly through the air with the solar array and boom equipment positioned in various orientations.
“All the experiments were completed and provided a large amount of data that will be analyzed in the coming weeks for guiding the next steps of the instrument’s development and to improve the modeling of our software simulations developed in the laboratory,” says principal investigator Lorenzo Bruzzone from the University of Trento, Italy.
“The test was a fundamental step towards understanding the behavior of the real antenna that will ultimately allow us to perform highly accurate measurements of the radar echoes reflected from the deep subsurface of the Jovian icy moons.”
We have a while to go yet before the JUICE probe is put together and launched into space, but this data is essential for building a fully-working piece of equipment that will deliver useful scientific results.
It should be interesting to see what JUICE will uncover when that day finally comes. | 0.864628 | 3.67038 |
Living in the Galactic Danger Zone
Not every place within a galaxy experiences the same conditions for habitability – some parts are lethal thanks to supernovae, whilst others do not possess enough heavy elements to allow rocky planets and life to develop. Image: The Hubble Heritage Team (AURA/STScI/NASA)
We know for certain that life exists in the Milky Way galaxy: that life is us. Scientists are continually looking to understand more about how life on our planet came to be and the conditions that must be met for its survival, and whether those conditions can be replicated elsewhere in the Universe. It turns out that looking at our entire Galaxy, rather than focusing just on life-giving properties of our planet or indeed the habitability of regions of our own Solar System, is a good place to start.
How far our planet orbits from the Sun, along with other factors such as atmospheric composition, a carbon cycle and the existence of water, has told astronomers much about the conditions that are required for life to not only originate, but to survive on rocky worlds. This distance from a star is referred to, quite simply, as the ‘Habitable Zone’ or sometimes the ‘Goldilocks Zone’ because conditions here are neither too hot or too cold for water to be liquid on the planet’s surface — conditions just right for life as we know it to thrive.
Copernican theory tells us that our world is a typical rocky planet in a typical planetary system. This concept has spurred some astronomers to start thinking bigger, way beyond the simplicity of any one planetary system and instead towards much grander scales. Astronomers are exploring whether there is a Galactic Habitable Zone (GHZ) in our Galaxy – a region of the Milky Way that is conducive to forming planetary systems with habitable worlds. The Galactic Habitable Zone implies that if there are conditions just right for a planet around a star, then the same must go for a galaxy.
This concept was first introduced by geologist and paleontologist Peter Ward and Donald Brownlee, an astronomer and astrobiologist, in their book, ‘Rare Earth’. The idea of a GHZ served as an antagonistic view point to the Copernican principle. Despite scientists such as Carl Sagan and Frank Drake favoring the theory of mediocrity based on the Copernican model, which supports the probability of the Universe hosting other forms of complex life, Ward and Brownlee were certain our Earth and the conditions within our Galaxy that allowed such life to evolve are both extremely rare. Their answer to the famous Fermi paradox – if extraterrestrial aliens are common, why is their existence not obvious? – is that alien life more complex than microbes is not very common at all, requiring a number of factors, each of low possibility, to come into play. In short, Ward and Brownlee were suggesting that much of the Galaxy was inhospitable to complex life. In their view, only a narrow belt around the Galaxy was fertile: the Galactic Habitable Zone.
A supernova sterilizes an alien world in this artist’s impression. Credit: David A Aguilar (CfA)
Since then, many astronomers have looked at the idea of the GHZ. Not all believe that it necessarily supports Ward and Brownlee’s Rare Earth hypothesis.
One recent assessment of the GHZ, by Michael Gowanlock of NASA’s Astrobiology Institute, and his Trent University colleagues David Patton and Sabine McConnell, has suggested that while the inner sector of the MIlky Way Galaxy may be the most dangerous, it is also most likely to support habitable worlds.
Their paper, accepted for publication in the journal Astrobiology, modeled habitability in the Milky Way based on three factors: supernova rates, metallicity (the abundance of heavy elements, used as a proxy for planet formation) and the time taken for complex life to evolve. They found that although the greater density of stars in the inner galaxy (out to a distance of 8,100 light years from the galactic center) meant that more supernovae exploded, with more planets becoming sterilized by the radiation from these exploding stars, the chances of finding a habitable planet there was ten times more likely than in the outer Galaxy.
This contradicts previous studies that, for example, suggested the GHZ to be a belt around the Galaxy between distances of 22,800 light years (7 kiloparsecs) and 29,300 light years (9 kiloparsecs) from the galactic center. What’s noticeable is that our Sun orbits the Galaxy at a distance of about 26,000 light years (8 kiloparsecs) – far outside GHZ proposed by Gowanlock’s team. Why is their proposed galactic habitable zone so different?
“We assume that metallicity scales with planet formation,” says Gowanlock. Heavy elements are produced by dying stars, and the more generations of stars there have been, the greater the production of these elements (or ‘metals’ as they are termed by astronomers). Historically, the greatest amount of star formation has occurred in the inner region of the Milky Way. “The inner Galaxy is the most metal-rich, and the outer Galaxy is the most metal-poor. Therefore the number of planets is highest in the inner Galaxy, as the metallicity and stellar density is the highest in this region.”
However, amongst so much star formation lurks a danger: supernovae. Gowanlock’s team modeled the effects of the two most common forms of supernovae – the accreting white dwarfs that produce type Ia supernovae, and the collapsing massive stars of type II supernovae.
An artist’s impression of a potentially habitable planet around a Sun-like star. The habitability of such worlds not only depends on conditions on the planet and its distance from the star, but may also depend on where in the Galaxy it is located. Image: ESO/M Kornmesser
Measurements of the galactic abundance of the isotope aluminum-26, which is a common by-product of type II supernovae, have allowed astronomers to ascertain that a supernova explodes on average once every 50 years. Meanwhile, previous studies have indicated that a supernova can have a deleterious effect on any habitable planet within 30 light years.
“In our model, we assume that the build-up of oxygen and the ozone layer is required for the emergence of complex life,” says Gowanlock. “Supernovae can deplete the ozone in an atmosphere. Therefore, the survival of land-based complex life is at risk when a nearby supernova sufficiently depletes a great fraction of the ozone in a planet’s atmosphere.”
The team discovered that at some time in their lives, the majority of stars in our Galaxy will be bathed in the radiation from a nearby supernova, whereas around 30% of stars remain untouched or unsterilized. “Sterilization occurs on a planet that is roughly [at a distance] between 6.5 to 98 light years, depending on the supernovae,” says Gowanlock. “In our model, the sterilization distances are not equal, as some supernovae are more lethal than others.”
Although the outer regions of the Galaxy, with their lower density of stars and fewer supernovae, are generally safer, the higher metallicity in the inner Galaxy means that the chances of finding an unsterilized, habitable world are ten times greater, according to Gowanlock’s model. However, their model does not stipulate any region of the Galaxy to be uninhabitable, only that it’s less likely to find habitable planets elsewhere.
This explains why our Solar System can reside far outside of the inner region, and it also gives hope to SETI – Gowanlock’s model proposes that there are regions of the Galaxy even more likely to have life, and many SETI searches are already targeted towards the galactic center.
A multi-wavelength image of the Milky Way’s center. The highest number of stars and rocky planets reside towards the galactic center, but that is also where the most supernovae occur. Image: NASA/JPL-Caltech/ESA/CXC/STScI
However, not all are in favor of the new model. Ward and Brownlee noted that the Sun’s position in the Galaxy is far more favorable because planets that dance around stars that are too close to the galactic center are more likely to suffer from a perturbed orbit by the gravity of another star that has wandered too close. Others question some of the assumptions made in the research, such as the accuracy of the percentage of planets that are habitable in the galaxy (1.2 percent), or that tidally-locked worlds can be habitable.
“The authors may be making some assumptions that aren’t too well justified,” says Professor Jim Kasting of Penn State University and author of How to Find a Habitable Planet. “They seem well ahead of the rest of us who are still pondering these questions.”
However, others believe that the research is promising. “This is one of the most complete studies of the Galactic Habitable Zone to date,” says Lewis Dartnell, an astrobiologist at University College London. “The results are intriguing, finding that white dwarf supernovae are over five times more lethal to complex life on habitable worlds than core collapse supernovae.”
The GHZ isn’t static; the research paper written by Gowanlock’s team points out that over time the metallicity of the Galaxy will begin to increase the farther out one travels from the galactic center.
“This is why stars that form at a later date have a greater chance of having terrestrial planets,” says Gowanlock. As a result, perhaps the heyday for life in our Galaxy is yet to come.
This story has been translated into Spanish. | 0.827546 | 3.756095 |
Modelling Star Formation in the Early Universe
The light we detect from the most distant galaxies has taken many billions of years to reach us. It was emitted at a much earlier epoch of galaxy formation than the one we see around us today - when the Universe itself was young and the galaxies we observe had only undergone one or two phases of star formation. These early galaxies are likely to have been the building blocks from which the more massive systems we see today formed.
If we can understand them, then we can place constraints on the process of galaxy formation and evolution. New telescopes and instruments are opening new opportunities to study these systems - probing not only the stars in these galaxies, but also the dust those stars produce and the molecular gas that provides the fuel for star formation.
New and improved galaxy stellar populations are essential for interpreting these observations. In particular, the effects of stellar multiplicity (i.e. interactions with binary or tertiary companions) can be significant for the young, intensely star forming and often low metallicity populations which are now being probed. The Binary Population and Spectral Synthesis (BPASS) project is an ongoing effort to develop improved stellar population models in a range of environments, including in the earliest stages of galaxy evolution. Recent research focuses have included old stellar populations, gravitational wave event rates and the stellar mass distribution in galaxies.
A PhD project in this area would contribute to the development of the next version of these widely used models and in particular focus on the effects of changes in stellar chemical abundances over time and their observable consequences.
For further information please email Elizabeth Stanway
Please fill in our PhD enquiries form if you are interested in studying for a PhD in Astronomy at Warwick. | 0.802868 | 3.674498 |
Searching for Earth Life, from Venus
Venus Express Searching for Life – on Earth
Earth atmosphere’s molecules detected by Venus Express.
Scientists using ESA’s Venus Express are trying to observe whether Earth is habitable. Silly, you might think, when we know that Earth is richly stocked with life. In fact, far from being a pointless exercise, Venus Express is paving the way for an exciting new era in astronomy.
Venus Express took its first image of Earth with its Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) soon after its launch in November 2005. About a year after the spacecraft established itself in Venus’s orbit, David Grinspoon, a Venus Express Interdisciplinary Scientist from the Denver Museum of Nature & Science, Colorado, suggested a program of sustained Earth observation.
"When the Earth is in a good position, we observe it two or three times per month," says Giuseppe Piccioni, Venus Express VIRTIS Co-Principal Investigator, at IASF-INAF, Rome, Italy. The instrument has now amassed approximately 40 images of Earth over the last two years.
Atmospheric investigations by Venus Express.
The images of Earth cover both visible and near-infrared regions of the spectrum and can be split into spectra, in order to search for the signature of molecules in the Earth’s atmosphere.
The value of the images lies in the fact that Earth spans less than a pixel in Venus Express’s cameras. In other words, it appears as a single dot with no visible surface details. This situation is something that astronomers expect to soon face in their quest for Earth-sized worlds around other stars.
"We want to know what can we discern about the Earth’s habitability based on such observations. Whatever we learn about Earth, we can then apply to the study of other worlds," says Grinspoon.
Since 1995, astronomers have been discovering these extrasolar planets and now know of more than three hundred. As observational techniques have been refined and the data continuously taken, so smaller and smaller planets have been discovered.
Artist’s view of Venus Express at Venus.
Now, with CNES?ESA’s COROT and NASA’s Kepler missions, the prospect of discovering Earth-sized worlds in Earth-like orbits around other stars is better than ever. "We are now on the verge of finding Earth-like planets," says Grinspoon.
As has been proved with the discovery of gas giant planets, as soon as astronomers know that they are there, they invent all sorts of innovative methods to separate the planet’s feeble light from the overwhelming glare of the star.
One thing has become obvious from the study of Earth using Venus Express: determining whether a planet is habitable is not going to be easy. "We see water and molecular oxygen in Earth’s atmosphere, but Venus also shows these signatures. So looking at these molecules is not enough," says Piccioni.
Instead, astronomers are going to have to search for more subtle signals, perhaps the so-called red edge caused by photosynthetic life. "Green plants are bright in the near infrared," says Grinspoon. The analysis to see whether this red edge is visible is just beginning.
The team will also compare spectra of the Earth’s oceans with those taken when the continents are facing Venus Express. "We have initiated the first sustained programme of Earth observation from a distant platform," says Grinspoon. Although the observations may not tell us anything new about the Earth, they will allow us to unveil far-off worlds, making them seem more real than simply dots of light.
Related Web Sites | 0.878467 | 3.793324 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.