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Titan, Triton, Pluto, and Kuiper belt objects: A study of past and present atmospheres with grey and nongrey models
AuthorRao, Anupama M. N.
AdvisorLunine, Jonathan I.
Pinto, Philip A.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThis work is divided into two parts: a grey model for past Triton, Pluto, and Kuiper belt objects, and a nongrey model for current Titan's troposphere. Steady-state, planar models of early atmospheres for Triton, Pluto, and Kuiper belt objects are computed using a grey approach that tracks the transfer/distribution of heat via radiative transport. These objects are treated here together because they resemble one another in size, surface chemical composition, and exist in the same cold portion of the outer solar system. Beginning with present-day volatiles observed on the surfaces of Triton and Pluto (methane and molecular nitrogen), a trace of molecular hydrogen (present in most primordial atmospheres) is added. It is assumed that as the object is heated by solar, tidal, accretional, or radiogenic methods (this varies between the objects treated here) these chemical species then evaporate from the surface to create an atmosphere. Binary collisions among the molecules account for the sources of opacity, and absorption coefficients are provided by . The grey atmosphere calculations require a mean opacity, and its results are sensitive to the type of mean opacity used. Thus a variety of methods (Planck, Rosseland, and Chandrasekhar mean opacities) are used to accommodate this dependence and the variations in optical depth. Surface temperatures are then calculated as a function of the heating rate, molecular hydrogen abundance, and mean opacity type. As a result of these modelling experiments, tidal heating is found to be crucial to the formation of a thick atmosphere on Triton, and albedo and gravitational acceleration strongly affect the formation of atmospheres on less massive objects such as Pluto and Kuiper belt objects. A nongrey, steady-state, planar model of Titan's current troposphere is developed to study the effect of varying methane mass fraction. Methods from stellar atmosphere modelling are used to solve the equation of transfer as a two-point boundary problem. To additionally satisfy radiative, hydrostatic, and local thermodynamic equilibrium, an iterative correction procedure is utilized since the correct temperature and density profiles as a function of altitude are not known a priori. The volatile composition is taken from observation: molecular nitrogen, methane, and molecular hydrogen. Again, binary collisions among the molecules account for the sources of opacity, and absorption coefficients are provided by . The heating source for Titan is solar radiation absorbed and reradiated by the planet's surface in the infrared region of the spectrum, with a small amount of heat emanating from the stratosphere. The chemical species evaporate from the surface to create an atmosphere. Models of Titan's troposphere are calculated using different amounts of methane (within observational constraints) since the presence of methane is evolving in Titan's atmosphere due to photolytic processes. From model results it is shown that by solving the radiative transfer equation, subject to radiative, hydrostatic, and local thermodynamic equilibrium constraints, a model of Titan's troposphere with a maximum deviation of 8% from data can be obtained. The preliminary model of past Titan's troposphere is consistent with other analytic results .
Degree ProgramGraduate College | 0.80195 | 3.730752 |
Officially known as Aeolis Mons, Mount Sharp is a mountain formation on the planet Mars at around 5.08° South and 137.85° East. After its discovery in the 1970s, the mountain remained unnamed for close to forty years when it was given several names such as Gale crater mound. In 2012, NASA informally re-named the mountain to Mount Sharp in recognition of Robert P. Sharp, an American geologist. The naming was informal because the naming rules dictate that features such as the mountain cannot be officially named after people. The official name, Aeolis Mons, is a name that originated from the Izmir region located in Turkey.
The photographs available of Mount Sharp show that it is a rise of sedimentary rocks perched on top of the Gale Crater. The mountain forms the central peak and rises up to a height of 18,000 feet higher than the floor on the northern side of the crater. Compared to the southern floor of the crater, the mountain rises to a height of around 15,000 feet. The formation of the mountain is believed to have occurred around 2 billion years ago. The exact process is still being debated by scientists with several theories already in place. However, NASA issued a statement stating that a lake was responsible for the deposition of the lower sediments.
Comparison With Mountains In The Solar System
As stated earlier, Aeolis Mons is roughly 18,000 ft in height. Mount Sharp is roughly the same height as the grandest lunar mountain which is known as Mons Huygens. The Mons Hadley that was visited by Apollo 15 is dwarfed in size by Mount Sharp. However, compared to the tallest mountain in the solar system that is known to man, Mount Sharp is barely more than a bump. The tallest mountain is in the asteroid Vesta and has heights of approximately 72,000 feet or 14 miles. The closest challenger to this mountain’s height is Olympus Mons which is located on Mars with heights of approximately 13.6 miles.
On earth, the tallest mountain, Mount Everest, has a height of 29,000 feet while Mount Kilimanjaro rises to altitudes of 19,000 feet above sea level. However, from base to peak, these two giants on earth both have heights of 15,000 feet. Both of these mountains are shorter than Mount Sharp. The only mountain on earth that comes close to Mount Sharps’ altitude is Mount McKinley, also called Mount Denali, with elevations of about 18,000 feet from the base to the peak. Others include Mount Fuji (12,000 feet), Mont Blanc/Monte Bianco (16,000 feet), and a few others.
The exploration into the Gale Crater was done by the Curiosity Rover. The explorations showed that there was a lake in the crater that deposited sediments. However, all of the water drained out long ago. Scientists believe that the lake used to be a habitat for several life forms including plenty of different microbes. Recent photographs by the Curiosity rover, on January 2018, on the Vera Rubin Ridge, show the mountain in the background. Currently, the rover is attempting to provide data on the base sedimentary layers of Mount Sharp.
About the Author
Ferdinand graduated in 2016 with a Bsc. Project Planning and Management. He enjoys writing about pretty much anything and has a soft spot for technology and advocating for world peace.
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Your Harvard CitationRemember to italicize the title of this article in your Harvard citation. | 0.830504 | 3.59763 |
Prior to July, 1995 ZetaTalk stated that Life on Mars had existed prior to the giant hominoids from the 12th Planet pouring the Mars oceans into subterranean cavities while washing ore during their mining operations. On Dec 10, 1999, Science Magazine and the Brown University News Service reported definitive evidence of ancient oceans on Mars, and on June 12, 2000 NASA confirmed this. On Jan 25, 2007 scientists admitted that the water must be underground, as it could not have evaporated.
Science Magazine, Dec 12, 1999
Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data
High-resolution altimetric data define the detailed topography of the northern lowlands of Mars, and a range of data is consistent with the hypothesis that a lowland-encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle Mars history. The contact altitude is close to an equipotential line, the topography is smoother at all scales below the contact than above it, the volume enclosed by this contact is within the range of estimates of available water on Mars, and a series of extensive terraces parallel the contact in many places.
Brown geologist finds evidence supporting ancient ocean on Mars
News Service, Brown University
For Immediate Release: December 9, 1999
In an article to be published in Science magazine Dec. 10, 1999, Brown University planetary geologist James Head and five colleagues present topographical measurements which they say are consistent with an ocean that dried up hundreds of millions of years ago. The measurements were taken by the Mars Orbiter Laser Altimeter, an instrument aboard the unmanned spacecraft Mars Global Surveyor which is circling the planet.
Head's team set out to test the hypotheses of scientists who suggested the possibility of oceans on Mars in 1989 and 1991. The team used data from the Mars Orbiter Laser Altimeter, which beamed a pulsing laser to Mars' surface. Scientists measured the time it took for the laser to return to the satellite; the laser traveled a shorter length of time from mountain peaks and longer from craters. MOLA is the first instrument to provide scientists the information required to construct a topographic map of the entire surface of the planet. For years, scientists have known about channels in which water once flowed into the northern lowlands on the surface of Mars. "The question is whether it collected in large standing bodies," Head said. "This is the first time we could get instruments to comprehensively test these ideas."
According to Head, the team has found four types of quantitative evidence that points to the possible ancient ocean:
- The elevation of a particular contact (the border between two geological units, such as where one type of surface meets another) is nearly a level surface, which might indicate an ancient shoreline.
- The topography is smoother below this possible ancient shoreline than above it, consistent with smoothing by sedimentation.
- The volume of the area below this possible shoreline is within the range of previous estimates of water on Mars.
- A series of terraces exists parallel to the possible shoreline, consistent with the possibility of receding shorelines.
The results "should make all of us think more seriously about the possibility of the presence of large-scale standing bodies of water on Mars, big lakes and oceans," Head said. "We can't think of anything else to explain these things. They merit much closer scrutiny." Head's team concludes that further tests are necessary, including analysis of meteorites from Mars and of landing sites, checking for the presence of salts that may be related to former oceans. The importance of determining whether there were ancient oceans - and life - on Mars is that scientists may be able to learn more about long-term climate change and why climate changed on Mars, which has relevance to the future of the Earth, Head said.
Hints of huge water reservoirs on Mars
25 January 2007
Mars is losing little water to space, according to new research, so much of its ancient abundance may still be hidden beneath the surface. Dried up riverbeds and other evidence imply that Mars once had enough water to fill a global ocean more than 600 metres deep, together with a thick atmosphere of carbon dioxide that kept the planet warm enough for the water to be liquid. But the planet is now very dry and has a thin atmosphere. | 0.84606 | 3.026448 |
[Image: Betelgeuse, before dimming; photo by ESO, M. Montargès et al, via NASA.]
There are many interesting things about the dimming of Betelgeuse, a giant star in the constellation of Orion’s belt—perhaps a sign that the star is on the verge of exploding in a giant supernova—including the fact that I remember talking about this very scenario in a poetry workshop more than two decades ago. Here we are, still waiting for that light.
[Image: Betelgeuse, during dimming; photo by ESO, M. Montargès et al, via NASA.]
Betelgeuse, of course, is more than 700 lightyears from Earth, which means that it could very well have exploded centuries ago—it could, technically speaking, not even be there anymore, and wasn’t there for your parents or their parents—but the light from that catastrophe simply hasn’t reached Earth. We are always out of synch with the stars we think we’re seeing, unwitting recipients of dead news from above.
Delayed explosions, stars that are no longer there, constellations made of ghosts: the death–or not—of Betelgeuse is the metaphor that gives on giving, as evidenced by the fact that, even in my own lifetime, the topic has come up once again.
But what’s also so interesting about this sort of news is its juxtaposition between human timescales and astral ones, or human awareness colliding with cosmic time more generally: the implication that the universe is capable of extraordinary events that, in the long-term scheme of things, are actually extraordinarily common, but, from within the limits of a human lifetime, even the lifetime of an entire animal species, appear so rare as perhaps never to be encountered. To never be witnessed or even thought possible. There are things that happen only every 100 million years, every billion years, yet here we are right in the middle of it, unaware of strange gravitational inversions or churning, stroboscopic tides of light, of impossible stars and energy forms stranger than all mythology. Black chemistries in space, awaiting catalysis.
There could be physical processes as regular as clockwork pinging off like fireworks—constant, dead rhythms pulsing through the cosmos every two billion years—but our species will never see, hear, or know, because we simply never overlap.
We inhabit the same universe but not the same time. | 0.845802 | 3.713979 |
CO2 Filled Planetary Atmosphere Exposed to Plasma Discharge
In the process of searching for life in the approximate and remote solar systems, scientists often focused on the presence of oxygen in the atmosphere of the planet, considering it a sure sign of the presence of life. However, the findings of the new study recommend revising this statement.
Modeling in the laboratory the atmosphere of exoplanets, scientists have successfully created both organic compounds and oxygen, in the absence of life. This is an important conclusion, especially for those who, when looking for life, are guided exclusively by the oxygen marker.
New experiments allowed us to obtain oxygen and organic molecules that can serve as the building blocks of life in the laboratory. So, researchers will have to more carefully study how these molecules are produced in other worlds. Oxygen occupies 20% of the Earth’s atmosphere and is considered one of the most reliable signatures of life on our planet.
However, we do not have so much information about how different energy sources on exoplanets initiate chemical reactions that can create biogroups, like oxygen. Previously, scientists launched photochemical models on computers to predict which atmospheres oxygen can create, but only now was it possible to conduct an experiment. For the experiment, a PHAZER camera was used. The team checked 9 different gas mixtures in accordance with forecasts for exoplanet atmospheres such as super-Earth or mini-Neptune. These are the most common planets in the Milky Way galaxy. In each mixture there was a certain composition of gases, like carbon dioxide, ammonia and methane. Each was heated to 80-700 degrees Fahrenheit.
Each mixture was launched into the PHAZER facility, and then subjected to one of two types of energy that simulate energy that activates chemical reactions in the atmospheres of the planets: plasma from a glowing alternating current or light from an ultraviolet lamp. Plasma is a stronger source of energy than UV light, and is able to mimic electrical activity, like lightning. But UV light is the main engine of chemical reactions in the atmospheres of planets, such as Earth, Saturn and Pluto.
The experiments lasted continuously for 3 days. This time corresponds to the period during which the gas will be exposed to energy sources in space. Thus, it was possible to derive several scenarios that created both oxygen and organic molecules capable of forming sugars and amino acids (raw materials for life), as well as formaldehyde and hydrogen cyanide. | 0.892329 | 3.490151 |
The Pluto flyby was arguably one of 2015’s top scientific achievements, maybe even one of the most memorable moments in the last decade. We now know what our ex-ninth planet looks like, and it’s spectacular. Pluto turned out to have some surprising features like glaciers, nitrogen lakes, ice volcanoes, and the list is growing. The New Horizons mission to Pluto has surpassed everyone’s expectations, and the good news is, the team has no plans of stopping yet. This summer, they’re hoping to win an extended mission to explore another strange new world.
Onward And Outward
2014 MU69 is the official name of the icy rock that New Horizons hopes to explore next. Not much is known about MU69, but it orbits the sun a billion miles past Pluto, and NASA thinks it could be a time capsule from the earliest days of our solar system.
MU69 is one of several types of objects (or KBOs) in the Kuiper Belt–the ring of rock and ice debris that encircles our solar system. “Scattered KBOs,” like the dwarf planet Eris, were flung outward by the influence of Neptune, explaining their highly elliptical orbits. “Resonant objects” like Pluto are locked in a stable orbit with Neptune. MU69, on the other hand, is a “cold classical object,” meaning it has gone relatively undisturbed since the beginning of the solar system.
“The Kuiper Belt in general, and the cold classical objects especially, are the most primordial objects,” explains Simon Porter, post-doctoral researcher on the New Horizons mission. “They were never pushed around by the giant planets; they’re pretty much where they formed and haven’t been disturbed except for occasionally bumping into each other.”
The term “cold classical” doesn’t actually refer to the temperature of the objects, but rather that their orbits don’t bring them close to anything else.
Humankind has never visited a cold classical object before, so this flyby, if it gets funded, could be huge for filling in gaps about how our solar system formed some 4.6 billion years ago.
MU69 is a time capsule from the earliest days of our solar system
Because MU69 is so small and so far away, ground observations aren’t able to specify its exact brightness and size, but the educated guess is that MU69 is about 20-30 miles across. The team hopes to find a moon at MU69 as well.
“We can’t conclusively say if it has moons or not based on the Hubble images,” says Porter. “For the big cold classicals, something like 30 percent have known moons. There’s a pretty good chance that this thing’s got at least one satellite. It could be a small one. It could be a big one, could be several. We really don’t know.”
Porter and the team are also looking forward to counting the craters, if any, on MU69. “We are already using the craters on Pluto and its moons to constrain how many small Kuiper Belt objects there are. MU69 is an even better test, as it sees much fewer potential impactors than Pluto, we think.”
Prepping For Flyby
In November the New Horizons team executed a series of four fuel burns to send the spacecraft in the direction of MU69, even though the team is still awaiting an official mission extension approval from NASA. “The spacecraft is on its way to MU69, but in order to actually have the flyby, NASA has to approve keeping the spacecraft on for that long,” says Porter. “If they don’t then we would literally turn off the spacecraft this year. ”
New Horizons was one of the least expensive NASA missions to date, costing only $700 million, which works out to a mere $0.15 per person per year. Because of its small original budget and what the research has already yielded, the team is hopeful about getting permission to study MU69. If the mission extension does get approved, the science team will turn on the spacecraft’s instruments while it flies through the Kuiper Belt, studying other bodies along the way.
New Horizons will get turned off this year if NASA doesn’t approve the mission extension
Team members John Spencer and Marc Buie started searching for the second flyby target almost immediately after the mission was funded in 2003 to see whether or not it was a plausible option. Because Pluto is currently passing by our Milky Way’s galactic core, the brightness of the dense star field made it difficult to find anything, let alone an object convenient enough to visit. The search began on the ground and then moved to the Hubble Space Telescope, leading scientists to the path of MU69.
The flyby is due to take place on New Year’s Eve of 2018, but by the time the team receives the signal of confirmation it will be 2019. At the time of the flyby, MU69 will be 4.2 billion miles away from Earth. Because of this extreme distance it will take the signal from New Horizons 6.2 hours to reach Earth, and that’s just one way. New Horizons will sweep past MU69 at a blistering 45,931 feet per second. During the flyby it’ll turn on its imaging instruments, RALPH and LORRI, as well as its UV imaging spectrometer, Alice, to gather data about MU69’s surface composition, brightness and size. The details will help to complete the puzzle of the Kuiper Belt.
“It’s the last unknown type of object in the solar system that we’re going to visit.”
Right now there are more questions than answers when it comes to average cold classicals like MU69. There are no clues as to its surface composition, whether or not it has craters, or what types of surface geology it might have, if any.
“We’ve never been to one of these objects before, so we really have no idea what it’s like,” says Porter. “We’ve been to comets, but comets are degraded versions of these things. We’ve been to moons that are about that size, around Pluto, around Saturn, but they’re moons so they’re formed in a completely different way. They’re probably made of completely different stuff. It’s the last unknown type of object in the solar system that we’re going to visit.”
The team expects to hear back from NASA sometime this summer with a yea or nay on a mission extension. Since there’s already a perfectly good spacecraft en route, let’s hope that NASA chooses to get more science done while we’re in the neighborhood.
source: popsci.com By Shannon Stirone | 0.861745 | 3.816598 |
Researchers from the University of Bern in Switzerland have shed new light on the mysterious ninth planet in the outer solar system.
Earlier this year, scientists made the astounding announcement that there may be a massive mystery planet lurking in the outer reaches of the solar system. Researchers noticed a strong gravitational effect acting on some of Pluto’s moons, which led them to deduce that there must be an unseen massive body beyond the Kuiper belt.
According to a report from CS Monitor, a team of astrophysicists from the University of Bern in Switzerland recently unveiled a model chronicling the possible evolution of the mysterious Planet Nine. The study was published in the journal Astronomy and Astrophysics.
The team’s model shows the potential size, brightness, and even temperature of the planet. According to Professor Christoph Mordasini, the lead author of the recent research, “With our study, candidate Planet Nine is now more than a simple point mass, it takes shape having physical properties.”
Astrophysicists Michael Brown and Konstantin Batygin from the California Institute of Technology in Pasadena, CA initially announced their study making a case for Planet Nine’s existence in January. The planet would exist so far from the sun, however, that it’s likely shrouded in a cloud of darkness, only adding to the mystery.
While a visual confirmation of Planet Nine remains elusive, scientists are confident that a massive body that could only be a planet is acting on some of the smaller bodies near Pluto.
The recent study was funded by the Swiss National Science Foundation and the National Center for Competence in Research. Together with his PhD student Esther Linder, Professor Mordasini developed a model that allows them to see possible orbital paths for the strange planet.
The team asserted that if Planet Nine does indeed exist, it would likely have a mass nearly ten times that of Earth, and a frigid temperature of 47 degrees Kelvin, or nearly -375 degrees Fahrenheit. Linder says that the planet would likely emitting heat from its core – if it relied on the sun for warming, the planet would be much colder.
A press release from the University of Bern describing the details of the new model can be found here. | 0.843173 | 3.23262 |
At the beginning of this year, the scientists found themselves puzzled by a mysterious aurora dubbed as Steve (Strong Thermal Emission Velocity Enhancement), which presented some unique features in comparison to the common auroras. But a new study conducted by the researchers from the Universtiy of Calgary, also involved in the research carried out earlier this year, found that the mysterious Steve is not an aurora.
Commonly, auroras occur when particles hit the magnetic field of the Earth charging the atmospheric molecules and atoms which radiate light. At its turn, Steve phenomenon, although it’s similar in appearance to auroras, is not an aurora, the new study concludes.
“The aurora you see in the sky, at least from our data, is moving at a certain speed, and then you have [Steve] moving crazy fast at lower latitudes, passing from east to west, super narrow, almost like a comet,” explained Bea Gallardo-Lacourt from the University of Calgary and the study’s leading author.
According to Eric Donovan, a professor of physics and astronomy at the University of Calgary, he knew since the beginning that Steve is not an aurora. However, he said the scientists are still struggling to find out what Steve is.
Steve is not an aurora – Then what is it?
“With Steve what’s happening is we can’t find evidence of that particle precipitation, so it seems like the energy that’s causing the light is coming from somewhere else,” added Eric Donovan.
The mysterious phenomenon known as Steve is under scientists’ focus for a long time, but it became thoroughly researched only in 2016. Since then, many researchers came up with different theories, but none proved correct.
However, the new study carried out by the Universtiy of Calgary analyzed Steve using the All-Sky Imagers, the so-called Canadian sky cameras, and the National Oceanic and Atmospheric Administration’s Polar-orbiting Environmental Satellites’ particle detectors. They revealed that Steve is not forming in the same way as regular auroras do.
Thus, according to the scientists, the mysterious aurora known as Steve is not an aurora, but it might be a new and yet unknown phenomenon in the ionosphere, its glow being given by a different mechanism than auroras. | 0.83374 | 3.302886 |
ESA's XMM-Newton orbiting X-ray telescope has uncovered a celestial Rosetta stone: the first close-up of a white dwarf star, circling a companion star, that could explode into a particular kind of supernova in a few million years. These supernovae are used as beacons to measure cosmic distances and ultimately understand the expansion of our Universe.
Astronomers have been on the trail of this mysterious object since 1997 when they discovered that something was giving off X-rays near the bright star HD 49798. Now, thanks to XMM-Newton’s superior sensitivity, the mysterious object has been tracked along its orbit. The observation has shown it to be a white dwarf, the dead heart of a star, shining X-rays into space.
Sandro Mereghetti, INAF–IASF Milan, Italy, and collaborators also discovered that this is no ordinary white dwarf. They measured its mass and found it to be more than twice what they were expecting. Most white dwarfs pack 0.6 solar masses into an object the size of Earth. This particular white dwarf contains at least double that mass but has a diameter just half that of Earth. It also rotates once every 13 seconds, the fastest of any known white dwarf.
The mass determination is reliable because the XMM–Newton tracking data allowed the astronomers to use the most robust method for ‘weighing’ a star, one that uses the gravitational physics devised by Isaac Newton in the 17th century. Most likely, the white dwarf has grown to its unusual mass by stealing gas from its companion star, a process known as accretion. At 1.3 solar masses, the white dwarf is now close to a dangerous limit.
The star is likely to explode in a few million years’ time... Calculations suggest that it will blaze initially with the intensity of the full moon and be so bright that it will be seen in the daytime sky with the naked eye.
When it grows larger than 1.4 solar masses, a white dwarf is thought to either explode, or collapse to form an even more compact object called a neutron star. The explosion of a white dwarf is the leading explanation for type Ia supernovae, bright events that are used as standard beacons by astronomers to measure the expansion of the Universe. Until now, astronomers have not been able to find an accreting white dwarf in a binary system where the mass could be determined so accurately.
“This is the Rosetta stone of white dwarfs in binary systems. Our precise determination of the masses of the two stars is crucial. We can now study it further and try to reconstruct its past, so that we can calculate its future,” says Mereghetti.
That future is a spectacular one. The star is likely to explode in a few million years’ time. Although it is far enough to pose no danger to Earth, it is close enough to become an extraordinarily spectacular celestial sight. Calculations suggest that it will blaze initially with the intensity of the full moon and be so bright that it will be seen in the daytime sky with the naked eye.
Our descendants are in for quite a show. Thanks to XMM-Newton, we can already start looking forward to it.
Note for editors:
‘An ultra massive fast-spinning white dwarf in a peculiar binary system’ by S Mereghetti, A Tiengo, P Esposito, N La Palombara, GL Israel, L. Stella will be published in Science on 4 September 2009.
For more information:
Sandro Mereghetti, IASF-INAF, Milan, Italy
Email: Sandro @ iasf-milano.inaf.it
Norbert Schartel, ESA XMM-Newton Project Scientist
Email: Norbert.Schartel @ esa.int | 0.907928 | 4.047186 |
A suffix denoting spatial or temporal direction, as specified by the initial element. Also -wards (Dictionary.com).
-su, → direction.
Fr.: après, ensuite, plus tard
At a later or subsequent time; subsequently.
Fr.: naine d'Antlia
A → dwarf spheroidal galaxy located about 4.3 million → light-years from. Earth. It is a very faint object, with an apparent magnitude of 16.2. The galaxy was not discovered until 1997. (PGC 29194) The Antlia Dwarf lies on the outer rim of the Local Group of galaxies, possibly even beyond it, and there is evidence suggesting that it is tidally interacting with another small galaxy, NGC 3109, in the → Hydra constellation.
Fr.: logiciel d'application
A software with a specific function, such as a word processor or game. Contrast with operating system software.
Having knowledge; conscious; informed; alert. → awareness.
M.E., variant of iwar, O.E. gewær; cf. O.S. giwar, M.Du. gheware, O.H.G. giwar, Ger. gewahr.
Âgâh "aware, knowing," related to negâh "look, attention;" Mid.Pers. âkâh; Av. ākas- "to look;" Proto-Iranian *kas- "to look, appear;" cf. Skt. kāś- "to become visible, appear;" Gk. tekmar, tekmor "sign, mark;"
The state or condition of being aware; having knowledge; consciousness
Fr.: en arrière
1) Toward the back or rear.
Fr.: effet de rétro-réchauffement
A sort of → greenhouse effect in → stellar atmospheres where the deeper layers heat up due to overlying → opacity. The presence of numerous → bound-bound opacities of → metals amplifies the → scattering of → photons, in particular their → backscattering, forcing the → temperature to increase in order to conserve the radiation flux and the transport of energy from the interior to the outer parts of the atmosphere.
blue compact dwarf galaxy
kahkešân-e kutule-ye âbi-ye hampak
Fr.: galaxie naine bleue compacte
An small → irregular galaxy undergoing → violent star formation activity. These objects appear blue by reason of containing clusters of hot, → massive stars which ionize the surrounding interstellar gas. They are chemically unevolved since their → metallicity is only 1/3 to 1/30 of the solar value. Same as → H II galaxy.
Fr.: naine brune
A star-like object whose mass is too small to sustain → hydrogen fusion in its interior and become a star. Brown dwarfs are → substellar objects and occupy an intermediate regime between those of stars and giant planets. With a mass less than 0.08 times that of the Sun (about 80 → Jupiter masses), nuclear reactions in the core of brown dwarfs are limited to the transformation of → deuterium into 3He. The reason is that the cores of these objects are supported against → gravitational collapse by electron → degeneracy pressure (at early spectral types) and → Coulomb pressure (at later spectral types). Brown dwarfs, as ever cooling objects, will have late M dwarf spectral types within a few Myrs of their formation and gradually evolve as L, T and Y dwarfs → brown dwarf cooling. As late-M and early-L dwarfs, they overlap in temperature with the cool end of the stellar → main sequence (→ M dwarf, → L dwarf, → T dwarf, → Y dwarf). In contrast to the OBAFGKM sequence, the M-L-T-Y sequence is an evolutionary one. These objects were first postulated by Kumar (1963, ApJ 137, 1121 & 1126) and Hayashi & Nakano (1963, Prog. Theor.Phys. 30, 460).
brown dwarf cooling
sardeš-e kutule-ye qahve-yi
Fr.: refroidissement de naine brune
The process whereby a → brown dwarf cools over time after the → deuterium burning phase, which lasts a few 107 years. The → effective temperature and luminosity decrease depending on the mass, age, and → metallicity. Even though massive brown dwarfs may start out with star-like luminosity (≥ 10-3→ solar luminosities), they progressively fade with age to the point where, after 0.5 Gyr all → substellar objects are less luminous than the dimmest, lowest mass stars. More explicitly, brown dwarfs may start as star-like objects hotter than 2200 K, with → M dwarf spectral types, and, as they get older, pass through the later and cooler L, T, and Y spectral types (→ L dwarf, → T dwarf, → Y dwarf).
brown dwarf desert
kavir-e kutulehâ-ye qahvei
Fr.: désert des naines brunes
The observational result indicating a deficit in the frequency of → brown dwarf companions to Sun-like stars, either relative to the frequency of less massive planetary companions or relative to the frequency of more massive stellar companions. However, this desert exists mainly for low-separation brown dwarfs detected using orbital velocity surveys. No brown dwarf desert is noticed at wide separations (J. E. Gizis et al. 2001, ApJ 551, L163).
DA white dwarf
sefid kutule-ye DA
Fr.: naine blanche DA
DB white dwarf
sefid kutule-ye DB
Fr.: naine blanche DB
A → white dwarf whose spectrum shows strong He I in the absence of hydrogen or metal lines.
DC white dwarf
sefid kutule-ye DC
Fr.: naine blanche DC
A → white dwarf showing a continuous spectrum with no readily apparent lines.
Fr.: naine dégénérée
Same as → white dwarf.
Fr.: dewar, vase dewar
Insulated bottle containing a cryogenic fluid. The electronic detectors operated at very low temperature are mounted inside a dewar.
Named after its inventor Sir James Dewar (1842-1923), Scottish chemist and physicist.
DO white dwarf
sefid kutule-ye DO
Fr.: naine blanche DO
A → white dwarf whose spectrum shows strong lines of singly ionized helium He II; He I or H may be present. As a DO star cools, the He II will recombine with free electrons to form He I, eventually changing the DO type into a DB white dwarf.
double white dwarf
sefid kutule-ye dotâyi
Fr.: naine blanche double
A → double-lined binary with two → white dwarf components. Short-period double white dwarfs can lose → orbital angular momentum by emitting → gravitational radiation and if the total mass of the binary exceeds the → Chandrasekhar limit, their eventual → merger might produce a → Type Ia supernova.
DQ white dwarf
sefid kutule-ye DQ
Fr.: naine blanche DQ
A → white dwarf whose spectrum shows carbon features of any kind. | 0.8613 | 3.100377 |
The Hayabusa 2 spacecraft‘s latest photo of the Ryugu asteroid, taken from a distance of just 25 miles (40 km), shows for the first time surface features like boulders and craters, in addition to revealing the object’s unique dice-like appearance.
Remember the Rosetta spacecraft’s first photos of Comet 67P/Churyumov-Gerasimenko and how it looked like a rubber ducky? We’re now going through a similar phase with Japan’s Hayabusa 2 spacecraft as it gets progressively closer to the Ryugu asteroid, and we’re starting to get the first glimmerings of what this remote object, located 175 million miles (280 million km) from Earth, actually looks like.
This new photo of Ryugu, taken by the spacecraft’s ONC-W1 (Optical Navigation Camera - Wide angle) on June 24, reveals an object that appears to have roughly the shape of an eight-sided die—a game piece that players of “Dungeons and Dragons” are very familiar with. Hayabusa 2 project manager Yuichi Tsuda said it looks like a piece of fluorite, or even an abacus bead. The new photo also shows craters, rocks, and other geographical features, which means project planners can start to think about where the space probe will dispatch its four landers.
Launched on December 3, 2014, Hayabusa 2 is now tantalizing close to its target. The purpose of the mission is to collect samples of the Ryugu asteroid and then return them to Earth for analysis. Ryugu is a Type C asteroid, containing traces of water and organic material, and is 2,854 feet (870 meters) wide. By analyzing the material found on this distant rock, scientists will have a better idea of what the early conditions were like at the time the Solar System formed some 4.6 billion years ago. Hayabusa 2 is expected to return to Earth with its samples in late 2020.
As Tsuda pointed out in a press release, the surprising shape of Ryugu is both good and bad news for the mission.
“First of all, the rotation axis of the asteroid is perpendicular to the orbit,” he said. “This fact increases the degrees of freedom for landing and the rover decent operations. On the other hand, there is a peak in the vicinity of the equator and a number of large craters, which makes the selection of the landing points both interesting and difficult.”
Ryugu’s seemingly octahedron-like shape means the direction of gravitational force on the wide areas of the asteroid will not point directly down; it’s not a perfect sphere. “We therefore need a detailed investigation of these properties to formulate our future operation plans,” said Tsuda.
This latest pic is great, but it’s just the beginning. In addition to Hayabusa 2's ONC-W1 camera, the landers will also be able to snap pictures. We’re about to get up close and personal with this intriguing celestial object. | 0.864126 | 3.673141 |
|“||(a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.||”|
The definition was adopted on 24 August 2006, as part of a three-way classification of bodies orbiting the Sun. This classification defines planets as "a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and (c) has cleared the neighborhood around its orbit."
Next follows dwarf planets, followed by Small Solar System Bodies, which are defined as "celestial bodies that are not massive enough to be rounded by their own gravity."
As of March 19, 2013; scientists have identified 394 objects which could possibly be classified as dwarf planets by the IAU.
- Main Article: Eris
The concept of "dwarf planet" properly dates to the discovery of the scatter-disk object named Eris on January 5, 2005. With the confirmation of the identification of Eris, a formal debate began on the subject of what does, and what does not, constitute a planet. The community of astronomers decided that relying on history and tradition simply would not serve. The eight celestial bodies that now remain under the present definition of planet do not share their orbits with any other objects. The objects now called dwarf planets do not have this distinction. And yet these objects are significantly heavier than mere asteroids, in that they are so heavy that their own weight, and more particularly their own gravity, forces them to assume the round or nearly-round shape that all planets have.
Eris has another distinction that forced the debate: it is more massive even than Pluto (by twenty-seven percent) and is therefore the heaviest dwarf planet yet found. The mass of Eris is inferred from the orbital parameters, including the apsides and period, of the small body that orbits Eris. If Pluto could still be called a planet, then Eris deserved that distinction as well.
In 2006, the International Astronomical Union settled the issue. They determined that Eris was not a planet, and neither was Pluto. But the criteria they set also provoked yet another reassessment of the status of Ceres, the largest and first-discovered object in the asteroid belt. Upon consideration, the IAU declared that Ceres was a dwarf planet as well.
|Name||Perihelion||Aphelion||Eccentricity||Sidereal year||Inclination||Mass||Sidereal day|
|Ceres||2.545 AU||2.987 AU||0.0798||4.599 a||10.587 °||0.0158% earth||0.378 da|
|Pluto||29.658 AU||49.305 AU||0.249||248.09 a||17.142 °||0.218% earth||-6.387 da|
|Haumea||34.623 AU||51.538 AU||0.196||282.77 a||28.22 °||(4.2 ± 0.1)×1021 kg||Unknown|
|Makemake||38.509 AU||53.074 AU||0.159||309.88 a||28.96 °||~4 × 1021 kg||Unknown|
|Eris||37.77 AU||97.56 AU||0.442||577 a||44.187 °||0.278% earth||0.333 da|
The name plutoid was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), to describe celestial bodies "in orbit around the Sun at a semi-major axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit."
The four known and named plutoids are Pluto, Haumea, Makemake and Eris.
It is important to note that while all plutoids are dwarf planets, not all dwarf planets are plutiods. Ceres, for example, is a dwarf planet, but not a plutoid, as its orbit lies well within that of Neptune.
- "IAU0602: the Final IAU Resolution on the Definition of 'Planet' Ready for Voting," International Astronomical Union, 2005. Accessed January 14, 2008. | 0.841089 | 3.915514 |
A European probe roared into space Thursday (Dec. 19), kicking off an ambitious mission to map a billion Milky Way stars in high resolution.
The European Space Agency's Gaia spacecraft lifted off its pad at Europe's spaceport in Kourou, French Guiana at 4:12 a.m. EST (0912 GMT) Thursday, carried aloft by a Russian Soyuz-Fregat rocket. Gaia is on its way to a gravitationally stable point about 930,000 miles (1.5 million kilometers) from Earth, which it should reach in about three weeks.
Over the next five years, Gaia aims not only to pinpoint the locations of 1 billion stars in our Milky Way galaxy, but also to determine where these stars are moving, what they are made of and how luminous they are. These are all steps to help scientists better understand the history of the universe, ESA officials have said. [See photos of the Gaia spacecraft]
As a side benefit, Gaia's powerful twin telescopes will likely find thousands of new exoplanets, asteroids and other small, faint and hard-to-see objects.
"Gaia will conduct the biggest cosmic census yet, charting the positions, motions and characteristics of a billion stars to create the most precise 3D map of our Milky Way," ESA officials said in a statement.
A long journey
Thursday's launch ended a long wait for the Gaia team, who saw the $1 billion (740 million euros) mission delayed from an initial 2011 launch due to telescope mirror issues, among other things.
But there is more waiting yet to come, as Gaia still has a lot of ground to cover before reaching its ultimate destination, a spot called the sun-Earth Lagrange Point 2 (L2). Lagrange points are regions in space where gravitational and orbital interactions allow spacecraft to essentially park in one spot.
And once at L2, Gaia will undergo a four-month commissioning period to make sure the spacecraft, its telescopes and other gear are working properly.
Gaia also sports a sunshield, which has two purposes: To hold solar panels to generate electricity, and to be a barrier around Gaia's base against the heat of the sun. The spacecraft's instruments require a temperature of minus 166 degrees Fahrenheit (minus 110 degrees Celsius) to function. With the sunshield deployed, Gaia will stretch more than 33 feet (10 meters) across.
Mapping the sky
During science operations, Gaia will spin to get a view of the entire sky. Images will be stored using a single digital camera that has almost 1 billion pixels of resolution, making it the largest digital camera ever to fly in space.
Gaia is designed to be 100 times more accurate than Hipparcos, the last high-profile ESA star-mapping mission, which flew between 1989 and 1993. Hipparcos tracked down the locations of 100,000 stars precisely, and 1 million stars with less accuracy.
Gaia's name originally stood for Global Astrometric Interferometer for Astrophysics, but the interferometer was dropped early in the mission design because astronomers felt they could get a better view of fainter stars with an optical telescope. The name remained for project continuity. | 0.916782 | 3.258515 |
It has been said that the atmosphere on Titan is so dense that a person could strap a pair of wings on their back and soar through its skies.
It’s a pretty fascinating thought. And Titan – Saturn’s largest moon – is a pretty fascinating place. After all, it’s the only other body in our solar system (besides Earth, of course) that has that type of atmosphere and evidence of liquid on its surface.
“As far as its scientific interest, Titan is the most interesting target in the Solar System,” Dr. Jason W. Barnes of the University of Idaho told Universe Today.
That’s why Barnes and a team of 30 scientists and engineers created an unmanned mission concept to explore Titan called AVIATR (Aerial Vehicle for In-situ and Airborne Titan Reconnaissance). The plan, which primarily consists of a 120 kg plane soaring through the natural satellite’s atmosphere, was published online late last month.
The goal of the plane concept – which according to Barnes can serve as a standalone mission or as part of a larger Titan-focused exploration program – is to study the moon’s geography (its mountains, dunes, lakes and seas), as well as its atmosphere (the wind, haze, clouds and rain. Did you know that Titan is the only other place is our solar system where it rains?)
AVIATR is composed of three vehicles: one for space travel, one for entry and descent into Titan, and a plane to fly through the atmosphere. AVIATR, estimated to cost $715 million, would not prevent other missions from occurring on Titan, Barnes said. Instead, it would supplement the science being done by other projects.
“The science that AVIATR could do complements the science that can be accomplished from both orbiting and landed platforms,” the article stated.
Unfortunately, it seems like the plane concept won’t be happening anytime soon.
That’s because Titan didn’t make the National Research Council’s “Decadal Survey” – a prioritization of future planetary missions. (Read more about the survey in this Universe Today post.)
“Titan was deferred to another decade,” Barnes said.
But, he hopes to continue to build support for AVIATR so that it can get onto the next decadal survey in 2020. “We certainly had a lot of interest from people. We are breaking the paradigm that a balloon was the right way to go to Titan,” Barnes said.
So, why send an unmanned plane to study Titan’s atmosphere?
“Titan is the best place to fly an airplane in the whole solar system. We can go when and where we want,” Barnes said, adding that when compared to Earth, there’s four times more air and seven times less gravity on Titan. “A balloon is stuck in the wind.”
According to the article:
“A balloon entrained in primarily zonal winds near the equator would have no mechanism by which to travel to the polar regions to observe lakes and shoreline processes. Even if it were possible to get there, it is not clear that it would be desirable to send a balloon to the poles where Titan’s most violent meteorological activity takes place. AVIATR is both able to fly to the poles and is sufficiently robust to survive there.”
There’s also this issue: A shortage of plutonium-238.
“The radioactive decay of plutonium-238 provides the heat that powers RTGs, which can power spacecraft where there is insufficient sunlight for solar panels to operate. NASA is presently investing in a new type of RTG, called the ASRG,” the article stated. “A traditional hot-air balloon will not work on Titan with an ASRG owing to its lower heat production. In contrast, the AVIATR mission is specifically enabled by the use of ASRGs. The power density (in Watts per kilogram) and longevity of the ASRG allow an electrically-powered aircraft to fly on Titan.”
A plane could also find potential landing spots for future exploration. And, “since we are flying, we fly west the whole time so we can stay on the day side of Titan,” Barnes said.
That daylight would also help AVIATR collect photographic data during its travels and, according to Barnes, when it’s time to downlink that information, the plane would conserve energy by gliding through the air.
“And in doing so, we can also sample of bunch of altitude ranges,” Barnes said. “We are sampling the whole time.”
The plan seems interesting enough, but it’ll be quite a while before any data from the prospective mission would be coming back to Earth. If the plan is accepted (the earliest being 2020), the project would still have to be built, then once completed it would take 7 1/2 years to reach Titan. Once there, the mission would take about a nominal Earth year to study.
“I now realize that it’s a career-long project,” Barnes said to Universe Today. “The plan at this point is to keep this in the forefront of people’s minds and take whatever new ideas that people suggest and try to improve its prospect for selection.
To view the complete proposal, published in Experimental Astronomy, go here. | 0.845267 | 3.33308 |
The weather here on our little blue world has, of late, been somewhat turbulent. Storms lash my hometown on the UK’s Southern coast, Australia slowly bakes under oppressive heat, North America is deep frozen by the errant polar vortex, and here in Tokyo we’ve seen the heaviest snow in over a decade. At this point, I think it would require some degree of active ignorance to still be denying climate change on our world. Though while it may be little comfort to those of us plagued by violent weather, Earth isn’t the only place in the galaxy which has chaotic weather systems…
WISE J104915.57-531906.1B (mercifully nicknamed Luhman 16B) is a tiny brown dwarf star. A failed stellar ember which never caught aflame. At just 6 light years distance, this tiny gas-ball is right on our galactic doorstep, the closest brown dwarf to us. Close enough that astronomers using the VLT (Very Large Telescope) in Chile can actually see weather systems on its surface!
If you could sit and watch Luhman 16B through a telescope for a few hours, you’d see that its brightness varies a lot. It gets dimmer and brighter as the hours go by. Regular stars don’t work this way – stars which vary in brightness typically do so fairly predictably, and not nearly as quickly. The reason is that brown dwarfs have active weather systems, and the variations in brightness are because of clouds in the star’s atmosphere – not entirely unlike those here on Earth.
Well, I say not entirely unlike. They follow similar patterns, but the rains and snows on brown dwarfs are nothing like those on a planet like Earth. Instead of water, these clouds are made of hot silicates, salt, and molten iron. The snow on a brown dwarf is technically made of sand. And using infrared telescopes like the VLT, we can actually watch these curious clouds forming, growing, and dissipating. This was the principle used by a group of astronomers led by the Max Planck Institute’s Ian Crossfield to create a weather map for a brown dwarf star! Yes, you read that correctly!
And there it is! Ok, so it isn’t as detailed as the weather maps you might find on Weather Underground, but that’s still pretty amazing. Those three pictures you see there are maps showing the varying luminosity across the surface of Luhman 16B (there’s a video you can watch too). You’re looking at clouds in the skies of a star. Personally, I think that’s pretty amazing.
Apparently, using Crossfield’s techniques, you can even watch clouds and weather patterns move over the star’s surface. Astrometeorology could even become a new scientific field, as we learn how to predict weather patterns on these stars. This would tell us a huge amount about how things work on brown dwarfs, and younger gas giants (which appear to work in much the same way). After all, while we understand fairly well, the things which drive weather patterns here on Earth, weather patterns in a place so different as a brown dwarf must have entirely different mechanisms behind them.
It’s been known for quite a while now, that brown dwarfs have weather systems. Some are even expected to have one or more vast storms in their atmospheres, much like Jupiter’s great red spot. In fact, a study performed with the Spitzer space telescope, poetically entitled “Weather on Other Worlds” suggests that most, if not all, brown dwarfs are stormy little stars.
I’ve long been amazed by exactly how much detail modern technology can see at such huge distances. Amazed and excited. It looks like it won’t be too long before these mysterious objects elsewhere in the galaxy won’t be quite so mysterious anymore…
The Crossfield et al paper was published in Nature at the end of last month.
Top – Brown Dwarf artist’s impression. Created by yours truly.
Middle – Stellar weather maps, created by Crossfield et al.
Bottom – Artist’s impression of a stormy brown dwarf atmosphere, by NASA-JPL/Caltech. | 0.865793 | 3.648509 |
Many moons in our Solar System have very special characteristics.
One of them is Nereid, Neptune’s third largest moon located behind Triton and Proteus.
It has a diameter of approximately 340 kilometers (211 miles) and its most interesting characteristic is that it has the most fluctuating orbit of any moon in the Solar System!
Its orbital period is 360.16 Earth days and the age of this moon is estimated to be about 4.5 billion years.
Nereid is an irregular satellite orbiting Neptune in a very eccentric and inclined orbit, varying from 9.65 million kilometers (6 million miles) away from the planet to just 1.37 million kilometers (854,000 miles) at its closest position.
It was discovered by Dutch-American astronomer Gerard Kuiper, in 1949, while he was working at the McDonald Observatory in Texas.
Over the years, researchers have also reported Nereid’s unusual brightness according to observations conducted in different periods of time, also from night-to-night.
Nereid is the second of Neptune’s moons to be discovered (and last moon of Neptune to be discovered before the arrival of Voyager 2).
Astronomers have long tried to solve a mystery of Nereid’s eccentric trajectory.
According to one theory, the satellite might be an asteroid captured from the Kuiper asteroid belt in the outer Solar System, which could easier explain its unusual orbit.
It is also possible that Nereid was once an inner moon and was perturbed during the capture of Neptune’s largest moon Triton.
However, to learn much more about Nereid is not any easy task for astronomers.
It is difficult to make astronomical observations of a dark moon Nereid. This celestial body has a surface, composed mostly of ice and silicon, which means it reflects only 14 percent of sunlight it receives..
It is extremely faint and Voyager 2 was only able to take a low-resolution image of it when it passed in 1989. | 0.900721 | 3.479839 |
Kaus Borealis, Lambda Sagittarii (λ Sgr), is an orange giant or subgiant star located in the constellation Sagittarius. With an apparent magnitude of 2.82, it is the fifth brightest star in Sagittarius, after Kaus Australis, Nunki, Ascella, and Kaus Media. Kaus Borealis lies at a distance of 78.2 light years from Earth. It marks the northern tip of the celestial Archer’s bow and is one of the bright stars that form the Teapot, a conspicuous asterism that dominates the constellation.
Kaus Borealis has the stellar classification of K0 IV or K1IIIb, indicating a subgiant or giant star appearing orange in colour. It has a mass 2.6 times that of the Sun and is about 52 times more luminous. Its outer envelope has an effective temperature of 4,770 K.
Lambda Sagittarii has an angular diameter of 4.24 ± 0.05 milliarcseconds, which translates into a physical radius 11 times that of the Sun. The star is a relatively slow spinner, with a projected rotational velocity of 3.81 kilometres per second.
Kaus Borealis forms the Teapot in Sagittarius with the brighter Kaus Australis (Epsilon Sagittarii), Kaus Media (Delta Sagittarii), Nunki (Sigma Sagittarii) and Ascella (Zeta Sagittarii), and the fainter Alnasl (Gamma2 Sagittarii), Tau Sagittarii and Phi Sagittarii. Kaus Borealis marks the top of the lid of the celestial Teapot.
Like many other bright stars in zodiac constellations, Kaus Borealis lies close to the ecliptic (the Sun’s apparent path across the sky). It is located only 2.1 degrees south of the ecliptic and can sometimes be occulted by the Moon. Occultations by planets are also possible, but extremely rare. The last recorded occultation by a planet (Venus) occurred on November 19, 1984. Before that, the star was occulted by Mercury on December 5, 1865.
The 17th century Egyptian astronomer Al Achsasi al Mouakket called Lambda Sagittarii Rai al Naaim, meaning “the keeper of the ostriches,” in his Calendarium. The name was translated into Latin as Pastor Struthionum.
The 16th-century Arabian astronomer Al Tizini also called Kaus Borealis Rāʽi al Naʽāïm. In Arabic astronomy, Kaus Borealis and Polis (Mu Sagittarii) were seen as keepers of two groups of ostriches represented by two asterisms, Al Naʽām al Wārid (“the going ostriches”) and Al Naʽām al Ṣādirah (“the returning ostriches”). The asterisms were formed by the brightest stars in Sagittarius.
The name Kaus Borealis (pronunciation: /ˈkɔːs bɒriˈælɪs/) means “the northern bow.” It is derived from the Arabic qaws, meaning “bow,” and the Latin borealis, meaning “northern.” The name refers to the star’s position in Sagittarius, marking the northern tip of the Archer’s bow. Kaus Australis marks the southern tip and Kaus Media, the midpoint of the bow.
The name was officially approved by the International Astronomical Union’s (IAU) Working Group on Star Names (WGSN) on July 20, 2016.
The Chinese name for Lambda Sagittarii is 斗宿二 (Dǒu Sù èr), the Second Star of Dipper. The Chinese Dipper asterism also consists of the stars Nunki (Sigma Sgr), Ascella (Zeta Sgr), Polis (Mu Sgr), Phi Sagittarii, and Tau Sagittarii. It is one of the seven mansions of the Black Tortoise.
Kaus Borealis is very easy to find because it belongs to a prominent southern asterism. The Teapot is visible to northern observers in the summer months, when it appears above the southern horizon in the evening. Kaus Borealis is the top star of the asterism.
The star can be used to find several bright clusters that lie in the vicinity. The Sagittarius Cluster (Messier 22) is located only 2.5 degrees northeast of the star. M22 is a globular cluster with an apparent magnitude of 5.5. At a distance of 10,600 light years from Earth, it is one of the nearest globular clusters to the Sun, as well as the brightest cluster of its kind that can be seen from mid-northern latitudes.
Messier 28, another bright (mag. 7.66) globular cluster, is located less than a degree northwest of the star. It lies at a distance of 17,900 light years.
The globular cluster NGC 6638 is located only a half of a degree east of the star. At magnitude 9.5, it is considerably fainter than the other two clusters, as well as more distant. It lies about 30,600 light years from the Sun.
The magnitude 4.6 open cluster Messier 25 can be found 6.5 degrees north-northeast of the star, while the Sagittarius Star Cloud (Messier 24) lies about 7 degrees north-northwest. The open cluster Messier 18 can be found about 8.5 degrees in the same direction.
Kaus Borealis is located in the constellation Sagittarius. Sagittarius is one of the Greek constellations, first listed by the Greco-Roman astronomer Ptolemy in the 2nd century CE. It is the 15th largest constellation in the sky and, due to its proximity to a rich field of the Milky Way, it contains more Messier objects (bright deep sky objects catalogued by the French astronomer and comet hunter Charles Messier) than any other constellation.
In addition to those already mentioned, these include the Lagoon Nebula (Messier 8), the Omega Nebula (Messier 17), the Trifid Nebula (Messier 20), the globular clusters Messier 54, Messier 55, Messier 69, Messier 70 and Messier 75, and the open clusters Messier 21 and Messier 23.
Other notable deep sky objects in the constellation include the planetary nebulae NGC 6537, also known as the Red Spider Nebula, and NGC 6445 (the Little Gem Nebula or Box Nebula), the star-forming region NGC 6559, and the open clusters known as the Arches Cluster and the Quintuplet Cluster, both home to some of the most massive and most luminous stars discovered to date.
Sagittarius also contains the centre of the Milky Way, marked by the radio source designated as Sagittarius A.
The best time of year to observe the stars and deep sky objects in the constellation is during the month of August, when Sagittarius is prominent in the evening sky.
The 10 brightest stars in Sagittarius are Kaus Australis (Epsilon Sgr, mag. 1.85), Nunki (Sigma Sgr, mag. 2.05), Ascella (Zeta Sgr, mag. 2.59), Kaus Media (Delta Sgr, mag. 2.70), Kaus Borealis (Lambda Sgr, mag. 2.82), Albaldah (Pi Sgr, mag. 2.89), Alnasl (Gamma² Sgr, mag. 2.98), Eta Sagittarii (mag. 3.11), Phi Sagittarii (mag. 3.17), and Tau Sagittarii (mag. 3.326).
Kaus Borealis – Lambda Sagittarii
|Spectral class||K0 IV or K1IIIb|
|U-B colour index||+0.903|
|B-V colour index||+1.045|
|Absolute magnitude||1.07 ± 0.008|
|Distance||78.2 ± 0.3 light years (23.97 ± 0.09 parsecs)|
|Parallax||41.72 ± 0.16 mas|
|Radial velocity||–43.5 km/s|
|Proper motion||RA: −44.76 mas/yr|
|Dec.: −185.66 mas/yr|
|Rotational velocity||3.81 km/s|
|Surface gravity||2.90 cgs|
|Right ascension||18h 27m 58.24072s|
|Declination||−25° 25′ 18.1146″|
|Designations||Kaus Borealis, Lambda Sagittarii, λ Sgr, 22 Sagittarii, HD 169916, HR 6913, HIP 90496, GC 25180, GCRV 10927, SAO 186841, PPM 268438, FK5 692, CD-25 13149, CPD-25 6523, GJ 713.1, GJ 9627, IRAS 18248-2527, 2MASS J18275824-2525175, WDS J18280-2525A, TYC 6861-3180-1, Gaia DR2 4076915349748285952| | 0.822378 | 3.888256 |
These alien geysers spew lifeâs building blocks
Is the subsurface ocean on Saturn’s moon Enceladus habitable? Could it be home to existing life forms? While we still don’t know the answer to the second question, evidence continues to build that this small moon’s ocean is habitable by earthly standards. On October 2, 2019, scientists announced another piece of the puzzle: the discovery of additional kinds of organic compounds that originate from Enceladus’ ocean, and were found by the Cassini spacecraft to be gushing out through geysers at the moon’s south pole. These compounds are the ingredients for amino acids, the building blocks of life on Earth.
The findings come from continued analysis of data from the Cassini mission at Saturn, which ended in 2017. The spacecraft had sampled water vapor in the huge geyser-like plumes that erupt from fractures called Tiger Stripes at the south pole of the moon. The results showed water vapor, ice grains, salts, methane and organic molecules of various sizes existing in the plumes.
Cassini also found evidence for active hydrothermal vents on the ocean floor, similar to ones seen on the ocean bottoms of Earth. The new organic compounds were found to be nitrogen- and oxygen-bearing, condensed onto the ice grains. On Earth, those same compounds are produced by hydrothermal vents, and are part of the chemical reactions that produce amino acids. Is the same thing happening on Enceladus? As Nozair Khawaja, at the Free University of Berlin, explained:
If the conditions are right, these molecules coming from the deep ocean of Enceladus could be on the same reaction pathway as we see here on Earth. We don’t yet know if amino acids are needed for life beyond Earth, but finding the molecules that form amino acids is an important piece of the puzzle.
The ice grains from Enceladus’ plumes also get injected into Saturn’s E ring. The new compounds were found on these ice grains by Cassini’s Cosmic Dust Analyzer (CDA). The composition of the organic material was determined by the CDA’s mass spectrometer.
So how did these and other organics get into space? First, they were dissolved in the subsurface ocean itself. They were then evaporated out of the water, condensing and freezing onto ice grains inside the fractures in the moon’s crust. As the plumes of water vapor from the ocean move upward through the fractures to the surface, they transport the ice grains and organics with them. After being injected into space, these grains can then be sampled and analyzed by spacecraft such as Cassini.
Cassini had already found found larger organic molecules in the plumes. These new compounds, however, although smaller, are tied directly to the hydrothermal processes that would create amino acids. According to co-author Jon Hillier:
Here we are finding smaller and soluble organic building blocks – potential precursors for amino acids and other ingredients required for life on Earth.
Another co-author, Frank Postberg, added:
This work shows that Enceladus’ ocean has reactive building blocks in abundance, and it’s another green light in the investigation of the habitability of Enceladus.
Another recent study showed that Enceladus’ ocean is also apparently just the right age to support life.
The discovery of these smaller – but vital – organic compounds is another significant piece of the puzzle in understanding Enceladus’ possible habitability. Although completely frozen on the outside surface, on the inside, Enceladus is a most remarkable little world. Beneath the outer ice crust lies a global warm salty ocean, that, it appears, is not too different from oceans on Earth. The rocky bottom, including the hydrothermal vents, provides chemical nutrients just as it does on our planet. The environment is similar to that around hydrothermal vents – or “smokers” – on Earth’s ocean bottoms. The vents provide heat and nutrients, and at least on Earth, serve as an oasis for a multitude of life forms despite the surrounding colder waters and complete lack of sunlight.
These new findings make Enceladus and other ocean moons in the solar system, such as Europa and Titan, even more enticing targets in the search for life elsewhere in the solar system. Not that long ago, it was thought that Earth was the only world in our solar system with liquid water. Now we know of several moons in the outer solar system that do as well (and maybe even Pluto!), it’s just that the water is hidden below an outer layer of ice. We don’t know yet if any of those water worlds actually host any kind of life, but being able to study some of these alien oceans both now and with more advanced future missions is certainly one of the most exciting developments in planetary exploration.
Bottom line: Further analysis of material in Enceladus’ water vapor plumes has revealed the existence of additional organic compounds, the kind that are the ingredients of amino acids, the building blocks of life on Earth. | 0.852316 | 3.80235 |
Who invited you?
FOR five decades astronomers have searched the vast ocean of space in the hope of picking up some kind of radio message from the neighbours. That nothing has been found has not deterred the search for extraterrestrial intelligence, or SETI to the cognoscenti. Despite those years of effort, SETI has done little more than dip a glass into the cosmic ocean, having looked closely at only 750 of the Milky Way's billion or so star systems.
That will soon change. The Allen Telescope Array, a cluster of radio telescopes being built in California with SETI in mind, will dramatically speed up the rate at which such systems can be explored. On top of that, as astronomers get better at discovering planets, and find more habitable ones, the number of plausible targets for SETI will increase.
Until recently, SETI has been uncontroversial. What could be more wholesome than answering the question of whether humans are alone in the universe? A SETI subcommittee within the International Academy of Astronautics (IAA), a scientific lobby group, even fashioned a protocol on how to respond if a signal from aliens is received. This concludes by saying that no reply should be sent until appropriate international consultations have taken place. Mazlan Othman, the head of the UN's Office for Outer Space Affairs (yes, there really is one) has suggested that her agency is “ready-made” for such co-ordination—leading one newspaper to dub her the “alien ambassador”.
Where things have become difficult is over whether or not researchers should be allowed to send signals into space pre-emptively, in order to attract the attention of any alien listeners who might be out there. This is called active SETI, or METI, where the “M” stands for messaging. Attempts to draft a second SETI protocol to deal with this foundered several years ago, and the chairman and two members of the IAA's committee resigned.
The acrimony was aired on October 4th at a meeting organised by the Royal Society at Chicheley Hall, in Britain. Those opposed to METI argue that broadcasting signals into space announcing the location of Earth is tantamount to ringing a dinner gong for any carnivorous, colonising or anti-social aliens who might be listening. Although Earth would be a rather long way to go for lunch, the argument is that the decision to take such a risk is not one for a handful of scientists.
Alexander Zaitsev, chief scientist at the Kotelnikov Institute of Radio Engineering and Electronics, disagrees. Dr Zaitsev has access to one of the world's most powerful radio transmitters, the Evpatoria, and he has already sent a number of “hello” signals to nearby star systems. He argues that radar astronomy, which is used to probe things like asteroids and the surface of Venus, already gives off signals that could be picked up by aliens. He is also on record, though, as saying that humans have a moral obligation to announce their presence.
Even without the intervention of people like Dr Zaitsev, that may already have happened—if anyone is listening. Some people think signals emitted by television and radio stations would be detectable from nearby stars, thus rendering the debate irrelevant. Indeed, some at the meeting argued that if aliens were to use an astronomical phenomenon called gravitational lensing (in which the gravitational field of the sun bends and amplifies radio waves and light from Earth), human signals could be amplified to the point where even the light from cities would be visible.
Michael Michaud, who resigned as chairman of the IAA's SETI group in 2007, said that METI is not science but rather “an attempt to provoke a reaction”. He wants wider consultation. Seth Shostak, the group's current chairman, disagrees. He says consultation does not guarantee a “correct” answer; it seeks merely to “spread the blame if Earth gets wiped out”—though who would be left to point the finger is unclear. He also says that because there is a small but real risk to sending messages, any international consultation would be likely to conclude that the broadcasters should “shut up”.
David Brin, an author of science fiction who also resigned from the SETI group, accused it of attempting to stage-manage the discussion. He said that those proposing METI should involve more of humanity in the debate and must accept that a moratorium may be necessary. But he is also realistic. In the not too distant future, he thinks, so many people will have the power to send signals into space that it will not be possible to control intergalactic messaging. If that turns out to be true, then hope it is ET listening, not the Daleks.
This article appeared in the Science & technology section of the print edition under the headline "Phoning ET" | 0.86617 | 3.075113 |
Look up in nighttime sky anytime between now and July 16, and you just might spy our solar system's brightest asteroid.
Vesta, a 326-mile-wide object residing in the asteroid belt between Jupiter and Mars, is about to make its closest approach to Earth in nearly two decades. But don't worry, unlike other close calls with asteroids in recent history, Vesta is in a stable orbit around the sun that will only bring it within 106 million miles of Earth. Nonetheless, this convergence will make it visible to the naked eye, with a magnitude brightness approaching a maximum of 5.3 this week.
Unlike other asteroids, Vesta's internal geology mimics those of terrestrial planets, with a metallic iron-nickel core covered by a surface crust of basaltic rock. In fact, it's this "frozen lava" that gives Vesta its beautiful reflectivity, casting back 43 percent of all light that hits it. (For comparison, our moon only reflects about 12 percent of all light.)
A 2011 visit by the NASA space probe Dawn confirmed Vesta as our solar system's lone remaining protoplanet, an embryonic remnant of the material that created future worlds like Earth.
"We now know that Vesta is the only intact, layered planetary building block surviving from the very earliest days of the solar system," Carol Raymond, deputy principal investigator for the Dawn spacecraft, said during a 2012 press conference.
An imposing mountain borne from a violent past
Ancient pedigree isn't the only feature of Vesta that makes it a geologic celestial wonder. Its south pole is also home to one of the tallest known mountains in the solar system.
Whereas Olympus Mons on Mars rises nearly 13.3 miles (70,538 feet) above the surface of Mars, the unnamed peak on Vesta is just around 14 miles (72,178 feet) tall. It's located in a 314-mile-wide crater, also one of the largest in the solar system, named Rheasilvia, after the mythological vestal virgins of Rome. It's theorized that Rheasilvia and its central peak were formed roughly 1 billion years ago from a massive planetary scale impact that delivered a glancing blow at an estimated 11,000 miles per hour.
"Vesta was lucky," Peter Schultz, professor of earth, environmental, and planetary sciences at Brown University, said in a statement. "If this collision had been straight on, there would have been one less large asteroid and only a family of fragments left behind." Schultz published a study on the asteroid's violent past in 2014.
A eucrite meteorite, originating from Vesta, that fell during a meteor shower over Australia in 1960. (Photo: H. Raab/Wikimedia Commons)
Vesta's scrape with disaster would turn into a rare opportunity for scientists on Earth an eon later. The collision that rocked its south pole is estimated to have ejected at least 1 percent of the asteroid's mass into space, scattering a vast swath of debris throughout the solar system. Some of those rocks later made their way to Earth. In fact, it's estimated that some 5 percent of all space rocks found on Earth originated from Vesta, making it only a handful of solar system objects beyond Earth (including Mars and the moon) where scientists have a laboratory sample.
Look for Saturn to point the way
While Vesta is our brightest asteroid, its distance and small size still make it a sporting challenge to pick out with the naked eye. Your best bet is to use some high-powered binoculars or a telescope. Either way, follow these instructions from Bob King at Sky and Telescope to locate the correct patch of sky.
"To find it, begin at Saturn then star-hop with the naked eye or binoculars to 3.8-magnitude Mu (μ) Sagittarii. The asteroid is located 2.5°–4° northwest of that star through mid-June. Despite its location in star-rich Sagittarius, Vesta has little competition from similarly bright stars, making it easy to spot."
According to those who have previously spotted Vesta, the asteroid exhibits a yellowish hue and looks very much like a star. Grab a lawn chair, ditch the light pollution and look up! Vesta won't be this close to Earth again until 2040. | 0.904228 | 3.889065 |
There's a "hydrogen wall" at the edge of our solar system, and NASA scientists think their New Horizons spacecraft can see it.
That hydrogen wall is the outer boundary of our home system, the place where our sun's bubble of solar wind ends and where a mass of interstellar matter too small to bust through that wind builds up, pressing inward. Our host star's powerful jets of matter and energy flow outward for a long stretch after leaving the sun — far beyond the orbit of Pluto. But at a certain point, they peter out, and their ability to push back the bits of dust and other matter — the thin, mysterious stuff floating within our galaxy's walls — wanes. A visible boundary forms. On one side are the last vestiges of solar wind. And on the other side, in the direction of the Sun's movement through the galaxy, there's a buildup of interstellar matter, including hydrogen.
And now NASA researchers are pretty sure that New Horizons, the probe that famously skimmed past Pluto in 2015, can see that boundary.
What New Horizons definitely sees, the researchers reported in a paper published Aug. 7 in the journal Geophysical Research Letters, is some extra ultraviolet light — the kind the researchers would expect such a wall of galactic hydrogen to produce. That replicates an ultraviolet signal the two Voyager spacecraft — NASA's farthest-traveling probes, which launched in the late 1970s — spotted all the way back in 1992. [Images: Dust Grains from Interstellar Space]
However, the researchers cautioned, that signal isn't a sure sign that New Horizons has seen the hydrogen wall, or that Voyager did. All three probes could have actually detected the ultraviolet light from some other source, emanating from much deeper in the galaxy, the researchers wrote.
But Alice, the instrument on board New Horizons responsible for this finding, is much more sensitive than anything the Voyagers had on board before beginning their own journey out of the solar system, the researchers wrote. And they said they expect Alice to function 15 to 20 more years.
New Horizons will continue to scan the sky for ultraviolet light twice a year, the researchers wrote, and report what it sees back to Earth.
Editor's note: This story, written by a reporter for Space.com's sister site Live Science, included a quote mistakenly attributed to a press release by the researchers. The quoted phrase was in fact written by reporter Lisa Grossman of Science News in her coverage of this paper, and his been removed.
Originally published on Live Science. | 0.90097 | 3.643315 |
With the recent launch of the Transiting Exoplanet Survey Satellite (TESS) – which took place on Wednesday, April 18th, 2018 – a lot of attention has been focused on the next-generation space telescopes that will be taking to space in the coming years. These include not only the James Webb Space Telescope, which is currently scheduled for launch in 2020, but some other advanced spacecraft that will be deployed by the 2030s.
Such was the subject of the recent 2020 Decadal Survey for Astrophysics, which included four flagship mission concepts that are currently being studied. When these missions take to space, they will pick up where missions like Hubble, Kepler, Spitzer and Chandra left off, but will have greater sensitivity and capability. As such, they are expected to reveal a great deal more about our Universe and the secrets it holds.
As expected, the mission concepts submitted to the 2020 Decadal Survey cover a wide range of scientific goals – from observing distant black holes and the early Universe to investigating exoplanets around nearby stars and studying the bodies of the Solar System. These ideas were thoroughly vetted by the scientific community, and four have been selected as being worthy of pursuit.
“This is game time for astrophysics. We want to build all these concepts, but we don’t have the budget to do all four at the same time. The point of these decadal studies is to give members of the astrophysics community the best possible information as they decide which science to do first.”
The four selected concepts include the Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR), a giant space observatory developed in the tradition of the Hubble Space Telescope. As one of two concepts being investigated by NASA’s Goddard Space Flight Center, this mission concept calls for a space telescope with a massive segmented primary mirror that measures about 15 meters (49 feet) in diameter.
In comparison, the JWST‘s (currently the most advanced space telescope) primary mirror measures 6.5 m (21 ft 4 in) in diameter. Much like the JWST, LUVOIR’s mirror would be made up of adjustable segments that would unfold once it deployed to space. Actuators and motors would actively adjust and align these segments in order to achieve the perfect focus and capture light from faint and distant objects.
With these advanced tools, LUVOIR would be able to directly image Earth-sized planets and assess their atmospheres. As Study Scientist Aki Roberge explained:
“This mission is ambitious, but finding out if there is life outside the solar system is the prize. All the technology tall poles are driven by this goal… Physical stability, plus active control on the primary mirror and an internal coronagraph (a device for blocking starlight) will result in picometer accuracy. It’s all about control.”
There’ also the Origins Space Telescope (OST), another concept being pursued by the Goddard Space Flight Center. Much like the Spitzer Space Telescope and the Herschel Space Observatory, this far-infrared observatory would offer 10,000 times more sensitivity than any preceding far-infrared telescope. Its goals include observing the farthest reaches of the universe, tracing the path of water through star and planet formation, and searching for signs of life in the atmospheres of exoplanets.
Its primary mirror, which would measure about 9 m (30 ft) in diameter, would be the first actively cooled telescope, keeping its mirror at a temperature of about 4 K (-269 °C; -452 °F) and its detectors at a temperature of 0.05 K. To achieve this, the OST team will rely on flying layers of sunshields, four cryocoolers, and a multi-stage continuous adiabatic demagnetization refrigerator (CADR).
According to Dave Leisawitz, a Goddard scientist and OST study scientist, the OST is especially reliant on large arrays of superconducting detectors that measure in the millions of pixels. “When people ask about technology gaps in developing the Origins Space Telescope, I tell them the top three challenges are detectors, detectors, detectors,” he said. “It’s all about the detectors.”
Specifically, the OST would rely on two emerging types of detectors: Transition Edge Sensors (TESs) or Kinetic Inductance Detectors (KIDs). While still relatively new, TES detectors are quickly maturing and are currently being used in the HAWC+ instrument aboard NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA).
Then there’s the Habitable Exoplanet Imager (HabEx) which is being developed by NASA’s Jet Propulsion Laboratory. Like LUVOIR, this telescope would also directly image planetary systems to analyze the composition of planets’ atmospheres with a large segmented mirror. In addition, it would study the earliest epochs in the history of the Universe and the life cycle of the most massive stars, thus shedding light on how the elements that are necessary for life are formed.
Also like LUVOIR, HabEx would be able to conduct studies in the ultraviolet, optical and near-infrared wavelengths, and be able to block out a parent star’s brightness so that it could see light being reflected off of any planets orbiting it. As Neil Zimmerman, a NASA expert in the field of coronagraphy, explained:
“To directly image a planet orbiting a nearby star, we must overcome a tremendous barrier in dynamic range: the overwhelming brightness of the star against the dim reflection of starlight off the planet, with only a tiny angle separating the two. There is no off-the-shelf solution to this problem because it is so unlike any other challenge in observational astronomy.”
To address this challenge, the HabEx team is considering two approaches, which include external petal-shaped star shades that block light and internal coronagraphs that prevent starlight from reaching the detectors. Another possibility being investigated is to apply carbon nanotubes onto the coronagraphic masks to modify the patterns of any diffracted light that still gets through.
Last, but not least, is the X-ray Surveyor known as Lynx being developed by the Marshall Space Flight Center. Of the four space telescopes, Lynx is the only concept which will examine the Universe in X-rays. Using an X-ray microcalorimeter imaging spectrometer, this space telescope will detect X-rays coming from Supermassive Black Holes (SMBHs) at the center of the earliest galaxies in the Universe.
This technique consists of X-ray photos hitting a detector’s absorders and converting their energy to heat, which is measured by a thermometer. In this way, Lynx will help astronomers unlock how the earliest SMBHs formed. As Rob Petre, a Lynx study member at Goddard, described the mission:
“Supermassive black holes have been observed to exist much earlier in the universe than our current theories predict. We don’t understand how such massive objects formed so soon after the time when the first stars could have formed. We need an X-ray telescope to see the very first supermassive black holes, in order to provide the input for theories about how they might have formed.”
Regardless of which mission NASA ultimately selects, the agency and individual centers have begun investing in advanced tools to pursue such concepts in the future. The four teams submitted their interim reports back in March. By next year, they are expected to finish final reports for the National Research Council (NRC), which will be used to inform its recommendations to NASA in the coming years.
As Thai Pham, the technology development manager for NASA’s Astrophysics Program Office, indicated:
“I’m not saying it will be easy. It won’t be. These are ambitious missions, with significant technical challenges, many of which overlap and apply to all. The good news is that the groundwork is being laid now.”
With TESS now deployed and the JWST scheduled to launch by 2020, the lessons learned in the next few years will certainly be incorporated into these missions. At present, it is not clear which of the following concepts will be going to space by the 2030s. However, between their advanced instruments and the lessons learned from past missions, we can expect that they will make some profound discoveries about the Universe. | 0.865527 | 3.790195 |
With the GRAIL data, the astronomers were able to map the gravity field both in and around over 1,200 craters on the lunar far side. This region--the lunar highlands--is our Moon's most heavily cratered, and therefore oldest, terrain. Heavily cratered surfaces are older than smoother surfaces that are bereft of craters. This is because smooth surfaces indicate that more recent resurfacing has occurred, erasing the older scars of impact craters.
Ganymede: Ganymede is both the largest moon of Jupiter, our Solar System's planetary behemoth, as well as the largest moon in our entire Solar system. Observations of Ganymede by the HST in 2015 suggested the existence of a subsurface saline ocean. This is because patterns in auroral belts and rocking of the magnetic field hinted at the presence of an ocean. It is estimated to be approximately 100 kilometers deep with a surface situated below a crust of 150 kilometers.
The team's findings can also be applied to exoplanets, which are planets that circle stars beyond our own Sun. Some super-Earth exoplanets, which are rocky planets more massive than our own, have been proposed as "water worlds" covered with churning oceans. Could they have life? Perhaps. The potential would certainly be there. Dr. Vance and his team believe laboratory experiments and more sophisticated modeling of exotic oceans might help to find answers to these very profound questions. | 0.813454 | 3.299324 |
As you know now, in radio astronomy we study objects in the sky by catching radio waves. But what does that exactly mean? And what do radio astronomers see when they look at the sky? We will tell you all about that here.
You know now that there are different kinds of radiation which can be seen at different frequencies. Each radiation can be seen with different kind of telescopes. Radio astronomers can look at different elements depending on the wavelengths they attempt to receive. If they study the same objects using different wavelengths, they will obtain images very different one from an other, allowing different analyses.
In the picture below you see the Crab Nevel in different kinds of radiation. The Crab Nevel exploded 1000 years ago as a supernova. This was observed by the Chinese and was one of the first reports of a supernova. This nebula is about 6500 lightyears from Earth. As you can see the shape of the nebula is different in each radiation. You can also see different kind of structures in the nebula. This gives us a lot of information about what is in the nebula.
Below you see an image of the Andromeda Galaxy, also in different kinds of radiation. From the top left to the bottom right you see: Radio, far infrared, near infrared, visible, ultra-violet and X-ray light.
Some galaxies were discovered in radio light first, such as Cygnus A (in the constellation of Swan the strongest radio source, and one of the strongest sources in the sky). At high frequencies we see a small dot in the middle, with two huge rays that end in some kind of dumbbell. This is not light as it is made in the sun (nuclear fusion), but light that arises because matter moves enormously fast in a magnetic field. This intensity can only occur if there is a black hole at the base. | 0.834615 | 3.408479 |
While the handlers of NASA's venerable Voyager 1 spacecraft are still waiting for it to depart the solar system, a new study argues that the probe actually popped free into interstellar space last year.
Voyager 1 left the sun's sphere of influence on July 27, 2012, according to the study, which employs a new model to explain and interpret the probe's data. The new model is different from NASA's take, which suggests Voyager 1 remains within the solar system, though just barely.
"It's a somewhat controversial view, but we think Voyager has finally left the solar system, and is truly beginning its travels through the Milky Way," lead author Marc Swisdak of the University of Maryland said in a statement. [NASA's Voyager Probes: 5 Surprising Facts]
Swisdak and co-authors James Drake and Merav Opher — of the University of Maryland and Boston University, respectively — are not Voyager mission scientists. Their findings contrast with recent papers by the mission team and other researchers, which have concluded that the spacecraft is likely plying a strange transition zone at the edge of the solar system.
A long journey
Voyager 1 and its twin, Voyager 2, launched a few weeks apart in 1977 to study Saturn, Jupiter, Uranus and Neptune. The duo completed this "grand tour" and then kept right on flying toward interstellar space.
Voyager 1 will get there first. It's about 11.6 billion miles (18.7 billion kilometers) from Earth, making it the farthest-flung manmade object in the universe. Voyager 2, for its part, is now 9.4 billion miles (15.2 billion km) from home.
Both spacecraft are exploring the outer layers of the heliosphere, the huge bubble of charged particles and magnetic fields emanating from the sun. But things are really getting interesting for Voyager 1; it has detected a dramatic drop in solar particles and a simultaneous jump in high-energy galactic cosmic rays, which originate from outside the solar system.
NASA's Voyager mission scientists don't think the probe has left the heliosphere yet, however, because it hasn't measured a shift in the direction of the ambient magnetic field. (The team thinks the observed magnetic field will change orientation from roughly east-west within the solar system to north-south outside of it.)
A different interpretation
But Swisdak and his colleagues present a different view in a paper published online today (Aug. 15) in The Astrophysical Journal Letters. They devised a new model, which envisions the heliosphere boundary not as a relatively homogeneous surface but rather as a porous and multilayered structure.
Magnetic reconnection — the breaking and rejoining of field lines — creates a complex set of nested "magnetic islands" in the solar system's outer reaches, allowing the mixing of interstellar and solar material near the heliosphere's edge, the researchers say.
This model provides a better explanation of Voyager 1's data, Swisdak and his team say, and it suggests that the probe cruised into interstellar space on July 27, 2012.
Voyager mission chief scientist Ed Stone, a physicist at the California Institute of Technology in Pasadena, said he and his team will keep the new model in mind as they continue to study the data Voyager 1 beams home.
"Their model would mean that the interstellar magnetic field direction is the same as that which originates from our sun," Stone said in statement released by NASA today. "Other models envision the interstellar magnetic field draped around our solar bubble and predict that the direction of the interstellar magnetic field is different from the solar magnetic field inside. By that interpretation, Voyager 1 would still be inside our solar bubble."
"The fine-scale magnetic connection model will become part of the discussion among scientists as they try to reconcile what may be happening on a fine scale with what happens on a larger scale," Stone added. "The Voyager 1 spacecraft is exploring a region no spacecraft has ever been to before. We will continue to look for any further developments over the coming months and years as Voyager explores an uncharted frontier." | 0.856217 | 3.653163 |
AbstractThis research demonstrates the potential of novel technology for space-based remote sensing of the topside ionosphere-plasmasphere, supported by ionospheric imaging, which can augment and enhance our current understanding of the Earth’s plasmasphere.The research was conducted in two phases. The first was the development of a technology demonstrator ‘TOPCAT’ that installed a dual-frequency GPS receiver dedicated for topside ionosphere-plasmasphere imaging into a Low Earth Orbit (LEO). The novelties of TOPCAT were that it was designed from commercial-off-the-shelf (COTS) components and was installed on-board the CubeSat ‘UKube-1’, greatly reducing development and launch costs of the instrument. The successful launch of TOPCAT for space-borne remote sensing of the topside ionosphere and plasmasphere could provide the necessary proof of concept for the installation of a constellation of CubeSats – a possible next phase that may be implemented in the future. Thus, in its first stage, the thesis discusses the development of TOPCAT, together with design challenges encountered from constraints imposed by CubeSat technology. The discussion also includes the series of qualification tests performed to successfully qualify TOPCAT as a space-worthy payload design that can remotely image regions beyond the ionosphere.The second phase of research was the validation of the Multi-Instrument Data Analysis System (MIDAS) for the topside ionosphere and plasmasphere. A tomography algorithm originally developed for the ionosphere, MIDAS uses total electron content (TEC) measurements from differential phase of GPS signals, and inverts them to derive the electron density of the region. The thesis investigates the extension of MIDAS to image regions beyond the ionosphere by validating the algorithm for the topside ionosphere and plasmasphere. The process was carried out by first reconstructing a simulation by Gallagher et al. to verify the quality of the images. This was followed by the use of real GPS phase data from the COSMIC constellation to reconstruct the topside ionosphere-plasmasphere, and the qualitative comparison of the images with previous independent observations obtained through COSMIC and Jason-1 missions. Results showed that MIDAS can successfully reconstruct the undisturbed (quiet) topside ionosphere-plasmasphere using COSMIC data. However, imaging the storm-time topside ionosphere-plasmasphere requires better data coverage (i.e. more receivers) as the resolution offered by COSMIC was not sufficient to reconstruct fast-evolving structures – thereby emphasising the need for more data sources providing high resolution global coverage, such as a constellation of CubeSats with LEO-based GPS receivers.
|Date of Award||24 Jun 2015|
|Supervisor||Cathryn Mitchell (Supervisor) & Robert Watson (Supervisor)|
- Plasmapshere, CubeSat, GPS, Tomography
Topside Ionosphere/Plasmasphere Tomography Using Space-Borne Dual Frequency Gps Receivers
Pinto Jayawardena, T. (Author). 24 Jun 2015
Student thesis: Doctoral Thesis › PhD | 0.863578 | 3.466008 |
Astronomers this week at last captured an image of the unobservable: a black hole, a cosmic abyss so deep and dense that not even light can escape it.
For years, and for all the mounting scientific evidence, black holes have remained marooned in the imaginations of artists and the algorithms of splashy computer models of the kind used in Christopher Nolan's outer-space epic Interstellar. Now they are more real than ever.
"We have seen what we thought was unseeable," said Shep Doeleman, an astronomer at the Harvard-Smithsonian Centre for Astrophysics, and director of the effort to capture the image, during a Wednesday news conference in Washington.
The image, of a lopsided ring of light surrounding a dark circle deep in the heart of the galaxy known as Messier 87, some 55 million light years away from Earth, resembled the Eye of Sauron. It is a smoke ring framing a one-way portal to eternity.
To capture the image, astronomers reached across intergalactic space to Messier 87, a giant galaxy in the constellation Virgo. There, a black hole several billion times more massive than the sun is unleashing a violent jet of energy some 5000 light years into space.
The image offered a final, ringing affirmation of an idea so disturbing that even Einstein, from whose equations black holes emerged, was loath to accept it. If too much matter is crammed into one place, the cumulative force of gravity becomes overwhelming, and the place becomes an eternal trap. Here, according to Einstein's theory, matter, space and time come to an end and vanish like a dream.
On Wednesday morning that dark vision became a visceral reality. As far as the Event Horizon team could ascertain, the shape of the shadow is circular, as Einstein's theory predicts.
The results were announced simultaneously at news conferences in Washington and five other places around the world, befitting an international collaboration involving 200 members, nine telescopes and six papers for The Astrophysical Journal Letters. When the image was put up on the screen in Washington, cheers and gasps, followed by applause, broke out in the room and throughout a universe of astrofans following the live-streamed event.
"Einstein must be totally chuffed," said Priyamvada Natarajan, an astrophysicist at Yale. "His theory has just been stress-tested under conditions of extreme gravity, and looks to have held up."
Kip Thorne, an astrophysicist at the California Institute of Technology who shared a Nobel Prize in 2017 for the discovery of gravitational waves from colliding black holes, wrote in an email: "It is wonderful to see the nearly circular shadow of the black hole. There can be no doubt this really is a black hole at the centre of M87, with no signs of deviations from general relativity."
Janna Levin, a cosmologist and professor at Barnard College in New York, said: "What a time to be alive."
A telescope the size of Earth
The image emerged from two years of computer analysis of observations from a network of radio antennas called the Event Horizon Telescope. In all, eight radio observatories on six mountains and four continents observed the galaxy in Virgo on and off for 10 days in April 2017.
The network is named after the edge of a black hole, the point of no return; beyond the event horizon, not even light can escape the black hole's gravitational pull.
The mystery of black holes has tantalised astronomers for more than half a century. In the 1950s, astronomers with radio telescopes discovered that pearly, seemingly peaceful galaxies were spewing radio energy from their cores - far more energy than would be produced by the ordinary thermonuclear engines that make stars shine.
Perhaps, astrophysicists thought, the energy was being liberated by matter falling onto supermassive, dense objects - later called black holes.
Since then, scientists have devised detailed models of how this would work. As hot, dense gas swirls around the black hole, like water headed down a drain, the intense pressures and magnetic fields cause energy to squirt from either side. As a paradoxical result, supermassive black holes can be the most luminous objects in the universe.
Einstein's least favourite idea
The unveiling took place almost exactly a century after images of stars askew in the heavens made Einstein famous and confirmed his theory of general relativity as the law of the cosmos. That theory ascribes gravity to the warping of space and time by matter and energy, much as a mattress sags under a sleeper.
To Einstein's surprise, the equations indicated that when too much matter or energy was concentrated in one place, space-time could collapse, trapping matter and light in perpetuity. He disliked that idea, but the consensus today is that the universe is speckled with black holes furiously consuming everything around them.
Many are the gravitational tombstones of stars that burned up their fuel and collapsed. But others, hidden in the centres of nearly every galaxy, are millions or billions of times more massive than our sun.
Nobody knows how such behemoths of nothingness could have been assembled. Dense wrinkles in the primordial energies of the Big Bang? Monster runaway stars that collapsed and swallowed up their surroundings in the dawning years of the universe?
Nor do scientists know what ultimately happens to whatever falls into a black hole, nor what forces reign at the centre, where, theoretically, the density approaches infinity and smoke pours from nature's computer.
Zeroing in on cosmic monsters
Any lingering doubts about the reality of black holes dissolved three years ago when the Laser Interferometer Gravitational-Wave Observatory, or LIGO, detected the collision of a pair of distant black holes, which sent a shiver through the fabric of space-time.
Still, questions about gravity and the universe abound. "We know there must be something more," Avery Broderick, a member of the Event Horizon team, told the audience in Washington. "Black holes are one of the places to look for answers."
Proving that the monsters in Virgo and the centre of the Milky Way were really black holes required measuring the sizes of their shadows. That was no easy job. Both are exceedingly small, at this distance, and resolving their tiny details would be a challenge for even the biggest individual telescope.
Moreover, the view is blurred by the charged particles such as electrons and protons that fill interstellar space. "It's like looking through frosted glass," said Doeleman.
To see into the shadows, astronomers needed to be able to tune their radio telescope to shorter wavelengths. And they needed a bigger telescope.
Enter the Event Horizon Telescope, the dream-child of Doeleman. By combining data from radio telescopes as far apart as the South Pole, France, Chile and Hawaii, using a technique called Very Long Baseline Interferometry, Doeleman and his colleagues created a telescope as big as Earth itself, with the power to resolve details as small as an orange on the lunar surface.
In April 2017, the network of eight telescopes, including the South Pole Telescope, synchronised by atomic clocks, stared at the two targets off and on for 10 days.
For two years, the Event Horizon team reduced and collated the results. The data were too voluminous to transmit over the internet, so they were placed on hard disks and flown back to MIT's Haystack Observatory in Westford, Massachusetts, and the Max Planck Institute for Radio Astronomy in Bonn, Germany.
Last year the team divided into four groups to assemble images from the data dump. To stay objective and guard against bias, the teams had no contact with each other. They readied themselves for an inconclusive or ambiguous result - a blur, perhaps, that they couldn't quite read.
'It was a surprise how clear this image is'
Doeleman grew optimistic last year at a dinner attended by some of the younger members of the team, who showed him the first data for M87.
"There were clear signatures of a ringlike structure," he said. After dinner, he went to his office and made some crude calculations. "That was one of those great moments," he said. "It was a surprise how clear this image is."
The measurement also gave a firm estimate of the mass of the Virgo black hole: 6.5 billion solar masses. That is heavier than most previous determinations, and it suggests that the masses of other big black holes may need to be revised upward.
The telescope network continues to grow. In April 2018, a telescope in Greenland was added to the collaboration. Another observation run was made of the Milky Way and M87, and captured twice the amount of data gathered in 2017. That data was not part of the results released on Wednesday, but will be used to confirm them and monitor the behaviour of the black holes. Two more antennas are waiting to join the Event Horizon Telescope.
"The plan is to carry out these observations indefinitely and see how things change," said Doeleman, embarking on his new career as a tamer of extra-galactic beasts.
"It's astonishing to think humans can turn the Earth into a telescope and see a black hole," and still more amazing to do it with this team, he said. "That's the best."
The New York Times | 0.918618 | 3.650117 |
Feb 05, 2013
According to astronomers and their theories about the Solar System, the space beyond Neptune is getting stranger all the time.
Near the end of the eighteenth century the nebular hypothesis was born. It grew in popularity for more than 100 years and then appeared to die in the early twentieth. The cause of death was said to be contradictory evidence and careful analysis of the premises, leaving no foundation for its continued existence. However, after vigorously applying new modifications of the theory so that black hole physics could also remain alive, it experienced a resuscitation of sorts and continues with us to this day.
The hypothesis suggests that the Solar System condensed out of a cloud of molecular gases and dust in a period measuring billions of years. Eventually, the dust and gas shrank to the point where compression heating started a nuclear chain reaction in the dense ball of hydrogen and helium at the center of the cloud, giving birth to a new star. As the material continued to be gravitationally attracted toward the center of the ever-shrinking mass, it formed a structure called an accretion disc circling its equatorial plane.
Much like the rings of Saturn, only much more dense and far larger, the accretion disc extended out beyond the orbit of Neptune. During the collapse phase of the Solar System’s evolution, according to scientists, eddies and whirlpools of matter formed in the ring of dust and gas. Those eddies grew larger as they attracted more material into them, slowly sucking in larger and larger particles, then pebbles, then boulders, until hundreds of millions of impacts from nebular condensates gradually formed the planets.
The theory was later amended in order to explain the origin and “holding area” for the many comets that enter the Solar System every year. The Oort Cloud is supposed to be a giant nimbus of small fragments left over from those early days when the Sun was a newborn star. It is said to be a spherical region enclosing the Sun at a maximum radius of about 5 trillion kilometers and contains billions of objects, some as big as small planets, but most around the size of a medium asteroid. Closer in to the Sun is another region of primordial planetoids called the Kuiper Belt.
The Kuiper Belt theory is the creation of astronomer Kenneth Edgeworth from Ireland and also separately by American astronomer Gerard Kuiper in 1951. The first Kuiper Belt Object (KBO) was discovered in 1992. Sometimes known as “trans-Neptunian Objects” dozens of KBOs the size of small moon-sized planets have recently been added to the Solar System’s repertoire of family names.
Eris is the largest KBO, approximately 5% larger than Pluto and is located 1.4 trillion kilometers from the Sun. Eris has its own small moon called Dysnomia. Quaoar is about 6 billion kilometers from the Sun and revolves in the region of the Kuiper Belt beyond Pluto’s orbit. Quaoar is the third largest KBO, half the size of Pluto and about as large as Pluto’s moon Charon. The fourth largest KBO yet discovered is Varuna, which is about 40% as large as Pluto.
After the recent vote by the astronomical community, Pluto is no longer considered a planet and has been relegated to the status of KBO, making it the second largest such object in the Solar System. So, Eris, Pluto, Quaoar, Charon and Varuna are the five largest Kuiper Belt Objects.
There is a kink in the order and arrangement of the so-called KBOs, however. An object called Sedna has been discovered in an orbit that is much farther out than the grouping that includes Eris, Quaoar and Varuna. Sedna is large, about as big as Pluto, but it is nearly 10 trillion kilometers from the Sun, making it too far away to technically be considered a Kuiper Belt Object. The theory has yet to accommodate Sedna other than to say that it might be from the Oort Cloud and not the Kuiper Belt.
In passing, it must be noted that the Star Dust cometary mission demonstrated that the existence of comets in such a far away and frigid nursery as the Oort Cloud was impossible because of the minerals found in the coma of Comet Wild II. Their presence indicates that the comet formed in a much hotter environment than what the hypothetical Oort Cloud could provide.
On January 19, 2006, NASA launched the New Horizons spacecraft, a mission designed to explore the outer Solar System, including Pluto, Charon and recently discovered Kuiper Belt Objects. When New Horizons gains its mission objective sometime in 2015, Electric Universe theorists expect the researchers to be surprised. Because the nebular hypothesis reached preeminence before scientists realized that 99 percent of the Universe is plasma, the conclusions derived from the hypothesis are therefore not connected with real observations. | 0.878488 | 3.937346 |
Earth is a beautiful living planet of the Universe as the common habitat of more than 7.6 billion human population and millions of species of biodiversity. Our Earth provides us with food, shelter, medicine, water and what not. The story of the emergence of the earth is very old and strange and scholars of the world have presented the story of the birth of earth in different ways propounding their own theories. Before knowing about the earth we need to know about the universe, which is infinite and unlimited in time and space.
The most popular and accepted theory regarding the origin of the universe is the Big Bang Theory. This theory is also called expanding universe hypothesis.
Edwin Hubble (November 20, 1889-September 28, 1953), an American astronomer, in 1920, provided evidence that the universe is expanding. He was of the view that as time passes, galaxies move further and further apart. According to Edwin Hubble everything in the universe emerged from a point known as singularity, about 13.7 billion years ago.
In 2001, ekpyrotic universe theory was introduced by Burt Ovrut, Justin Khoury, Paul Steinhardt and Neil Turok. In this theory, these scholars propounded this cosmological model of the early universe explaining the origin of the structure of the cosmos. This theory also answers the questions arising in the scholars about what happened before the Bing Bang. According to this theory, Bing Bang was a big bounce, a transition from a previous epoch of contraction to the present epoch of expansion. These scholars are of the view that the major events that shaped our universe took place earlier than the bounce.
This theory received impressive success in accurately describing what we know so far about our universe. According to this theory universe is a uniform, flat universe having patterns of hot spots and cold spots visible in the cosmic microwave background. Discovery of the cosmic microwave background was considered a landmark test of the big bang, but according to proponents of the ekpyrotic and cyclic theories, the CMB is also consistent with a big bounce.
Scientists and geologists across the world have put forth their hypotheses regarding the origin of the earth. One of the earliest scientists Kant in his 1755 work, “The Universal Natural History and Theories of the Heavens,” gave two important theories about heavens; the first is Kant’s “Nebular Hypothesis” on star and planetary formations. In this, he presented theory that thin, dim clouds of dust and gas out in the cosmos would collapse on themselves due to force of gravity, causing them to spin to form a disk. In his view, from this spinning disk, stars and planets would form.
Laplace modified it in 1796 by presenting Nebular Hypothesis. He opined that planets were formed out of a cloud of material associated with a slowly rotating youthful sun. Laplace also proved that the birth of the Earth was due to the horrific explosions occurring in the sun.
In 1900, Chamberlain and Moulton said that a wandering star came near to the sun resulting in a cigar-shaped extension of material that separated from the solar surface. They propounded that when the transitory star moved away, the material alienated from the solar surface kept on revolving around the sun. This material gradually reduced into planets.
Sir James Jeans and later Sir Harold Jeffrey supported this view. In fact, the arguments considered of a companion to the Sun to have been co-existing.
In 1950, Otto Schmidt in Russia and Carl Weizsacker in Germany somewhat revised the ‘nebular hypothesis’, though differing in details. They are of views that sun was surrounded by solar nebula which contained mostly the hydrogen and helium.
In fact, the friction and collision of particles formed disk-shaped cloud and the planets were formed through the process of accumulation.
Interestingly, scientists in later period took up the problems of origin of universe rather than that of just the earth or the planets.
Enormous mass of stars, nebulae and stellar remnants and interstellar medium of gas dust and dark matter is called Galaxy. Universe consists of billions of galaxies. Our solar system is an integral part of Milky Way Galaxy. Our galaxy is called Milky Way. Galaxies are of three types – spiral galaxy, elliptical galaxy and irregular galaxy.
The earth belongs to the Milky Way, which is consists of the sun, the earth, planets, satellites and other stars. Milky Way contains millions of stars including our solar system. It is estimated that Milky Way has approximately 151,000 million stars. The disk of the Milky Way has a diameter of nearly 180, 00 light years and thickness of 15,000 light years.
THE SOLAR SYSTEM
Our solar system consists of the star Sun, eight planets and a large number of satellites. Often it is called a Solar Family with the sun as its head.
Earlier there were nine planets but due to planetary definition put forth by the International Astronomical Union on 24th August, 2006 at Prague, the Pluto lost its status as a planet and was reduced to the status of dwarf planet. The distance of these planets in increasing order from the Sun is – Mercury, Venus, Earth Mars, Jupiter, Saturn, Uranus and Neptune. These planets have not their own light, in fact; they receive light from the sun.
Discovery of the cosmic microwave background was considered a landmark test of the big bang, but according to proponents of the ekpyrotic and cyclic theories, the CMB is also consistent with a big bounce.
The Sun is the major source of light and energy on the earth. It is the center of solar system. It is huge and made of very hot gases. It is estimated that one million Earths could fit inside the Sun. It possesses the strong gravity binding the entire Solar System including planets, satellites, asteroids and meteors in its orbit. Sun has a radius of 700000 km making it the largest object in the Solar System. The Sun consists of 99.86% of the mass in the Solar System. The Sun is made of 70% hydrogen, 28% Helium & 2% other gases. The temperature is about 6000 °c and it is about 150 millions Kilometers away from the earth. The light takes 8 minutes to reach the earth. All the planets of the Solar System move around the Sun in a fixed path called that is called orbits.
The eight planets in the Solar System are Mercury, Venus, Earth, Mars Jupiter Saturn, and Uranus & Neptune. The planets can be divided into two groups – a) Terrestrial Planets – Mercury, Venus earth & Mars and, b) Jovian or Outer planets – Jupiter, Saturn Uranus, and Neptune.
Mercury is the closest planet to the Sun. It is a bit larger than Earth’s moon. Its temperature can reach 450 degree Celsius, but at the night it drops to hundreds of degrees below freezing. Mercury has not any atmosphere to absorb impacts of meteor over its four-year mission, (nearest to the sun). It is the smallest planet. It is visible to the naked eyes. Its diameter is about 4,878 km. Its rotation period is longer than its orbital (revolution) period. It has no natural satellites.
Venus is a rocky planet and it is also known as a terrestrial planet. Its solid surface is volcanic. Its atmosphere is made up mostly of carbon dioxide and nitrogen, with clouds of sulfuric acid droplets. Venus is the brightest planet. Venus is hotter than Mercury. Its size and structure are similar to earth. This spins slowly in the opposite direction of most of the other planets. It has diameter of 12,104 km.
- It is known as Earth’s twin. It has the longest rotation period. Rotational period of this hottest planet is longer than its orbital period.
- It revolves around the sun in clockwise manner while most others are revolving in anti-clockwise direction. It is the second brightest object in the night sky after the Moon. Venus may be seen from the earth only before sunrise and after sunset. For it, it is called Morning Star and Evening Star.
The Earth is third planet from the Sun. It ranks fifth in size in the solar system. The Earth is the only planet in the solar system to be known to support life.
It is slightly larger than Venus. Earth is the largest planet of the terrestrial planets. Nitrogen and Oxygen are in abundance in earth. Apart from it, there are gases like Carbon Dioxide, Hydrogen etc. Earth’s surface rotates about its axis at 467 meters per second. It has diameter of 12,760 km. There is water in all three states – liquid, solid and gas. The Earth takes 23 hour 56 minutes 46 seconds to rotate around its axis. It takes 365.26 days to revolve around the Sun. The Ozone layer present in the Earth’s atmosphere protects it from the ultra violet rays coming directly from the Sun. It has one natural satellite called Moon.
Mars is the fourth planet from the Sun. It is rocky, cold and dusty and has mountains and valleys. Scientists are of view that the conditions of this planet may be quite suitable for existence of life. Its diameter is 6,787 Kilometers and it is known as the ‘Red Planet’ due to presence of iron-rich red soil. Mars has two moons- Phobos and Deimos. It has polar ice caps and traces of sub-terrestrial liquid water have been found. It has the largest known volcano in the solar system – Mons Olympus.
Jupiter is the largest and the fifth planet from the sun. It is composed of gases, mostly hydrogen and helium. Its clouds are swirling and colorful. It is due to different types of trace gases. Great Red Spot is a main feature of this planet. It is a giant storm which has raged for hundreds of years. It has a strong magnetic field and 53 moons. It is the largest planet of the solar system and has 67 satellites. It has the shortest rotation period. It has diameter of 139,822 km.
Saturn is famous for its rings and is the sixth planet from the sun. This gaseous planet is mostly consists of hydrogen and helium. Its radius is about nine times than that of Earth. Its diameter is about 120,500 km.
It is the second largest planet. Its density is less than the water. It has a band of concentric rings that revolves around it. These rings are made up of tiny rocks and pieces of ice. It has 62 moons.
Uranus is the planet equator of which is nearly at right angles to its orbit. It basically orbits on its side. William Herschel discovered in 1781. Its diameter is about 51,120 km and is blue-green (cyan) in color. It is the third largest planet. It is composed of Hydrogen, Helium, Water, Ammonia, and Methane. It is tilted sideways. That is why its poles lie where most other planets have their equators. It has faints rings. It has 27 known moons. .
Strong winds are major features of the Neptune. These winds are sometimes faster than the speed of sound. It has a rocky core. Neptune is about 17 times massive than that the Earth. It was discovered by John Couch Adams in 1946. Its diameter is 49,530 km. it was discovered by mathematical predictions and disturbances in Uranus’ orbit. It is farthest planet from the Sun. it is primarily composed of hydrogen, helium, nitrogen, water, ammonia, methane. It is blue colored due to presence of methane. It has 14 known satellites.
Pluto (Dwarf Planet)
Once the ninth planet from the Sun, the Pluto was demoted to status of ‘Dwarf Planet’. It is icy and rocky. It has five satellites. It is smaller than Earth’s moon. From 1979 to 1999, Pluto had been the eighth planet from the sun. Then, on Feb. 11, 1999, until it was demoted to dwarf planet status. Its diameter is 1,430 2,301 km.
It is newly found hypothetical planet. According to NASA, it is hard to imagine our solar system without the unseen world. This hypothetical planet is believed to be about 10 times more massive than Earth and located in the dark, outer reaches of the solar system, approximately 20 times farther from the sun than Neptune is. The mystery has yet to be revealed. Astronomers have discovered several strange features of the solar system. The strange planet’s orbit is about 600 times farther from the sun than the Earth’s orbit is from the star. Scientists have not seen Planet Nine directly.
Asteroids are almost like planets but smaller in size. They have no spherical in appearance. They revolve around the Sun. Most of them are found in a belt between the planets Mars and Jupiter. Ceres is the largest asteroid.
When collisions occurred among asteroids meteoroids are formed. Meteorites are fragments of rocks floating in space. Sometimes they come across the earth and fall into the earth’s atmosphere. Most of these meteors are unable to reach earth’s surface and burn up in the atmosphere due to the friction. This friction takes place with air. The meteors that reach the earth’s surface are known as meteorites.
Comets are small icy bodies that travel in elliptical orbits around the sun. Comets are generally rocky. When they pass close to the sun, water and gases heat up. It leads to the formation of a tail behind the rocky core. This core is in the direction opposite to the Sun.
Constellations are various pattern formed by different group of stars. In a simple language they are group or clusters of stars.
Satellites move around the planets. Human has also made several artificial satellites. Satellite orbits a planet or star. Earth revolves around the sun and it makes it a satellite. Likewise, the moon is a satellite as it revolves around the earth.
Satellites may also be artificial and they are made by man. These are launched into space and moves around Earth or another body in space.
Thousands of man-made satellites orbit Earth. Some of these satellites take pictures of the planet to help meteorologists in predicting weather and track hurricanes. These pictures assist scientists better understand the solar system and universe. Apart from it, they are used for communications, such as beaming TV signals and phone calls around the world.
Moon is the only satellite of the Earth. In term of distance, it is 3,84,4000 km away from the earth. It takes about 27 days to orbit around the earth and about the same time to rotate at its own axis. This is the reason that we can see only one side of the moon at a given time. As the Moon revolves around the earth once in a month, thus the angle between the Earth, the Moon and Sun get changed. It is called the cycle of the Moon’s phases. Due to its size and composition, the Moon is sometimes referred as a terrestrial planet. | 0.879998 | 3.261811 |
Crescent ♒ Aquarius
Moon phase on 17 November 2099 Tuesday is Waxing Crescent, 5 days young Moon is in Aquarius.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 5 days on 12 November 2099 at 11:29.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing first ∠0° of ♒ Aquarius tropical zodiac sector.
Lunar disc appears visually 5.8% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1831" and ∠1941".
Next Full Moon is the Beaver Moon of November 2099 after 10 days on 27 November 2099 at 21:22.
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 1235 of Meeus index or 2188 from Brown series.
Length of current 1235 lunation is 29 days, 11 hours and 40 minutes. It is 2 hours and 7 minutes shorter than next lunation 1236 length.
Length of current synodic month is 1 hour and 4 minutes shorter than the mean length of synodic month, but it is still 5 hours and 5 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠27.7°. At beginning of next synodic month true anomaly will be ∠49.8°. 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°).
6 days after point of perigee on 10 November 2099 at 19:35 in ♎ Libra. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 5 days, until it get to the point of next apogee on 22 November 2099 at 17:25 in ♓ Pisces.
Moon is 391 477 km (243 253 mi) away from Earth on this date. Moon moves farther next 5 days until apogee, when Earth-Moon distance will reach 404 988 km (251 648 mi).
8 days after its descending node on 8 November 2099 at 18:31 in ♍ Virgo, the Moon is following the southern part of its orbit for the next 4 days, until it will cross the ecliptic from South to North in ascending node on 21 November 2099 at 23:18 in ♓ Pisces.
22 days after beginning of current draconic month in ♓ Pisces, the Moon is moving from the second to the final part of it.
2 days after previous South standstill on 15 November 2099 at 04:28 in ♐ Sagittarius, when Moon has reached southern declination of ∠-28.455°. Next 12 days the lunar orbit moves northward to face North declination of ∠28.380° in the next northern standstill on 29 November 2099 at 16:41 in ♊ Gemini.
After 10 days on 27 November 2099 at 21:22 in ♉ Taurus, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.119229 |
Black holes are big influencers for the early universe; these singularities that were close to ancient stars heated up gas and affected star formation across the cosmos. A new study, however, says that heating happened later than previously thought.
“It was previously believed that the heating occurred very early, but we discovered that this standard picture delicately depends on the precise energy with which the X-rays come out,” stated Rennan Barkana, a co-author of the paper who is an astronomer at Tel Aviv University.
“Taking into account up-to-date observations of nearby black-hole binaries changes the expectations for the history of cosmic heating. It results in a new prediction of an early time (when the universe was only 400 million years old) at which the sky was uniformly filled with radio waves emitted by the hydrogen gas.”
These so-called “black-hole binaries” are star pairs where the larger star exploded into a supernova and left behind a black hole. The strong gravity then yanked gas away from the stellar companion, emitting X-rays in the process. The radiation, as it flows across the universe, is cited as the factor behind gas heating in other parts of space.
You can read more details of the model in the journal Nature. The study was led by Anastasia Fialkov, a fellow TAU researcher. | 0.81455 | 3.769511 |
Yale’s EXPRES instrument ready to find the next Earth analog
A new, ground-based spectrometer designed and built at Yale represents the most powerful step yet in the effort to identify Earth-sized planets in neighboring solar systems.
The new instrument, the Extreme Precision Spectrometer (EXPRES), is now operational and collecting data at the Lowell Observatory Discovery Channel Telescope in Arizona. EXPRES will improve measurement precision by a factor of 10, enabling the detection of small, rocky planets around nearby stars.
“Up until now, the only planets we could detect with ground-based spectrographs were the bigger ones, the Saturns and Jupiters,” said Yale professor Debra Fischer, whose team designed EXPRES. “We know the smaller planets are out there, but they’ve slipped through our nets.”
Better data is particularly important, Fischer noted, because although astronomers have identified thousands of new planets in the past few years, none are analogs of Earth. Understanding which planets are similar in size to Earth and orbiting at distances from their host stars where water is likely to pool into lakes or oceans will be essential in the search for life elsewhere in the cosmos, she added.
Fischer announced initial details about the installation of EXPRES at the 2018 annual meeting of the American Association for the Advancement of Science in Austin, Texas.
“The future trajectory of exoplanet research depends critically on how well we improve radial velocity precision in spectrometers today,” Fischer said.
Spectrometers are instruments astronomers use to study light that is emitted by planets, stars, and galaxies. They are used in tandem with either a ground-based or orbital telescope. Spectrometers stretch out a beam of light into a spectrum of frequencies — which is then analyzed to determine an object’s speed, direction, chemical composition, or mass. The gravity of a star holds a planet in its orbit, but the planet also tugs on the star. Radial velocity refers to the motion of the star along our line of sight.
The challenge for astronomers has been designing spectrometers with enough stability and fidelity to measure tiny wobbles from Earth-like planets. For EXPRES, Fischer worked with Jessi Cisewski, an assistant professor of statistics and data science at Yale, to develop software that disentangles subtle noise sources in the stellar spectrum.
Fischer said the result should be quite telling. “It’s equivalent to the difference between early digital cameras from 10 years ago and the latest smartphone photography,” she said.
With EXPRES up and running in Arizona, and the similarly advanced ESPRESSO spectrometer built by Swiss astronomers in Chile, Fischer and other exoplanet researchers are preparing for a wealth of new data that might dramatically advance the search for extrasolar life.
“We’ve designed some very clever tests,” she explained. “It’s going to be amazing.”
EXPRES was funded by an instrumentation grant from the National Science Foundation. | 0.877747 | 3.73954 |
Planets with binary stars – such as Star Wars’ Tatooine – may be dangerous places to live, even risking the chance of being ejected into interstellar space.
The orbits of very distant binary stars often become very eccentric, passing very close to the planets. This can then wreak havoc on planetary systems, triggering planetary scatterings and even ejections.
“The stellar orbits of wide binaries are very sensitive to disturbances from other passing stars as well as the tidal field of the Milky Way,” says Nathan Kaib of Northwestern University.
“This causes their stellar orbits to constantly change their eccentricity – their degree of circularity. If a wide binary lasts long enough, it will eventually find itself with a very high orbital eccentricity at some point in its life.”
When a wide binary orbit becomes very eccentric, the two stars will pass very close together once per orbit on one side of the orbital ellipse, while being very far apart on the other.
Kaib’s team added a a hypothetical wide binary companion to Earth’s solar system which eventually triggered at least one of four giant planets (Jupiter, Saturn, Uranus and Neptune) to be ejected in almost half of the simulations.
“This process takes hundreds of millions of years if not billions of years to occur in these binaries. Consequently, planets in these systems initially form and evolve as if they orbited an isolated star,” he says.
“It is only much later that they begin to feel the effects of their companion star, which often times leads to disruption of the planetary system.”
And there’s plenty of evidence that this process occurs regularly in known extrasolar planetary systems. Planets that are known to reside in wide binaries are shown to be statistically more eccentric than planets around isolated stars like our sun.
“The eccentric planetary orbits seen in these systems are essentially scars from past disruptions caused by the companion star,” says Sean Raymond of the University of Bordeaux.
This only seems to happen whe the planetary system extends from its host star as much as 10 times the distance between Earth and the sun. Otherwise, the planetary system is too compact to be affected by even a stellar companion on a very eccentric orbit.
“Recently, planets orbiting at wide distances around their host stars have been directly imaged. Our work predicts that such planets are common but have so far gone largely undetected,” says Queen’s University physics professor Martin Duncan. | 0.88495 | 3.915699 |
“Black holes don’t exist!” It’s a popular comment made nearly every time I write about black holes. Often such claims come from folks who also don’t believe in things like relativity or the big bang, but another group has a more subtle argument: black holes haven’t yet been proven. In a way, they have a point.
There are basically two lines of evidence to support the existence of black holes. The first is observational. For small (stellar mass) black holes, the best evidence is through micro-quasars, also known as x-ray binaries. These objects emit strong x-rays from an Earth-sized region in space. Since these objects are part of a binary system with another star, we can determine their mass by the way the two stars orbit each other. What we find is these dense objects have masses that range from 1 – 10 times the mass of our Sun.
Stellar mass black holes are expected to emit strong x-rays when material near the black hole gets super heated due to all the gravitational compression. So this is exactly what we expect from a black hole. The problem is that neutron stars can also emit strong x-rays because they also have strong gravitational and magnetic fields. But it turns out that neutron stars, like our Sun undergo an effect known as differential rotation. Instead of rotating like a solid object, the equator region of a neutron star makes a complete rotation in less time than their polar regions. As a result their magnetic fields get twisted up until they snap back into alignment. For the Sun differential rotation leads to things like sunspots and solar flares. A similar effect occurs for neutron stars. As a result, some x-ray binaries are known to have differential rotation, and there therefore neutron stars. Other x-ray binaries don’t undergo differential rotation, so they are known as black hole candidates (BHCs).
We have similar observational evidence for supermassive black holes. For example, we know that quasars can emit more light than 250 billion stars from a region no larger than a light year across. When we observe the motions of stars near the centers of galaxies, they reveal the presence of a dense mass on the order of millions or billions of solar masses. In some cases we can even determine the mass of these central objects with great precision. But some of the strongest evidence comes from our own galaxy. With modern telescopes we’re able to image stars in the center of our galaxy. Over the years we’ve watched these stars as they clearly orbit a large dense mass. We know that this object has a mass of 4.1 million solar masses, and that all this mass can be no larger than our solar system (about 100 astronomical units across to be precise).
The other line of evidence is theoretical, specifically the theory of general relativity. Einstein’s theory of gravity makes very clear predictions about the motions of planets, how light is affected by gravity, gravitational redshift, the timing of GPS, and even the twisting of space and time. Every experimental test we’ve tried so far, general relativity has passed.
General relativity also makes several predictions about black holes. One is that given enough mass, an object will collapse into a black hole. This is true no matter what the mass is made of, since any energy or force trying to prevent the collapse actually starts helping gravity more than it opposes it. As we’ve seen in an earlier post, that upper limit is around 2.5 – 3 solar masses. Interestingly, of all the x-ray binaries we’ve observed, differential rotation has only been observed in ones less than 2 solar masses. The smallest black hole candidate (with so such differential rotation) has a mass of about 3 solar masses.
Another clear prediction is that black holes don’t have visible surfaces. Black holes are so dense that light can’t escape them. Surrounding a black hole is a “distance of no return” known as the event horizon. Anything that crosses that line is forever trapped. While we’ve not yet observed an event horizon, we do have indications that at least one supermassive dense object does not have a surface. A team looked at matter falling into the supermassive object at the center of the M87 galaxy. Unlike the small 4-million solar mass object in our galaxy, M87’s object has a mass of 6 billion suns. If this object had a surface, then matter falling into the object would strike the surface, and the energy released would cause a burst of light. If the object doesn’t have a surface, then there wouldn’t be a secondary brightening as the matter falls into it. The team found no indication of a secondary brightening.
So we know very clearly that neutron stars exist, and that somewhere between 2 – 3 solar masses they switch from being neutron stars to something that looks like a black hole. General relativity predicts that beyond 2.5 – 3 solar masses these objects must be black holes. We know that supermassive objects exist in most galaxies, and there is evidence that such objects do not have a visible surface. Again, according to general relativity, these objects should be black holes. In addition, there’s been a great deal of work modeling the dynamics of black holes within galaxies, and these models are in good agreement with the dynamics we observe. So there is a wealth of evidence to support the existence of black holes, and this is why most astronomers feel that black holes exist.
But there are some who would argue that all of this is still insufficient. All we’ve shown is that either black holes exist, or there are dense objects that closely approximate black holes. Perhaps these objects are all really dense, but don’t have an event horizon. For example the black hole in our galaxy would need to be the size of Earth’s orbit, which is a hundred times smaller than the observational limit thus far. All this evidence implies the existence of black holes, but it doesn’t prove black holes exist.
While technically that’s true, it doesn’t gain you much. Any such dense object would violate both the standard model of particle physics and general relativity, which are deeply robust theories. So technically the claim is either these things are black holes, or they are objects that mimic black holes by violating known physics. Of course that could be said about anything. Either electrons exist, or they are objects that mimic electrons through unknown physics. Either neutron stars exist, or they mimic neutron stars through unknown physics. It becomes a game of the “science of the gaps” where one can always demand just one more piece of evidence before they are truly convinced.
So the broad consensus is that black holes definitely exist. There are some astronomers who prefer to withhold judgment until we resolve the region around an event horizon. There are projects in development such as the Event Horizon Telescope which hope to achieve such observations. Even then, such observations will be compared to the predictions of general relativity. If the EHT makes observations in agreement with general relativity, then we can say either there’s an event horizon, or there’s something that mimics an event horizon in a way that defies known physics. Its always a question of how far down that rabbit hole you want to go.
So it’s absolutely clear to me that black holes exist. But as with anything, I could be wrong.
Paper: Avery E. Broderick et al. The Event Horizon of M87. ApJ 805 179 (2015) | 0.884508 | 4.013968 |
Arsia Mons is an extinct shield volcano in the Tharsis region near the equator. It is part of the Tharsis Montes group of volcanos. Its location is 8.35 S and 120.09 W (239.91 E) in the Phoenicis Lacus quadrangle. Its name is a classical feature name and comes from a corresponding albedo feature on a map by Giovanni Schiaparelli, which he named in turn after the legendary Roman forest of Arsia Silva. Researchers have found much evidence for glaciers on Arsia Mons.
Seven cave entrances have been discovered on the sides of Arsia Mons. These caves could contain reserves of water ice or even life. They are possible locations for a cave settlement. With the low gravity of Mars, lava tubes may be over 800 feet in width. A lava tube on Mars could protect colonists from meteorites and radiation. Because of the lack of a magnetic field at present, Mars has a fair amount of radiation, especially from cosmic ray sources. A mini-series produced by National Geographic in 2016 depicted how people could establish a base in a cave.
Repeated Clouds over Arsia Mons there is some debate about the nature of the clouds whether they are dust particles or water vapor If this is in fact Water Vapor, that indicates the presence of Water Ice around Arsia Mons.
- Scanlon, K., J. Head, D. Marchant. 2015. REMNANT BURIED ICE IN THE ARSIA MONS FAN-SHAPED DEPOSIT, MARS. 46th Lunar and Planetary Science Conference. 2266.pdf
- "Recent glaciation at high elevations on Arsia Mons, Mars: Implications for the formation and evolution of large tropical mountain glaciers" (PDF) (2007). Journal of Geophysical Research 112 (E3). doi:10.1029/2006JE002761.
- Jet Propulshion Lab, California Institute of Technology Repeated Clouds over Arsia Mons , https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA04294
- THEMIS: Ice-rich clouds over Arsia Mons’ caldera, ASU, R Burnham THEMIS: Ice-rich clouds over Arsia Mons’ caldera , http://redplanet.asu.edu/?p=30885, Sep 2018.
- 43rd Lunar and Planetary Science Conference, USRA - Universities Space Research Association VOLCANO-ICE INTERACTIONS RECORDED IN THE ARSIA MONS FAN-SHAPED GLACIAL DEPOSITS , https://www.lpi.usra.edu/meetings/lpsc2012/pdf/2183.pdf, 2012.
- LAPL HIRISE, Kelly Kolb, University of Arizona Glacier-Like Flow on Arsia Mons Flank , https://www.uahirise.org/PSP_002922_1725, 4 April 2007. | 0.859388 | 3.110203 |
Using data from NASA’s Great Observatories, astronomers have found the best evidence yet for cosmic seeds in the early universe that should grow into super massive black holes.
Researchers combined data from NASA’s Chandra X-ray Observatory, Hubble Space Telescope, and Spitzer Space Telescope to identify these possible black hole seeds. They discuss their findings in a paper that will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.
“Our discovery, if confirmed, explains how these monster black holes were born,” said Fabio Pacucci of Scuola Normale Superiore (SNS) in Pisa, Italy, who led the study. “We found evidence that supermassive black hole seeds can form directly from the collapse of a giant gas cloud, skipping any intermediate steps.”
Scientists believe a super massive black hole lies in the center of nearly all large galaxies, including our own Milky Way. They have found that some of these super massive black holes, which contain millions or even billions of times the mass of the sun, formed less than a billion years after the start of the universe in the Big Bang.
One theory suggests black hole seeds were built up by pulling in gas from their surroundings and by mergers of smaller black holes, a process that should take much longer than found for these quickly forming black holes.
These new findings suggest instead that some of the first black holes formed directly when a cloud of gas collapsed, bypassing any other intermediate phases, such as the formation and subsequent destruction of a massive star.
“There is a lot of controversy over which path these black holes take,” said co-author Andrea Ferrara, also of SNS. “Our work suggests we are narrowing in on an answer, where the black holes start big and grow at the normal rate, rather than starting small and growing at a very fast rate.”
The researchers used computer models of black hole seeds combined with a new method to select candidates for these objects from long-exposure images from Chandra, Hubble, and Spitzer.
The team found two strong candidates for black hole seeds. Both of these matched the theoretical profile in the infrared data, including being very red objects, and also emit X-rays detected with Chandra. Estimates of their distance suggest they may have been formed when the universe was less than a billion years old
“Black hole seeds are extremely hard to find and confirming their detection is very difficult,” said Andrea Grazian, a co-author from the National Institute for Astrophysics in Italy. “However, we think our research has uncovered the two best candidates to date.”
The team plans to obtain further observations in X-rays and the infrared to check whether these objects have more of the properties expected for black hole seeds. Upcoming observatories, such as NASA’s James Webb Space Telescope and the European Extremely Large Telescope will aid in future studies by detecting the light from more distant and smaller black holes. Scientists currently are building the theoretical framework needed to interpret the upcoming data, with the aim of finding the first black holes in the universe.
“As scientists, we cannot say at this point that our model is ‘the one’,” said Pacucci. “What we really believe is that our model is able to reproduce the observations without requiring unreasonable assumptions.”
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program while the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington.
NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission, whose science operations are conducted at the Spitzer Science Center. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. | 0.838239 | 4.061511 |
Crescent ♎ Libra
Moon phase on 31 August 2019 Saturday is Waxing Crescent, 1 day young Moon is in Virgo.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 1 day on 30 August 2019 at 10:37.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing about ∠23° of ♍ Virgo tropical zodiac sector.
Lunar disc appears visually 3.6% wider than solar disc. Moon and Sun apparent angular diameters are ∠1972" and ∠1901".
Next Full Moon is the Harvest Moon of September 2019 after 13 days on 14 September 2019 at 04:33.
There is medium ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at very acute angle, so their combined tidal force is moderate.
The Moon is 1 day young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 243 of Meeus index or 1196 from Brown series.
Length of current 243 lunation is 29 days, 7 hours and 49 minutes. It is 1 hour and 23 minutes shorter than next lunation 244 length.
Length of current synodic month is 4 hours and 55 minutes shorter than the mean length of synodic month, but it is still 1 hour and 14 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠356.3°. At beginning of next synodic month true anomaly will be ∠11.4°. 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°).
1 day after point of perigee on 30 August 2019 at 15:57 in ♍ Virgo. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 13 days, until it get to the point of next apogee on 13 September 2019 at 13:32 in ♓ Pisces.
Moon is 363 560 km (225 906 mi) away from Earth on this date. Moon moves farther next 13 days until apogee, when Earth-Moon distance will reach 406 378 km (252 512 mi).
4 days after its ascending node on 27 August 2019 at 01:50 in ♋ Cancer, 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 8 September 2019 at 17:35 in ♑ Capricorn.
4 days after beginning of current draconic month in ♋ Cancer, the Moon is moving from the beginning to the first part of it.
4 days after previous North standstill on 26 August 2019 at 17:53 in ♋ Cancer, when Moon has reached northern declination of ∠22.473°. Next 7 days the lunar orbit moves southward to face South declination of ∠-22.539° in the next southern standstill on 8 September 2019 at 09:39 in ♑ Capricorn.
After 13 days on 14 September 2019 at 04:33 in ♓ Pisces, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.155261 |
The peculiar duck shape of Comet 67P/Churyumov-Gerasimenko, revealed by ESA’s Rosetta space probe, was produced by the catastrophic collision of two icy bodies, according to new research.
Some previous comets that were closely observed by passing spacecraft have also displayed elongated or distorted shapes, as opposed to the “icy snowballs” that had once been expected by astronomers.
This suggests that collisions between frozen fragments in the Kuiper Belt beyond Neptune have been a common occurrence during the history of the Solar System.
The new research was made by an international team led by Patrick Michel of France’s National Center for Scientific Research (CNRS). It suggests that the cosmic collisions completely destroyed the original comets, but that their debris clumped together again.
This explanation apparently can explain some of the more enigmatic structures that were observed on Comet 67P by Rosetta during its long journey accompanying the celestial visitor through the Solar System.
It had been thought that such collisions between two icy bodies would have to have been at low speed since they were objects with very low density and moving slowly through space.
However the team’s simulations show that a more destructive impact could have produced Comet 67P. During a high-speed collision, only a small amount of material would be reduced to dust.
On the opposite sides of the impacting bodies, materials rich in volatile elements withstand the collision and are ejected at low enough speeds for them to be drawn back to each other and clump together again.
Surprisingly, the whole process takes only between hours and a few days, say the scientists, whose work is reported in the journal Nature Astronomy. But it explains how Comet 67P keeps its low density and abundance of volatile elements – chemical compounds such as water with low boiling points.
Team leader Michel is based at the laboratoire Lagrange (CNRS/Observatoire de la Côte d’Azur/Université de Nice-Sophia Antipolis).
Other comets imaged by spacecraft
Before the space age, our best views of comets were made with astronomical telescopes. They showed nothing more than a fuzzy blur with a star-like nucleus, plus tails of gas and dust for the brighter ones.
A number of comets have now been photographed close up by spacecraft. The first to be visited, by a flotilla of international probes, was the best known, Halley’s Comet, in March 1986.
The European Space Agency’s Giotto space probe flew by at a distance of around 2000 km (1200 miles). Its close-up images showed the heart of the comet – 15km (9miles) long and called the nucleus – was not round but shaped like a peanut.
In September 2001, a NASA technology demonstration spacecraft called Deep Space 1 flew by Comet Borrelly at a distance of 3417 km (more than 2000 miles). Its images showed the comet’s 8 km (5 mile) long nucleus was once again not round but more like a bowling pin.
The first comet found to have a vaguely round nucleus, about 5 km (3 miles) wide, was Comet Wild 2, otherwise known as 81P/Wild. It was visited by NASA’s Stardust mission in January 2004.
Probably the most dramatic encounter was made with Comet 9P/Tempel, otherwise known as Tempel 1, by NASA’s Deep Impact spacecraft. It fired an impactor directly into the comet’s 7.6 km (4.7 mile) long nucleus on July 4, 2005, to see what lay beneath the surface. The impact blast was so bright however that it blinded the camera. Another NASA spacecraft later returned to the comet.
This comet, also known as Comet Hartley 2, was also imaged by NASA’s Deep Impact probe, on its new EPOXI mission, in November, 2010. It showed that the comet was another elongated, twin-lobed nucleus, which is only about 2.4 km ( 1.5 miles) long. Skymania reported on the flyby.
★ Keep up with space news and observing tips. Click here to sign up for alerts to our latest reports. No spam ever - we promise! | 0.848202 | 4.063577 |
B.S., Geology, University of Massachusetts, Amherst, 1982
Ph.D., Geosciences, The Pennsylvania State University, 1992
What sets Cody apart from other geochemists is his pioneering use of sophisticated techniques such as enormous facilities for synchrotron radiation, and sample analysis with nuclear magnetic resonance (NMR) spectroscopy to characterize hydrocarbons. Today, Cody applies these techniques to analyzing the organic processes that alter sediments as they mature into rock inside the Earth and the molecular structure of extraterrestrial organics.
Wondering about where we came from has occupied the human imagination since the dawn of consciousness. Using samples from comets and meteorites, George Cody tracks the element carbon as it moves from the interstellar medium, through Solar System formation, ultimately to the origin of life.
Primitive meteorites, interplanetary dust particles, and comets are remnants of the early Solar System. The abundant organic matter contained in these primitive bodies records a long chemical history, beginning with reactions that occurred in the interstellar medium, and continuing with reactions that occurred during the formation and evolution of the early solar nebula, and in the formation and evolution of the parent bodies of meteorites. To untangling this record is a challenge: the vast majority of the organic carbon exists as an extremely complex polymer—large molecules with repeating units—that is insoluble by most means.
Cody and colleagues pioneered procedures applying solid-state nuclear magnetic resonance (NMR) spectroscopy to get around the insolubility problem. NMR spectroscopy reveals molecular information when nuclei of certain atoms are placed in an enormous magnetic field and then resonantly excited with radio-frequency pulses. The emission signal from the excited nuclei yield a spectral “fingerprint” characteristic of the electronic structure of the host molecule.
Cody also employs Carbon X-ray Absorption Edge Structure spectroscopy, which is essential to the analysis of comet particles. Results from both methods ultimately provide essential clues regarding the origin of extraterrestrial organic carbon and the history of chemical processing as the molecular cloud coalesced into the Solar System.
The retention of carbon in the inner Earth is a prerequisite to the origin of the global carbon cycle. Cody with colleagues have conducted NMR-based experiments that reveal how some carbon was retained even during the magma-ocean phase of Earth history. Such carbon may have been essential for the emergence of life.
The transition from a chemical world to a biological one remains a profound mystery. One promising area of this research is to investigate Earth’s natural catalysts and the environments in which they are found. Cody and colleagues study catalytic properties of so-called transition metal minerals that are abundant in deep-sea ore-bodies to help piece together the puzzle of life’s origins.
Cody received his B.S. from University of Massachusetts in geology in 1982. He then taught and conducted research there for two years. He then joined Exxon Research and Engineering and studied the chemical structure of coal, work that inspired his Ph.D. thesis at Pennsylvania State University. After receiving his Ph.D., Cody was an Enrico Fermi Scholar at the Argonne National Laboratory. He joined Carnegie in 1995 and was made acting director of the Geophysical Laboratory in 2013. He is principal investigator in charge of W. M. Keck Solid State NMR Laboratory and principal investigator of Carnegie's NASA Astrobiology Insititute. | 0.843911 | 3.844172 |
Impressive ongoing galactic fireworks, about 23 million light years away. Rather than paper, powder and fire, this galactic light show involves a giant black hole, shock waves and vast reservoirs of gas.
Image credit: NASA/CXC/Caltech/P.Ogle et al; Optical: NASA/STScI; IR: NASA/JPL-Caltech; Radio: NSF/NRAO/VLA
This galactic fireworks display is taking place in NGC 4258, also known as M106, a spiral galaxy like the Milky Way. This galaxy is famous, however, for something that our galaxy doesn’t have – two extra spiral arms that glow in X-ray, optical and radio light. These features, or anomalous arms, are not aligned with the plane of the galaxy, but instead intersect with it.
The anomalous arms are seen in this new composite image of NGC 4258, where X-rays from NASA’s Chandra X-ray Observatory are blue, radio data from the NSF’s Karl Jansky Very Large Array are purple, optical data from NASA’s Hubble Space Telescope are yellow and infrared data from NASA’s Spitzer Space Telescope are red.
A new study made with Spitzer shows that shock waves, similar to sonic booms from supersonic planes, are heating large amounts of gas – equivalent to about 10 million suns. What is generating these shock waves? Researchers think that the supermassive black hole at the center of NGC 4258 is producing powerful jets of high-energy particles. These jets strike the disk of the galaxy and generate shock waves. These shock waves, in turn, heat the gas – composed mainly of hydrogen molecules – to thousands of degrees.
The Chandra X-ray image reveals huge bubbles of hot gas above and below the plane of the galaxy. These bubbles indicate that much of the gas that was originally in the disk of the galaxy has been heated and ejected into the outer regions by the jets from the black hole.
The ejection of gas from the disk by the jets has important implications for the fate of this galaxy. Researchers estimate that all of the remaining gas will be ejected within the next 300 million years – very soon on cosmic time scales – unless it is somehow replenished. Because most of the gas in the disk has already been ejected, less gas is available for new stars to form. Indeed, the researchers used Spitzer data to estimate that stars are forming in the central regions of NGC 4258, at a rate which is about ten times less than in the Milky Way galaxy.
Read more NASA | 0.820413 | 4.016715 |
TheEuropean Space Agency's Herschel telescope is up and running, with its firstobservations revealing water and carbon as well as dozens of distant galaxies.
The newspace telescope, which launched on May 14 with its sibling Planck, has nowcarried out its first test observations with all of its instruments.
Herschel isthe largest, mostpowerful infrared telescope ever launched into space. Its observations inthe far-infrared to sub-millimeter wavelengths of light will allow astronomersto study some of the coldest objects in space, not visible in other wavelengths.
Herscheltook a "sneak preview" image of the distant galaxy M51 in June in anearly attempt to demonstrate that its camera eye works. ?In particular, scientistswanted to be sure the telescope is focused and correctly aligned with thescience instruments
WhileHerschel was making its test observations, Planck cooledits instruments down to their operational temperature of minus 459.49degrees Fahrenheit (minus 273.05 Celsius). This temperature is just 0.1 Celsiusabove absolute zero, the coldest temperature theoretically possible in ouruniverse.
On June 24,Herschel?s Spectral and Photometric Imaging Receiver (SPIRE) was trained on twogalaxies for its first look at the Universe. The galaxies showed upprominently, providing astronomers with their best images yet at thesewavelengths, and revealing other, more distant galaxies in the background ofthe images.
Thepictures show galaxies M66 and M74 at a wavelength of 250 microns, longer thanany previous infrared space observatory, but still the shortest SPIREwavelength.
SPIRE isdesigned to look at star formation in our own Milky Way galaxy and in nearbygalaxies, but it will also search for star-forming galaxies in the very distantuniverse.
"Thesequick first light observations have produced dramatic results when we considerthat they were made on day one," said SPIRE Principal Investigator MattGriffin of Cardiff University of Wales.
Scientistsused Herschel?s Heterodyne Instrument for the Far-Infrared (HIFI) on June 22 tolook for warm molecular gas heated by newborn massive stars in the DR21star-forming region in the constellation Cygnus, or the Swan.
It works byzooming in on specific wavelengths, revealing the spectral fingerprints ofatoms and molecules and even the physical conditions of the object observed.This makes it a powerful tool to study the role of gas and dust in theformation of stars and planets and the evolution of galaxies.
Herschelobserved ionized carbon, carbon monoxide, and water in DR21.
The firstobservation with Herschel?s Photodetector Array Camera and Spectrometer (PACS)instrument was carried out on June 23. It targeted a dying star known as theCat?s Eye Nebula. Discovered by William Herschel in 1786, this nebula consistsof a complex shell of gas thrown off by a dying star.
With thePACS spectrometer it is possible for the first time to take images in spectrallines and see how the wind from the star shapes the nebula in three dimensions.
Followingthese images, Herschel is now in the performance verification phase, where theinstruments will be further tested and calibrated. This phase will last untilthe end of November, after which the mission will begin its routine sciencephase.
- Video -The Herschel and Planck Missions
- Bounty of Space Telescopes Fuels Golden Age of Astronomy
- SPACE.com Video Show - Bad Astronomy with Phil Plait | 0.884064 | 3.894443 |
Editors note — Science journalist and author Bruce Dorminey spoke to two NASA scientists about the possibility of mounting a telescope on a spacecraft for an outer planets mission.
Light pollution in our inner solar system, from both the nearby glow of the Sun and the hazy zodiacal glow from dust ground up in the asteroid belt, has long stymied cosmologists looking for a clearer take on the early Universe.
But a team at NASA, JPL and Caltech has been looking into the possibility of hitching an optical telescope to a survey spacecraft on a mission to the outer solar system.
Escaping our Inner Solar System’s Polluted Purple Haze
The idea is to use the optical telescope in cruise phase to get a better handle on extragalactic background light; that is, the combined optical background light from all sources in the Universe. They envision the telescope’s usefulness to kick in around 5 Astronomical Units (AU), about the distance of Jupiter’s orbit. The team then wants to correlate their data with ground-based observations.
One goal is to shed light on the early universe’s epoch of reionization. Reionization refers to the time when ultraviolet (UV) radiation from the universe’s first stars ionized the intergalactic medium (IGM) by stripping electrons from the IGM’s gaseous atoms or molecules. This period of reionization is thought to have taken place no later than 450 million years after the Big Bang.
ZEBRA, the Zodiacal dust, Extragalactic Background and Reionization Apparatus, is a NASA JPL concept that calls for a $40 million dollar telescope comprised of three optical/near-infrared instruments; consisting of a 3 cm wide-field mapper and a 15 cm high-resolution imager. However, NASA has yet to select the ZEBRA proposal for one of its missions.
But to learn more, we spoke with the ZEBRA Concept lead and instrument cosmologist Jamie Bock and astronomer Charles Beichman, both of NASA JPL and Caltech.
Dorminey: What is zodiacal light?
Beichman: It’s a bright source of diffuse light in our own solar system from dust grains that emit because they have been heated by the sun and are radiating by themselves
or reflect sunlight. If you go out on a very clear dark moonless light, you can see the band of this light from this dust. It follows the plane of the ecliptic. That dust mostly originates from material in the asteroid belt that gets ground up into little particles after some big collision.
Dorminey: What would getting past this zodiacal dust mean for observations?
Beichman: Imagine sitting in the Los Angeles basin and you’ve got all this smog and haze and you want to measure how clear the air is out at Palm Springs. You have to be able to subtract off all the haze between here and there and there’s just no way to do it with any accuracy. You have to drive out of the basin to get out of the smog.
Dorminey: How would this help in studying this extragalactic background?
Bock: The Extragalactic Background Light (EBL) measures the total energy density of light coming from outside our galaxy. This light gives the sum of the energy produced by stars and galaxies, and any other sources, over the history of cosmic time. The total background can be used to check if we correctly understand the formation history of galaxies. We expect a component of the background light from the first stars to have a distinct spectrum that peaks in the near-infrared; this can tell us how bright and how long the epoch was when the first stars were forming. Unfortunately, zodiacal light is much brighter than this background. But by going to the orbit of Jupiter, the zodiacal light is 30 times fainter than at Earth, and at the orbit of Saturn it is 100 times fainter.
Dorminey: Would you have to hitchhike on a NASA mission or could it be a partnership with another space agency, like ESA for instance?
Bock: We have been exploring the cheapest incremental cost approach, partnering with a NASA planetary mission. But we could partner with another space agency. The European Jupiter Icy Moons Explorer (formerly JGO) is now competing for the next L-class mission launch in the early 2020’s and is an attractive possibility for a contributed cruise-phase science instrument. Each approach comes with a different cost and partnership environment.
Dorminey: Is the prime driver for the EBL telescope to get beyond the zodiacal dust or does 5 AU also offer an observational advantage in terms of achieving faintness of magnitude?
Bock: There is an observing advantage due to the [darker solar system] background. With such a small telescope, we are not trying to exploit this benefit but future observatories could. We will measure the zodiacal brightness to Jupiter and beyond, and this may motivate astronomical observations with telescopes in the outer solar system in the future.
Dorminey: What sort of data downlink challenges would you encounter?
Bock: The data requirements are perhaps smaller than one might first expect, because our images are obtained with long [observational] integrations at moderate spatial resolution. For the planetary proposal we studied in detail, the total data volume was 230 gigabytes, with about 65 percent of this data being returned from Jupiter and out to Saturn. The telescope pointings operate autonomously.
Dorminey: What about radiation from Jupiter interfering with the optics and CCD cameras on the telescope?
Beichman: What you’d do is stop making the EBL observations while close to Jupiter. The radiation problems are significant, so you would only do observations before and after passing Jupiter.
Dorminey: What would your instruments do that NASA’s planned James Webb Space Telescope (JWST) wouldn’t?
Bock: JWST will likely detect the brightest first galaxies, and depending exactly how galaxies formed, will miss most of the total radiation due to the contribution of many faint galaxies. Measuring the extragalactic background gives the total radiation from all the galaxies and provides the total energy. Furthermore, we don’t need a large telescope; 15 cm is sufficient.
Dorminey: What about planetary science with the telescope?
Bock: Our instrument specializes in making low surface-brightness measurements. We made specific design choices to map the zodiacal dust cloud from the inner to the outer solar system. A 3-Dimensional view will let us trace the origins of interstellar dust to comets and asteroid collisions. We know there are Kuiper-belt objects beyond the orbit of Neptune, and it is likely there is dust associated with them as well.
Dorminey: How long would this telescope function?
Bock: After the prime observations complete, it would certainly be possible that the original team or an outside party could propose to operate the telescope. One exciting science case is parallax micro-lensing observations; observations that use the parallax between Earth and Saturn to study the influence of exo-planets orbiting the stars producing a micro-lensing event. Other science opportunities include maps of the Kuiper Belt in the near-infrared; stellar occultations by Kuiper Belt Objects; and mapping more EBL fields for comparison with other surveys.
Dorminey: How would the telescope’s initial observations potentially shake up theoretical cosmology?
Beichman: Whenever you do a measurement that’s a factor of a hundred times better than before, you always get a surprise. | 0.924187 | 3.879133 |
The brittle, white material in chalk --a form of carbonate-- may seem rather ordinary, but finding carbonates on Mars would have some extraordinary implications. The discovery would provide strong evidence that liquid water once flowed on the Red Planet. Such carbonates might also harbor the fossils of ancient Martian bacteria.
"If you were lucky enough to find some carbonates in the layered terrains on Mars, scientists would get very excited about it," said Ken Nealson, director of the Center for Life Detection at NASA's Jet Propulsion Laboratory.
"It would be just a zinger of a finding."
Right: Nanxu arch in the Guilin karst region, China. Note the white color of the carbonate cliff face. Carbonate rock can also be pink or other colors, depending on the impurities present. Image courtesy of Peter L. Smart, University of Bristol.
Carbonate rocks on Earth are formed in two ways: through a purely chemical process or via the action of living things. Both means require liquid water.
Because Mars's atmosphere contains mostly carbon dioxide, scientists would expect liquid surface waters (if they ever existed on Mars) to produce carbonate deposits in a similar fashion.
Another way carbonates are formed on Earth is by marine organisms that produce carbonates for shells or other hard parts. When these organisms die, the shells sink to the bottom, where they accumulate and eventually form a carbonate deposit. Blackboard chalk is one example of this type of carbonate, which comprises the majority of carbonates in our planet's crust.
"Not only are carbonates often a product of life, they preserve the life that was in and around them very well," Nealson continued. "The whole notion of looking for certain mineral types that ... tend to harbor life here on Earth is an important part of the search strategy [for signs of life on Mars]."
Roaming the entire surface of Mars searching for carbonate rocks would take a very long time. Fortunately, carbonates can be detected from orbit by looking at radiated heat.
Like all substances, carbonates emit heat as infrared (IR) radiation. Carbonate compounds have a distinctive infrared signature when viewed through an IR spectrometer.
Above: The thermal infrared spectrum of a calcium carbonate sample. Courtesy of the Arizona State University Thermal Emission Spectral Library.
NASA's Mars Global Surveyor spacecraft, which is currently orbiting Mars, carries such an instrument --the "Thermal Emission Spectrometer" (TES)-- which is able to read the infrared "fingerprints" of rocks on the Martian surface below. Scientists had hoped this sensor would find regions of exposed carbonate among the Martian landscape.
So far, the TES has not discovered any carbonate deposits.
"If they're really not there, it's very discouraging," Nealson said. "But we may not have seen them just because we haven't had the right instrument yet."
An improved version of the TES will be on its way to Mars soon. Called the Thermal Emission Imaging System (THEMIS), this new instrument will take more detailed infrared images of the Martian surface than the TES, enabling THEMIS to detect smaller carbonate deposits than TES can.
THEMIS will fly on board NASA's 2001 Mars Odyssey spacecraft, which is scheduled to launch in April.
Above: The world through infrared eyes. The bottom image was taken with the THEMIS instrument, which "sees" the heat given off by objects by detecting infrared light. In the foreground is the image produced by the warm body of a person. In the distance, the warm transformer on the telephone pole can be seen as well as the hot roof of the house. In the far distance, rock outcroppings warmed by the sun can be seen along the mountain range.
While scientists wait for the results of THEMIS, it may be that evidence for carbonates on Mars has already been found here on Earth.
A rock from Mars, which was apparently ejected from the Red Planet by an asteroid impact millions of years ago, came to rest in Antarctica about 13,000 years ago, where it was found by scientists in 1984. The "Mars Rock," also known as the "Allen Hills meteorite," caused a stir in 1996 when scientists announced that the rock contained signs of ancient Martian microbial life.
That conclusion has since been criticized by other scientists, but one of the pieces of evidence cited were small patches of carbonate mineral inside the rock. The location of the carbonate patches along with other clues suggested that the carbonate was there millions of years ago when the rock was still on Mars.
Below: A close-up shot of carbonate pancakes in the meteorite.
"We know there are carbonates (on Mars), because we see them as weathering products in a variety of Martian meteorites," said Everett Gibson, an astrobiologist at NASA's Johnson Space Center in Houston, Texas.
"The big question is, Where are the carbonates on the surface of Mars? Shouldn't they be seen by some of the spectrometers that are looking at Mars now?"
Tiny patches of carbonate like those found in the "Mars rock" would not be detected by the thermal emission spectrometer currently in orbit around Mars, Gibson continued. Even THEMIS's 100-meter resolution isn't likely to reveal such diminutive deposits.
But if lakes or oceans once adorned the Martian landscape, scientists expect that sooner or later their instruments will reveal carbonate deposits. Such a discovery would prove, once and for all, that Mars was not always the barren desert it is today.
Multicellular organisms like clams make shells out of carbonates. Simple prokaryotic microbes in the ocean also collect carbonates on their bodies. This happens when they pull CO2 from the water for photosynthesis. Extracting CO2 causes the water to become more alkaline, which in turn causes carbonate to precipitate. This carbonate eventually weighs down the microbe and sinks it ... leading to the formation of carbonate deposits on the seafloor.
Mars Exploration Program -- home page of NASA's Mars Exploration Program
Thermal Emission Spectrometer -- more information on the instrument aboard Mars Global Surveyor
What is TES? -- a closer look at the Thermal Emission Spectrometer instrument
Spectroscopy of Rocks and Minerals -- U.S. Geological Survey document offering a detailed look at how scientists can identify minerals from a distance by looking at their thermal emission spectra.
Related Science@NASA articles:
Layers of Mars -- Last year Mars Global Surveyor spotted terrains on Mars that look like sedimentary rock deposits. If the mysterious layers formed underwater, as some scientists suspect, they may be a good place to hunt for Martian fossils.
Sedimentary Mars -- New Mars Global Surveyor images reveal sedimentary rock layers on the Red Planet that may have formed underwater in the distant martian past.
The Case of the Missing Mars Water -- Plenty of clues suggest that liquid water once flowed on Mars --raising hopes that life could have arisen there-- but the evidence remains inconclusive and sometimes contradictory.
Making a Splash on Mars -- On a planet that's colder than Antarctica and where water boils at ten degrees above freezing, how could liquid water ever exist? Scientists say a dash of salt might help.
Unearthing Clues to Martian Fossils -- The hunt for signs of ancient life on Mars leads scientists to Mono Lake, CA.
Martian Micro-Magnets -- The Allan Hills meteorite from Mars is peppered with tiny magnetic crystals that on our planet are made only by bacteria.
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|For lesson plans and educational activities related to breaking science news, please visit Thursday's Classroom||Author: Patrick L. Barry
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Responsible NASA official: Ron Koczor | 0.863365 | 4.015275 |
Meteorites are a bit like fruitcake – chunks of mineral held together by a stone matrix. Those mineral inclusions can contain some pretty fascinating glimpses into the stuff of the Solar System – but now scientists have found something they’ve never seen before.
In a meteorite recovered from Antarctica in 2002 is a tiny, ancient sliver of the building blocks of comets – encased, the researchers said, like an insect in amber.
The meteorite is called LaPaz Icefield 02342 (LAP 02342 for short), and it’s a type of meteorite known as a carbonaceous chondrite.
Meteorites come in a variety of types, broken off from larger pieces of space rock such as asteroids or even planets, and sent hurtling through space until they collide with Earth, after surviving the often explosive effects of atmospheric entry.
Their composition can vary, and that’s used for meteorite classification. Carbonaceous chondrites are among the most primitive, thought to originate from asteroids that formed around 4.5 billion years ago – when the Solar System was also forming – out past the orbital range of Jupiter.
Comets, too, formed from the same protoplanetary disc of dust and gas that circled the newborn Sun, but much farther away than asteroids, so their composition is different. They have a lot more water ice – that is what creates the famous tail when they get close to the Sun. And they have a lot more carbon.
The team wasn’t actually looking for comet giblets. Meteorites are a sort of time capsule to the early Solar System, rich with presolar grains, and information about the heating and chemical processes present during the system’s formation.
But comet giblets is what they got.
“When I saw the first electron images of the carbon-rich material,” said cosmochemist Jemma Davidson of Arizona State University, “I knew we were looking at something very rare. It was one of those exciting moments you live for as a scientist.”
That tiny carbon-rich sliver, measuring just a tenth of a millimetre, bore strong similarities to interplanetary dust particles and micrometeorites thought to originate in comets that formed in the Kuiper Belt at the icy outskirts of the Solar System.
The team conducted isotopic analysis of the sliver, and concluded that it likely formed in the same place and in the same way.
Its inclusion in a meteorite suggests that it must have migrated inward from this starting position, drawing slowly closer to the Sun until it reached the region where the carbonaceous chondrites formed.
Then, around 3 to 3.5 million years after the formation of the Solar System, this microscopic sliver somehow, perhaps via a collision, became incorporated into the asteroid that would fragment to produce LAP 02342.
The comet speck has opened up a window into the dynamics and chemistry of the early Solar System, and the chemistry of the protoplanetary disc at various distances.
“Because this sample of cometary building-block material was swallowed by an asteroid and preserved inside this meteorite, it was protected from the ravages of entering Earth’s atmosphere,” said cosmochemist Larry Nittler of the Carnegie Institution for Science.
“It gave us a peek at material that would not have survived to reach our planet’s surface on its own, helping us to understand the early Solar System’s chemistry.”
The research has been published in Nature Astronomy. | 0.864921 | 4.010086 |
This newly released Hubble images shows star R Sculptoris, a red giant located 1,500 light-years from Earth in the constellation of Sculptor.
Recent observations have shown that the material surrounding R Sculptoris actually forms a spiral structure — a phenomenon probably caused by a hidden companion star orbiting the star. Systems with multiple stars often lead to unusual or unexpected morphologies, as seen, for example, in the wide range of striking planetary nebulae that Hubble has imaged.
R Sculptoris is an example of an asymptotic giant branch (AGB) star. All stars with initial masses up to about eight times that of the Sun will eventually become red giants in the later stages of their lives. They start to cool down and lose a large amount of their mass in a steady, dense wind that streams outwards from the star. With this constant loss of material, red giants like R Sculptoris provide a good portion of the raw materials — dust and gas — used for the formation of new generations of stars and planets. They also show what is likely to happen to the Sun in a few billion years from now, and help astronomers to understand how the elements we are made up of are distributed throughout the Universe.
R Sculptoris itself is located outside the plane of the Milky Way and is easily visible using a moderately sized amateur telescope. In this part of the sky far from the galactic plane, there are relatively few stars but many faint and distant galaxies can be seen.
The black region at the centre of the image has been artificially masked.
Image: ESA/Hubble & NASA | 0.878544 | 3.751223 |
The sun, moon, and stars are all rotating around a central point over the North Pole. The underlying cause for this rotation is due to vast cornucopia of stellar systems orbiting around its center of attraction - an imaginary point of shared attraction. This is an extrapolated and more complex binary star movement. Think of a binary star system which moves around an invisible common barycenter. Now add a third body which shares that common center of attraction. Now a fourth. When we add enough bodies the system looks like a swirling multiple system.
The stars in the night sky rotate around common barycenters above the earth just as the sun and moon do. From a location on the earth's surface the stars in the sky might seem to scroll across the night sky with Polaris at the hub. The underlying cause for this rotation is due to vast cornucopia of stellar systems orbiting around its center of mass - an imaginary point completely compliant with the Newtonian system. This is an extrapolated and more complex binary star movement.
Each star in a cluster is attracted to one another through gravitational vectors. Formation is created through gravitational capture - at least three objects are actually required, as conservation of energy rules out a single gravitating body capturing another. The stars maintain their movement over the years through Newton's first law: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
The stars in the night sky trace almost perfect circles around the hub of the earth because by necessity the mechanics of a multiple system rely intimately on the movements and vectors of every member body. Circular movement is the most perfect, stable movement. If one celestial body is out of place or moves in a different fashion than the other bodies of the group the entire system becomes inherently imbalanced. Eddies, or stars that move out of tandem, will either leave the system entirely or are compelled by the stellar system to move back into its locked pace and apogee. This is why there are no elliptical orbits.
Instability can be avoided if the system is what astronomer David S. Evans has called "hierarchical." In a hierarchical system, the stars in the system can be divided into two smaller groups, each of which traverses a larger orbit around the system's center of mass. Each of these smaller groups must also be hierarchical, which means that they must be divided into smaller subgroups which themselves are hierarchical, and so on. In this case, the stars' motion will continue to approximate stable non-elliptical Keplerian orbits around the system's center of mass.
Here is an animation of a Multiple System, what one would see in the night sky over the hub of the earth: http://www.ifa.hawaii.edu/faculty/hu/movies/neigh.gif
Here is a scientific paper which describes the movements and behavior of Multiple Systems: http://adsabs.harvard.edu/abs/1968QJRAS...9..388E | 0.822504 | 3.961259 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2019 January 29
Explanation: How do distant asteroids differ from those near the Sun? To help find out, NASA sent the robotic New Horizons spacecraft past the classical Kuiper belt object 2014 MU69, nicknamed Ultima Thule, the farthest asteroid yet visited by a human spacecraft. Zooming past the 30-km long space rock on January 1, the featured image is the highest resolution picture of Ultima Thule's surface beamed back so far. Ultima Thule does look different from imaged asteroids of the inner Solar System, as it shows unusual surface texture, relatively few obvious craters, and nearly spherical lobes. Its shape is hypothesized to have formed from the coalescence of early Solar System rubble in into two objects -- Ultima and Thule -- which then spiraled together and stuck. Research will continue into understanding the origin of different surface regions on Ultima Thule, whether it has a thin atmosphere, how it obtained its red color, and what this new knowledge of the ancient Solar System tells us about the formation of our Earth.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U. | 0.869743 | 3.119714 |
Crescent ♉ Taurus
Moon phase on 29 January 2088 Thursday is Waxing Crescent, 6 days young Moon is in Aries.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 5 days on 23 January 2088 at 19:38.
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 ♈ Aries tropical zodiac sector.
Lunar disc appears visually 0.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1937" and ∠1948".
Next Full Moon is the Snow Moon of February 2088 after 8 days on 6 February 2088 at 21:33.
There is medium ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at very acute angle, so their combined tidal force is moderate.
The Moon is 6 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 1089 of Meeus index or 2042 from Brown series.
Length of current 1089 lunation is 29 days, 15 hours and 31 minutes. It is 2 hours and 40 minutes longer than next lunation 1090 length.
Length of current synodic month is 2 hours and 47 minutes longer than the mean length of synodic month, but it is still 4 hours and 16 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠241.2°. At the beginning of next synodic month true anomaly will be ∠278.3°. 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°).
10 days after point of apogee on 18 January 2088 at 17:28 in ♏ Scorpio. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 5 days, until it get to the point of next perigee on 3 February 2088 at 18:12 in ♊ Gemini.
Moon is 369 956 km (229 880 mi) away from Earth on this date. Moon moves closer next 5 days until perigee, when Earth-Moon distance will reach 366 292 km (227 603 mi).
12 days after its ascending node on 17 January 2088 at 02:46 in ♏ Scorpio, 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 31 January 2088 at 03:49 in ♉ Taurus.
12 days after beginning of current draconic month in ♏ Scorpio, the Moon is moving from the beginning to the first part of it.
9 days after previous South standstill on 20 January 2088 at 07:04 in ♐ Sagittarius, when Moon has reached southern declination of ∠-19.974°. Next 4 days the lunar orbit moves northward to face North declination of ∠19.864° in the next northern standstill on 2 February 2088 at 22:41 in ♊ Gemini.
After 8 days on 6 February 2088 at 21:33 in ♌ Leo, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.146023 |
The collaboration across cultural leaders, astronomers, and UH Hilo’s student cohort culminated in the selection of Hawaiian names for two major astronomical discoveries.
Hawaiʻi is the first place in the world to weave traditional indigenous practices into the process of officially naming astronomical discoveries, thanks to a unique educational program called A Hua He Inoa, a collaborative effort by ʻImiloa Astronomy Center of Hawaiʻi at the University of Hawaiʻi at Hilo.
Hawaiian speaking students from throughout Hawaiʻi Island and Maui spent two days immersed in knowledge from ʻōlelo Hawaiʻi experts, education leaders and top research scientists from the state’s astronomical observatories. Students peered into the world of scientific research, learned about the recent discovery of two unusual celestial bodies, ascended the summit of Maunakea and expanded their understanding of the vital relationship, and role, of tradition and culture in modern day science.
“This notion of astronomers working with the local, indigenous community to name discoveries may seem novel to most,” says Kaʻiu Kimura, executive director at ʻImiloa Astronomy Center of Hawaiʻi. “But if the research is in and from this place, that relationship should be acknowledged and honored. A Hua He Inoa is a critical step towards integrating indigenous perspectives and place-based scientific research.”
One great example is the first inter-stellar object to be tracked through our solar system, named ʻOumuamua. Larry Kimura of Ka Haka ʻUla o Keʻelikolani, College of Hawaiian Language at UH Hilo named the object which gained massive media attention worldwide and propelled the use of ʻolelo Hawaiʻi as part of the coverage.
The collaboration across cultural leaders, astronomers and UH Hilo’s student cohort culminated in the selection of Hawaiian names for two major astronomical discoveries. These names will serve as the official names for 2016 HO3 (Kamoʻoalewa)—an asteroid that orbits the Sun like the Earth but in a slightly different orbit, and 2015 BZ509 (Kaʻepaokaʻāwela)—an asteroid near the orbit of Jupiter that moves in an opposite “retrograde” direction.
“I never thought I would be part of giving a heavenly body a Hawaiian name that would be globally recognized,” says Kauakea Helekahi-Kaiwi, a senior at Nāwahīokalaniʻōpuʻu School.
As the A Hua He Inoa program moves forward, ʻImiloa Astronomy Center of Hawaiʻi will work to continue it’s goals of inspiring the community and extending the culture of Hawaiʻi and the immense value of indigenous practices out into the world. | 0.909383 | 3.048431 |
In a rare spectacle, a “Super Pink Moon” lit up the skies around Gran Alacant on the 7th April. Ancient people thought this cosmic event was linked to the appearance of pink flowers called wild ground phlox, which bloom in early spring and appear throughout the United States and Canada. While others claimed it signified the end of the world.
Although it is called a “Pink Moon” this name is deceiving because it is actually a pale shade of orange. It is a rare result of several space phenomena occurring at once and the Earth’s atmosphere filtering out the blue wavelengths. My photo of the Moon that appeared over Gran Alacant doesn’t do justice to just how bright orange and yellow the colours were.
April’s supermoon is the third of the year, following the “Worm Moon”, which was on the 9th March. The next full moon is referred to as the “Flower Moon” and we will be able to see it on the 7th May.
This natural phenomenon is always linked to the date of Easter because it appears after the spring equinox. Easter is always on the 4th full moon of the New Year. The “Super Moon” will also bring the largest tides of the year. This is because the closer the Moon is to Earth, the stronger the gravitational pull it exerts, this creates more variation between the tides. The distance to the moon was 356,906 km.
There may even be a correlation between the appearance of a full moon and sleep. Astrologers know this all too well. However, scientifically, it’s unclear exactly how the full moon affects sleep. Research by scientists in Switzerland has found that around a full moon phase, people may take longer to fall asleep, feel sleepless, and sleep less deeply. Humans are made up of 50 to 70 percent water. As the moon controls the oceans and waters on Earth, the human body may also be affected by the lunar phases.
A “Blood Moon” happens when Earth’s moon is in a total lunar eclipse. While it has no special astronomical significance, the view in the sky is striking as the usually whitish moon becomes red or ruddy-brown. The last blood moon on the 20th-21st of January 2019, coincided with a supermoon and the Full Wolf Moon, earning it the title “Super Blood Wolf Moon.”
When are all of the Full Moons:
Eclipse Moon – January 10
Snow Moon – February 9
Strawberry Moon – June 5
Buck Moon – July 5
Sturgeon Moon – August 3
Full Corn Moon – September 2
Hunter’s Moon – October 1
Beaver Moon – November 30
Cold Moon – December 30
Have fun cheers, Bryan Thomas | 0.842146 | 3.298617 |
Imagine that you could see right through your own skin. You could see the bones inside your body. You could watch food go down your throat when you swallow it. Imagine looking inside someone’s suitcase to see what’s inside. Does that sound impossible? Not when you know about X rays!
WHAT ARE X RAYS?
X rays are very powerful light rays that your eyes can’t detect. These light rays can slip through objects that visible light bounces off. We use X rays as a powerful tool to detect and discover things our eyes can’t see.
Asteroids are rocks in space that never quite made it as planets. Astronomers think that our solar system began as a cloud of gas and dust. Gravity pulled parts of the cloud together to make the Sun and the nine planets. Astronomers think that the asteroids formed in that cloud but never grew large enough to be planets.
HOW BIG ARE ASTEROIDS?
There are thousands of asteroids, and they come in all sizes. The biggest asteroid ever found is called Ceres. Ceres is more than 600 miles (1,000 kilometers) wide.
The universe contains everything that exists: Earth, the Sun, the stars, galaxies (collections of billions of stars), and everything else in space. People have wondered how the universe got started for thousands of years. Most scientists now think they have the answer. They think the universe began about 14 billion years ago with a kind of big explosion. They call the explosion the big bang.
WHAT HAPPENED AFTER THE BIG BANG?
No one knows what caused the big bang, but scientists think they know what happened all the way back to the first seconds after the big bang.
Every time you take a breath, you are inhaling Earth’s atmosphere. You cannot see, smell, or taste Earth’s atmosphere. It is the air all around you. Other planets also have an atmosphere. An atmosphere is a blanket of gases that wraps around a planet or any other object in space.
EARTH’S ATMOSPHERE IS AIR
Earth’s atmosphere is made up of a mix of gases called air. Air contains more nitrogen than any other gas. Nitrogen makes up 78 percent of the air. Oxygen, the gas that is most important for keeping you alive, makes up 21 percent.
Black holes are some of the strangest things in space. A black hole sucks in anything that gets near it. Nothing can escape from a black hole—not even light.
BLACK HOLES ARE STRONG
Nothing escapes from a black hole because its gravity is so strong. Gravity is a force that pulls one thing to another. Gravity is the force that holds you down on Earth. When you jump up, Earth’s gravity pulls you right back down. Earth’s gravity also makes the Moon orbit (go around) Earth. | 0.828641 | 3.448076 |
Researchers using NASA's Chandra X-ray Observatory have found evidence that the normally dim region very close to the supermassive black hole at the center of the Milky Way Galaxy flared up with at least two luminous outbursts in the past few hundred years.
This discovery comes from a new study of rapid variations in the X-ray emission from gas clouds surrounding the supermassive black hole, a.k.a. Sagittarius A*, or Sgr A* for short. The scientists show that the most probable interpretation of these variations is that they are caused by light echoes.
The echoes from Sgr A* were likely produced when large clumps of material, possibly from a disrupted star or planet, fell into the black hole. Some of the X-rays produced by these episodes then bounced off gas clouds about thirty to a hundred light years away from the black hole, similar to how the sound from a person's voice can bounce off canyon walls. Just as echoes of sound reverberate long after the original noise was created, so too do light echoes in space replay the original event.
While light echoes from Sgr A* have been seen before in X-rays by Chandra and other observatories, this is the first time that evidence for two distinct flares has been seen within a single set of data.
More than just a cosmic parlor trick, light echoes provide astronomers an opportunity to piece together what objects like Sgr A* were doing long before there were X-ray telescopes to observe them. The X-ray echoes suggest that the area very close to Sgr A* was at least a million times brighter within the past few hundred years. X-rays from the outbursts (as viewed in Earth's time frame) that followed a straight path would have arrived at Earth at that time. However, the reflected X-rays in the light echoes took a longer path as they bounced off the gas clouds and only reached Chandra in the last few years.
A new animation shows Chandra images that have been combined from data taken between 1999 and 2011. This sequence of images, where the position of Sgr A* is marked with a cross, show how the light echoes behave. As the sequence plays, the X-ray emission appears to be moving away from the black hole in some regions. In other regions it gets dimmer or brighter, as the X-rays pass into or away from reflecting material. Note that there is a slightly smaller field of view at the end of the sequence so the apparent disappearance of emission in the top-left hand corner is not real.
The X-ray emission shown here is from a process called fluorescence. Iron atoms in these clouds have been bombarded by X-rays, knocking out electrons close to the nucleus and causing electrons further out to fill the hole, emitting X-rays in the process. Other types of X-ray emission exist in this region but are not shown here, explaining the dark areas.
This is the first time that astronomers have seen both increasing and decreasing X-ray emission in the same structures. Because the change in X-rays lasts for only two years in one region and over ten years in others, this new study indicates that at least two separate flares were responsible for the light echoes observed from Sgr A*.
There are several possible causes of the flares: a short-lived jet produced by the partial disruption of a star by Sgr A*; the ripping apart of a planet by Sgr A*; the collection by Sgr A* of debris from close encounters between two stars; and an increase in the consumption of material by Sgr A* because of clumps in the gas ejected by massive stars orbiting Sgr A*. Further studies of the variations are needed to decide between these options.
The researchers also examined the possibility that a magnetar - a neutron star with a very strong magnetic field - recently discovered near Sgr A* might be responsible for these variations. However, this would require an outburst that is much brighter than the brightest magnetar flare ever observed.
A paper describing these results has been published in the October 2013 issue of the journal Astronomy and Astrophysics and is available online. The first author is Maïca Clavel from AstroParticule et Cosmologie (APC) in Paris, France. The co-authors are Régis Terrier and Andrea Goldwurm from APC; Mark Morris from University of California, Los Angeles, CA; Gabriele Ponti from Max-Planck Institute for Extraterrestrial Physics, Garching, Germany; Simona Soldi from APC and Guillaume Trap from Palais de la découverte - Universcience, Paris, France.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra Program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass. | 0.812757 | 4.125638 |
Does the Moon Have an Atmosphere and What Is It Made Of?
The moon is a barren landscape when viewed at night. Nowhere do you see traces of life or color but a bland grey with moments of black. Okay, so maybe that is too bleak of a picture to paint for the moon. It is actually an awesome place with many surprises like volcanic activity and even water. And it has an atmosphere too, but it is not quite like ours and that makes it all the better.
Most scientists in the past felt that the moon had nothing that could sustain an atmosphere for a majority of reasons but they still took a glance to see what they could find. Radio astronomers looked at the edge of the moon as the sun moved from behind it and found that if a lunar atmosphere existed it would have a max pressure of 1/10,000,000,000 of a pascal. The gravity of the moon would be strong enough to hold onto it but it would not take much for it to dissipate. But what would such an atmosphere be? The prevailing thought at the time was solar wind from the sun but we would need data from the surface of the moon if any theories were to be proven (Stern 37).
And so the Apollo missions were our different approach to getting that data. Several of the astronauts reported a glow along the horizon of the moon, calling it “Lunar Horizon Glow.” Besides a visual report, astronauts left special instruments designed by scientists in the hopes of measuring any sign of an atmosphere including 9 spectrometers and 5 pressure gauges. At first, it seemed like nothing was found of merit from them and even Apollo 17 hunted for solar wind (hydrogen, helium, carbon, and xenon) on the surface with a UV spectrometer but again no dice. However, alpha particle spectrometers from Apollo 15 and 16 later detected small amounts of radon and polonium gases that seemed to be emitted from the surface of the moon. Scientists believe it comes from decaying uranium inside the moon, but a gas on the surface was still an interesting find and the first hints of something more (37).
The Data Rolls In
Slowly, data began to trickle in that gave a deeper picture of the atmospheric nature of the moon. Surface detectors from Apollo 12 and 14 showed that an average of 100,000 particles per cubic centimeter were in their vicinity during the lunar night. In fact, as the night progressed, ion detectors from Apollo’s 12, 14, and 15 all saw fluctuations in the levels of several particles but mainly in neon and argon. On top of that, the Apollo 17 mass spectrometer found argon-40, helium-4, nitrogen, oxygen, methane, carbon monoxide and carbon dioxide, and changes in both argon and helium as the solar wind flowed from the sun. However, the Lunar Atmospheric Composition Experiment (LACE) found that argon levels also changed as seismic activity did and peaked at 40,000 particles per cubic centimeter. This seems to indicate that argon may come from within the moon, just like the radon and polonium. So why did argon change with the solar wind then? Pressure from the stream of particles pushed the argon along the surface, scientists suspect. Clearly, the moon does not have a traditional atmosphere but gases are present on its surface, despite the low levels and fluctuations. But what else is present? (Stern 38, Sharp, NASA)
After sodium and potassium were found on Mercury, scientists wondered if any was on the moon. After all, both objects share many similarities in composition and appearance so drawing parallels between them isn't unreasonable. Drew Patten and Tom Morgan (the scientists who found the Mercury gases) used a sensitive and large telescope, the 2.7-meter Mc-Donald Observatory, in 1987 to gather data about those potential elements. They did indeed find them on the moon but in low concentrations: sodium is concentrated at an average of 201 particles per cubic centimeter while potassium is at 67 particles per cubic centimeter! (Stern 38)
Now, how can we quantify the atmosphere in terms of altitude? We need a scale height, or the vertical distance it takes the moon’s atmosphere to decrease by a third (and with density and pressure closely related to altitude, we gain even more insights). Now, the scale height is affected by the molecular energy aka collisions of particles which increase kinetic energy. If the atmosphere was solely based on solar wind, one would expect the scale height to be 50-100 kilometers with a temperature of 100 degrees Kelvin. But data seems to indicate that the scale height is likely 100’s of kilometers, which corresponds to a temperature of 1000-2000 Kelvin! To add to the mystery, the surface of the moon has a max temperature of 400 Kelvin. What causes such a spike in heat? Sputtering, perhaps. This is when photons and solar wind strike the surface and free atoms from their molecular bonds, escaping upward with an initial temperature of 10 million Kelvin (38).
Final Closing Facts
If you take the entire atmosphere of the moon, it weighs a mere 27.5 tons and is fully replaced every few weeks. In fact, the average density of gas molecules at the moon’s surface is 100 molecules per cubic centimeter. To compare, Earth’s is 1*10^18 molecules per cubic centimeter! (Stern 36, Sharp) And I have no doubt that with the moon even bigger surprises await. Why, the atmosphere has even been postulated to help with the water cycle of the moon! Stay tuned, fellow readers…
NASA. "LADEE spacecraft finds neon in lunar atmosphere." Astronomy.com. Kalmbach Publishing Co., 18 Aug. 2015. Web. 04 Sept. 2018.
Sharp, Tim. “Atmosphere of the Moon.” Space.com. Space.com, 15 Oct. 2012. Web. 16 Sept. 2015.
Stern, Alan. “Where The Lunar Winds Blow Free.” Astronomy Nov. 1993: 36-8: Print.
Questions & Answers
© 2015 Leonard Kelley | 0.836223 | 3.855079 |
the trouble with an infinite universe is that no matter where you look in the night sky, you should see a star. Stars should overlap each other in the sky like tree trunks in the middle of a very thick forest. But, if this were the case, the sky would be blazing with light.
This is the famous Olber Paradox. Though articulated in the 1800s for an infinite steady-state universe, it still offers a puzzle today. The universe may not be infinite, but it’s very very big with very very many stars. Why do I see so much dark sky between stars?
Because the universe is expanding, the light that reaches us is subject to a phenomenon called “redshift…” the wavelengths of light [stars] emit appear to stretch out. Go far enough, and the light will redshift below the level discernible by the human eye, and eventually telescopes.
Some of this radiation shows up as background light, a faint diffuse glow of light that appears to have no source. The rest, however, disappears before it ever reaches us.
Thanks to Astronomy.com for the explanation. Try to remember this for when some little kid asks. Of course, when a kid asked “why is the night sky dark?” the best answer may be “It isn’t.” The sky, that is – isn’t – it isn’t dark. Human eyes simply don’t register the emmissions. There really is a pervasive radiation from the Big Bang. So cool. | 0.819919 | 3.368107 |
Right after the Mifflin Meteorite fell in SW Wisconsin in April 2010 the Robert A. Pritzker Assistant Curator of Meteoritics and Polar Studies Dr. Philipp R. Heck coordinated an international study to determine the time it spent in space and to calculate its size in space before it got ablated and broke apart in our atmosphere. Now, first results obtained from this study are published as extended abstracts, and will be presented in more detail in March at the Lunar and Planetary Science Conference in Texas: The new results show that Mifflin was travelling through space as a small 3 feet object for about 20 Million years before it landed in Wisconsin.
At the time of the meteorite fall Heck was visiting a lab in Europe and stayed in touch with the Robert A. Pritzker Center in Chicago by phone and e-mail. Collections manager for meteorites James L. Holstein sent out the meteorite as quickly as possible. “It is critical to do measurements as quickly as possible after the meteorite fall, because many of the radioactive elements that were produced in space, who are essential to measure, decay rapidly”, Heck says, “only thanks to the rapid donation of a large piece of Mifflin to us by private collector Mr. Terry Boudreaux, this study was possible.”
The natural radioactivity from the meteorite is not harmful for humans and is in fact so low, that the measurement was done in a special laboratory shielded from other natural sources of radioactivity. The Gran Sasso National Laboratory is located deep beneath the Apennines Mountains in Italy. Collaborator Dr. Matthias Laubenstein was ready to do this high-sensitivity measurement right after the meteorite fall. Longer-lived radioactive elements were analyzed by collaborators Dr. Kees Welten at the University of California at Berkeley and Dr. Marc Caffee at Purdue University in West Lafayette, Indiana. Radioactive elements are produced when cosmic rays hit the meteorite in space. Their concentrations depend on the size of the meteorite in space and the results from the three different labs show that Mifflin was about 3 feet in diameter before it entered Earth’s atmosphere. This confirms the first size estimates from video footage of the fireball.
The same cosmic rays also produce stable elements in the meteorite such as the noble gases, neon and argon. The concentration of these noble gases and their production rates tell us how much time the meteorite spent in space – from its ejection from its parent asteroid to its fall on Earth – its interplanetary flight time or cosmic-ray exposure age. Matthias Meier, a graduate student at ETH Zurich in Switzerland analyzed a piece of a Field Museum’s Mifflin specimen with a noble gas mass spectrometer dedicated only for meteorites and determined its interplanetary flight time to be 20 million years. This is not unusual for this type of meteorite. He also found that Mifflin has not been shocked much by impacts since almost two billion years, and was only slightly affected by the large parent asteroid breakup event 470 million years ago. Dr. Heck, who is also a co-advisor of Meier, comments, "This is a good example that meteorites do not just sit around and ‘gather dust’ once they arrive at a natural history museum."
The results from this study are interesting on their own but also serve as puzzle pieces to improve our understanding of the evolution of the Solar System.
The public Mifflin Meteorite exhibit at the Field Museum (upper level, south) now features a beautiful cut slice of the meteorite which reveals the brecciated nature of the rock, signs of impacts on the parent asteroid in space. Numerous clasts and shiny specks of metal can be easily seen with the naked eye. Also new on exhibit is the piece of Mifflin found by an elementary school student on the Iowa-Grant school ground. Private meteorite collectors Terry Boudreaux and Michael Farmer each donated two pieces. | 0.889666 | 3.692763 |
The moment the Sun reaches its southernmost point in the sky marks the December solstice, the official beginning of winter in the Northern Hemisphere (where it is called the winter solstice) and a time of great celebration in many northern cultures.
The seasons' starting times are governed by Earth's motion around the Sun — or equivalently, from our point of view, the Sun's annual motion in Earth's sky. The start of winter (for the Northern Hemisphere) is defined as the moment when the Sun hovers over Earth's Tropic of Capricorn (the line of latitude 23½° south of the equator) before heading north — a moment called, by Northerners, the winter solstice.
The Sun appears to move north and south in our sky during the year because of what some might consider an awkward misalignment of our planet. Earth's axis is tilted with respect to our orbit around the Sun. So when we're on one side of our orbit, the Northern Hemisphere is tipped sunward and gets heated by more direct solar rays, making summer. When we're on the opposite side of our orbit, the Northern Hemisphere is tipped away from the Sun. The solar rays come in at a lower slant to this part of the world and heat the ground less, making winter.
The effect is opposite for inhabitants of the Southern Hemisphere; for them the December solstice signals the beginning of summer, while winter starts at the June solstice.
For a skywatcher on Earth (at north temperate latitudes), the effect is to make the Sun appear to move higher in the midday sky each day from December to June, and back down again from June to December. A solstice comes when the Sun is at the upper or lower end of its journey; an equinox comes when the Sun is halfway through each journey.
The word solstice comes from the Latin solstitium — sol meaning "sun" and -stitium "stoppage." The winter solstice marks the shortest day and longest night of the year. From now on, the days begin to grow longer and the nights shorter. In ancient cultures, the winter solstice was an auspicious moment. It meant the end of declining hours of sunlight and provided a sense of renewal as the Sun began its daily climb higher in the sky.
Winter-solstice celebrations could well be the world's oldest holidays. There are more known rituals associated with this solstice than for any other time of the year. Prior to the Christian era, Romans called this day Dies Natalis Invicti Solis, the Birthday of the Unconquered Sun. Earlier in Rome it was the time of Saturnalia, a notoriously wild holiday. In 46 BC the winter solstice fell around December 25th. Despite calendar reforms, these celebrations — and the observance of Christmas by early Christians — remained locked to the 25th. | 0.823641 | 3.834492 |
At around 1 a.m. local standard time on April 29, 2017, a fireball flew over Kyoto, Japan. Compared to other fireballs spotted from Earth, it was relatively bright and slow. Now, scientists have determined not only what the fireball was, but also where it came from.
“We uncovered the fireball’s true identity,” says Toshihiro Kasuga, paper author and visiting scientist at the National Astronomical Observatory of Japan and Kyoto Sangyo University. “It has a similar orbit to that of the near-Earth asteroid 2003 YT1, which is likely its parent body.”
2003 YT1, a binary asteroid first detected in 2003, appears to have been active in the past, meaning it fissured and released dust particles, such as the one responsible for the 2017 fireball. It does not currently show any activity, though, according to Kasuga. However, the researchers found that the orbit, estimated radiant point, velocity and appearance date of the 2017 fireball are all consistent with dust particles that originated from 2003 YT1.
“The potential break-up of the rock could be dangerous to life on Earth,” Kasuga says. “The parent body 2003 YT1 could break up, and those resulting asteroids could hit the Earth in the next 10 million years or so, especially because 2003 YT1 has a dust production mechanism.”
The researchers found that this dust production mechanism, or the asteroid’s likelihood of releasing dust and rock particles, stems from its rotational instability in a process called the YORP effect. When the asteroid is warmed by the Sun, the energy results in a small thrust, which can produce a corresponding recoil, depending on the gravitational pull and other physical variables. The recoil can twist the asteroid, introducing a rotational change. The change can be at physical odds with the gravity and/or other forces, and force the asteroid to physically break — even just a little, a process which produces dust.
“The released particles can enter Earth’s atmosphere and appear as fireballs, which is exactly what happened in 2017,” says Kasuga.
According to Kasuga, that particular fireball was not a threat to Earth, as it was estimated to only be a few centimeters in size. Something so small would burn up before it reached the surface.
“The 2017 fireball and its parent asteroid gave us a behind-the-scenes look at meteors,” says Kasuga. “Next, we plan to further research predictions for potentially hazardous objects approaching the Earth. Meteor science can be a powerful asset for taking advanced steps towards planetary defense.”
Other contributors include Mikiya Sato, Masayoshi Ueda, and Yasunori Fujiwara, all of the Nippon Meteor Society. Chie Tsuchiya and Jun-Ichi Watanabe, both of the National Astronomical Observatory of Japan, also co-authored the paper.
These results appeared as Kasuga et al. "A Fireball and Potentially Hazardous Binary Near-Earth Asteroid (164121) 2003 YT1" in The Astronomical Journal on January 13, 2020. | 0.834251 | 4.017313 |
(NEW YORK) — A New York teen reached for the stars last summer and found a one-of-a-kind planet.
Wolf Cukier, 17, an intern at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, last July, was tasked with going through data on star brightness from the facility’s ongoing Transiting Exoplanet Survey Satellite mission or TESS. The Scarsdale High School senior was looking at a foreign system located 1,300 light-years from Earth. He said he then observed what appeared to be a slight darkness in one of the system’s suns.
It turned out that darkness was a planet 6.9 times larger than Earth that orbited two stars, what scientists call a circumbinary planet.
“I had a lot of data in my notes that day about extremities in the binaries,” Cukier said. “But when I saw this one, I put 10 asterisks next to it.”
Once he flagged the discovery to his research mentors, Cukier spent weeks with them and other scientists confirming his hypothesis. NASA said the teen’s discovery was rare because circumbinary planets are usually difficult to find and scientists can only detect these planets during a transit event, when one of the suns shows a decrease in brightness.
The two suns in the solar system in question, TOI 1338, varied in size, with one being about 10% more massive than Earth’s sun and the other 30% of the sun’s mass, NASA said. Because the two suns orbit each other every 15 days, it was harder to distinguish the transit events from the planet, dubbed TOI 1338-b, which take place every 93 to 95 days, according to NASA.
Cukier said it was tough trying to prove his discovery but the data kept pointing to a stronger confirmation.
“Our confidence went up and down a couple of times, but by the end of the internship, we were confident that what we found was a planet,” he said.
Cukier’s discovery and further research that he did with other NASA scientists marked the first time the TESS program discovered a planet in orbit of two stars. Their work was featured at a panel this week at the 235th American Astronomical Society meeting in Honolulu. Cukier and his mentors are looking for a science journal to publish a paper they wrote about the discovery.
Cukier said he plans on continuing research into astronomy and eclipsing binaries in the future and stays in touch with his mentors at NASA frequently.
“Future research would involve finding more planets,” he said. “We don’t have a large sample size of binary system planets.”
Copyright © 2020, ABC Audio. All rights reserved. | 0.86767 | 3.324496 |
The stillness of the night sky is deceiving. Because of the sheer vastness of space, stars appear unmoving like celestial fixtures. In actuality, though, they're zipping through the cosmos - some at ridiculously high speeds: thousands, and even tens of thousands of kilometres per second.
That's roughly 100,000 times faster than the speediest train and 1,000 times faster than the fastest spacecraft that's ever flown. That's fast enough for a few spins around Earth in the time it takes to put on your socks. The point is, that's fast.
These individual stars basically travel from one side of the universe to the other
Some astrophysicists have suggested that, in principle, stars could go even faster - even as fast as light. Such stars may even harbour planets, prompting speculation that they could serve as intergalactic transport for alien life.
But you don't need to speculate to find stars rocketing out of our own Milky Way Galaxy. A speed of a thousand or so kilometres per second is already fast enough to send a star hurtling toward the lonesome expanse. These hypervelocity stars, as they're called, were only discovered about 10 years ago. So far, astronomers have found a total of about two dozen leaving the Milky Way. And they're trying to find more.
Despite their name, however, hypervelocity stars aren't the fastest known stars. That title belongs to the handful of stars whirling around the supermassive black hole at the galactic centre. One of the fastest reaches 12,000 km/s. But these stars are so close to the behemoth, which weighs as much as four million suns, that such speeds aren't enough to escape its gravitational grip. These stars, however, may have played an integral role in kicking hypervelocity stars out of the galaxy.
In 1988, astrophysicist Jack Hills of Los Alamos National Laboratory in the US described a hypothetical encounter between a supermassive black hole and a binary star system, which consists of two stars orbiting each other.
These stars would be one way for alien life to spread from galaxy to galaxy. No fancy spaceships needed
He realised that if the binary got too close, the gravitational dance with the black hole would fling one of the stars out at thousands of kilometres per second. He dubbed these exiled stars hypervelocity stars. Meanwhile, the black hole pulls the other star into a tight orbit.
But for years, no one paid much attention to this idea. After all, no one had ever seen a star escaping the galaxy.
Then, in 2005, an astronomer named Warren Brown was searching for a certain type of bright, blue star in the Milky Way. By tracking their motions, and thus the galaxy's gravitational influence on them, he was trying to measure the mass of the galaxy. But what he found instead was a star moving really fast. Too fast. It was leaving the galaxy at 853 km/s - more than 3 million km/h. "The speed was unlike anything I'd ever seen before," says Brown, who's at the Harvard-Smithsonian Center for Astrophysics in the US.
Then he came across Hills's paper, which seemed to explain the discovery perfectly. "If you have a supermassive black hole at the very centre of the galaxy, every so often it should slingshot a star out of the galaxy," Brown says. This mechanism would also leave a lot of stars in tight orbits around the central black hole, which is exactly what astronomers observe.
Buoyed by this discovery, Brown and other astronomers set out to find more fast stars. Today, they've found about two dozen of them - a number that's about right considering how often the galaxy's black hole should be tossing out stars. "The numbers add up," Brown says. "It's pretty likely that even though they're now hundreds of thousands of light years away from the Milky Way proper, these stars were indeed formed right in the heart of the Milky Way."
But Brown wants to find more. The ones he detected were big, blue, and bright - a hundred times more luminous than the sun - simply because those were the ones that stand out amidst the hundreds of billions of stars in the galaxy. According to estimates, Brown says, about a thousand hypervelocity stars might be in the galaxy's vicinity, and chances are that many of them are smaller and dimmer, making them hard to find.
To know for sure if a star is escaping the galaxy, astronomers need to pinpoint its speed. As a star moves away, its light turns redder, stretching to longer wavelengths. So by measuring how much a star's spectrum - its light broken up into its constituent wavelengths - is shifted toward redder colours, astronomers can determine its speed.
Above: Breath-taking time-lapse of the stars seen in the Southern sky
But that technique only reveals how fast it's moving away along the line of sight. To know the true speed, you need to know its trajectory - and thus how fast it's moving across the sky, which requires incredibly precise measurements beyond the capability of most current techniques. Pinpointing a star's trajectory will also show whether it's indeed coming from the centre of the galaxy.
Fortunately, that's exactly what ESA's Gaia spacecraft will do. Launched in 2013, Gaia is measuring the velocities and positions of about a billion of the galaxy's stars. When it's done, astronomers expect it will identify yet more hypervelocity stars. And that will help them better understand the galaxy.
These stars are born and launched from the galactic centre, and their speeds and properties will offer a unique glimpse as to what it's like in the bustling and crowded environment near the central black hole.
The stars can also help astronomers map out all the mass in the galaxy. "Any deviation of their trajectory betrays the influence of the underlying mass pulling on them," Brown explains. Most of the galaxy's mass is composed of the mysterious, invisible stuff known as dark matter. To figure out what it is, astronomers want to know exactly how much there is and how it's distributed across the galaxy.
The weird one
While most hypervelocity stars seem to have come from the galactic centre, that's not necessarily the case for all of them. In fact, the fastest known hypervelocity star - an object dubbed US 708 hurtling outward at 1,200 km/s (more than four million km/h) - has a completely different origin. "This thing," Brown says, "is weird."
When a team of astronomers discovered the star in 2005, they clocked it at 750 km/s. It wasn't until this year that a team led by Stephan Geier of the European Southern Observatory in Germany realised that the star was going much faster than that.
Comparing new observations from the Pan-STARRS survey with archival images dating back to the 1950s, the astronomers did what Gaia is now doing for other stars: determine the star's motion across the sky. They revealed not only its faster speed, but also its trajectory. And apparently, US 708 did not come from the galactic centre, ruling out a black hole origin.
While no one's sure yet, astronomers think it was a huge explosion that launched the star. The first clue is the fact that US 708 is a rare type of star called a hot subdwarf.
In the past, however, it was once a normal star. According to the hypothesis, it was part of a binary system with a white dwarf - a hot, dense object that's the remnant of a star such as the sun. The two were in a tight orbit, and during its normal aging process, US 708 expanded into a red giant and engulfed the white dwarf. Meanwhile, the white dwarf continued orbiting, and as it did so, it plowed away US 708's outer layers. With only its hot, helium-burning core remaining, US 708 became a subdwarf.
Then, the two objects spiraled toward each other, losing energy by emitting gravitational waves, ripples in the space-time fabric of the universe. Eventually, they got so close that the subdwarf started spilling helium over onto the white dwarf. So much helium accumulated that it ignited nuclear fusion, causing the core to explode and destroy the white dwarf.
"Nuclear fusion of helium is much more violent than nuclear fusion of hydrogen in our sun," Geier explains. "This does not go slowly. This happens in a flash."
Before the blast, though, the two stars had been orbiting each other extremely fast - about once every 10 minutes, according to calculations. So when the white dwarf blew up, and there was no longer anything holding onto US 708, the subdwarf was promptly thrown out. Think of two figure skaters spinning in each other's arms. If one lets go, the other flies away.
Above: Breath-taking time-lapse of the stars seen in the Northern sky
US 708 is the fastest star seen dashing out of the galaxy, but it couldn't have gone much faster. Because it was orbiting its partner so closely, it was already going as fast is it could. Which raises the question: If not via stellar explosions, how could you accelerate stars even faster?
The answer might be with supermassive black holes, according to astrophysicists Avi Loeb and James Guillochon, of the Harvard-Smithsonian Center for Astrophysics. But unlike with the other hypervelocity stars, you don't just need one black hole. You need two.
If you got two supermassive black holes - millions or even billions of times as massive as the sun - together with a star, their interactions could kick that star out at a speed ten times greater than any of the hypervelocity stars known.
These high-speed rendezvous can happen relatively often in the universe. Almost every galaxy, such as the Milky Way, has a supermassive black hole at its centre. And galaxies tend to gravitate toward one another, making collisions somewhat commonplace. When they do, the two central black holes spiral in toward each other and eventually merge. Stars that get in the way either fall into the black holes, are tossed aside but remain in the galaxy, or are completely ejected.
Most of those ejected stars will be about as fast as the conventional hypervelocity stars. But about one percent of them could surpass 10,000 km/s, reaching up to 100,000 km/s, or one-third the speed of light. "Beyond 10,000 km/s - this is really the only game in town," Guillochon says. "There's really no other way to accelerate stars up to that speed."
While the observable universe could have a trillion of these speedsters zooming around at 10 percent the speed of light, only a few thousand would reach the Milky Way's neighborhood. That may sound like a lot, but they would account for only one out of every hundred million stars in the galaxy. They wouldn't be easy to find.
But it's possible, Guillochon says. The next generation of telescopes, such as the James Webb Space Telescope or the Large Synoptic Survey Telescope now being built in Chile, could detect one of these stars. While the normal hypervelocity stars are moving too slowly to get very far, these super speedsters can cover lots of ground. "These individual stars basically travel from one side of the universe to the other," Guillochon says.
And that makes them useful for science. By combining the ages of the stars with their speeds, astronomers could estimate the distance the stars have traveled, providing a new way to measure cosmic distances.
These superfast stars would also act as beacons that herald the merging of two supermassive black holes. Astronomers can then follow up with ESA's eLISA satellite, slated for launch in 2028, which will detect the gravitational waves produced from these violent collisions.
A tiny fraction of the stars could conceivably be even faster. If a supermassive black hole were spinning rapidly, and a star were orbiting in the same direction as the spin, an incoming secondary black hole could expel the star to speeds approaching that of light. But, Guillochon says, that would require such a rare configuration that even in a universe of possibilities, it would be practically impossible to detect such a star.
Still, even sub-light-speed stars would be the ultimate spacefarers, fast enough to have crossed large swaths of intergalactic space. A planet could orbit one of these stars, and if the orbit were tight enough - comparable to the distance between Earth and the sun - the planet would survive the expulsion from its galaxy.
But given the harsh environment around a black hole, it would be difficult for life to evolve, Guillochon says. If it could, however, these stars would be one way for alien life to spread from galaxy to galaxy. No fancy spaceships needed.
Of course, that scenario is more science fiction than anything. But it's something to think about the next time you look up at those stars, sparkling and seemingly still. | 0.846822 | 3.870041 |
The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the radial velocity is the component of the object's velocity that points in the direction of the radius connecting the object and the point. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from or approaches the Earth.
In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity, which is determined by spectroscopy. i.e. by measuring the frequencies of light received from the object. By contrast, astrometric radial velocity is determined by astrometric observations (for example, a secular change in the annual parallax).
- Spectroscopic radial velocity 1
- Detection of exoplanets 2
- Data reduction 3
- See also 4
- References 5
Spectroscopic radial velocity
Light from an object with a substantial relative radial velocity at emission will be subject to the Doppler effect, so the frequency of the light decreases for objects that were receding (redshift) and increases for objects that were approaching (blueshift).
The radial velocity of a star or other luminous distant objects can be measured accurately by taking a high-resolution spectrum and comparing the measured wavelengths of known spectral lines to wavelengths from laboratory measurements. A positive radial velocity indicates the distance between the objects is or was increasing; a negative radial velocity indicates the distance between the source and observer is or was decreasing.
In many binary stars, the orbital motion usually causes radial velocity variations of several kilometers per second (km/s). As the spectra of these stars vary due to the Doppler effect, they are called spectroscopic binaries. Radial velocity can be used to estimate the ratio of the masses of the stars, and some orbital elements, such as eccentricity and semimajor axis. The same method has also been used to detect planets around stars, in the way that the movement's measurement determines the planet's orbital period, while the resulting radial-velocity amplitude allows the calculation of the lower bound on a planet's mass. Radial velocity methods alone may only reveal a lower bound, since a large planet orbiting at a very high angle to the line of sight will perturb its star radially as much as a much smaller planet with an orbital plane on the line of sight. It has been suggested that planets with high eccentricities calculated by this method may in fact be two-planet systems of circular or near-circular resonant orbit.
Detection of exoplanets
The radial velocity method to detect exoplanets is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. When the star moves towards us, its spectrum is blueshifted, while it is redshifted when it moves away from us. By regularly looking at the spectrum of a star – and so, measuring its velocity – one can see if it moves periodically due to the influence of a companion.
From the instrumental perspective, velocities are measured relative to the telescope's motion. So an important first step of the data reduction is to remove the contributions of
- the Earth's elliptic motion around the sun at approximately ± 30 km/s,
- a monthly rotation of ± 12 m/s of the Earth around the center of gravity of the Earth-Moon system,
- the daily rotation of the telescope with the Earth crust around the Earth axis, which is up to 400 m/s at the equator and proportional to the cosine of the telescope's latitude,
- small contributions from the Earth polar motion,
- contributions of 220 km/s from the motion around the Galactic center and associated proper motions.
- The Radial Velocity Equation in the Search for Exoplanets ( The Doppler Spectroscopy or Wobble Method ) | 0.887988 | 4.149981 |
Some 3,700 years ago, a meteor or comet exploded over the Middle East, wiping out human life across a swath of land called Middle Ghor, north of the Dead Sea, say archaeologists who have found evidence of the cosmic airburst. The airburst “in an instant, devastated approximately 500 km2 [about 200 square miles] immediately north of the Dead Sea, not only wiping out 100 percent of the [cities] and towns, but also stripping agricultural soils from once-fertile fields and covering the eastern Middle Ghor with a super-heated brine of Dead Sea anhydride salts – a mix of salt and sulfates – pushed over the landscape by the event’s frontal shock waves.“
“Based upon the archaeological evidence, it took at least 600 years to recover sufficiently from the soil destruction and contamination before civilization could again become established in the eastern Middle Ghor,” they wrote. Among the places destroyed was Tall el-Hammam, an ancient city that covered 89 acres (36 hectares) of land.
Among the evidence that the scientists uncovered for the airburst are 3,700-year-old pieces of pottery from Tall el-Hammam that have an unusual appearance. The surface of the pottery had been vitrified (turned to glass).
The temperature was also so high that pieces of zircon within the pottery turned into gas. That is something that requires a temperature of more than 7,230 degrees Fahrenheit (4,000 degrees Celsius), said Phillip Silvia, a field archaeologist and supervisor with the Tall el-Hammam Excavation Project.
However, the heat, while powerful, did not last long enough to burn through entire pottery pieces, leaving parts of the pottery beneath the surface relatively unscathed.
The only naturally occurring event capable of causing such an unusual pattern of destruction, Silvia said, is a cosmic airburst — something that has occurred occasionally throughout Earth’s history, such as the explosion in 1908 at Tunguska in Siberia.
Also, archaeological excavations and surveys at other towns within the impacted area suggest a sudden wipeout of life around 3,700 years ago, Silvia said. So far, no craters have been found nearby, and it’s unclear whether the culprit was a meteor or comet that exploded above the ground.
The fact that only 200 square miles of land was destroyed indicates that the airburst occurred at a low altitude, possibly not more than 3,280 feet (1 km) above the ground said Silvia. In comparison, the Tunguska airburst heavily damaged 830 square miles, or 2,150 square kilometersof land.
Maybe the explosion looked like the launch of NASA’s Solar Dynamics Observatory on Feb. 11, 2010… well, just a bit:
That must have been a hell of an explosion! | 0.89424 | 3.466554 |
The mission of Zond 2
by Andrew J. LePage
|Even before the last transmission from Mars 1 had been received, the decision had been made to send another half dozen spacecraft towards Venus and Mars during 1964 launch opportunities using an improved spacecraft designated 3MV.|
Unfortunately, all three of the 2MV-series spacecraft launched towards Venus in August and September of 1962 never made it beyond Earth orbit due to problems with the Molniya 8K78 launch vehicle. Likewise, two of the 2MV spacecraft bound for Mars also succumbed to launch vehicle failures two months later. Only the 894-kilogram (1,970-pound) Mars 1, launched on November 1, 1962, managed to survive launch and was sent on its way to Mars. Despite the successful launch, a malfunction in the spacecraft’s attitude control system doomed the mission of Mars 1 to failure months before it ever reached its target.
Even before the last transmission from Mars 1 had been received on March 21, 1963, the decision had been made to send another half dozen spacecraft towards Venus and Mars during 1964 launch opportunities using an improved spacecraft designated 3MV. Like its predecessors, the 3MV series of planetary explorers were designed at OKB-1 led by famed Chief Designer Sergei Korolev. As with the earlier 2MV, the 3.6-meter-tall (12-foot-tall) 3MV consisted of two sections. The first was an orbital compartment that contained control systems, power supplies, and communications gear, as well as some instrument electronics. Mounted on the exterior of this compartment was a pair of solar panels with hemispherical radiators for thermal control mounted on their ends, an umbrella-like high-gain antenna, as well as low-gain antennas and a variety of sensors. The 3MV included a number of design improvements based on the experiences with the earlier 2MV design, such as significantly more redundancy of key systems and the inclusion of a set of experimental plasma engines to serve as a backup to the conventional nitrogen gas jets used for attitude control, which had failed during the flight of Mars 1.
The second section of the 3MV was the planetary compartment that was geared towards specific investigations of the target planet. As before, the planetary compartment came in two varieties: one contained a film-based camera system and a set of ultraviolet and infrared instruments designed to study the target planet during a close flyby, while the other was a roughly spherical lander with a diameter of about 0.9 meters (3 feet), designed to detach from the orbital compartment before the encounter and touchdown on the target planet. Both the orbital and planetary compartments were pressurized to provide a laboratory-like environment for the internal equipment in order to simplify the design and testing of various systems as well as provide easier thermal control.
As with the 2MV, the 3MV design had four design variants. The 3MV-1 carried a planetary compartment designed to land on Venus, while the 3MV-2 had instruments designed to study Venus during a close flyby. Because the launch window to Mars in November 1964 was so much more favorable than the earlier launch window used by Mars 1 in November 1962, the Mars-bound 3MV spacecraft could be significantly more massive than their earlier 2MV counterparts. The 3MV-3, designed to land on Mars, would have a launch mass of 1,042 kilograms (2,297 pounds), while the 3MV-4 flyby craft would weigh in at 1,037 kilograms (2,286 pounds). These craft would carry a significantly larger instrument payload as a result. The 3MV-3 and 3MV-4 would be four times more massive and much more capable that the pair of 261-kilogram (575-pound) American Mariner-Mars 1964 flyby spacecraft that were also under development at this time.
Russian diagram of the 3MV-4A “Zond 2” spacecraft. (credit: RKK Energia)
While the 3MV incorporated many design improvements to address the problems uncovered in the 2MV spacecraft, Korolev and his engineers realized that test flights of the 3MV would be desirable to reveal any additional issues well before the launches to Venus and Mars in order to improve the chances of these missions succeeding. Since these test missions would not be directed specifically towards Venus or Mars, after launch they would receive the generic name of “Zond” which means simply “probe” in Russian.
The first Zond version was a stripped down model of the Venus lander craft designated 3MV-1A. It was to be launched into a solar orbit that would bring it back to Earth after a flight of five to six months. The 275-kilogram (606-pound) entry probe would then separate from the orbital compartment and reenter Earth’s atmosphere to simulate the Venus landing mission of the 3MV-1. The second Zond variant was a modified version of the Mars flyby spacecraft designated 3MV-4A. This spacecraft was to carry a planetary compartment equipped with an updated miniaturized film-based imaging system as well as other scientific instruments. After being launched into a simulated trajectory towards the orbit of Mars, the 3MV-4A would turn its camera back towards the receding Earth at a distance of 40,000 to 200,000 kilometers (25,000 to 124,000 miles) and acquire a sequence of photographs that would subsequently be developed automatically on board. The spacecraft would then transmit its scanned photographs and other data gathered on the interplanetary environment out to distances as great as 200 to 300 million kilometers (125 to 185 million miles) as part of a long distance communications test.
|But before a triumphant launch announcement for what would have been “Venera 2” could be made, a major problem was discovered during the first communication session with the probe. With bleak prospects for success, the Soviets announced the probe simply as “Zond 1” making no mention of its mission to Venus.|
On March 21, 1963, the Soviet government officially approved the 3MV program. It would consist of two 3MV-1A flights and a single 3MV-4A flight to be launched in 1963, as well as a total of six operational 3MV spacecraft to be launched to Venus and Mars in 1964 (See “…Try, try again”, The Space Review, April 28, 2014). Inevitable problems during the construction and testing of the new 3MV spacecraft delayed the launch of the engineering test flights and forced the Venus mission to be scaled back to just a pair of 3MV-1 landers. Despite the best efforts of all involved, both 3MV-1A Zond test flights failed. The first spacecraft launched on November 11, 1963, was stranded in Earth parking orbit to become Kosmos 21. The second, launched on February 19, 1964, on the first flight of the improved 8K78M Molniya, lifted off only a month before the ideal Venus launch window opened but failed to reach even Earth parking orbit.
Without the benefit of a test flight, the first of the 3MV-1 Venus landers was launched on March 27, 1964, but was stranded in its Earth parking orbit due to a wiring fault in the escape stage, becoming Kosmos 27. With the wiring problem corrected, the second 3MV-1 was successfully launched towards Venus on April 2. But before a triumphant launch announcement for what would have been “Venera 2” could be made, a major problem was discovered during the first communication session with the probe. The pressurized orbital compartment was leaking and all its gas would be lost within a week, severely compromising the ability of its equipment to operate. With bleak prospects for success, the Soviets announced the probe simply as “Zond 1” making no mention of its mission to Venus.
The leak in the orbital compartment of Zond 1 was eventually linked to a bad weld near the quartz window for the probe’s star and Sun sensors. While it would not help Zond 1, future 3MV craft would have their welds X-rayed as a new quality control check. In the meantime, as ground controllers made valiant attempts to keep Zond 1 alive and made excellent use of the various redundancies built into the new 3MV design, the craft finally succumbed to its growing list of problems and fell silent on May 24, 1964, some two months shy of its encounter with Venus.
Russian diagram showing the advanced film-based imaging system carried by Zond 2. (credit: NASA)
With this latest failure, the launch of the 3MV-4A Zond test flight that had been scheduled for the April-May 1964 timeframe was postponed to address ongoing issues with the 3MV. Despite the problems, Korolev and his team still intended to launch a pair of 3MV-3 landers and another pair of 3MV-4 flyby spacecraft towards Mars in November. But in addition to the ongoing hardware issues, Soviet ambitions for this Mars launch window were now being threatened by the latest revelations about Mars gleaned from ground-based observations.
When design work on the first generation Soviet Mars landers started in 1960, the general consensus of the astronomical community was that Mars had an atmosphere dominated by nitrogen, much like the Earth’s, with traces of carbon dioxide. Based on decades of photometric and polarimetric observations of how the Martian atmosphere scattered sunlight, it was estimated that the atmospheric surface pressure on Mars was about 85 hectopascals (hPa) compared to Earth’s 1,013 hPa (where the hectopascal is equivalent to the now-obsolete millibar in common use back then). Of course today we now know that the Martian atmosphere is composed primarily of carbon dioxide with a mean surface pressure of only 6 hPa—less than a tenth as dense as had been generally assumed at the beginning of the Space Age. As a result, the original Soviet Mars lander design was simply inadequate for such a thin atmosphere and would crash during any landing attempt.
The low pressure of the Martian atmosphere started to become apparent at about the same time as the 3MV-3 landers were in the process of being developed and manufactured. The first indications of trouble came from Soviet astronomer Vassili I. Moroz at the Sternberg State Astronomical Institute in Moscow. A pioneer in infrared spectral studies of bodies in the solar system, his analysis of the infrared spectra he had obtained of Mars during its opposition in early 1963 showed that the surface pressure of Mars was likely only about 24 hPa and possibly much less. While Korolev and his engineers must have been aware of this work, which had been submitted for publication in September of 1963, and might have dismissed it as an isolated anomalous result, similar results were being published in peer-reviewed scientific journals in the West starting on New Years Day 1964. By the summer of 1964, NASA-sponsored studies for Mars landing missions were now reflecting this new reality of a much thinner Martian atmosphere with a surface pressure possibly as low as 10 hPa. Only later did scientists determine that the large amounts of fine dust in the Martian atmosphere had biased earlier measurements, making the atmosphere scatter more light and appear denser than it actually is.
|The original Soviet Mars lander design was simply inadequate for such a thin atmosphere and would crash during any landing attempt.|
With the continuing delays in the development of the Mars-bound 3MV spacecraft and the realization that the 3MV-3 lander was doomed to fail, Soviet officials eventually scrapped the original plans to launch four spacecraft to Mars in November 1964. Since it was already in an advanced state of preparation, officials decided instead that only the single 950-kilogram (2,094-pound) 3MV-4A test craft would be launched towards Mars. But given the poor track record of the previous planetary missions, they recognized that the chances of this spacecraft actually surviving all the way to Mars were slim even if it followed a faster 195-day trajectory that would allow it to reach Mars a full month before NASA’s Mariner spacecraft. As a result, Mars would be only a secondary objective for this mission, with the primary objective being the original engineering test flight. The 3MV-4A, which would receive a “Zond” designation, would be launched into a slow trajectory with a 249-day transit time. This would simulate a future Mars lander mission profile, with the spacecraft essentially performing a very long-duration engineering test flight.
Unlike NASA’s Mariner-Mars 1964 spacecraft, this Zond mission would attempt no Mars photography despite the fact that its more advanced camera system could return more than an order of magnitude more imaging data. Instead, the Zond would presumably photograph the Earth shortly after its departure as planned for the original test flight. Aside from engineering data and exercising the new imaging system, the spacecraft would acquire scientific data on fields and particles during its interplanetary cruise. If the test craft managed to survive its long flight to the Red Planet in good condition, it would be redirected to impact Mars and deliver a set of commemorative pennants it was carrying. While Mariner 4 would be the first spacecraft to flyby Mars and return images of its surface, the Soviet probe could be the first to impact its surface to at least satisfy propaganda purposes.
Of the three spacecraft launched towards Mars in November 1964, only NASA’s Mariner 4 reached the Red Planet. (credit: NASA)
The unsuccessful launch of NASA’s first Mars-bound spacecraft, Mariner 3, on November 5, 1964, was followed by a crash program to correct the fault with the rocket’s new launch shroud that caused the failure. With its new shroud barely ready in time, Mariner 4 successfully lifted off on November 28 with a scheduled encounter date of July 14, 1965. The Soviet’s Mars-bound engineering test craft, 3MV-4A No. 2, lifted off two days later on November 30 from the Baikonur Cosmodrome at 1312 UT with its 8K78M launch vehicle placing it into a 153-by-219-kilometer (95-by-136-mile) parking orbit. After a short coast, the Blok L escape stage came to life and successfully injected Zond 2 into a much slower trajectory that would not reach Mars until three weeks after Mariner 4.
As had happened during earlier Soviet planetary missions, problems were already apparent during the first communication session with Zond 2, when the spacecraft reported that only half of the expected power was being generated by its solar panels. As the problem was being diagnosed, controllers took measures to conserve power, including the apparent cancellation of the Earth imaging session as well as postponing the first scheduled course correction maneuver. In the end, they determined that one of the two solar panels on Zond 2 failed to deploy as intended. When the Blok L finished its burn, protective shrouds that were connected to the solar panels with lines were suppose to jettison, pulling the solar panels out of their stowed position. It seems that one of the two pull-cords had broken, resulting in the failure of one of the solar panels to deploy. After several engine firings to shake the spacecraft, the stuck panel finally deployed on December 15. But by this point it was already too late to perform the first planned midcourse correction.
This would prove to be only the beginning of Zond’s problems. A failed timer resulted in the thermal control system not functioning properly, hampering operation of onboard equipment. While the new plasma engines were test-fired successfully, communications with the probe apparently became increasingly erratic after its scheduled December 18 communication session. Some accounts of the mission suggest that a course correction was finally made around February 17, 1965, that further refined the path of Zond 2 towards Mars. At some point in time after this maneuver, and possibly as late as May 2, controllers finally lost contact with Zond 2 with an official public announcement being made by Soviet authorities on May 5, 1965. Three months later on August 6, Zond 2 flew silently past Mars at a reported distance of 1,500 kilometers (930 miles).
With this latest failure, it was obvious that the 3MV design still required much improvement and that better quality control was necessary to ensure success during the next missions to Venus, which had already been approved for launch in November 1965. Another Zond test flight would be attempted before then to test design changes and improvements resulting from the experience with Zond 2. In the meantime, responsibility for the Soviet lunar and planetary probes was officially transferred from the overworked teams at OKB-1 to NPO Lavochkin in April 1965 under Chief Designer Georgi Babakin—an organization known for its intensive testing and quality control of the hardware it built.
|In October 1965, all further work to redesign the first generation Mars lander was finally abandoned ending the Soviet Union’s initial attempts to reach Mars.|
While the engineers under Babakin struggled to get up to speed with the 3MV design in preparation for the next planned flights, a team at Lavochkin took on the task of examining a redesign of the first generation Mars lander. Based on the measurements made by Mariner 4 as well as new ground-based observations, it was now known that the Martian atmosphere was dominated by carbon dioxide with a surface pressure of only 6 hPa. This required a significant increase in the size of the lander’s heat shield and parachute system. This, in turn, forced a redesign of the “standard” orbital compartment to make it lighter in order to keep the total spacecraft mass within the one metric ton lift capability of the Molniya 8K78M launch vehicle.
In the end, they found it impossible to design a lander within these limitations that could survive landing or transmit any usable amount of atmospheric data during a brief descent. In October 1965, all further work to redesign the first generation Mars lander was finally abandoned ending the Soviet Union’s initial attempts to reach Mars. Early the following year, Mars-oriented development work at NPO Lavochkin shifted towards designing the significantly larger M-69 spacecraft to be launched in 1969 by the newly introduced Proton 8K82K rocket. A new chapter in the Soviet Union’s attempts to reach Mars was about to begin.
Brian Harvey, Russian Planetary Exploration: History, Development, Legacy and Prospects, Springer-Praxis, 2007
Bart Hendrickx, “Managing the News: Analyzing TASS Announcements on the Soviet Space Program (1957-1964)”, Quest, Vol. 19, No. 3. pp. 44–58, 2012
Wesley T. Huntress and Mikhail Ya. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer-Praxis, 2011
Andrew J. LePage, “The Mystery of Zond 2”, Journal of the British Interplanetary Society, Vol. 46, No. 10, pp. 401-404, October 1993
Andrew LePage, “Zond 2: Old Mysteries Solved & New Questions Raised”, Drew Ex Machina, July 17, 2014
Andrew LePage, “50 Years Ago Today: The Launch of Mariner 3”, Drew Ex Machina, November 5, 2014
V.G. Perminov, The Difficult Road to Mars: A Brief History of Mars Exploration in the Soviet Union, Monographs in Aerospace History No. 15, NASA History Division, July 1999
Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 5: The First Planetary Probe Attempts, 1960–1964”, Spaceflight, Vol. 40, No. 3, pp. 85–88, March 1998
Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 6: The Improved Four-Stage Launch Vehicle, 1964–1972”, Spaceflight, Vol. 40, No. 5, pp. 181–184, May 1998 | 0.85108 | 3.46144 |
PG 1159 star
Fr.: PG 1159
A member of the class of stars in transition between → post-AGB and → white dwarf stars, with temperatures as high as 200,000 K, mean mass about 0.6 Msun, and log g = 5.5-8. PG 1159 stars have no hydrogen or He I lines in their spectra, but do show weak He II lines and stronger lines of ionized carbon and oxygen. These stars are thought to be the exposed inner core of a star that has exploded as a → planetary nebula and is on its way to become a white dwarf. Also called → pre-degenerate star
Named after their prototype PG 1159-035, from the Palomar-Green Catalog of Ultraviolet Excess Stellar Objects (Green et al. 1986, ApJS 61, 305); → star. | 0.808884 | 3.078528 |
ICMEs (Interplanetary Coronal Mass Ejections) are violent phenomena of solar activity that affect large regions of the heliosphere. The prediction of their impact on the Earth and other solar system bodies is one of the primary goals of the planetary space weather forecasting. The travel time of an ICME from the Sun to the Earth can be computed through the Drag-Based Model (DBM). A DBM is based on a simple equation of motion for the ICME defining its acceleration as a=-Γ(v-w)|v-w|, where a and v are the CME acceleration and speed, w is the ambient solar-wind speed and Γ is the so-called drag parameter (Vršnak et al., 2013). To run the codes, forecasters use empirical input values for Γ and w, derived by pre-existent knowledge of solar wind. In the ‘Ensemble’ approaches (Dumbovich et al., 2018; Napoletano et al. 2018), the uncertainty about the actual values of such inputs are rendered by Probability Distribution Functions (PDFs), accounting for their variability and our lack of knowledge. Employing a list of past ICME events, for which initial conditions when leaving the Sun and arrival conditions at the Earth are known, we apply a statistical approach to the DBM to determine a measure of Γ and w for each case. This allows to obtain distributions for the model parameters on an experimental basis and to test whether different conditions of relative velocity to the solar wind influence the value of the drag efficiency. This is a promising approach when considering the extremely short computation time needed by the model to propagate ICMEs, to forecast ICME arrival to planetary bodies or spacecraft in the whole heliosphere, with relevant application to space-mission short-term planning. | 0.821439 | 3.717301 |
The picture shows the galaxy NGC 6744, distant by 30 million light years. This is one of the 50 galaxies observed as part of the ultragalactic UV survey of the Hubble Space Telescope (LEGUS) - the most acute and complete review of the UV light of stellar-born galaxies in the nearest Universe
Thanks to the unprecedented accuracy and spectral range of the NASA Hubble Space Telescope, scientists have been able to produce the most complete high-resolution UV-light imagery of nearby stellar-born galaxies.
The researchers combined the new Hubble observations with archived images for 50 spiral and dwarf galaxies in the local Universe. The project was named LEGUS, and it compiled star catalogs for each galaxy and cluster catalogs for 30 galaxies. The data contains information about young, massive stars and star clusters, as well as how the environment affects their development.
There has never been a catalog of stars and star clusters that includes observations in UV light. This is the main indicator of the tiniest and hottest star populations, which are an important addition to the stellar history. It is still unclear exactly how the process of star formation occurs. Therefore, the researchers carefully selected targets for LEGUS from 500 galaxies that are 11-58 million light-years distant from us. The criteria were the mass, the rate of star birth and the abundance of elements heavier than hydrogen and helium.
UGCA 281 is a blue compact dwarf galaxy living in the Hounds of Dogs territory. Inside, two large-scale star clusters appear shiny and white, and also diluted with green clouds of hydrogen gas. They are responsible for much of the recent star formation in the galaxy. The rest is represented by more ancient stars and is red. Reddish objects in the background - background stars
The team used a wide 3 Hubble camera and an extended camera to capture images of galaxies and the most massive young stars and star clusters. Also added archival footage with visible light to provide a complete picture. The catalogs contain approximately 8,000 young clusters, whose age ranges from 1 million to 500 million years. They are 10 times more massive than the largest clusters in the Milky Way.
There are approximately 39 million stars in star catalogs, which are at least 5 times more massive than the Sun. Stars in visible light reach an age from 1 million to several billion years, the youngest - 1-100 million years. Hubble telescope data provides all the information for analyzing such galaxies. There are also computer models to help interpret data in star and cluster catalogs.
6 frames show the diversity of star formation regions in neighboring galaxies. Included in the LEGUS part of the program - the most accurate and complete overview of UV light for stellar-forming galaxies. Here you will find 2 dwarf galaxies (UGC 5340 and UGCA 281) and 4 large spiral (NGC 3368, NGC 3627, NGC 6744 and NGC 4258). One of the goals of the project is to sample the stellar birth regions in each galaxy. Because of the relative proximity, Hubble manages to resolve individual stars. In the spiral type, star formation waves occur along dark filaments representing spiral arms. Birth begins in the inner sleeves and moves outward. The milky-white areas in the center are the glow of many stars. These galaxies are 19 to 42 million light years distant from us. They were watched from January to July 2014 When reviewing a spiral galaxy, we encounter an already ordered structure. But there are many competing theories for connecting individual stars into clusters in similar objects. Observation with the smallest details makes it possible to identify the physical parameters underlying this ordering of stellar populations.
The LEGUS project will also help to interpret the types of galaxies in the distant Universe, where the UV light of young stars stretches to IR wavelengths due to the expansion of space. In the future, these reviews will be complemented by a fresh and deeper view of the telescope of James Webb. | 0.854953 | 3.940995 |
NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission has released its fourth year of survey data. Since the mission was restarted in December 2013, after a period of hibernation, the asteroid- and comet-hunter has completely scanned the skies nearly eight times and has observed and characterized 29,375 objects in four years of operations. This total includes 788 near-Earth objects and 136 comets since the mission restart.
Near-Earth objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of the planets in our solar system into orbits that allow them to enter Earth's neighborhood. Ten of the objects discovered by NEOWISE in the past year have been classified as potentially hazardous asteroids (PHAs). Near-Earth objects are classified as PHAs, based on their size and how closely they can approach Earth's orbit.
"NEOWISE continues to expand our catalog and knowledge of these elusive and important objects,” said Amy Mainzer, NEOWISE principal investigator from NASA's Jet Propulsion Laboratory in Pasadena, California. “In total, NEOWISE has now characterized sizes and reflectivities of over 1,300 near-Earth objects since the spacecraft was launched, offering an invaluable resource for understanding the physical properties of this population, and studying what they are made of and where they have come from.”
The NEOWISE team has released an animation depicting detections made by the telescope over its four years of surveying the solar system.
More than 2.5 million infrared images of the sky were collected in the fourth year of operations by NEOWISE. These data are combined with the year one through three NEOWISE data into a single publicly available archive. That archive contains approximately 10.3 million sets of images and a database of more than 76 billion source detections extracted from those images.
Originally called the Wide-field Infrared Survey Explorer (WISE), the spacecraft launched in December 2009. It was placed in hibernation in 2011 after its primary astrophysics mission was completed. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission: to assist NASA's efforts to identify and characterize the population of near-Earth objects. NEOWISE also is characterizing more distant populations of asteroids and comets to provide information about their sizes and compositions.
NASA's Jet Propulsion Laboratory in Pasadena, California, manages and operates the NEOWISE mission for NASA's Planetary Defense Coordination Office within the Science Mission Directorate in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science data processing takes place at the Infrared Processing and Analysis Center at Caltech in Pasadena. Caltech manages JPL for NASA. | 0.930902 | 3.757233 |
(NEWSER) – Meet your new but shy galactic neighbor: A black hole left over from the death of a fleeting young star, per the AP. European astronomers have found the closest black hole to Earth yet, so near that the two stars dancing with it can be seen by the naked eye.
Of course, close is relative on the galactic scale. This black hole is about 1,000 light-years away and each light-year is 5.9 trillion miles. But in terms of the cosmos and even the galaxy, it is in our neighborhood, said European Southern Observatory astronomer Thomas Rivinius, who led the study published Wednesday in the journal Astronomy & Astrophysics.
The previous closest black hole is probably about three times further, about 3,200 light-years. The new discovery, in the constellation Telescopium in the Southern Hemisphere, hints that there are more of these out there.
Astronomers found this one because of the unusual orbit of a star. The black hole is part of what used to be a three-star dance in a system called HR6819. The two remaining super-hot stars aren’t close enough to be sucked in, but the inner star’s orbit is warped.
Using a telescope in Chile, they confirmed that there was something about four or five times the mass of our sun pulling on the inner star. It could only be a black hole, they concluded. “It will motivate additional searches among bright, relatively nearby stars,” said Ohio State University astronomer Todd Thompson, who wasn’t part of the research.
Like most of these type of black holes this one is tiny, maybe 25 miles in diameter. “Washington, DC, would quite easily fit into the black hole, and once it went in it, would never come back,” said study co-author Dietrich Baade… see more | 0.918769 | 3.185455 |
Looking at Mercury Reveals How the Sun is Losing Its Mass
So what does this mean for the rest of the solar system? Eventually it's going to have some Earth-destroying implications, but that's a few billion years down the line. For now, it's beginning to throw some orbits out of whack, according to a group of researchers at NASA and MIT who thought they could use a planet's orbit to learn more about the sun.
Mercury, being the closest planet to the sun, is showing the most signs of change as its own orbit begins shifting. The researchers, who just published their findings in Nature Communications, have been charting a road map of Mercury's orbit (which is called an "ephemeris") and studying various changes in that road map, especially its closest point to the sun and its farthest point from the sun.
These two points, called the perihelion (when it's closest to the sun) and aphelion (farthest from the sun) can be altered by other planets in the solar system, who exert their own gravitational pull over tiny Mercury, but those aren't strong enough to account for all the changes. Something else must be messing with Mercury, and the pull of other planets had to be removed from the equation.
Like humans, our Sun loses mass as it ages, weakening its gravitational pull. To study the dynamics of our aging star, @NASASun researchers have enlisted Mercury, the smallest, innermost planet in the solar system. See how: https://t.co/IaUqVgW9Zx pic.twitter.com/a8U55nPdsJ— NASA (@NASA) January 19, 2018
There are plenty of other factors that could change Mercury's orbit as well, including factors related to Einstein's theory of general relativity: because the sun is so massive, it's capable of warping spacetime to the point that this, too, can impact Mercury's orbit. So all of these factors had to be separated, if anyone wanted to get a specific look at how much the sun's loss of mass was impacting all this.
Eventually the researchers did separate it all, creating a new process where they examined both Mercury's orbit, and the orbit of the MESSENGER probe that circled Mercury until its fiery death back in 2015, when it crashed into the planet's surface. Using all this data, they could get a look at how the sun's internal workings were shifting and impacting Mercury. According to Goddard geophysicist Erwan Mazarico:
In the end, the researchers found that Mercury's changing orbit meant the sun was losing 0.1 percent of its mass over a period of ten billion years - a very small amount, but significant enough to shuffle things around the solar system just because the sun is so massive. This matches up with previous predictions, but it had never been observed like this before.
So how does the sun losing that tiny amount of its mass change things? It means that every planet, Earth included, could be pushed back by up to half an inch per year.
Like we said, a tiny loss of mass in our giant local star can make ripples throughout our solar system, so we should know what's going on. | 0.862228 | 3.759166 |
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One hundred and twenty after two years came the following eight-year match of Venus travels. Amid that time the prominent stargazer Edmond Halley had recommended that researchers could pick up an exact gauge of the separation between the Earth and the Sun utilizing the logical primary of parallax. Parallax is the distinction in the clear position of a question saw along two unique observable pathways, and is estimated by the point or semi-edge of slant between those two lines.
Halley effectively contemplated that if the Venus travel was seen and estimated from extremely removed focuses on the Earth, that the joined estimations, utilizing parallax, could be utilized to compute the real separation between the Earth and the Sun (AU). Up to that time, the researchers were utilizing Horrocks assurance of AU, however acknowledged they required numerous more precise perceptions to get a more genuine estimation. Hence the Venus travels of 1761 and 1769 propelled an uncommon flood of logical perceptions to the most remote purposes of the Globe.
This was one of the most punctual cases of universal logical coordinated effort. Getting to these areas was as much an enterprise as acquiring the principal precise information for a Venus travel. Researchers, for the most part from England, France, and Austria, made a trip to places as far separated as Newfoundland, South Africa, Norway, Siberia, and Madagascar.
In South Africa great estimations were acquired by Jeremiah Dixon and Charles Mason who might later go ahead to add their name to the notable Mason-Dixon Line in the USA. Noted purposes of the globe for the 1769 travel included Baja, Mexico; Saint Petersburg, Russia; Philadelphia Pennsylvania, USA; Hudson Bay, Canada; and from Tahiti, the immense British adventurer Captain Cook watched the travel from a place he called “Point Venus.”
Effect of Black Drop
While watching the Venus travel, the most basic circumstances are the principal, second, third, and fourth contact. Having the capacity to plainly observe and time these advances – from the shadow of Venus not touching, to simply first touching the suns plate the time the shadow of Venus completely travels into the circle of the Sun, and afterward while leaving, the point where the main edge of the shadow of Venus again touches off the plate of the Sun, once more into space, and the time the whole shadow has left the plate of the Sun and is not any more unmistakable – is critical to increase exact information.
Lamentably, an optical wonder called the dark drop impact makes it hard to see the second and third contacts. Soon after second contact, and again just before third contact amid the travel, a little dark “tear” seems to associate Venus’ circle to the appendage of the Sun, making it difficult to precisely time the correct snapshot of second or third contact.
This negative effect on the planning of the second and third contact added to the mistake in computation of the genuine estimation of AU, in 1761 and 1769 travels. It was first idea the dark drop impact was caused by the thick climate of Venus, yet it is currently trusted it is caused generally by impedance in the Earth’s air. Today, better telescopes and optics are limiting the dark drop impact for cosmologists watching Venus travels.
Different travels are, extremely uncommon events, however do happen. It is feasible for there to be a sun based obscuration and a travel of Venus in the meantime. The last time this occurred was in the year 15,607 BC. The following sun powered obscuration in addition to Venus travel will happen on April 5, 15,232.
It is likewise feasible for Mercury and Venus to travel the Sun in the meantime. Truth is stranger than fiction, both of Earth’s internal planetary neighbors impeccably agreeing with the Earth’s circle and the Sun so a spectator on Earth could see both little shadows going before our Sun in the meantime. The last time this happened was in the year 373,173 BC. Whenever the synchronous travel of the Sun by the two planets will happen will be July 26, 69,163. Will man even be around to see this far away travel?
Guillaume Le Gentil
A French researcher and cosmologist who took long names to another extraordinary – Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière (Guillaume Le Gentil) made some critical commitments to space science, particularly a portion of the principal perceptions of a few Messier items. Be that as it may, it was his part as a component of the universal drive to record the 1761 Venus travel that makes him such an intriguing and sad figure.
Le Gentil was one of over a hundred spectators from around the globe who walked or cruised off to far away areas of the globe in order to increase different far flung vantage purposes of the travel to help ascertain a more precise assurance of an AU. Not these campaigns met with progress, truth be told, many were foiled by shady skies, rain, antagonistic locals, trouble getting to where they needed to go, and defective gear. Be that as it may, nobody was as unfortunate as Le Gentil.
Guillaume le Gentil set out from Paris in March 1760 headed for Pondicherry, a French settlement in India. He achieved Mauritius in July. However, by then he discovered that France and Britain were at war. Prior to his ship arrived, he took in the British had involved Pondicherry so the ship redirected back to Mauritius. On June 6, 1761 the travel touched base as anticipated, however Le Gentil was still on board the ship. In spite of the fact that the skies were clear he couldn’t mention objective facts on board the moving deck of a ship adrift. Don’t sweat it, he thought, I came this far, I will sit tight for the following travel, eight years away.
As Galileo designed his first telescope in 1609 the principal opportunity to watch a Venus travel utilizing present day optical gadgets accompanied the travels of 1631 and 1639. Five years previously the 1631 travel, in 1627, Johannes Kepler turned into the primary individual to foresee a travel of Venus. Kepler effectively anticipated the 1631 occasion.
Be that as it may, Kepler was not able figure out where might be the best area to watch the travel, nor did he understand that in 1631 the travel would not be discernible in the greater part of Europe. In this manner, nobody made plans to movement to where they could see it, and this travel was missed.Fortunately, after 8 years on December 4, 1639, a youthful beginner cosmologist by the name of Jeremiah Horrocks turned into the principal individual in present day history to anticipate, watch, and record a Venus travel. Horrocks redressed Kepler’s before computations and acknowledged what we now think about Venus travels, that they happen eight years separated after pauses.
It is usually expressed that he played out his perceptions from Carr House in Much Hoole, close Preston England. Horrocks likewise told his companion, another beginner cosmologist by the name of William Crabtree, about the coming anticipated travel and he additionally detected the planet’s outline on the sun based plate. Crabtree presumably saw close Broughton, Manchester England. In spite of the fact that Horrocks was questionable when the travel would start, he was sufficiently fortunate to figure the time with the goal that he could watch some portion of it. He utilized a telescope to sparkle the picture onto a white card, along these lines securely watching the travel without hurting his eyes. Utilizing his observational information, Horrocks thought of the best estimation for an Astronomical Unit (AU). | 0.830507 | 3.667386 |
Here’s a question: what color is Venus? With the unaided eye, Venus just looks like a very bright star in the sky. But spacecraft have sent back images of the cloud tops of Venus, and some have even returned images from the surface of Venus.
If you could actually fly out to Venus and look at it with your own eyes, you wouldn’t see much more than a bright white-yellowish ball with no features. You wouldn’t actually be able to see any of the cloud features that you can see in photographs of Venus. That’s because those photos are taken using different wavelengths of light, where differences in the cloud layers are visible. For example, the photo that accompanies this story was captured in the ultraviolet spectrum.
Although the atmosphere of Venus is almost entirely made up of carbon dioxide, the clouds that obscure our view to the surface are made of sulfur dioxide. These are opaque to visible light, and so we can’t see through them to the surface of Venus. These clouds actually rain droplets of sulfuric acid.
If you could get down beneath the cloud tops of Venus, you wouldn’t be able to see much either. That’s because the clouds are so thick that most of the light from the Sun is blocked before it reaches the surface. You would see a dim landscape, like you might see at twilight. The surface of the planet is littered with brownish-red volcanic rocks. The bright red color you see in the Soviet Venera images of Venus have been brightened to show more surface detail.
So, what color is Venus? Yellowish-white.
We’ve also recorded an entire episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus. | 0.817092 | 3.446862 |
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Triangulum Galaxy, also known as Messier 33. Enjoy!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these objects is known as Messier 34, an open star cluster located in the northern Perseus constellation. Located at a distance of about 1,500 light years from Earth, it is one of the closest Messier objects to Earth, and is home to an estimated 400 stars. It is also bright enough to be seen with the naked eye or binoculars, where light conditions permit.
What You Are Looking At:
This cluster of stars started its journey off together through our galaxy some 180 million years ago as part of the “Local Association”… groups of stars like the Pleiades, Alpha Persei Cluster and the Delta Lyrae Cluster that share a common origin, but have become gravitationally unbound and are still moving together through space. We know the stars are related by their common movement and ages, but what else do we know about them?
Well, one thing we do know is that out of the 354 stars in the region survey, 89 of them are actual cluster members and that all six of the visual binaries and three of the four known Ap stars are members of the cluster. There’s even a giant among them! But like almost all stars out there, we know they usually aren’t singles and actually have companions. As Theodore Simon wrote in his 2000 study regarding NGC 1039 and NGC 3532:
“Roughly half the sources detected in both images have likely optical counterparts from earlier ground-based surveys. The remainder are either prospective cluster members or foreground/background stars, which can be decided only through additional photometry, spectroscopy, and proper-motion studies. There is some indication (at the 98% confidence level) that solar-type stars may lack the extreme rotation and activity levels shown by those in the much younger Pleiades and alpha Persei clusters, but a detailed assessment of the coronal X-ray properties of these clusters must await more sensitive observations in the future. If confirmed, this finding could help to rule out the possibility that stellar dynamo activity and rotational braking are controlled by a rapidly spinning central core as stars pass through this phase of evolution from the Pleiades stage to that represented by the Hyades.”
If there’s companion stars to be discovered, what else might be in the field that we just can quite “see”? Try white dwarfs. As Kate Rubin (et al.) published in the May 2008 issue of the Astronomical Journal:
“We present the first detailed photometric and spectroscopic study of the white dwarfs (WDs) in the field of the ~225 Myr old (log ?cl = 8.35) open cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field UBV imaging, we photometrically select 44 WD candidates in this field. We spectroscopically identify 19 of these objects as WDs; 17 are hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool DC WD that exhibits no detectable absorption lines. Of the 17 DAs, five are at the approximate distance modulus of the cluster. Another WD with a distance modulus 0.45 mag brighter than that of the cluster could be a double-degenerate binary cluster member, but is more likely to be a field WD. We place the five single cluster member WDs in the empirical initial-final mass relation and find that three of them lie very close to the previously derived linear relation; two have WD masses significantly below the relation. These outliers may have experienced some sort of enhanced mass loss or binary evolution; however, it is quite possible that these WDs are simply interlopers from the field WD population.”
While it sounds a little confusing, it’s all about how star clusters evolve. As David Soderblom wrote in a 2001 study:
“We analyze Keck Hires observations of rotation in F, G, and K dwarf members of the open cluster M34 (NGC 1039), which is 250 Myr old, and we compare them to the Pleiades, Hyades, and NGC 6475. The upper bound to rotation seen in M34 is about a factor of two lower than for the 100 Myr-old Pleiades, but most M34 stars are well below this upper bound, and it is the overall convergence in rotation rates that is most striking. A few K dwarfs in M34 are still rapid rotators, suggesting that they have undergone core-envelope decoupling, followed by replenishment of surface angular momentum from an internal reservoir. Our comparison of rotation in these clusters indicates that the time scale for the coupling of the envelope to the core must be close to 100 Myr if decoupling does, in fact, occur.”
History of Observation:
M34 was probably first found by Giovanni Batista Hodierna before 1654, and independently rediscovered by Charles Messier in on August 25, 1764. As he described it in his notes:
“I have determined the position of a cluster of small stars between the head of the Medusa and the left foot of Andromeda almost on the parallel of the star Gamma of that letter constellation. With an ordinary refractor of 3 feet, one distinguishes these stars; the cluster may have 15 minutes in extension. I have determined its position with regard to the star Beta in the head of the Medusa; its right ascension has been concluded at 36d 51′ 37″, and its declination as 41d 39′ 32″ north.”
Over the years, a great many historic observers would turn a telescope its way to examine it – also looking for more. Said Sir William Herschel: “A cluster of stars; with 120, I think it is accompanied with mottled light, like stars at a distance.” Yet very little more can be seen except for the fact that most of the stars seem to be arranged in pairs – the most notable being optical double in the center – h 1123 – which was cataloged by Sir John Herschel on December 23rd, 1831.
Charles Messier discovered it independently on August 25th, 1764, and included it in the Messier Catalog. As he wrote in the first edition of the catalog:
“In the same night of [August] 25 to 26, I have determined the position of a cluster of small stars between the head of the Medusa [Algol] & the left foot of Andromeda almost on the parallel of the star Gamma of that letter constellation. With an ordinary [non-achromatic] refractor of 3 feet [FL], one distinguishes these stars; the cluster may have 15 minutes in extension. I have determined its position with regard to the star Beta in the head of the Medusa; its right ascension has been concluded at 36d 51? 37?, & its declination as 41d 39? 32? north.”
But as always, it was Admiral William Henry Smyth who described the object with the most florid prose. As he wrote in his notes when observing the cluster in October 1837, he noted the following:
“A double star in a cluster, between the right foot of Andromeda and the head of Medusa; where a line from Polaris between Epsilon Cassiopeiae and Alpha Persei to within 2deg of the parallel of Algol, will meet it. A and B, 8th magnitudes, and both white. It is in a scattered but elegant group of stars from the 8th to the 13th degree of brightness, on a dark ground, and several of them form into coarse pairs. This was first seen and registered by Messier, in 1764, as a “mass of small stars;” and in 1783 was resolved by Sir W. Herschel with a seven-foot reflector: with the 20-foot he made it “a coarse cluster of large stars of different sizes.” By the method he applied to fathom the galaxy, he concluded the profundity of this object not to exceed the 144th order.”
Locating Messier 34:
M34 is easily found in binoculars about two fields of view northwest of Algol(Beta Persei). You will know when you have found this distinctive star cluster because “X” marks the spot! In a telescope finderscope, it will appear as a faint, hazy spot and will fully resolve to most average telescopes. Messier 34 makes an excellent target for moonlit nights or light polluted areas and will stand up well to less than perfect sky conditions.
It can even be seen unaided from ideal locations! Enjoy your observations!
And as always, we’ve included the quick facts on this Messier Object to help you get started:
Object Name: Messier 34
Alternative Designations: M34, NGC 1039
Object Type: Galactic Open Star Cluster
Right Ascension: 02 : 42.0 (h:m)
Declination: +42 : 47 (deg:m)
Distance: 1.4 (kly)
Visual Brightness: 5.5 (mag)
Apparent Dimension: 35.0 (arc min)
We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons. | 0.898113 | 3.794263 |
New images reveal "golf ball asteroid" has seen its share of hits
Astronomers have taken the clearest-ever shots of asteroid Pallas, a large rock orbiting out beyond Mars. The new images revealed the surface of this tiny world to be heavily dotted with craters, to the point where it’s been dubbed the “golf ball asteroid.”
With a diameter of 512 km (318 mi), Pallas is the third-largest object in the asteroid belt, behind Ceres and Vesta. It has a pretty weird orbit too, which sends it on an angle of 35 degrees off-kilter compared to the path of most asteroids in the belt.
Although Pallas was originally discovered way back in 1802, it remains largely unexplored and under-studied. To try to change that, researchers examined it using the SPHERE instrument on the Very Large Telescope (VLT) in Chile. Over two observing runs, two years apart, the team took 11 images of Pallas at different angles. This was then used to create a 3D reconstruction of its shape and surface.
These images revealed several features of Pallas that had never been seen before. There’s a bright spot in its southern hemisphere, which may be a large deposit of reflective salts, much like those seen on Ceres.
But the most striking discovery (pun intended) was the sheer number of craters that mark Pallas. The astronomers spotted 36 craters larger than 30 km (18.6 mi) wide, which is impressive for such a small body. They estimate that craters cover more than 10 percent of its surface, making it the most heavily-cratered object in the asteroid belt. The reason for the golf ball nickname is pretty clear from the images.
To determine how Pallas ended up like this, the team ran simulations of the asteroid belt, with a focus on Pallas, Ceres and Vesta, and how they interacted with smaller debris. They found that Pallas’ weird orbit goes a long way towards explaining its pockmarked surface.
The object periodically smashes its way back through the asteroid belt on an angle, increasing the chances of collisions with other debris. And when it does, those collisions are up to four times more damaging than when something the same size strikes other objects.
“Pallas’ orbit implies very high-velocity impacts,” says Michaël Marsset, lead author of the study. “Pallas experiences two to three times more collisions than Ceres or Vesta, and its tilted orbit is a straightforward explanation for the very weird surface that we don’t see on either of the other two asteroids.”
Another feature the team noticed for the first time was a gigantic impact crater at Pallas’ equator, measuring some 400 km (249 mi) wide. This, the simulations suggest, could have been created by an impact with an object between 20 and 40 km (12.4 and 24.9 mi) wide, and would have sent fragments flying into space. Interestingly, this matches a trail of debris that’s known to follow Pallas around.
The research was published in the journal Nature Astronomy. | 0.823106 | 3.926228 |
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A little interesting about space life.
"From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of year are not physically possible. The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude--much higher than the 6 miles that modeling tells us the new features are located," Dr. Rodriguez explained in the September 24, 2018 JPL Press Release.
and here is another
Jupiter is circled by a bewitching duo of moons that are potentially capable of nurturing delicate tidbits of life as we know it. Like its more famous sister-moon, Europa, Ganymede might harbor a life-loving subsurface ocean of liquid water in contact with a rocky seafloor. This special arrangement would make possible a bubbling cauldron of fascinating chemical reactions--and these reactions could potentially include the same kind that allowed life to evolve on our own planet!
A moon is defined as a natural satellite that orbits a larger body--such as a planet--that, in turn, orbits a star. The moon is kept in its position both by the gravity of the object that it circles, as well as by its own gravity. Some planets are orbited by moons; some are not. Some dwarf planets--such as Pluto--possess moons. In fact, one of Pluto's moons, named Charon, is almost half the size of Pluto itself, and some planetary scientists think that Charon is really a chunk of Pluto that was torn off in a disastrous collision with another object very long ago. In addition, some asteroids are also known to be orbited by very small moons.
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Furthermore, the icy stuff that collected on Methone's surface could even be more lightweight than that which lies beneath. It is possible that such fluffy, snowy, stuff can actually flow--at least over long periods of thousands to millions of years--thus filling in the tell-tale scars of impact craters.
Now, the fishing magazines and sites around the Internet will have you believe that the relationship between solar/lunar cycles and fishing is much more complex than I have explained here. In reality it's not. In fact, if you try to follow most of the charts out there, you will find no direct correlation between those charts and the number and size of fish you catch.
The moon, unlike other celestial objects, or even earthly objects for that matter, has ambivalent connotations in the pages of tradition and folklore. The full moon is more so because of its enigmatic aura and understated presence. The full moon has always been witness to many incidents; pages of descriptions dot more books than not about several events unfolding on a full moon night. It somehow brings out an ominous feeling in a storyline. | 0.870179 | 3.009841 |
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature. Like magnets, they also have two poles. Although they are at temperatures of roughly 3000–4500 K (2727–4227 °C), the contrast with the surrounding material at about 5,780 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of temperature to the fourth power. If the sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the Sun and can be as large as 80,000 kilometers (50,000 mi) in diameter, making the larger ones visible from Earth without the aid of a telescope. They may also travel at relative speeds (“proper motions”) of a few hundred m/s when they first emerge onto the solar photosphere. | 0.803397 | 3.542008 |
Database of historical data of indexes
Usually abreviated as SSN. Higher sunspot numbers indicate increased ionizing radiation from the sun which enhances the ionosphere's ability to refract HF signals, The sunspot number can vary from zero to over 200 during the peak of the 11-year solar cycle.
Usually abreviated as SFI (and often simply as "I"). Measurement of radio signals from the sun. The index is taken once a day at a frequency of 2800 MHz (10.7 cm). Increased radio noise from the sun means more ionizing radiation and correlates with the sunspot number. Solar flux values range from 60 (no sunspots) to 300.
K indexes reflect the geomagnetic conditions (solar particle effects on the earth's magnetic field) and their values range from 0 to 9. Lower numbers mean quieter ionosphere. Trends in the K indexes are important to watch. When K rises you can expect HF propagation conditions to worsen, particularly towards the polar regions. On VHF bands a high K index would mean the possibility of an Aurora openning.
K index: Siebert (1971) defines "K variations are all irregular disturbances of the geomagnetic field caused by solar particle radiation within the 3-h interval concerned. All other regular and irregular disturbances are non K variations. Geomagnetic activity is the occurrence of K variations". K is a local index, describing disturbances in the vicinity of each observatory.
Ks index: Using statistical methods, J. Bartels generated conversion tables to eliminate these disturbances. By applying the conversion tables, a standardized index Ks for each of the 13 selected observatories is determined. In contrast to the K values, the Ks index is expressed in a scale of thirds (28 values: 0o, 0+, 1-, 1o, 1+, 2-, 2o, 2+, ... , 8o, 8+, 9-, 9o). The main purpose of the standardized index Ks is to provide a basis for the global geomagnetic index Kp.
Kp index: Kp is the average of the Ks indexes from a number of "Kp stations" distributed around the globe and gives a "planetary" overview of the geomagnetic activity.
A indexes are derived from K indexes but converted to a linear scale in gammas (nanoTeslas). They can range from 0 to 400 but it is rare to see it go above 75 o 100. More often you will see A index readings between about 4 and 50. Values below 10 are very desirable for HF commnunications. Higher A numbers can mean excesive absortion of HF radio waves due to increased storm conditions in the ionosphere.
A index: Indicates the disturbances for the last 24 hours in the vicinity of an observatory. It's obtained averaging the eight K indexes and converting the result according to the table below.
ap index: Is the direct result of the conversion of the three-hour Kp index according to the table below.
Ap index: The daily index Ap is obtained by averaging the eight values of ap for each day.
|Ionospheric condition||K index||A index|
|Severe storm||6-9||> 99|
|Kp index||ap index| | 0.806744 | 3.837324 |
Posted on March 9, 2017
Previously on the Eloquent Nature blog: Photograph the Milky Way: Part One
Viewing the Milky Way requires nothing more than a clear, dark sky. The Milky Way’s luminosity is fixed, so our ability to see it is largely a function of the darkness of the surrounding sky—the darker the sky, the better the Milky Way stands out. But because our eyes can only take in a fixed amount of light, there’s a ceiling on our ability to view the Milky Way with the unaided eye.
A camera, on the other hand, can accumulate light for a virtually unlimited duration. This, combined with technological advances that continue increasing the light sensitivity of digital sensors, means that when it comes to photographing the Milky Way, well…, the sky’s the limit. As glorious as it is to view the Milky Way with the unaided eye, a camera will show you things your eyes can’t see. In fact, not only does the right camera in the right hands resolve far more Milky Way detail than we can see, it also reveals color too faint for the human eye.
Knowing when and where to view the Milky Way is a great start, but photographing the Milky Way requires a combination of equipment, skill, and experience that doesn’t just happen overnight (so to speak). But Milky Way photography doesn’t need to break the bank, and it’s not rocket science.
Bottom line, photographing the Milky Way is all about maximizing your ability to collect light: long exposures, fast lenses, high ISO.
In general, the larger your camera’s sensor and photosites (the “pixels” that capture the light), the more efficiently it collects light. Because other technology is involved, there’s not an absolute correlation between sensor and pixel size and light gathering capability, but a small, densely packed sensor almost certainly rules out your smartphone and point-and-shoot cameras anything more than a fuzzy snap of the Milky Way. At the very least you’ll want a mirrorless or DSLR camera with an APS-C (1.5/1.6 crop) size sensor. Better still is a full frame mirrorless or DSLR camera. (A 4/3 Olympus or Panasonic sensor might work, but I’ve not been overly impressed with the high ISO images I’ve seen from these smaller sensors.)
Another general rule is that the newer the technology, the better it will perform in low light. Even with their smaller, more densely packed sensors, many of today’s top APS-C bodies outperform in low light full frame bodies that have been out for a few years, so full frame or APS-C, if your camera is relatively new, it will probably do the job.
If you’re shopping for a new camera and think night photography might be in your future, compare your potential cameras’ high ISO capabilities—not their maximum ISO, but read some reviews to see how your camera candidates fare in objective tests by credible sources like DP Review or Imaging Resource (there are many others).
An often overlooked consideration is the camera’s ability to focus in extreme low light. Autofocusing on the stars or landscape will be difficult to impossible, and you’ll not be able to see well enough through a DSLR’s viewfinder to manually focus. Some bodies with a fast lens will autofocus on a bright star or planet, but it’s not something I’d count on (though I expect within a few years before this capability becomes more common).
Having photographed for years with Sony and Canon, and working extensively with most other mirrorless and DSLR bodies in my workshops, I have lots of experience with cameras from many manufacturers. In my book, focus peaking makes mirrorless the clear winner for night focusing. Sony’s current mirrorless bodies (a7R II, a7S, and a7S II) are by far the easiest I’ve ever used for focusing in the dark—what took a minute or more with my Canon, I can do in seconds using focus peaking with my Sony bodies. That said, of the major DSLR brands, I’ve found Canon’s superior LCD screen makes it much easier to focus in extreme low light than Nikon. (More on focus later.)
Put simply, to photograph the Milky Way you want fast, wide glass—the faster the better. Fast to capture as much light as possible; wide to take in lots of sky. A faster lens also makes focus and composition easier because its larger aperture gathers more light. How fast? F/2.8 or faster—preferably faster. How wide? At least 28mm, and 24mm or wider is better still. I do enough night photography that I have a dedicated, night-only lens—my original night lens was a Canon-mount Zeiss 28mm f/2; my current night lens is a Rokinon 24mm f/1.4.
It goes without saying that at exposure times up to 30 seconds, you’ll need a sturdy tripod and head for Milky Way photography. You don’t need to spend a fortune, but the more you spend, the happier you’ll be in the long run (trust me). Carbon fiber provides the best combination of strength, vibration reduction, and light weight, but a sturdy (heavy) aluminum tripod will do the job.
An extended centerpost is not terribly stable, and a non-extended centerpost limits your ability to spread the tripod’s legs and get low, so I avoid tripods with a centerpost. But if you have a sturdy tripod with a centerpost, don’t run out and purchase a new one—just don’t extend the centerpost when photographing at night.
Read my tips for purchasing a tripod here.
To eliminate the possibility of camera vibration I recommend a remote release; without a remote you’ll risk annoying all within earshot with your camera’s 2-second timer beep. Don’t forget a flashlight or headlamp for the walk to and from the car. And it’s never a bad idea to toss an extra battery in your pocket.
Keep it simple
There are just so many things that can go wrong on a moonless night when there’s not enough light to see camera controls, the contents of your bag, and the tripod leg you’re about to trip over. After doing this for many years, both on my own and helping others in workshops, I’ve decided that simplicity is essential.
Simplicity starts with paring down to the absolute minimum gear: a sturdy tripod, one body, one lens, and a remote release (plus an extra battery in my pocket). Everything else stays at home, in the car, or if I’m staying out after a sunset shoot, in my bag.
Upon arrival at my night photography destination, I extract my tripod, camera, lens (don’t forget to remove the polarizer), and remote release. I connect the remote and mount my lens—if it’s a zoom I set the focal length at the lens’s widest—then set my exposure and focus (more on exposure and focus below). If I’m walking to my photo site, I carry the pre-exposed and focused camera on the tripod (I know this makes some people uncomfortable, but if you don’t trust your head enough to hold onto your camera while you’re walking, it’s time for a new head), trying to keep the tripod as upright and stable as possible as I walk.
Flashlights/headlamps are essential for the walk/hike out to to and from my shooting location, but while I’m there and in shoot mode, it’s no flashlights, no exceptions. This is particularly important when I’m with a group. Not only does a flashlight inhibit your night vision, its light leaks into the frame of everyone who’s there. And while red lights may be better for your night vision, they’re particularly insidious about leaking into everyone’s frame (so before you ask, no red light!). If you follow my no flashlight rule, you’ll be amazed at how well your eyes adjust. I can operate my camera’s controls in the dark—it’s not hard with a little practice, and well worth the effort to learn. If I ever do need to see my camera to adjust something, or if I need to see to move around, my cell phone screen (not the phone’s flashlight, just its screen) gives me all the light I need.
A good Milky Way image is distinguished from an ordinary Milky Way image by its foreground. Simply finding a location that’s dark enough to see the Milky Way is difficult enough; finding a dark location that also has a foreground worthy of pairing with the Milky Way usually takes a little planning.
Since the Milky Way’s center is in the southern sky (for Northern Hemisphere observers), I look for remote (away from light pollution) subjects that I can photograph while facing south. Keep in mind that unless you have a ridiculous light gathering camera (like the Sony a7S or a7S II) and an extremely fast lens (f/2 or faster), your foreground will probably be more dark shape than detail. Water’s inherent reflectivity makes it a good foreground subject as well, especially if the water includes rocks or other features to add a little visual weight.
When I encounter a scene I deem photo worthy, not only do I try to determine its best light and moon rise/set possibilities, I also consider its potential as a Milky Way subject. Can I align it with the southern sky? Are there strong subjects that stand out against the sky? Is there any water I can include in my frame?
I’ve found views of the Grand Canyon from the North Rim, the Kilauea Caldera, and the bristlecone pines in California’s White Mountains that work spectacularly. On the other hand, while Yosemite Valley has lots to love, you don’t see a lot of Milky Way images from Yosemite Valley because there just aren’t that many south views there, and Yosemite’s towering, east/west trending granite walls give its south views an extremely high horizon that blocks much of the galactic core from the valley floor.
To maximize the amount of Milky Way in my frame, I generally (but not always) start with a vertical orientation that’s at least 2/3 sky. On the other hand, I do make sure to give myself more options with a few horizontal compositions as well. Given the near total darkness required of a Milky Way shoot, it’s often too dark to see well enough to compose that scene. If I can’t see well enough to compose I guess at a composition, take a short test exposure at an extreme (unusable) ISO to enable a relatively fast shutter speed (a few seconds), adjust the composition based on the image in the LCD, and repeat until I’m satisfied.
Needless to say, when it’s dark enough to view the Milky Way, there’s not enough light to autofocus (unless you have a rare camera/lens combo that can autofocus on a bright star and planet), or even to manually focus with confidence. And of all the things that can ruin a Milky Way image (not to mention an entire night), poor focus is number one. Not only is achieving focus difficult, it’s very easy to think you’re focused only to discover later that you just missed.
Because the Milky Way’s focus point is infinity, and you almost certainly won’t have enough light to stop down for more depth of field, your closest foreground subjects should be far enough away to be sharp when you’re wide open and focused at infinity. Before going out to shoot, find a hyperfocal app and plug in the values for your camera and lens at its widest aperture. Even though it’s technically possible to be sharp from half the hyperfocal distance to infinity, the kind of precise focus this requires is difficult to impossible in the dark, so my rule of thumb is to make sure my closest subject is no closer than the hyperfocal distance.
For example, I know with my Rokinon 24mm f/1.4 wide open on my full frame Sony a7S II, the hyperfocal distance is about 50 feet. If I have a subject that’s closer (such as a bristlecone pine), I’ll pre-focus (before dark) on the hyperfocal distance, or shine a bright light on an object at the hyperfocal distance and focus there, but generally I make sure everything is at least 50 feet away. Read more about hyperfocal focus in my Depth of Field article.
By far the number one cause of night focus misses is the idea that you can just dial any lens to infinity; followed closely by the idea that focused at one focal length means focused at all focal lengths. Because when it comes to sharpness, almost isn’t good enough, if you have a zoom lens, don’t even think of trying to dial the focus ring to the end for infinity. And even for most prime lenses, the infinity point is a little short of all the way to the end, and can vary slightly with the temperature and f-stop. If you know your lens well enough to be certain of its infinity point by feel (and are a risk taker), go for it. And that zoom lens that claims to be parfocal? While it’s possible that your zoom will hold focus throughout its entire focal range, regardless of what the manufacturer claims, I wouldn’t bet an entire shoot on it without testing first.
All this means that the only way to ensure night photography sharpness is to focus carefully on something before shooting, refocus every time your focal length changes, and check focus frequently by displaying and magnifying an image on your LCD. To simplify (there’s that word again), when using a zoom lens, I usually set the lens at its widest focal length, focus, verify, then never change the focal length again once I know I’m focused. And remember, the best way to ensure focus is to set your focal length and focus before it gets dark.
But sometimes pre-focusing isn’t possible, or for some reason you need to refocus after darkness falls. If I arrive at my destination in the dark, I autofocus on my headlights, a bright flashlight, or a laser 50 feet or more away. And again, never assume you’re sharp—always magnify your image and check it after you focus.
For more on focusing in the dark, including how to use stars to focus, read my Starlight Photo Tips article.
Exposing a Milky Way image is wonderfully simple once you realize that you don’t have to meter because you can’t (not enough light)—your goal is simply to capture as many photons as you can without damaging the image with noise, star motion, and lens flaws.
Basically, you can’t give a Milky Way image too much light. What I mean by that is, capturing the amount of light required to overexpose a Milky Way image is only possible if you’ve chosen an ISO and/or shutter speed that significantly compromises the quality of the image with excessive noise and/or star motion.
In a perfect world, I’d take every image at ISO 100 and f/8—the best ISO and f-stop for my camera and lens. But that’s not possible when photographing in near total darkness—a usable Milky Way image requires exposure compromises. What kind of compromises? Each exposure variable causes a different problem when pushed too far:
Again: My approach to metering for the Milky Way is to give my scene as much light as I can without pushing the exposure compromises to a point I can’t live with. Where exactly is that point? Not only is that a subjective question that varies with each camera body, lens, and scene, as technology improves, I’m less forgiving of exposure compromises than I once was. For example, when I started photographing the Milky Way with my Canon 1DS Mark III, the Milky Way scenes I could shoot were limited because my fastest wide lens was f/4 and I got too much noise when I pushed my ISO beyond 1600. This forced me compromise by shooting wide open with a 30-second shutter speed to achieve even marginal results. In fact, given these limitations, despite trying to photograph the Milky Way from many locations, the only foreground that worked well enough was Kilauea Caldera, because it was its own light source.
Today (early 2017) I photograph the Milky Way with a Sony a7S II and a Rokinon 24mm f/1.4 lens. I get cleaner images from my Sony at ISO 6400 than got a ISO 1600 on my Canon 1DSIII, and the light gathering capability of an f/1.4 lens revelatory. Now I can stop down slightly to reduce lens aberrations, drop my shutter speed to 20 or 15 seconds to cut star motion 33-50 percent, and still get usable foreground detail by starlight.
I can’t emphasize enough how important it is to know your camera’s and lens’s capabilities in low light, and how for you’re comfortable pushing them. For each of the night photography equipment combos I’ve used, I’ve established a general exposure upper threshold, rule-of-thumb compromise points for each exposure setting that I won’t exceed until I’ve reached the compromise threshold of the other exposure settings. For example, with my a7SII/Rokinon combo, I usually start at ISO 3200, f/2, 20 seconds. Those settings will usually get me enough light for Milky Way color and a little foreground detail. But if I want more light (for example, if I’m shooting into the black pit of the Grand Canyon from the North Rim), my first exposure compromise is to increase to ISO 6400; if I decide I need even more light, my next compromise is to open up to f/1.4; if that still isn’t enough light, my next compromise is to bump my shutter speed to 30 seconds. Finally, if I want more light that ISO 6400, f/1.4, 30 seconds delivers, I’ll try ISO 12,800 (and cross my fingers)*. If that’s not enough, I go home (or just sit and enjoy the view).
These thresholds are guidelines rather than hard-and-fast rules, and they apply to my setup only—your results may vary. And even though I’m pretty secure with this workflow, for every Milky Way composition I try a variety of exposure combinations before moving to another composition. Not only does this give me a range of options to choose between when I’m at home and reviewing my images on a big monitor, it also gives me more insight into my camera/lens capabilities, allowing me to refine my exposure compromise threshold points.
It’s time to click that shutter
You’re in position with the right gear, composed, focused, and exposure values set. Before you actually click the shutter, let me remind you of a couple of things you can do to ensure the best results: First, lower that center post. A tripod center post’s inherent instability is magnified during long exposures, not just by wind, but even by nearby footsteps, the press of the shutter button, and slap of the mirror (and sometimes it seems, by ghosts). And speaking of shutter clicks, you should be using a remote cable or two-second timer to eliminate the vibration imparted when your finger presses the shutter button.
When that first Milky Way image pops up on the LCD, it’s pretty exciting. So exciting in fact that sometimes you risk being lulled into a “Wow, this isn’t as hard as I expected” complacency. Even though you think everything’s perfect, don’t forget to review your image sharpness every few frames by displaying and magnifying and image on your LCD. In theory nothing should change unless you changed it, but in practice I’ve noticed a distinct inclination for focus to shift mysteriously between shots. Whether it’s slight temperature changes or an inadvertent nudge of the focus ring as you fumble with controls in the dark, you can file periodically checking your sharpness falls under “an ounce of prevention….” Believe me, this will save a lot of angst later.
And finally, don’t forget to play with different exposure settings for each composition. Not only does this give you more options, it also gives you more insight into your camera/lens combo’s low light capabilities.
The bottom line
Though having top-of-the-line low-light equipment helps a lot, it’s not essential. If you have a full frame DSLR that’s less than five years old, and a lens that’s f/2.8 or faster, you probably have all the equipment you need to get great the Milky Way images. Even with a cropped sensor, or an f/4 lens, you have a good chance of getting usable Milky Way images. If you’ve never done it before, don’t expect perfection the first time out. What you can expect is improvement each time you go out as you learn the limitations of your equipment and identify your own exposure compromise thresholds. And success or failure, at the very least you’ll have spent a magnificent night under the stars.
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Posted on January 26, 2017
(How many photography blogs out there quote Yogi Berra? Just sayin’….) During the 1973 baseball season, Yogi Berra was asked about his last place Mets’ chances in the pennant race. His reply, “It ain’t over till it’s over,” was greeted with chuckles, but Yogi got the last laugh when the Mets rallied to make it all the way to the World Series. I couldn’t help thinking of Yogi’s quote on my drive home Monday night with this image, my final click of the day, still fresh in my mind.
When the weatherman promised snow down to 2500 feet on Monday, I drove to Yosemite late Sunday night so I could beat sunrise and have an entire day to play. And snow I found, lots and lots of it, and still falling. The snowfall continued throughout morning, so heavy that my first few hours were limited to photographing close scenes, interspersed with lots of waiting for conditions to improve. But a little before noon the clouds started to thin and the snow became more showery and I was in business.
When the clearing started in earnest I was at Valley View (but it didn’t look anything like this). The rest of the day I spent dashing around Yosemite Valley, chasing the clouds’ parting and the light that came with it. It’s so much fun watching a storm clear in Yosemite, poised beneath Yosemite Falls or Half Dome or El Capitan, and wait for the big reveal when the clouds to pull back.
For sunset I ended up trudging through about 18 inches of virgin snow to a favorite Half Dome reflection spot by the Merced River, recently rendered much less accessible by major roadwork underway in the valley. Throughout the day I’d crossed paths several times with good friend Don Smith who had driven up for the day with our mutual friends Scott and Mike, and they eventually joined me at sunset. As we shot we shared stories of the day—for example, how they had just missed getting crushed by a falling tree (true story). After a half hour of really nice photography, a large cloud set up shop atop Half Dome right around sunset, completely obscuring the scene’s main attraction. Satisfied with a tremendous day of photography, we declared the day, “Over.”
It wasn’t until I was back at my car that fully appreciated how wet everything was—my gear, my car, and even me (a day of plunging through snowdrifts had been enough for the snow to find its way over the top my waterproof boots and underneath my waterproof outer pants). I decided I’d swing into Valley View on my way out of the valley to use the bathroom and change into drier clothes. In the back of my mind was possibility of a parting shot of El Capitan in the late, blue twilight.
The west end of Yosemite Valley gets much less winter sunlight, so while trees had already started shedding the snow on the east side (where I’d photographed sunset), I pulled in at Valley View to find virtually every exposed surface still glistening white. Bridalveil Fall and Cathedral Rocks clearly visible in the fading light, but El Capitan was cloud-shrouded from top to bottom. Still quite cold, tired, and more than a little hungry, this would have been a perfect excuse to beeline home. But the scene was so beautiful, and the light so perfect, that after changing my clothes I just sat in my car, peeled an orange, and waited for El Capitan to show itself.
I didn’t have to wait long. At the first sign of clearing I hopped out and was completely set up by the river before El Capitan appeared. Bumping my ISO to 800, I composed the standard horizontal frame with El Capitan on the left, Leaning Tower on the right, and the Merced River in the foreground. Often the most difficult thing about shooting in low light like this is finding focus, but despite the fact that it was more 30 minutes after sunset, my Sony a7RII was able to autofocus on Cathedral Rocks. I spent a several clicks refining that original composition and was about to call the day “Over” one more time when something moved me to shift my view to the right. As soon as the image popped up on my LCD I knew I was onto something. I refined for about a half dozen more frames, culminating with the one you see here, until I was satisfied that a great day truly was over.
The lesson here, one I learned many years ago but I see many photographers struggle to grasp, is that the camera can still do fantastic things long after your eyes tell you the show is over. Another satisfying reminder from this day is that it’s still possible to enjoy Yosemite in glorious peace. As someone who has seen Yosemite at its congested worst, I relish the solitude possible when I choose times that the average person (tourists, fair weather photographers) won’t venture out: miserable weather, late at night, before sunrise. The entire time I was out there at Valley View that evening I was alone, and only two cars drove by. As Yogi would say, “Nobody goes there anymore—it’s too crowded.”
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Posted on December 31, 2016
Tonight the calendar clicks over to a new year, ready or not. Most are ready. The general consensus is that 2016 has been a difficult year. Our warming planet lost too many creative souls, and was rubbed raw by contentious elections in every hemisphere. But here we are knocking on the door of 2017.
I’m lucky to have photography and the dose of perspective it provides. Whether it’s a double rainbow above the Grand Canyon, fountains of lava on Kilauea, or a meteor slicing the Milky Way above 4000-year-old trees, our terrestrial problems just seem a little less significant when I’m behind my camera.
As I review 2016’s contributions to my portfolio, I have to admit that the year wasn’t a complete loss. To me these images are so much more than photographs, they’re a reminder that I was there to witness each of these gifts from Nature.
So, without further adieu, here’s a selection of personal highlights from this emotional, transformative, contentious, unforgettable year.
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Happy New Year, everyone. Here’s to a great 2017.
Posted on August 12, 2016
My relationship with the night sky started when I was ten. Astronauts were my generation’s cowboys, so when I was given a castoff, six-inch reflector telescope by an amateur astronomer friend of my dad, I jumped at the opportunity to explore the celestial frontier on my terms. On clear nights my best friend Rob and I dragged that old black tube onto the front lawn and pointed it, randomly and full of wonder, at the brilliant points of light overhead. With guidance from our dads and the books of Herbert S. Zim, we learned the difference between stars, which despite their great size and temperature, are at such great distance that even the strongest telescope only sees discrete points of light, and planets, nearby worlds reflecting sunlight, which my telescope revealed as glowing disks.
With that telescope Rob and I searched in vain for comets and galaxies, watched Venus and Mercury cycle through phases just like the moon’s, tracked the nightly dance of Jupiter’s Galilean moons, and monitored the changing tilt of Saturn’s rings. Suddenly and hopelessly infected with the astronomy bug, on camping trips I declined the luxury of the family tent in favor of a sleeping bag beneath more stars than I imagined possible. There, nestled to my neck in the bag’s warmth, I’d stretch beneath the boundless ceiling, counting “shooting stars” and scouring the sky for satellites, fighting sleep for as long as my eyelids could hold out. In my later teen years I discovered backpacking and with it skies that inspired ponderings of infinity. My first college major was astronomy, a most impractical aspiration that I managed to correct before quantification of the universe spoiled my appreciation of its elegance.
In my early twenties I discovered photography, but, frustrated by my film camera’s inability to capture the night sky’s beauty, quickly moved on to more terrestrial subjects. Fast forward to the twenty-first century, when the advent of digital photography offered light capturing and processing capabilities impossible with film. My first night subject was the Big Dipper; since then I’ve tried to include some form of night photography in most of my workshops and as many personal shoots as possible, seeking to use my camera’s unique perspective to convey the emotion the night experience brings me, rather than attempt the impossible task of recreating the sky literally.
Among other subjects, I’ve developed a particular fondness for photographing the gold/blue transition-zone separating day and night. Arriving on location well before sunrise gives me a front-row view of the indigo night’s slow retreat in favor of the golden promise of a new day; lingering long after the sun sets, I watch the day’s vestiges linger on the horizon, as if waiting with me for the stars to materialize.
About this image
This year’s Yosemite Moonbow and Wildflowers workshop group had the good fortune to photograph Yosemite brimming with more water than I’ve seen in years. A particular highlight was this location beside the Merced River, one of my favorite early morning spots. The morning we arrived we found my normal vantage points flooded beyond recognition, but rather than let the flooding turn us around, I explored the new shoreline and found view through the trees onto a crystal clear reflection. We stayed and photographed here until bad light and empty stomachs finally drove us to breakfast.
Excited by our good fortune that morning (read The Power of Reflections), I offered to return that night with anyone who wanted to photograph the scene by moonlight. Though I already had a moonbow shoot scheduled for later in the workshop, the moonlight potential here was so great that I wanted to at least give everyone the option of photographing it (on the other hand, with such early mornings, I knew from experience that I needed to give everyone the option to return to the hotel for an early bedtime).
Despite a long drive back from our sunset at Glacier Point, about half the group still joined me for what turned out to be a very memorable moonlight shoot. The already somewhat limited space was made even more difficult by the darkness (we were shaded from the moonlight by trees and the valley wall behind us), but we made it work with great cooperation and no shortage of laughter.
Among other things, this image highlights one of the great joys of photography with today’s advanced technology: the camera’s improving ability to reveal a world previously obscured by night’s dark curtain. (It will only get better.)
Posted on August 20, 2015
How to offend a photographer
Gallery browser: “Did you take that picture?”
Gallery browser: “Wow, you must have a good camera.”
Few things irritate a photographer more than the implication that it’s the equipment that makes the image, not the photographer. We work very hard honing our craft, have spent years refining our vision, and endure extreme discomfort to get the shot. So while the observer usually means no offense, comments discounting a photographer’s skill and effort are seldom appreciated.
As much as we’d like to believe that our great images are 100 percent photographic skill, artistic vision, and hard work, a good camera sure does allow us to squeeze the most out of our skill, vision, and effort.
As a one-click shooter (no HDR or image blending of any kind), I’m constantly longing for more dynamic range and high ISO capability. So, after hearing raves about Sony sensors for several years, late last year (October 2014) I switched to Sony. My plan was a gradual transition, shooting Sony for some uses and Canon for others, but given the dynamic range and overall image quality I saw from my Sony a7R starting day one, I haven’t touched my Canon bodies since picking up the Sony.
While I don’t think my Sony cameras have made me a better photographer, I do think ten months is long enough to appreciate that I’ve captured images that would have been impossible in my Canon days. I instantly fell in love with the resolution and 2- to 3-stop dynamic range improvement of my Sony a7R (and now the a7R II) over the Canon 5D III, the compactness and extra reach of my 1.5-crop a6000 (with little loss of image quality), and my a7S’s ability to pretty much see in the dark.
But what will Sony do for my night photography?
I need more light
I visit Grand Canyon two or three times each year, and it’s a rare trip that I don’t attempt to photograph its inky dark skies. But when the sun goes down and the stars come out, Grand Canyon’s breathtaking beauty disappears into a deep, black hole. Simply put, I needed more light.
Moonlight was my first Grand Canyon night solution—I’ve enjoyed many nice moonlight shoots here, and will surely enjoy many more. But photographing Grand Canyon by the light of a full moon is a compromise that sacrifices all but the brightest stars to achieve a night scene with enough light to reveal the canyon’s towering spires, receding ridges, and layered red walls.
What about the truly dark skies? For years (with my Canon bodies) the only way to satisfactorily reveal Grand Canyon’s dark depths with one click was to leave my shutter open for 30 minutes or longer. But the cost of a long exposure is the way Earth’s rotation stretches those sparkling pinpoints into parallel arcs.
As with moonlight, I’m sure I’ll continue to enjoy star trail photography. But my ultimate goal was to cut through the opaque stillness of a clear, moonless Grand Canyon night to reveal the contents of the black abyss at my feet, the multitude of stars overhead, and the glowing heart the Milky Way.
So, ever the optimist, on each moonless visit to Grand Canyon, I’d shiver in the dark on the canyon’s rim trying to extract detail from the obscure depths without excessive digital noise or streaking stars. And each time I’d come away disappointed, thinking, I need more light.
The dynamic duo
Early this year, with night photography in mind, I added a 12 megapixel Sony a7S to my bag. Twelve megapixels is downright pedestrian in this day of 50+ megapixel sensors, but despite popular belief to the contrary, image quality has very little to do with megapixel count (in fact, for any given technology, the lower the megapixel count, the better the image quality). By subtracting photosites, Sony was able to enlarge the remaining a7S photosites into light-capturing monsters, and to give each photosite enough space that it’s not warmed by the (noise-generating) heat of its neighbors.
With the a7S, I was suddenly able to shoot at ridiculously high ISOs, extracting light from the darkest shadows with very manageable noise. Stars popped, the Milky Way throbbed, and the landscape glowed with exquisite detail. I couldn’t wait to try it at Grand Canyon.
My first attempt was from river level during this year’s Grand Canyon raft trip in May. Using my a7S and Canon-mount Zeiss 28mm f2 (after switching to Sony, I was able to continue using my Zeiss lens with the help of a Metabones IV adapter), I was immediately blown away by what I saw on my LCD, and just as excited when I viewed my captures on my monitor at home.
But I wasn’t done. Though I’d been quite pleased with my go-to dark night Zeiss lens, I wanted more. So, in my never-ending quest for more light, just before departing for the August Grand Canyon monsoon workshop, I purchased a Rokinon 24mm f1.4 to suck one more stop’s worth of photons from the opaque sky. The new lens debuted last Friday night, and I share the results here.
About this image
Don Smith and I were at Grand Canyon for our annual back-to-back monsoon workshops. On the night between workshops, Don and I photographed sunset at Cape Royal, then walked over to Angel’s Window where we ate sandwiches and waited for the Milky Way to emerge. The sky was about 80 percent clouds when the sun went down and we debated packing it in, but knowing these monsoon clouds often wane when the sun drops, we decided to stick it out.
Trying to familiarize myself with the capabilities of my new dark night lens, I photographed a handful of compositions at varying settings. To maximize the amount of Milky Way in my frame, everything oriented vertically. As with all my images, the image I share here is a single click.
Despite the moonless darkness, exposing the a7S at ISO 6400 for 20 seconds at f1.4 enabled me to fill my entire histogram from left to right (shadows through highlights) without clipping. Bringing the shadows up a little more in Lightroom revealed lots of detail with just a moderate amount of very manageable noise.
This is an exciting time indeed for photographers, as technology advances continue to push the boundaries of possibilities. Just a few years ago an image like this would have been unthinkable in a single click—I can’t wait to see what Sony comes up with yet.
Some comments on processing night images
Processing these dark sky images underscores the quandary of photography beyond the threshold of human vision—no one is really sure how it’s supposed to look. We’re starting to see lots of night sky images from other photographers, including many featuring the Milky Way, and the color is all over the map. Our eyes simply can’t see color with such little light, but a long exposure and/or fast lens and high ISO shows that it’s still there—it’s up to the photographer to infer a hue.
So what color should a night scene be? It’s important to understand that an object’s color is more than just a fixed function of an inherent characteristic of that object, it varies with the light illuminating it. I can’t speak for other photographers, but I try to imagine how the scene would look if my eyes could capture as much light as my camera does.
To me a scene with blue cast is more night-like than the warmer tones I see in many night images (they look like daylight with stars), so I start by cooling the color temperature below 4,000 degrees in Lightroom. The purplish canyon and blue sky in this image is simply the result of the amount of light I captured, Grand Canyon’s naturally red walls, and me cooling the image’s overall color temperature in Lightroom. For credibility, I actually decided to desaturate the result slightly. (The yellow glow on the horizon is the lights of Flagstaff and Williams, burned and desaturated in Photoshop.)
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Posted on October 12, 2014
So what’s happening here? The orange glow at the bottom of this frame is light from 1,800° F lava bubbling in Halemaʻumaʻu Crater inside Hawaii’s Kilauea Caldera, reflecting off a low-hanging bank of clouds. The white band above the crater is light cast by billions of stars at the center our Milky Way galaxy. So dense and distant are the stars here, their individual points are lost to the surrounding glow. Partially obscuring the Milky Way’s glow are large swaths of interstellar dust, the leftovers of stellar explosions and the stuff of future stars. Completing the scene are stars in our own neighborhood of the Milky Way, stars close enough that we see them as discrete points of light that we imagine into mythical shapes—the constellations.
The Milky Way galaxy is home to every single star we see when we look up at night, and 300 billion more we can’t see—that’s nearly 50 stars for every man, woman, and child on Earth. Our Sun, the central cog in the solar system that includes Earth and the other planets wandering our night sky, is a minor player in a spiral arm near the outskirts of the Milky Way. But before you get too impressed with the size of the Milky Way, consider that it’s just one of 500 billion or so galaxies in the known Universe—that’s right, there are more galaxies in the Universe than stars in our galaxy.
Everything we see is the product of light—light created by the object itself (like the stars), or created elsewhere and reflected (like the planets). Light travels incredibly fast, fast enough that it can span even the two most distant points on Earth faster than humans can perceive, fast enough that we consider it instantaneous. But distances in space are so great that we don’t measure them in terrestrial units of distance like miles or kilometers. Instead, we measure interstellar distance by the time it takes for a beam of light to travel between two objects—one light-year is the distance light travels in one year.
The ramifications of cosmic distance are mind-bending. Imagine an Earth-like planet revolving the star closest to our solar system, about four light-years away. If we had a telescope with enough resolving power to see all the way down to the planet’s surface, we’d be watching that planet’s activity from four years ago. Likewise, if someone on that planet today (in 2014) were watching us, they’d see Lindsey Vonn claiming the gold in the Women’s Downhill at the Vancouver Winter Olympics, and maybe learn about the unfolding WikiLeaks scandal.
In this image, the caldera’s proximity makes it about as “right now” as anything in our Universe can be—the caldera and I are sharing the same instant in time. On the other hand, the light from the stars above the caldera is tens, hundreds, or thousands of years old—it’s new to me, but to the stars it’s old history. Not only that, every point of starlight here is a version of that star created in a different instant in time. It’s possible for the actual distance separating two stars to be so great, that we see light from the younger star that’s older than the light from the older star.
So what’s the point of all this mind bending? Perspective. It’s easy (essential?) for humans to overlook our place in this larger Universe as we negotiate the family, friends, work, play, eat, and sleep that defines our very own personal universes. I doubt we could cope otherwise. But when I start taking my life too seriously, it helps to appreciate my place in the larger Universe. Nothing does that better for me than quality time with the night sky.
About this image
My 2014 Hawaii Big Island photo workshop group made three trips to photograph the Kilauea Caldera beneath the Milky Way. On the first night we got a lot of clouds, with a handful of stars above, and just a little bit of Milky Way. Nice, but not the full Milky Way everyone hoped for. So I brought everyone back a couple nights later—this time we got about ten minutes of quality Milky Way photography before the clouds closed in. The following night we gave the caldera one more shot and were completely shut out by clouds. Such is the nature of night photography in general, and on Hawaii in particular. This image is from our second visit.
My concern that night was making sure everyone was successful, ASAP. I started with a test exposure to determine the exposure settings that would work best for that night (not only does each night’s ambient light vary with the volcanic haze, cloud cover, and airborne moisture, the caldera’s brightness varies daily too). Once I got the exposure down and called it out to the group, most of my time was spent helping people find and check their focus, and refine their compositions (“More sky! More sky!”). Bouncing around in the dark, I’d occasionally stop at my camera long enough to fire a frame, never staying long enough to see the image pop up on the LCD. I ended up with a half dozen or so frames, including this one from early in the shoot.
Click an image for a larger view, and to enjoy the slide show
Posted on September 16, 2014
September 16, 2014
It’s easy to envy residents of Hawaii’s Big Island—they enjoy some of the cleanest air and darkest skies on Earth, their soothing ocean breezes ensure that the always warm daytime highs remain quite comfortable, and the bathtub-warm Pacific keeps overnight lows from straying far from the 70-degree mark. Scenery here is a postcard-perfect mix of symmetrical volcanoes, lush rain forests, swaying palms, and lapping surf. I mean, with all this perfection, what could possibly go wrong?
Well, let me tell you….
Last month Tropical Storm Iselle, just a few hours removed from hurricane status, slammed Hawaii’s Puna Coast with tree-snapping winds and frog-drowning rain that cut electricity, flooded roads, and disrupted many lives for weeks. Touring the area in and around Hilo, it’s easy to appreciate Hawaiian resilience—thanks to quick action, hard work, and continuous smiles, most visitors would find it difficult to believe what happened here just a month ago. But on the drive south of Hilo along the Puna Coast, I witnessed firsthand Iselle’s power in its aftermath. There beaches have been rearranged beyond recognition and entire forests have been leveled.
But despite its impact, Iselle is already old news. This month residents of Hawaii’s Puna region have done a 180, turning their always vigilant eyes away from the ocean and toward the volcano. In late June Kilauea’s Pu`u `O`o Crater dispatched a river of lava down the volcano’s southeast flank. Since Pu`u `O`o has been erupting continuously since 1983, this latest incursion didn’t initially raise many eyebrows. But the flow has persisted, advancing now at about 250 yards per day. While this isn’t “Run-for-your life!” speed, it’s more like high stakes water torture because there’s very little that can be done to stop, slow, or even deflect the lava’s inexorable march. Residents of the communities of Kaohe and Pahoa can do nothing but watch, pray, and prepare—if the volcano persists, they’re wiped out. Not only that, the lava flow also threatens the Pahoa Highway, currently the only route in and out for the thousands of residents of the Puna region.
Recent reports of increased activity on Muana Loa have also notched up the anxiety. Lava from its last eruption, in 1984, threatened Hawaii’s capital, Hilo, before petering out with just a few miles to spare. Because Muana Loa eruptions tend to be larger and more explosive than Kilauea eruptions, any increased activity there is taken very seriously.
Had enough? Well, there’s more thing: With its funnel-shaped bay and bullseye placement in the Pacific Ring of Fire, Hilo is generally considered the most tsunami vulnerable city in the world. Fatal tsunamis have struck the Big Island in 1837, 1868, 1877, 1923, 1946, 1960, and 1975. Yesterday my photo workshop group photographed sunrise at Laupahoehoe Point, where damage from the most deadly tsunami to strike American soil is still visible. That tsunami, in 1946 (before Hawaii became a state), traveled 2,500 miles from the Aleutian Islands to kill 159 Hawaiians, including 20 schoolchildren and 4 teachers in Laupahoehoe.
Despite this shopping list of threats and hardship, I don’t get the sense the Hawaiians want sympathy. Despite the unknown but potentially devastating consequences facing them, both imminent and potential, no one here is feeling sorry for themselves. There’s much talk about the current lava flow that will directly or indirectly impact every resident of the Big Island’s Hilo side, but no hand-wringing—life goes on and smiles abound. Indeed, everyone here seems to have sprung into action in one way or another, shoring up old long abandoned roads (the jungle claims anything left unattended with frightening speed), helping people move possessions to safe ground, offering temporary shelter, and whatever else might help.
The Aloha spirit is alive and well, and I have no doubt that it will persevere in the face of whatever adversity Nature throws at them.
About this image
My Hawaii photo workshop began Monday afternoon, but my brother and I arrived on the Big Island on Friday because I hate doing any workshop without first running all my locations to make sure there are no surprises. And this time it turned out to be a wise move—not only did I get a couple of extra days in paradise, I did indeed encounter surprises, courtesy of Iselle, when I discovered two of my go-to locations rendered inaccessible by storm damage. I spent Saturday searching for alternatives and by Saturday’s end had a couple of great substitute spots. That night we celebrated with a night shoot on Kilauea. (I was going to visit Kilauea anyway, but if I’d still been stressing about my locations, I probably wouldn’t have been in the right mindset to photograph.)
We arrived to find the Milky Way glowing brightly above the caldera and immediately started shooting. Because I don’t have as many horizontal compositions of the caldera as vertical, I started horizontal. By the time I’d captured a half dozen or so frames, a heavy mist dropped into the caldera to quickly obscure the entire view (one more example of our utter helplessness to the whims of Nature).
In this frame I went quite wide, not only to capture as much of the Milky Way as possible, but also to include all of the thin cloud layer painted orange by the light of the caldera’s fire. This is a single click (no blending of multiple images), though I did clone just a little bit of color back into the hopelessly blown center of the volcano’s flame.
Click and image for a larger view, and to enjoy the slide slow | 0.911792 | 3.093175 |
I love this photo, because it shows that Mars is a lively place with wind and water. These dunes near the north pole, occupying a region the size of Texas, have been sculpted by wind into long lines with crests 500 meters apart. Their hollows are covered with frost, which appears bluish-white in this infrared photograph. The big white spot near the bottom is a hill 100 meters high.
For more info, go here:
• THEMIS, North polar sand sea.
If you download the full-sized version of this photo, either by clicking on my picture or going to this webpage, you’ll see it’s astoundingly detailed!
THEMIS is the Thermal Emission Imaging System aboard the Mars Odyssey spacecraft, which has been orbiting Mars since 2002. It combines a 5-wavelength visual imaging system with a 9-wavelength infrared imaging system. It’s been taking great pictures—especially of regions that are too rugged for rovers like Opportunity, Spirit and Curiosity.
Because those rovers landed in places that were chosen to be safe, the pictures they take sometimes make Mars look… well, a bit dull. It’s not!
Let me show you what I mean.
These are barchans on Mars, C-shaped sand dunes that slowly move through the desert like this:
And see the dark fuzzy stuff? More on that later!
Barchans are also found on Earth, and surely on many other planets across the Universe. They’re one of several basic dune patterns—an inevitable consequence of the laws of nature under fairly common conditions.
Sand gradually accumulates on the upwind side of a barchan. Then it falls down the other side, called the ‘slip face’. The upwind slope is gentle, while the slope of the slip face is the angle of repose for sand: the maximum angle it can tolerate before it starts slipping down. On Earth that’s between 32 and 34 degrees.
Puzzle: What is the angle of repose of sand on Mars? Does the weaker pull of gravity let sandpiles be steeper? Or are they just as steep as on Earth?
Barchans gradually migrate in the direction of the wind, with small barchans moving faster than big ones. And when barchans collide, the smaller ones pass right through the big ones! So, they’re a bit like what physicists call solitons: waves that maintain their identity like particles. However, they display more complicated behaviors.
This simulation shows what can happen when two collide:
Depending on the parameters, they can:
c: coalesce into one barchan,
b: breed to form more barchans,
bu: bud, with the smaller one splitting in two, or
s: act like solitons, with one going right through the other!
This picture is from here:
• Orencio Durán, Veit Schwámmle and Hans J. Herrmann, Simulations of binary collisions of barchan dunes: the collision dynamics and its influence on the dune size distribution.
In this picture there is no ‘offset’ between the colliding barchans: they hit head-on. With an offset, more complicated things can happen – check out this picture:
It may seem surprising that there’s enough wind on Mars to create dunes. After all, the air pressure there is about 1% what it is here on Earth! But in fact the wind speed on Mars often exceeds 200 kilometers per hour, with gusts up to 600 kilometers per hour. There are dust storms on Mars so big they were first seen from telescopes on Earth long ago. So, wind is a big factor in Martian geology:
The Mars rover Spirit even got its solar panels cleaned by some dust devils, and it took some movies of them:
This picture shows a dune field less than 400 kilometers from the north pole, bordered on both sides by flat regions—but also a big cliff at one end.
Here’s a closeup of those dunes… with stands of trees on top?!?
No, that’s an optical illusion. But whatever it is, it’s something strange. Robert Krulwich put it nicely:
They were first seen in 1998; they don’t look like anything we have here on Earth. To this day, no one is sure what they are, but we now know this: They come, then they go. Every Martian spring, they appear out of nowhere, showing up—70 percent of the time—where they were the year before. They pop up suddenly, sometimes overnight. When winter comes, they vanish.
In 2010, astronomer Candy Hansen tried to explain what’s going on, writing:
There is a vast region of sand dunes at high northern latitudes on Mars. In the winter, a layer of carbon dioxide ice covers the dunes, and in the spring as the sun warms the ice it evaporates. This is a very active process, and sand dislodged from the crests of the dunes cascades down, forming dark streaks.
She focused our attention on this piece of the image:
and she wrote:
In the subimage falling material has kicked up a small cloud of dust. The color of the ice surrounding adjacent streaks of material suggests that dust has settled on the ice at the bottom after similar events.
Also discernible in this subimage are polygonal cracks in the ice on the dunes (the cracks disappear when the ice is gone).
More recently, though, scientists have suggested that geysers are involved in this process, which might make it very active indeed!
Geysers formed as frozen carbon dioxide turns to gas, shooting out clumps of dark, basaltic sand, which slide down the dunes… that’s the most popular explanation. But maybe they’re colonies of photosynthetic Martian microorganisms soaking up the sunlight! Or maybe geysers are shooting up dark stuff that’s organic matter formed by some biological process. A bunch form right around sunrise, so something is being rapidly triggered by the sun.
This has some nice prose and awesome pictures:
• Robert Krulwich, Are those spidery black things on Mars dangerous? (maybe), Krulwich Wonders, National Public Radio, 3 October 2012.
The big picture above, and Candy Hansen’s explanation, can be found here:
HiRiSE, which stands for High Resolution Imaging Science Experiments, is a project based in Arizona that’s created an amazing website full of great Mars photos. For more clues, try this:
• Martian geyser, Wikipedia.
What’s going on in this region of Mars?
Candy Hansen writes:
There is an enigmatic region near the south pole of Mars known as the “cryptic” terrain. It stays cold in the spring, even as its albedo darkens and the sun rises in the sky.
This region is covered by a layer of translucent seasonal carbon dioxide ice that warms and evaporates from below. As carbon dioxide gas escapes from below the slab of seasonal ice it scours dust from the surface. The gas vents to the surface, where the dust is carried downwind by the prevailing wind.
The channels carved by the escaping gas are often radially organized and are known informally as “spiders.”
This is from:
• HiRISE, Cryptic terrain on Mars.
Here’s ice in a crater in the northern plains on Mars—the region with the wonderful name Vastitas Borealis:
Many scientists believe this huge plain was an ocean during the Hesperian Epoch, a period of Martian history that stretches from about 3.5 to about 1.8 billion years ago. Later, around the end of the Hesperian, they think about 30% of the water on Mars evaporated and left the atmosphere, drifting off into outer space… part of the danger of life on a planet without much gravity. The oceans then froze. Most of them slowly sublimated, disappearing into water vapor without ever melting. This water vapor was also lost to outer space.
• Linda M. V. Martel, Ancient floodwaters and seas on Mars.
But there’s still a lot of water left, especially in the polar ice caps. The north pole has an ice cap with 820,000 cubic kilometers of ice! That’s equal to 30% of the Earth’s Greenland ice sheet—enough to cover the whole surface of Mars to a depth of 5.6 meters if it melted, if we pretend Mars is flat.
And the south pole is covered by a slab of ice about 3 kilometers thick, a mixture of 85% carbon dioxide ice and 15% water ice, surrounded by steep slopes made almost entirely of water ice. This has enough water that if it melted it would cover the whole surface to a depth of 11 meters!
There’s also lots of permafrost underground, and frost on the surface, and bits of ice like this. The picture above was taken by the Mars Express satellite:
The image is close to natural color, but the vertical relief is exaggerated by a factor of 3. The crater is 35 kilometers wide and 2 kilometers deep. It’s incredible how they can get this kind of picture from satellite photos and lots of clever image processing. I hope they didn’t do too much stuff just to make it look pretty.
Here is the north pole of Mars:
As in Antarctica and Greenland, cold dense air flows downwards off the polar ice cap, creating intense winds called katabatic winds. These pick up and redeposit surface ice to make grooves in the ice. The swirly pattern comes from the Coriolis effect: while the winds are blowing more or less straight, Mars is turning around its pole, so they seem to swerve.
As you can see, the north polar ice cap has a huge canyon running through it, called Chasma Boreale:
Here’s an amazing picture of what it’d be like to stand near the head of this chasm:
Click to enlarge this—it deserves to be bigger! Here’s the story:
Climatic cycles of ice and dust built the Martian polar caps, season by season, year by year—and then whittled down their size when the climate changed. Here we are looking at the head of Chasma Boreale, a canyon that reaches 570 kilometers (350 miles) into the north polar cap. Canyon walls rise about 1,400 meters (4,600 feet) above the floor. Where the edge of the ice cap has retreated, sheets of sand are emerging that accumulated during earlier ice-free climatic cycles. Winds blowing off the ice have pushed loose sand into dunes, then driven them down-canyon in a westward direction, toward our viewpoint.
The above picture was cleverly created using photos from THEMIS. The vertical scale has been exaggerated by a factor of 2.5, I’m sad to say. You can download a 9-megabyte version from here:
• THEMIS, Chasma Boreale and the north polar ice cap.
and you can see an actual photo of this same canyon here:
• THEMIS, Dunes and ice in Chasma Boreale.
It’s beautifully detailed; here’s a miniature version:
and a sub-image that shows the layers of ice and sand:
Scientists are studying these layers in the ice cap to see if they match computer simulations of the climate of Mars. Just as the Earth’s orbit goes through changes called Milankovitch cycles, so does the orbit of Mars. These affect the climate: for example, when the tilt is big the tropics become colder, and polar ice migrates toward the equator. I don’t know much about this, despite my interest in Milankovitch cycles. What’s a good place to start learning more?
Here’s a closer view of icy dunes near the North pole:
As we’ve seen, Mars is a beautiful world, but a world in a minor key, a world whose glory days—the Hesperian Epoch—are long gone, whose once grand oceans are now reduced to windy canyons, icy dunes, and the massive ice caps of the poles. Let’s say goodbye to it for now… leaving off with this Martian sunset, photographed by the rover Spirit in Gusev Crater on May 19th, 2005.
• NASA Mars Exploration Rover Mission, A moment frozen in time.
This Panoramic Camera (Pancam) mosaic was taken around 6:07 in the evening of the rover’s 489th martian day, or sol. Spirit was commanded to stay awake briefly after sending that sol’s data to the Mars Odyssey orbiter just before sunset. This small panorama of the western sky was obtained using Pancam’s 750-nanometer, 530-nanometer and 430-nanometer color filters. This filter combination allows false color images to be generated that are similar to what a human would see, but with the colors slightly exaggerated. In this image, the bluish glow in the sky above the Sun would be visible to us if we were there, but an artifact of the Pancam’s infrared imaging capabilities is that with this filter combination the redness of the sky farther from the sunset is exaggerated compared to the daytime colors of the martian sky.
Because Mars is farther from the Sun than the Earth is, the Sun appears only about two-thirds the size that it appears in a sunset seen from the Earth. The terrain in the foreground is the rock outcrop “Jibsheet”, a feature that Spirit has been investigating for several weeks (rover tracks are dimly visible leading up to Jibsheet). The floor of Gusev crater is visible in the distance, and the Sun is setting behind the wall of Gusev some 80 km (50 miles) in the distance.
This mosaic is yet another example from MER of a beautiful, sublime martian scene that also captures some important scientific information. Specifically, sunset and twilight images are occasionally acquired by the science team to determine how high into the atmosphere the martian dust extends, and to look for dust or ice clouds. Other images have shown that the twilight glow remains visible, but increasingly fainter, for up to two hours before sunrise or after sunset. The long martian twilight (compared to Earth’s) is caused by sunlight scattered around to the night side of the planet by abundant high altitude dust. Similar long twilights or extra-colorful sunrises and sunsets sometimes occur on Earth when tiny dust grains that are erupted from powerful volcanoes scatter light high in the atmosphere. | 0.822103 | 3.750529 |
Charles Messier was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and faint star clusters, which came to be known as the Messier objects; the purpose of the catalogue was to help astronomical observers, in particular comet hunters like himself, distinguish between permanent and transient visually diffuse objects in the sky. Messier was born in Badonviller in the Lorraine region of France, the tenth of twelve children of Françoise B. Grandblaise and Nicolas Messier, a Court usher. Six of his brothers and sisters died while young, his father died in 1741. Charles' interest in astronomy was stimulated by the appearance of the great six-tailed comet in 1744 and by an annular solar eclipse visible from his hometown on 25 July 1748. In 1751 Messier entered the employ of Joseph Nicolas Delisle, the astronomer of the French Navy, who instructed him to keep careful records of his observations. Messier's first documented observation was that of the Mercury transit of 6 May 1753, followed by his observations journals at Cluny Hotel and at the French Navy observatories.
In 1764, Messier was made a fellow of the Royal Society. Messier discovered 13 comets: C/1760 B1 c/2760 C/1763 S1 C/1764 A1 C/1766 E1 C/1769 P1 D/1770 L1 C/1771 G1 C/1773 T1 C/1780 U2 C/1788 W1 C/1793 S2 C/1798 G1 C/1785 A1 He co-discovered Comet C/1801 N1, a discovery shared with several other observers including Pons, Méchain, Bouvard. Near the end of his life, Messier self-published a booklet connecting the great comet of 1769 to the birth of Napoleon, in power at the time of publishing. According to Meyer: As hard as it may seem to accept, the memoir is an ingratiation to Napoleon in order to receive attention and monetary support, it is full of opportunism. Messier did not refrain from utilizing astrology to reach his goal. Messier comes to the point on the first page of the memoir, by stating that the beginning of the epoch of Napoleon the Great... coincides with the discovery of one of the greatest comets observed. Messier is buried in Père Lachaise Cemetery, Paris, in Section 11; the grave is faintly inscribed, is near the grave of Frédéric Chopin to the west and directly north, behind the small mausoleum of the jeweller Abraham-Louis Breguet.
Messier's occupation as a comet hunter led him to continually come across fixed diffuse objects in the night sky which could be mistaken for comets. He compiled a list of them, in collaboration with his friend and assistant Pierre Méchain, to avoid wasting time sorting them out from the comets they were looking for; the entries are now known to be 39 galaxies, 4 planetary nebulae, 7 other types of nebulae, 55 star clusters. Messier did his observing with a 100 mm refracting telescope from Hôtel de Cluny, in downtown Paris, France; the list he compiled only contains objects found in the area of the sky Messier could observe, from the north celestial pole to a declination of about −35.7°. They are not organized scientifically by location; the first version of Messier's catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris. In addition to his own discoveries, this version included objects observed by other astronomers, with only 17 of the 45 objects being Messier's.
By 1780 the catalog had increased to 80 objects. The final version of the catalogue was published in 1781, in the 1784 issue of Connaissance des Temps; the final list of Messier objects had grown to 103. On several occasions between 1921 and 1966, astronomers and historians discovered evidence of another seven objects that were observed either by Messier or by Méchain, shortly after the final version was published; these seven objects, M 104 through M 110, are accepted by astronomers as "official" Messier objects. The objects' Messier designations, from M 1 to M 110, are still used by professional and amateur astronomers today and their relative brightness makes them popular objects in the amateur astronomical community; the lunar crater Messier and the asteroid 7359 Messier were named in his honor. Deep-sky object List of Messier objects Messier object Messier marathon Caldwell catalogue O'Meara, Stephen James. Deep Sky Companions: The Messier Objects. Cambridge University Press. "Charles Messier biography".
Students for the Exploration and Development of Space. Retrieved 1 July 2007. Zander, Jon. "Short biography of Charles Messier and history of the Messier Object Catalog". OurDarkSkies.com. Retrieved 1 July 2007. Brake, Mark. "Life of a Comet Hunter: Messier and Astrobiology". Astrobiology Magazine. Retrieved 1 July 2007. "Interactive Messier Catalog". Greenhawk Observatory. "Amateur Photos of Charles Messier Objects". "Messier biography". Messier.seds.org. "Messier marathon". Attempts to find as many Messier objects as possible in one night "Revisions of the New General Catalog and Index Catalog". Archived from the original on 27 February 2010. Retrieved 1 July 2007. NGC/IC Project is a collaborative effort between professional and amateur astronomers to identify all of the original NGC and IC objects, such that the identity of each of the NGC and IC objects is known with as much certainty as we can reasonably bring to it from the existing historical record. "Clickable table of Messier
Terror Inc. was an American comic-book horror series from Marvel Comics starring the antihero Terror, an eternal entity that absorbs the talents of others through their dismembered limbs. He was created by writers Dan Chichester and Margaret Clark and artist Klaus Janson as the villain Shreck in St. George #2, from Marvel's Epic Comics imprint. Terror was created for Marvel's Epic Comics line as part of writer Dan Chichester's Shadowline Saga of three interconnected titles. There were no superheroes in this world, but rather powerful, ageless beings known as "Shadows". In St. George #2, Chichester and co-writer Margaret Clark introduced a green-skinned killer who acted as the enforcer for the Ravenscore crime family, one of the books' recurring villains. According to Chichester, Marvel contacted him about bringing Shreck from the Shadowline books into the mainstream Marvel Universe to serve as a platform for reinventing and reintroducing the company's 1970s horror characters, such as Werewolf by Night and Morbius, the Living Vampire, but subsequent publishing plans changed directions.
The series Terror, Inc. was set for 15 issues but only ran for 13 issues, cover-dated July 1992 to July 1993. Terror next appeared in 2006's "League of Losers" storyline in Marvel Team-Up. Terror, Inc. editor Marc McLaurin maintained that Terror are two different characters. Writer Dan Chichester said, "Shreck was Terror and Terror was Shreck... but for the fact that Terror got to develop more of a back story as time went on"The comic books themselves gave no confirmation either way. The canonical Official Handbook of the Marvel Universe Horror 2005 confirmed that the two were in fact the same being. At some point in the distant past, a tribe of early humans hunted and fought a demon, preying upon them; the demon resembled a green bear, with a series of long, thin spikes protruding from its face and along its spine. The man who killed the bear was cursed by victory to assume the demon's form - his skin took on its green, decaying form, the spikes from its face appeared on his, he gained the beast's ability to merge the limbs of others with his own body, but was shunned by the tribe he had helped to protect.
Over the years, he adopted names that reflected people's reaction to him, by the Dark Ages he had adapted the Germanic "Schreck" as his name. At that point looking human, Shreck was the squire to a powerful Shadow, calling himself Draghignazzo. Gravely injured in battle, Draghignazzo had Shreck bury him to create the illusion that he was dead, so he could heal in peace - a process that would take centuries. In the meantime, Shreck became a full knight, fighting side-by-side with a woman he loved and who, loved him back, she soon died and Shreck had her left hand encased in metal and hermetically sealed so that he might remember her touch forever, the one part of his amalgamated body that would never decay. Shreck's activities from that time until the mid-1980s are unknown, but when he was next seen, he had been serving for several years as the enforcer for the Ravenscore crime family. During an argument, Eric Ravenscore blasted off one of Ripley Weaver's metal hands, which Shreck collected for use.
In Turkey, Shreck was found by two drug dealers, in a confrontation with the heroic Michael Devlin, knight in the order of St. George. Taking one of the dealers' eyes for his own, Shreck recognized Devlin, sought to prevent him from leaving Turkey, he crashed an airplane on the runway at the Turkish airport. The two fought and, with help from his traveling companions, Devlin won. Shreck's legs were chained to one car of the train, uncoupled. Determined to follow Devlin, he grabbed the rail of the next car forward, but the mass and momentum of the separating cars tore his legs off. Shreck survived, of course, but now held a personal grudge against Devlin, rather than the cold, impersonal "just business" attitude he displayed toward most of his victims. Shreck informed the Ravenscores that he would be leaving their employ temporarily, until he had taken his revenge on Devlin. By this time, Draghignazzo was posing as the superhero Dr. Zero. Shreck was denied. Tracking Devlin to Nicaragua, Shreck managed to get the best of him after a protracted brawl proceeded to crucify the man to a tree - he did not have permission to kill Devlin, but he could let him die.
Devlin freed himself and ambushed Shreck, continuing their fight. The pair tumbled over a waterfall, but the battle was only decided when Devlin dumped Shreck in a lake, teeming with piranhas, he offered Shreck his hand, but when it became obvious the killer was taking that he let go, Shreck sank to the bottom. Hours after the fish had departed, scavengers found Shreck's skeleton and prepared to remove the gold fillings in his teeth. Despite the massive damage he'd incurred, Shreck was still alive, rebuilt his body from the men who had found him, it was some time after this that Shreck journeyed through unknown means to Earth-616 and set himself up as the mercenary assassin Terror. He had an unspecified history with a "long-standing series of markers" between them. Terror turned over Mikal Drakonmegas to his demonic father, Beelzeboul, in return for Beelzeboul's contract with Roger Barbatos which had protected Barbatos from Terror's previous attempts to assassinate him. Terror turned against save Drakonmegas.
He destroyed the contract. Terror first appeared as part of the "modern" Marvel Universe w
The United Nations Educational and Cultural Organization World Heritage Sites are places of importance to cultural or natural heritage as described in the UNESCO World Heritage Convention, established in 1972. Iran accepted the convention on 26 February 1975, making its historical sites eligible for inclusion on the list; as of 2019, twenty-four sites in Iran are included. The first three sites in Iran, Meidan Emam, Isfahan and Tchogha Zanbil, were inscribed on the list at the 3rd Session of the World Heritage Committee, held in Paris, France in 1979, they remained the Islamic Republic's only listed properties until 2003, when Takht-e Soleyman was added to the list. The latest addition was the Hyrcanian forests, inscribed in 2019. In addition to its inscribed sites, Iran lists more than 50 properties on its tentative list. Site. If available, the size of the buffer zone has been noted as well. A lack of value implies. Nominations for the World Heritage list are only accepted if the site was listed on the tentative list.
As of February 2018, Iran lists fifty-six properties on its tentative list | 0.918326 | 3.328349 |
Table Of Contents: The Outer Planets
1. What Are the Outer Planets?
The outer planets beyond Mars are the gas giant planets, Jupiter, Saturn, Uranus and Neptune. They are also known as the Jovian planets. These planets are much larger and spaced further apart than the inner planets. They are primarily composed of hydrogen and helium.
Jupiter, the fifth planet from the Sun, is the largest planet in the solar system. Although primarily composed of gases, its magnetic field indicates that it may have a rocky core. It has a giant red spot that is actually an enormous storm in its atmosphere. There are 64 known moons that orbit Jupiter.
Saturn, the sixth planet from the Sun, is the second largest planet in the solar system. Winds can blow as fast as 1,800 km on this planet. Saturn's rings are primarily composed of ice particles with some dust and rock particles mixed in. There are 62 known moons that orbit Saturn.
Uranus, the seventh planet from the Sun, is the first planet to be discovered with the use of a telescope. Its cloudy atmosphere is primarily made of helium and hydrogen, but also has higher concentrations of frozen ammonia, water and methane. Uranus is sometimes referred to as an ice giant. This planet has two sets of rings and 27 known orbiting moons.
5. Rotation and Tilt of Uranus
Similar to Venus, Uranus spins on its axis in a clockwise direction, called retrograde rotation. It also has a rotation axis that is tilted almost parallel to its orbital plane. This makes it appear that Uranus is rotating on its side.
Neptune is the furthest planet from the Sun. This gas giant is similar to Uranus in that it has a higher amount of frozen gases like methane, water and ammonia, and therefore it is also called an ice giant. The highest known wind speeds in the solar system, measuring up to 2,100 kilometers per hour, are found on Neptune. Thirteen moons orbit Neptune. | 0.850131 | 3.112713 |
There’s a new concept in the works regarding the evolution of galactic arms and how they move across the structure of spiral galaxies. Robert Grand, a postgraduate student at University College London’s Mullard Space Science Laboratory, used new computer modeling to suggest that these signature features of spiral galaxies – including our own Milky Way – evolve in different ways than previously thought.
The currently accepted theory is as spiral galaxies rotate, the “arms” are actually transient structures that move across the flattened disc of stars surrounding the galactic bulge, yet don’t directly affect the movement of the individual stars themselves. This would work in much the same way as a “wave” goes across a crowd at a stadium event. The wave moves, but the individual people do not move along with it – rather, they stay seated after it has passed.
However when Grand researched this suggested motion using computer models of galaxies, he and his colleagues found that this was not what tended to happen. Instead the stars actually moved along with the arms, rather than maintaining their positions.
Also it was observed in these models that the arms themselves are not permanent features, but rather break up and reform over the course of 80 to 100 million years. Grand suggests that this may be due to the powerful gravitational shear forces generated by the spinning of the galaxy.
“We simulated the evolution of spiral arms for a galaxy with five million stars over a period of 6 billion years. We found that stars are able to migrate much more efficiently than anyone previously thought. The stars are trapped and move along the arm by their gravitational influence, but we think that eventually the arm breaks up due to the shear forces.”
– Robert Grand
The computer models also showed that the stars along the leading edge of the arms tended to move inwards toward the galactic center while the stars lining the trailing ends were carried to the outer edge of the galaxy.
Since it takes hundreds of millions of years for a spiral galaxy to complete even just one single rotation, observing their evolution and morphology is impossible to do in real time. Researchers like Grand and his simulations are key to our eventual understanding of how these islands of stars formed and continue to shape themselves into the vast, varied structures we see today.
“This research has many potential implications for future observational astronomy, like the European Space Agency’s next corner stone mission, Gaia, which MSSL is also heavily involved in. As well as helping us understand the evolution of our own galaxy, it may have applications for regions of star formation.”
– Robert Grand
The results were presented at the Royal Astronomical Society’s National Astronomy Meeting in Wales on April 20. Read the press release on the Royal Astronomical Society’s website here.
Top image: M81, a spiral galaxy similar to our own Milky Way, is one of the brightest galaxies that can be seen from Earth. The spiral arms wind all the way down into the nucleus and are made up of young, bluish, hot stars formed in the past few million years, while the central bulge contains older, redder stars. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA) | 0.849093 | 4.025744 |
Dubai: The UAE’s Hope Probe to Mars will monitor the Martian atmosphere for a year to help scientists not only understand the weather but also how Mars has lost some of its atmosphere over billions of years of planetary history.
These revelations came in an article on Space.com shared via the Dubai Media Office on twitter on Monday.
In it, the article stated that the UAE could become the fourth or fifth country to orbit Mars next February if all goes well with this summer’s launch, but insight into the real mission behind the mission is what is new.
“We’re not there just to declare arrival to Mars,” said Sarah Al Amiri, science lead for the mission and the UAE’s minister of state for advanced sciences. “It doesn’t really make sense to call it planetary exploration and just make it about technology demonstration and about arrival.”
“There was a large gap in the complete understanding of the atmosphere of Mars,” she added. “We don’t have a full understanding of the weather system of Mars throughout an entire year.”
‘Previous and current missions have gathered observations of the Martian weather, but only a couple of times throughout a day, Al Amiri said. These measurements have often come from surface missions and so are quite limited geographically. Weather is too complex and interconnected for scientists to really get a handle on how it works from such piecemeal data,’ read the article.
So, Hope aims to monitor what’s happening in the Martian atmosphere for a full local year, including making connections between layers of the atmosphere. That will help scientists understand not only Martian weather, but also how Mars has lost some of its atmosphere over billions of years of planetary history.
“That science was a sweet spot for us,” Al Amiri said. “You’re complementary to other current missions, so you maximise the benefit that scientists are going to get globally from this mission, because it feeds into the current areas of research and expands on human knowledge as a whole.”
‘The goal of integrating data collected across layers of the Martian atmosphere means that Hope’s three instruments — a camera sensitive to optical and ultraviolet wavelengths and spectrometers tuned to infrared and to ultraviolet light — need to take simultaneous measurements that scientists can stack together,’ explained the article.
To facilitate that process, Hope carries all its instruments on the same arm. The spacecraft also has a precisely tuned 55 hour–long orbit that enables two different views of Mars: One in which the planet rotates beneath the spacecraft, and one in which the spacecraft keeps pace and watches the same spot over time, Al Amiri said. That combination of views should make it easier for scientists to put together a complete map of the Martian atmosphere, she added.
Hope is scheduled to launch in late July or early August — the same window targeted by NASA’s Perseverance rover and China’s first Mars mission, Tianwen.
Until March, the European Space Agency and Russia were also planning missions, but parachute problems and coronavirus travel restrictions have pushed that mission to 2022.
The UAE's Hope Probe arrived at its launch site in Japan as planned last month. | 0.862904 | 3.246338 |
Sep 03, 2012
Astronomers have recently taken more precise measurements of the Sun’s shape over several years. They found that it was rounder and less variable than they expected from theory.
If gravity and centrifugal force from its rotation were the primary influences on its shape, then the Sun should have a larger equatorial bulge. And since most solar features vary with the sunspot cycle, astronomers expected the shape would vary, too.
These observations add to a long list of disappointed expectations:
· the deficit of neutrinos.
· the variation of neutrino numbers with the sunspot cycle.
· the sunspot cycle itself and the spots’ reversing magnetic polarity.
· the hot corona above the cooler surface.
· the acceleration of the solar wind after it leaves the surface.
· the surface granulation, thought to be convection, that contradicts all that’s known about convection.
· the differential rotation, where the equator rotates faster than the poles.
Any of these observations would make a textbook example of falsification: Scientists deduce an observational result from theory, and then they look at the actual condition. If it’s not what the theory predicted, the theory is falsified. The scientists start over, examining initial assumptions and alternative ideas. Patching the theory to fit or to “explain away” the data is sloppy science.
However, reputations and salaries are at stake. Also, changing theories is expensive: textbooks would have to be rewritten, curricula changed, computers re-programmed. The incentives are for patching. But that’s expediency, not science. For many decades now, expediency has crowded out science: We live in a dark age of science, a fact obscured by technological feats. The “thermonuclear Sun” theory has been patched so much that it has disappeared beneath the stitches. In the words of Richard Rorty, it’s become “a nuisance.”
The first assumption that this new observation should question is the one Eddington made in the 1920s. He couldn’t imagine any way that the Sun could be powered externally, so he settled for an internal source. The idea of nuclear energy had just become fashionable, and questions about the details of nuclear power could be hidden along with it in the Sun’s core. Patching was excusable because the patches couldn’t be checked directly.
With the advent of the space age, it became apparent that the universe—and in particular the Sun—was composed of plasma. A century of experiments with plasma had shown it to be electrically active, and space-age data indicated that it could transmit electrical energy over stellar and even galactic distances.
Now there is a way for the Sun to be powered externally. It’s shape would be determined by electromagnetic forces, not by gravity and centrifugal force. It’s rotation would also be driven electromagnetically, like an electric motor, not inertially as a residue from a collapsed nebula (another gravity theory that never worked). If galactic currents were powering the Sun—and all stars—much like an electrical plasma discharge in a lab “gas discharge” tube, the list of anomalous observations could be explained—without patching the theory.
Theoretical extensions of lab experiments could be checked directly with space probes. So far, inadvertent results from probes have been encouraging, but for the most part the probes have not been equipped with appropriate instruments nor have their missions been designed to test the assumption of an external power source.
There is money for computer simulations, for the “video games” that circularly verify the latest patches. But the “patches” mentality has shut out every penny for challenges to the de facto orthodoxy. The uncritical reliance on mathematical deductions and computer simulations has severed the space sciences from their roots in empirical testing. They need less math, more English, and some old-fashioned empiricism.
See related video on the Thunderbolts Project YouTube Channel: | 0.87402 | 3.840834 |
|Right ascension||02h 09m 41.27s|
|Declination||+00° 15′ 58.48″|
|Helio radial velocity||249.1 ± 17.7 km/s (154.8 ± 11.0 mi/s)|
|Distance||2 and 10 Gly (610 and 3,070 Mpc)|
9Spitch is a gravitationally lensed system of two galaxies. The nearer galaxy is approximately 2 billion light-years (610 Mpc) from Earth and is designated SDSS J020941.27+001558.4, while the lensed galaxy is 10 billion light-years (3.1 Gpc) distant and is designated ASW0009io9 (shortened to 9io9). It was discovered in January 2014 by Zbigniew "Zbish" Chetnik, an amateur astronomer from Northamptonshire, England, while classifying images on the website Spacewarps.org. The discovery was announced on the BBC television programme Stargazing Live.
The term Spitch comes from Chetnik's nickname Zbish, after a BBC producer misheard his nickname. Stargazing Live host Brian Cox supported the name 9Spitch over other suggestions as it would "highlight amateur astronomy".
The Red Radio Ring (RRR) was discovered by four independent groups, including the Space Warps project using deep images from the Canada–France–Hawaii Telescope, a cross-match with Herschel-SPIRE and Planck images at 350 μm to identify strongly lensed dusty star-forming galaxies (DSFGs) and follow up with Large Millimeter Telescope, a detection with Herschel-SPIRE 500 μm images to identify strongly lensed DSFGs, and identification of 9Spitch as the strongest lensed DSFG in the 278 GHz maps from the Atacama Cosmology Telescope (ACT) and follow-up with the Green Bank Telescope.
The galaxy was studied with the Large Millimetre Telescope, which detected carbon monoxide in the lensed galaxy, and the Subaru Telescope, which detected different spectroscopic lines associated with star formation in the lensed galaxy. This study suggests a high star forming rate of about 2500 Mʘ yr -1 or a thousand times the star forming rate of the Milky Way. In the paper the name 9io9 is used instead of 9Spitch. The source reconstruction supports a compact core and an extended region, maybe indicative of a jet or lobe coming from an active galactic nucleus (AGN). The galaxy might be in the center of a large galaxy group or cluster and it will likely evolve into a massive elliptical galaxy.
9Spitch was observed with the Atacama Large Millimeter Array (ALMA) 12-meter antennas in December 2017 as part of project 2017.1.00814.S. The data revealed the presence of atomic carbon and carbon monoxide as a tracer of star formation. It was estimated that the total star formation rate of the molecular ring is about 2800 M☉ yr-1. ALMA also detected the cyanide radical travelling twice the velocity of the rotation of the molecular ring, with a radial velocity of 680 km s-1. This is explained as a possible interaction between material outflowing from the AGN and interstellar material.
Harrington et al. (2019) reports four independent detections of the Red Radio Ring, including the detection with Space Warps. In their paper they report new Atacama Pathfinder Experiment (APEX) observations, presenting the detection of nitrogen [N II] 205 μm. The velocity structure of the nitrogen is similar to carbon monoxide and they concluded that both share the same volume. The ratio of the nitrogen luminosity and the infrared luminosity resembles more a normal star-forming galaxy and less a galaxy with star-formation influenced by a quasar.
- "SDSS J020941.27+001558.4". Sloan Digital Sky Survey. http://skyserver.sdss3.org/dr9/en/tools/explore/obj.asp?id=1237666408456585406. Retrieved 19 January 2015.
- Zolfagharifard, Ellie (16 January 2014). "Amateur astronomer discovers a new galaxy 10 billion light years away while taking part in BBC's Stargazing Live show". Daily Mail. http://www.dailymail.co.uk/sciencetech/article-2540578/Amateur-astronomer-discovers-new-galaxy-10-billion-light-years-away-star-gazing-BACK-GARDEN.html. Retrieved 19 January 2015.
- "Daily Fail". Zooniverse.org. 17 January 2014. http://daily.zooniverse.org/2014/01/17/daily-fail/. Retrieved 19 January 2015.
- Geach, J. E. et al. (September 2015). "The Red Radio Ring: a gravitationally lensed hyperluminous infrared radio galaxy at z = 2.553 discovered through the citizen science project Space Warps". Monthly Notices of the Royal Astronomical Society 452 (1): 502–510. doi:10.1093/mnras/stv1243. Bibcode: 2015MNRAS.452..502G.
- Harrington, K. C. et al. (June 2016). "Early Science with the Large Millimeter Telescope: Observations of Extremely Luminous High-z Sources Identified by Planck". Monthly Notices of the Royal Astronomical Society 458 (4): 4383–4399. doi:10.1093/mnras/stw614. Bibcode: 2016MNRAS.458.4383H.
- Nayyeri, H. et al. (May 2016). "Candidate Gravitationally Lensed Dusty Star-forming Galaxies in the Herschel Wide Area Surveys". The Astrophysical Journal 823 (1): 17. doi:10.3847/0004-637X/823/1/17. Bibcode: 2016ApJ...823...17N.
- Su, T. et al. (January 2017). "On the redshift distribution and physical properties of ACT-selected DSFGs". Monthly Notices of the Royal Astronomical Society 464 (1): 968–984. doi:10.1093/mnras/stw2334. Bibcode: 2017MNRAS.464..968S.
- Rivera, Jesus et al. (July 2019). "The Atacama Cosmology Telescope: CO(J = 3 – 2) Mapping and Lens Modeling of an ACT-selected Dusty Star-forming Galaxy". The Astrophysical Journal 879 (2): 95. doi:10.3847/1538-4357/ab264b. Bibcode: 2019ApJ...879...95R.
- Geach, J. E. et al. (October 2018). "A Magnified View of Circumnuclear Star Formation and Feedback around an Active Galactic Nucleus at z = 2.6". The Astrophysical Journal 866 (1): L12. doi:10.3847/2041-8213/aae375. Bibcode: 2018ApJ...866L..12G.
- Harrington, Kevin C. et al. (September 2019). "The 'Red Radio Ring': ionized and molecular gas in a starburst/active galactic nucleus at z ∼ 2.55". Monthly Notices of the Royal Astronomical Society 488 (2): 1489–1500. doi:10.1093/mnras/stz1740. Bibcode: 2019MNRAS.488.1489H.
- ASW0009io9 record at Spacewarps.org
- ASW0009io9 at SIMBAD
- 9Spitch on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
https://en.wikipedia.org/wiki/9Spitch was the original source. Read more. | 0.853786 | 3.671213 |
List of some of the main surveys used in the galactic structure studies.
In the last decades large data sets covering a wide range of both resolution and observed regions have been accumulated in the Astronomy. Follow-up technology involving the storage and the access to these data is also necessary to develop methods and tools that will allow their usage.
In this chapter, I will review the use of the large data sets in the galactic astronomy, most of them covering almost entire area of the sky in the several wavelengths, for both the diffuse data provided by IRAS, DIRBE/COBE, molecular and hydrogen surveys and point sources catalogues as provided by stellar large-scale surveys such as DENIS, 2MASS, SDSS, among others. A brief description of these surveys and how to access them in the context of Virtual Observatory will be also presented.
Numerical simulations have an important role in understanding and describing the nature of the observations. Particularly, large-scale surveys data can be also used to validate numerical models. I will present models and methods that describe the Galactic structure taking into account the hydrogen atomic distribution in our Galaxy, obtaining galactic parameters such as scale-height, spiral arms parameters, the co-rotation radius.
One of the biggest problems describing the spiral arms in the Galaxy from the gas distribution resides in the fact that some interpretations in the literature for -v the diagrams have not been updated in respect to rotation curves using old values for the distance from the Sun to the Galactic center. Another problem resides of the difficulty in describing the non-circular motion.
My choice in the present work is to describe the spiral structure by adopting an empirical model (section 3) which is based on the analysis of HI distribution by means its tangential directions and the observed -v. One of the aims of the present paper is to carry out self consistent inter-comparisons of our results regarding different tracers of the spiral structure.
The models of the spiral structure presented here were first introduced by Amôres & Lépine (2005, AL05) in which two models were proposed to describe the interstellar extinction in the Galaxy (see section 4 of this chapter). Model S consists in obtaining extinction predictions taking into account the spiral structure of our Galaxy. In this model, the extinction grows by steps each time a spiral arm is crossed and remains almost constant in the inter-arm regions. The models were also compared with other samples of objects and regions as pointed by Amôres & Lépine (2007).
As galactic interstellar extinction is a crucial obstacle when observing in the highly obscured regions, it is important to model it properly. I will present the recent efforts in this area. I will present my model for interstellar extinction, its applications and comparisons with other models and maps available in the context of the Virtual Observatory called GALExtin.
Star counts models are also important if one wants to estimate the counts that will be observed by large surveys (GAIA, DES, VVV, LSST, among others). A few simulations for large surveys using star counts are presented in section 5. Conclusions and final remarks are presented in section 6.
2. Large data sets
Large data sets are very important in whole Astronomy. In combination with models these can be used to construct methods to analyze and to interpretate the observed data. They can also be used in order to tune models allowing obtain the best values for a given set of parameters.
Particularly in the galactic Astronomy they can be used in order to obtain parameters of the galactic components, as the thin and thick disk, bulge, bar and galactic halo. Figure 1 shows a representation of our Galaxy structure that is composed basically of four components: disk (thin and thick), bulge, bar and halo. In the disk there is a presence of the spiral arms with young stars while in the halo there are most of the old stars (Robin et al. 2003 and references therein). The shape and properties for each component can be obtained by adjusting parameters of the galactic halo (such as eccentricity, shape) that can also allow us to identify, for instance, the existence of streams and satellite galaxies. (Majewski et al. 2003).
On the other hand, large data sets in the galactic Astronomy have an advantage to expand to a wide range of wavelength, from radio to high-energies. The first large surveys were obtained in the radio wavelengths in the decades of 1950-1960 (Kerr 1969) observing atomic hydrogen or HI. The author showed for the first time some interesting aspects of our Galaxy structure, as the warp, flare, spiral arms, among others and be also useful in the extragalactic astronomy, like for instance the extinction maps elaborated by Burstein & Heiles (1978,1982) based on them. The most recent HI survey is based on the LAB (Leiden-Argentine-Bonn) survey that observed each point of the sky spaced by 0.5 and 0.25 degrees for galactic longitude and latitude producing for each one, what is called spectrum, i.e. the variation of intensity with velocity (Kalberla et al. 2005).
Figure 2 shows the distribution of the integrated intensity, i.e. the sum of the spectra for each coordinate, for all-sky as observed by LAB survey. It can be seen that most of the emission is concentrated for galactic latitudes |b| ≤ 15º, denoted by green, yellow and red colors but a significant part of the emission extended up to|b| ~ 50º. One can see a long tail in the emission ranging from 120º to 200º reaching south galactic pole.
Table 1 shows some large surveys useful for galactic structure studies based on other wavelengths as CO that is particularly interesting to identify star-formation regions. Due to the distribution of the interstellar dust in the galactic plane, it obscurates the observations in some wavelengths as in the optical, for instance. Observations performed at infrared wavelengths penetrate through the dust grains and allow us to observe beyond. An extraordinary advance in the study of galactic structure was obtained with IRAS satellite (1983) that observed almost 96% of the sky in four infrared bands followed by DIRBE/COBE experiment in 1992.
Catalogs with stellar sources, as 2MASS (Cutri et al. 2003), SDSS, are also very important in the study of the galactic structure. Concerning 2MASS, Skrutskie et al. (2006) published a catalog which contains 1,647,599 observed extended sources using the classification algorithms provided by Jarett et al. (2000). As this catalog also contains sources with bad photometry quality, contamination or confusion source due to either intrinsic 2MASS properties or high crowded fields for more detailed works is mandatory to select those sources in respect to quality criteria.
Figure 3 shows a map in galactic coordinates for 2MASS extended sources for all-sky with region observed by Vista Variable in the Via Láctea (VVV) survey (Minniti et al. 2010) region (bulge and disk) represented by white dashed line. The grid of this map is one squared degree for both longitude and latitude.
3. Simulating galactic structure from HI data
This section is organized as follows. Section 3.1 presents the data used in the present work, an analysis from the main emission peaks observed in the HI and CO galactic distribution is presented in section 3.2. Section 3.3 presents the procedure adopted for describing the spiral arms as well the galactic rotation curve used in the present work. The -v diagrams obtained from the fitting of the parameters of the spiral arms for the HI is presented in section 3.4. A discussion concerning the co-rotation point in our Galaxy is presented in section 3.5.
|HI||Berkeley||10º < ℓ < 250º (│b│ ≤ 10º)||Weaver & Williams (1973)|
|Parkes||240º < ℓ < 350º (│b│ ≤ 10º)||Kerr et al.(1986)|
|NRAO||-11º < ℓ < 13º||Burton & Liszt (1983)|
|LAB||All-Sky||Kalberla et al.(2005)|
|Near infrared||2MASS (point sources)||All-Sky||Cutri et al.(2003)|
|2MASS (extended sources)||All-Sky||Skrutskie et al. (2006)|
|Optical||SDSS||10,000 square degrees||Adelman-McCarthy et al., (2009)|
|Proper motion||UCAC-3||All-Sky||Zacharias et al. (2010)|
|Mid and far-infrared||IRAS||All-Sky||Hauser et al.(1984)|
|Near/mid and far-infrared||DIRBE/COBE||All-Sky||DIRBE Explanatory Supplement|
|CO||Dame||0º < ℓ < 360º (│b│ ≤ 10º)||Dame et al. (1987,2001)|
|Stony-Brook||part of galactic plane||Clemens et al. (1986)|
Hartmann & Burton (1997) published a HI survey based on observations called Leiden/Dwingeloo HI survey that mapped the 21-cm spectral line emission over the entire sky above declinations of -30 degrees using a grid spacing of ~ 0.5 degree and a velocity sampling of ~ 1.03 km/s.
Kalberla et al. (2005) published the LAB (Leiden/Argentine/Bonn) survey which contains the final data release of observations of 21-cm emission from Galactic neutral hydrogen over the entire sky, merging the Leiden/Dwingeloo Survey of the sky north of -30º with the Instituto Argentino de Radioastronomia Survey of the sky south of -25º. The angular resolution of the combined material is HPBW ~ 0.6º. One of the improvements of this new survey consists of also doing corrections on the stray radiation. The LAB survey has been extensibly used in several applications as pointed by Bajaja et al. (2005), Kalberla et al. (2005), Haud & Kalberla (2007), Kalberla & Haud (2006) among others.
In the present chapter, I have employed the HI data from the LAB survey. This data comprises galactic longitudes from 0º to 360º and galactic latitudes from -90º to 90º for both the intervals the 0.5º and up to 1 km/s in velocity. The data are stored in 720 (b,v) fits file maps at longitude intervals stepped by 0.5º.
3.2. The HI and CO main emission complexes
The -v diagram constitutes an important and useful tool in studying the galactic structure. Reproducing it allows us to obtain relevant information about the distribution, the position and the gas density in the spiral arms, etc. Furthermore, the visualization and interpretation of the -v diagrams is also essential for their comparison with ones obtained from the predicted models, allowing us to analyze the structures that correspond to the spiral arms from the qualitative point of view, and also to obtain information about the velocity field for the HI and CO.
One way to perform a qualitative study of the -v diagram consists of estimating the points which correspond to the main peaks for these two gas components from their observed spectra. This task can be performed by fitting the gaussian for the observed HI and CO spectra. This procedure allows us to identify the regions that delineate the main structures observed in the -v diagrams. The fitting of gaussians allows us to obtain the central value, the intensity and the width of the peaks that contributed most in the observed spectra.
Gaussian fits were obtained in the observed HI and CO spectra at each interval of 1 and 2º in longitude for HI and CO (in the galactic plane, i.e. b = 0º, respectively. The results of these procedures are also available since they may also be useful in other studies. Since some points with lower intensities can cause confusion in the identification of the large HI structures, for each spectrum the points were excluded for which the intensity is 30% less than the peak with the maximum intensity. This represents approximately 20% of the points obtained with this fitting procedure.
The -v diagrams obtained with this gaussian fitting procedure are presented in Figure 4. It can be seen that the HI distribution (Figure 4a) is given almost for the entire Galaxy while the CO emission is mainly predominant in the inner Galaxy (Figure 4b) since the CO is mainly concentrated in the spiral arms (see also Figure 5 of AL05).
In Figure 4a, one notes the presence of a spiral arm feature for (,v) = (~ -20,-120º) which also can be seen for HII regions (Amôres 2005). In the case of CO (Figure 4b) it is widely know that this component is distributed in the molecular cloud complexes that constitute the main place for star formation in our Galaxy. The fact that the molecular clouds and the CO emission are good tracers of the spiral structure is related to the interstellar shocks that occur in the spiral arms which produce an increase of the density transforming HI into H2 (Marinho & Lépine 2000).
In Figure 4b, it is also possible to identify two tangential directions for ± 30º and ± 50º. In the northern Galaxy, the component ~ 30º splits into two other components, the first one at ~ 30º and the other at ~ 25º. This feature was first identified by Solomon et al. (1985) from his observations in CO and it is also mentioned by Englmaier (1999). A detailed overview of the main characteristics observed in the -v diagrams for CO can be found in Fux (1999).
3.3. Description of the empirical models for the spiral arms
From the analysis of external galaxies it can be seen that the spiral logarithm (θ α lnR) fits real galaxies better than any other spiral curves. In my models the spiral arms are represented by the logarithmic spiral:
in which r0 and are the polar coordinates which represent the initial arm radius and i is the pitch angle. In this way, to describe a spiral arm four parameters are necessary that specify the arm position in the galactic plane: r0, θ0, i, Δθ (the arm length). In addition to these variables, an extra term (δi) was added to the pitch angle in order to produce an effect of variable inclination angle.
Russell & Roberts (1992) from the morphological analysis of the galaxies NGC 5457 and NGC 1232 found an expression to describe the variation of the pitch angle in the spiral arm. This expression is given by in which An are the coefficients that represent the perturbation term A0 … A3 e r0 corresponds to the initial radius of the spiral arm.
A comparison between the observed -v diagrams and ones obtained from fitting the parameters of the spiral arms will be presented in the next section. The main procedure consists of tracing a sequence of points in the galactic plane, i.e., in the X-Y coordinates (Figure 5a) in order to draw a hypothetical spiral arm segment. The next step consists of verifying whether this represents an observed structure (Figure 5b). If so, it is determined the distance to the galactic center for each point of this arm segment. Once the distance is obtained and its galactocentric radius.
With the rotation curve, it is possible to plot the longitude and velocity for this point. In short, X-Y positions were transformed into velocities. One position in the X-Y plane gives an unique point in the -v diagram without distance ambiguity.
Lépine et al. (2001) also presented a similar method to perform the representation of the -v diagram for HII regions. The main differences between that work and the present one are: i-) I reproduce the -v diagrams following an empirical scheme which describes the observed characteristics in these diagrams and not for a purely theoretical model; ii-) introduction of the velocity perturbation; iii-) presentation of the tangential directions obtained with my model; iv-) presence of arms with several positions with different pitch angle and; v-) I have used Russeil's catalog instead the Kuchar & Clark (1997) catalog for the HII regions.
In the present work, I also have used a modified Clemens rotation curve which is presented in Figure 6 in which the points represent the original data obtained by Clemens (1985) from CO data for the interstellar medium. I introduced a modification in the original curve provided by Clemens in order to set R0 = 7.5 kpc and to use a double exponential as presented below:
A similar Clemens rotation curve represented as a double exponential was already presented by Lépine et al. (2001). However, in the present work, I performed a small modification in its parameters in order to improve the quality of the fit. In the present rotation curve, the rms errors from the comparison of the observed data and fitted expression by the first expression is equal to 5.043.
So, through the variation of parameters for the spiral arms (expression 1) were determined the best fit for the observed structures in the -v diagram which is also done verifying whether the face-on representation of the Galaxy is plausible as well whether the tangential directions are in agreement with the observed ones. It is also provide the Xi2 total estimate calculated by the expression below:
in which N denotes the number of fitted structures, l0 and lc are the observed and predicted longitude, with the same notation applying for the velocities v0 and vc. The function min represents the fact that we get only the point with the least difference. A similar formula was also used by Russeil (2003) in order to estimate the errors involved in the comparisons with her models of spiral arms with the observed HII regions.
Since a simple model of circular velocity does not adequately reproduce some of the characteristics observed in the -v diagrams, it is also necessary to introduce perturbation terms in the calculated velocities. The use and the justification of these terms were first described by Ogorodnikov (1958) and is explained in detail by Mishurov & Zenina (1999a b) and Lépine et al. (2001).
3.3.1. Calculating the perturbed velocities
As explained above, the procedure consists of transforming X-Y galactocentric coordinates of the arms into velocities. So each point with an X-Y coordinate has a corresponding point (,v) in the -v diagram that is calculated as explained below. The longitude is directly obtained from X-Y galactic coordinates:
in which R0 is equal to 7.5 kpc which corresponds to the distance from the Sun to the galactic center. This value is actually largely used and one of the first mentions of its use was by Reid (1993). The final velocity is given by:
in which vtanx and vtany are tangential velocities projected in the X-Y plane; and v1 is calculated from the expression below:
VR(R) means the value of the rotation curve for a given galactocentric radius (R), the prot term corresponds to the perturbation in rotation and vsun is the projected velocity of the Sun calculated by the relation:
in which vout = 12.8 km/s.
The term which describes the radial and angular perturbation components is given by:
The term a2 is described below:
in which rc was set equal to 8.3 kpc and represents the co-rotation radius (section 3.5). The term a1 = -0.4 represents the phase variation. The amplitude of the perturbation in the rotation is described by the expression:
in which a3 = 12.5*alog(R/rc). Due to the existence of the LindBlad internal resonance (ILR, see Amaral & Lépine (1997, AL97)), the terms a2 and a3 are set equal to zero for r <2.5 kpc. The final values of these constants were obtained after some tests in order to reproduce the characteristics observed in the -v diagrams for both HI and HII regions.
3.4. Fitting the spiral arm parameters
In the next sub-section, the results of fitting the observed -v diagrams for the HI will be presented. For each one, it is presented the estimate (Table 2) of the Xi2 obtained with models in comparison with the observed features as well as the same estimate with the ones obtained with a model of four arms and the superposition of 2+4 spiral arms. In order to reproduce these diagrams, I have manipulated the parameters r0, θ0, i, Δθ of the spiral arms described in expression 1.
It should be noted that in performing these fitting procedures the objective is not only to reproduce the observed -v diagram but also to ensure that the parameters obtained adequately reproduce the Galaxy face-on aspect and the observed tangential directions. In the case of the HI, they should also account for the tangential directions in the longitudinal profile for the integrated intensity (Figure 9).
Figure 7 presents the comparison between the observed -v and the one obtained after fitting the spiral arms parameters with the respective Galaxy face-on representation provided in Figure 8. In order to better visualize the results, the arms are represented by straight or dashed lines with different colors. The parameters are given in the Table 3. The final Xi2 for this adjustment calculated by expression 3 is presented in Table 2, which also shows the Xi2 expected with models of four and the superposition of 2 + 4 spiral arms.
For the model of 2 + 4 spiral arms I have used the Model proposed by Lépine et al. (2001) with pitch angles equal to 6.8º and 13.5º for the pattern of 2 and 4, respectively. In the case of four spiral arms, the model proposed by Ortiz & Lépine (1993) was used which consists of a model with four spiral arms, all of which begin at r0 equal to 2.3 kpc and with pitch angle equal to 13.8º, each one separated by a phase of 90º. I also add a local arm with i equal to 12.5º and size equal to 51º.
A number is presented next to each structure (according to the numbers presented in the Table 3). In total, there are 17 structures, among them: arms, bifurcations, bridges. The largest structures correspond to arms 1,2,3,4,7,11, located in the inner Galaxy with initial radius varying from 2.5 to 4.0 kpc.
Figure 9 shows the longitudinal profile for the integrated intensity for the HI (b = 0º) that was calculated from the HI surveys mentioned in section 3.1. The lines represent the tangential direction for each arm in which the color follows the same representation adopted above. Below a brief discussion is provided about each structure. Arm 7 with ri = 6.22 kpc is one exception of a long arm that does not begins at low radius. Arm 5, which is represented by the thin yellow line which can be seen in Figure 7, is a prolongation of arm 11 (green dashed). Arm 11 has ri = 3.95 kpc with pitch angle equal to 9.40º.
However, to continue describing this arm and reproduce adequately the observed -v diagram it is necessary to introduce a new arm structure with the pitch angle slightly changed. This is done changing mainly the parameters θ and ri in order to coincide with the arm end. Note that without this modification the loop extremity will fall in (~ -70,-10º) and not in (~-65,-20º) which represents a better description for the structures observed for the HI in this direction. In summary, structures 5 and 11 represent a unique arm with a modified pitch angle in order to reproduce the observed -v diagram. It should be noted that arms with variable pitch that can also can be seen in other galaxies, such as M 81, for example.
|arm||i (º)||radius (kpc)||initial phase (º)||δi (º)||size (º)|
A similar characteristic is noted for arms 2 (dashed red), 6 (light blue) and 17 (dashed blue light). In this case, if we increase the size of arm 2 (Figure 10a, 10b) without changing the i and ri we obtain an inadequate description of the HI distribution at 0º < < -100º. Arm 6 is a prolongation of arm 2, but with i = 7.5, which better represents the HI distribution in this region with the line that passes through arm 6 (light blue) providing a good match for almost all of the points in this direction. Arm 17 matches better the structures observed in -140º < < -170º than arm 2. The i of the arm 17 is equal to 11.1º. An interesting characteristic can be seen at the end of this structure which corresponds to a bifurcation (arm 14) as well as the beginning of the other spiral arm (arm 17).
In the Galaxy face-on representation one also notes three structures that resembles bridges (arms 8,10,14), two of them with i < 0. These structures were introduced in order to reproduce the observed -v diagram. Structure 14 matches most of the points from ~ -70º to ~ -150º. These structures could be explained by the proximity of the Sun to the co-rotation point (see section 5). Similar characteristics were also assumed by De Simone et al. (2004).
The violet dashed line (arm 14) in Figure 8 represents a structure that seems to be a bifurcation that begins in arm 15 (heavy green line). This arm describes the structures around < -100º in -v the diagram. Based on Figure 7, we observe that arm 9 reproduces adequately the structures observed in the -v diagram for > 80º. This arm is a prolongation of arm 4 with i = 11.55. The continuation of arm 9 is arm 16 (heavy blue line) with i = 9.0.
McClure-Griffiths et al. (2004), while analyzing ATCA data, detected a structure that extends from = 260º to 330º that they attributed to a spiral arm with i = 9.0º. This structure was also found in our results as represented by arm 12 with i = 11.5º. Kerr (1969) published latitude-velocity diagrams in which a bridge appears in the third quadrant toward positive velocities. Kerr (1969) also presented maps with this feature extending from = -150º to -70º. Davies (1972) also interpreted this region as relating to the end of a spiral arm associated with high velocity clouds.
3.5. Co-rotation radius
Since the first HI observations the existence of a hole was seen in its distribution in the Galaxy (Kerr 1969 and Burton & Gordon 1978). In these works, the authors noted a gas deficiency in the radial gas distribution for R = 11 kpc, assuming R0 = 10 kpc. From the theoretical point of view Marochnik et al. (1972), Crézé & Mennessier (1973) and AL97 also found evidence that the co-rotation point, i.e., the point where the rotation velocity of the spiral pattern coincides with the rotation curve of the gas and stars could be located in the Solar neighborhood. The effect of the co-rotation can be understood in the following terms: there is a region where movement exists pumping the gas inside and outside resulting in a deficiency of the gas in these regions. This effect was also studied in detail by Suchkov (1978), Goldreich & Tremaine (1978), Gorkavyi & Fridman (1994). Mishurov & Zenina (1999a) also found evidence that the co-rotation point would be located near the solar radius.
Amôres, Lépine & Mishurov (2009, ALM09) analyzed the HI spectra of the whole galactic longitudes range in steps of 0.5º, with galactic latitudes in steps of one degree in the range ± 5º, plus the additional latitudes ± 10º detecting for each spectrum the velocity of the deep minima which are present, simply by identifying the channel with the lowest value of antenna temperature.
They obtained that distribution of the density minima in the galactic plane, derived from their kinematic distances from the Sun (is shown in Figure 11). The minima observed at different latitudes are all projected on the galactic plane. The ring-shaped gap is circular and very clear. It looks like the Cassini division in Saturn's rings.
The analysis of HI spectra allows to determine the points in which the HI has a gap in its distribution by means of an empirical method. The histogram with the galactocentric radius of each one of these gaps showed that the most of them are located nearest the solar radius which highlights the fact that the Sun is located at the co-rotation point in the Galaxy.
4. Interstellar extinction
One of the main difficulties in the study of both properties of individual objects and the galactic structure resides in the interstellar extinction determination. However, due to the clumpiness distribution of the interstellar dust, it is difficult to model it. Several works have been done in order to model the interstellar extinction distribution in the Galaxy, as presented by Arenou et al. (1992), Hakkila et al. (1997), Méndez & van Altena (1997), Drimmel et al. (2003), Amôres & Lépine (2005), Marshall et al. (2006) among others. In addition, some maps were elaborated in order to provide the integrated extinction along the line of sight, as the Burstein & Heiles (1978,1982), Schlegel et al. (1998, SFD) for the whole Galaxy, Schultheis et al. (1998) and Dutra et al. (2003) for the galactic center region, as well as Dobashi et al. (2005) map for AV for the whole Galaxy (|b| < 40º) based on the star counts method.
It is very important and fundamental for many studies to know the interstellar distribution in our Galaxy. This could be useful for estimation of distances and color corrections of objects for which the distance can be obtained by some other method, for star counts and brightness models of the Galaxy, also for spectrum extinction correction, among other applications. In this context, we are developing a VO-Service called GALExtin (
The determination of the interstellar extinction is fundamental for all fields of astronomy, from stellar studies in which it is important to know the extinction towards a given object from its coordinates and distances (3D Models), to extragalactic astronomy field; in this case it is mandatory to know the contribution of the extinction of our Galaxy along the line of sight.
Amôres & Lépine (2005) proposed two models to describe the interstellar extinction in the Galaxy (
In this latter work, AL07 compared the extinction models with a sample of globular and open cluster and elliptical galaxies. From the comparison with elliptical galaxies the difference between Model A and Burstein & Heiles (1978) and Schlegel et al. (1998) were around 20-30 %. Figure 12 shows a map with the comparison with SFD maps for whole sky with δ E(B-V), i.e. difference between Model A and the SFD maps.
As pointed by AL07 it can be seen regions (indicated by white color) in which the Model A2 predicts less extinction than provided by SFD, i.e., the δE(B-V) < -0.4, notably around 150º ≤ ≤ 200º, in a region that extends towards negative latitudes. This region was also pointed by B03 as the region where there is a high variation in the gas-to-dust ratio.
The resolution and coverage of the different models and maps is another point that should be taken into account in the extinction studies. There are models that provide better estimates in the solar neighborhood up to distances equal to 1.0 kpc, while they fail to describe extinction outside this distance. On the other hand, there are models that provide better values at 3.0 kpc, but being imprecise at low distances. Depending on the assumptions used in their elaboration, some models can be used only for a given region in the sky.
Another interesting issue in galactic extinction is the combination of different models. In this sense, Amôres & Robin (2011) studied the variation for interstellar extinction along a line of sight joining the results from AL05 and Marshall et al. (2006, M06).
5. Star counts simulations
Star counts models have been largely used in astrophysics. They constitute an important and useful tool to study the galactic structure and its evolution. In particular, the Besançon Galaxy Model (BGM) provides a Galaxy description in the evolutive point of view joining both the kinematics and dynamics properties. One of the main differences in relation to others star counts models resides in the fact that the BGM is dynamically self-consistent (Bienayme et al. 1987).
The Besançon Galaxy Model (BGM) has been employed in a series of astrophysical applications (Robin et al. 2003). In the context of the GAIA mission, the BGM is the Model used to simulate the stellar content of our Galaxy. Amôres et al. (2007) presented a comparison and the improvements performed in the BGM - Java version in order to produce similar results as produced by the BGM in the Fortran version. Robin et al. (2009) also presented expected observations that will be performed by GAIA using BGM.
Amôres & Robin (2011) are using BGM in order to retrieve the parameters of spiral arms and other Galactic parameters, as warp flare by comparing BGM results with 2 MASS observations using the genetic algorithms.
On the other hand, Amôres et al. (2010) also presented simulations for the expected observations that will be performed by VVV. Vista Variables In The Via Láctea (VVV) is an ESO variability (Minniti, D., et al. 2010) survey that is performing observations in near infrared bands (Z,Y, J,H and Ks) towards the galactic bulge and part of the disk, totalizing an area of 520 square degrees. A total of 1920 observation hours (2009-2013) will be used at VISTA, within a 5 year time lapse.
In order to predict star counts distribution towards the VVV region we made use of TRI-Legal Galaxy Model (Girardi et al. 2005, G05) with galactic parameters as pointed by Vanhollebeke et al. (2009) and G05 considering VVV completeness limit, i.e. K = 20.0. For other filters, we have cut (after simulation) at other VVV limits, i.e. Z= 21.6, Y = 20.9, J = 20.6, H =19.0. The results are presented by Amôres et al. 2011b.
Since VVV observes galactic plane regions it is very important to know the interstellar extinction (Amôres et al. 2009) distribution towards them. We made use of 3D Marshall et al. (2006) interstellar extinction model. TRI-Legal predicts the star counts taking into account three galactic components, i.e. bulge, disk and halo. For each simulated star there is a set of properties as its distance, magnitude, gravity, temperature among others. From temperature we determine the spectral type.
Concerning HI model to describe spiral arms positions from HI data, the results presented in this chapter allow us to obtain the spiral arm positions based on HI distribution obtaining the spiral arm parameters (r0, θ0, i, Δθ) which reproduce the main observed features in the -v diagrams for HI. The tangential directions predicted by models are also consistent with the ones predicted by other models, such as for instance the one proposed by Englmaier (1999, see his Table 1), as can be seen in the peaks existent in the longitudinal profiles for HI (Figure 9).
It should be noted that it is not being proposed a Galaxy with too many spiral arms, 17 for the atomic hydrogen since many of the structures presented in this chapter only represent prolongations of arms with different pitch angles which was necessary in order to adequately reproduce the observed -v diagram.
This is because a more simplified model would not be realistic. Many arm segments with different pitch angles are needed because real arms are not well represented by a single logarithmic spiral that follows a long path around the Galaxy. Furthermore, there are bifurcations and some short bridges. Another difficulty related to HI consists in the fact that these components are not only predominantly concentrated in the spiral arms, such as the CO, for example. Instead, there is also an amount of HI in the inter-arm regions.
In this sense, the use of the method proposed by Amôres & Lépine (2004) will also allow to reproduce not only the positions of the arms but also their density, allowing the elaboration of numerical -v diagrams, to estimate width of the arms since they are not as thin and well-resolved as presented here.
In relation to interstellar extinction important results are also being obtained from the inter-comparisons of different values of interstellar extinction obtained from Planetary Nebulae (PNe). Köppen & Amôres (2011) have used a large sample of PNe towards the galactic disk and bulge in order to obtain average values for interstellar extinction as well as to review the old values, most of the times obtained with different extinction curves.
A good estimate of interstellar extinction is also important in the study of Supernovae. Arsenijevic & Amôres (2011) have compared the distribution of interstellar extinction towards supernovae and also presented a new method to reproduce observed spectra using the Genetic Algorithms and basic parameters as galactic and galaxy host extinction and RV (the ratio of the total to selective extinction). The use of global optimization methods can be a powerfull tool to obtain parameters from large surveys.
E. B. de Amôres acknowledges support from FCT under grant no. SFRH/BPD/42239/2007 and also Laboratory for Systems, Instrumentation and Modeling in Science and Technology for Space and the Environment (SIM), funded by "Fundação para a Ciência e a Tecnologia" thought Portuguese National Funds. | 0.850504 | 3.93862 |
This is a picture made by an artist to show what the Jupiter-like planet orbiting the star, 55 Cancri, might look like. We do not have photographs of what it actually looks like because the planet is about 41 light years from Earth. A small moon is shown in front of the planet because moons are thought to be common around this type of planet, but no moon has been found.
Click on image for full size
An Exoplanet that Looks Like Jupiter!
News story originally written on June 18, 2002
Astronomers Dr. Geoffrey Marcy and Dr. Paul Butler announced that, after 15 years of observation, their team has found 13 extrasolar planets (or exoplanets), and that one of these exoplanets may be somewhat like Jupiter. The planet that reminds the scientists of Jupiter is orbiting a star called 55 Cancri, within the Cancer constellation.
The research team is very excited about the discovery of this planet because it is very different from any of the other 90 or so exoplanets that have been identified so far. As Dr Marcy states, “all other extrasolar planets discovered up to now orbit closer to the parent star, and most of them have had elongated, eccentric orbits. This new planet orbits as far from its star as Jupiter orbits from the Sun.”
Jupiter is about four and a half times further from the Sun than Earth and it takes the planet about 12 years to complete one orbit around the Sun. The new planet, a similar distance from 55 Cancri, takes 13 years to orbit around the star.
The new planet is not the only one orbiting 55 Cancri. There is another exoplanet, discovered in 1996, that orbits very close to the star. Scientists suspect that there may be a third exoplanet orbiting the star as well.
The new planet is not exactly like Jupiter, however. It is much more massive than Jupiter, with a mass about 3.5-5 times greater. Its orbit is also different than Jupiter’s, taking an elliptical route around the star. Even though differences exist, the scientific team is encouraged that we may someday find more exoplanets that are like those in our own solar system.
Last modified June 24, 2002 by Lisa Gardiner.
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Sir Isaac Newton’s Universal Law of Gravitation can be applied both at cosmic level and atomic level. It follows inverse square law of force.
In daily life we observe things falling from a height. We often drop a pen or a pencil. A ball thrown up comes down. Isaac Newton saw an apple falling from a tree. He thought why not the apples go up?
The invisible force that attracts an apple towards the earth led to the idea of gravitation.
Gravitation is the force of attraction between any two objects. It exists between an apple and the earth as well as the moon and the earth.
In the solar system, the planets go around the sun due to gravitation. In general, every object in the universe attracts every other object with a force.
Sir Isaac Newton formulated a universal law of gravitation also called Newton’s Law of Gravitation.
Universal Law of Gravitation
Let A and B be two objects having masses m1 and m2. Let the distance of separation be‘d’. Then the force of attraction F between the two objects is
- directly proportional to the product of their masses
- inversely proportional to the square of the distance between them.
F α m1m2 —– 1
F α 1/d2 —– 2
Combining 1 & 2, F α m1m2 / d2
F = G m1m2 / d2
Here G is a constant of proportionality called Universal Gravitational Constant.
Henry Cavendish, a British Scientist, by experimental methods determined the
value of G as 6.67 x 10 – 11 Nm2kg-2.
Importance of Universal Law of Gravitation
The Universal Law of Gravitation explains;
- the motion of the moon around the earth
- the motion of planets around the sun
- the tides in the sea due to moon
- the force that binds us on earth
What is Free Fall?
When you just drop a stone from a height it is attracted by the earth’s gravity. The velocity of the body increases as it travels downward. This produces acceleration.
The acceleration due to gravity is called acceleration due to gravity and the symbol g is used. The acceleration due to gravity depends on how massive an object is.
Acceleration due to gravity of earth is approximately 9.8 m/s2 and that of moon is one-sixth of earth.
Let the mass of earth be M and that of the object be m.
From Newton’s Second law of motion for linear motion, F = ma
For a freely falling body it is modified as F = mg —— 1
From Universal Law of Gravitation, F = G Mm / d2 —– 2
Comparing equations 1 & 2,
mg = G Mm / d2
g = G M / d2
Acceleration due to gravity on earth
Replacing d with R, the radius of the earth
g = G M / R2
For earth: R = 6.4 x 106 m and M = 6.0 x 1024 kg
Substituting these values in
g = G M / R2
g = 6.67 x 10 – 11 x 6.0 x 1024 / (6.4 x 106)2
g = 9.8 m/s2
For calculation purposes usually g value is rounded off to 10 m/s2. | 0.830263 | 3.498035 |
Crescent ♈ Aries
Moon phase on 10 January 2076 Friday is Waxing Crescent, 5 days young Moon is in Pisces.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 4 days on 6 January 2076 at 10:14.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing about ∠17° of ♓ Pisces tropical zodiac sector.
Lunar disc appears visually 0.7% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1938" and ∠1951".
Next Full Moon is the Wolf Moon of January 2076 after 10 days on 21 January 2076 at 04:39.
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Length of current 940 lunation is 29 days, 10 hours and 47 minutes. It is 24 minutes longer than next lunation 941 length.
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A new study has caught a newborn star similar to the sun in a fiery outburst. X-ray observations of the flare-up, which are the first of their kind, are providing important new information about the early evolution of the sun and the process of planet formation. From Vanderbilt :
Unique observations of newborn star provide information on solar system’s origin
A new study has caught a newborn star similar to the sun in a fiery outburst. X-ray observations of the flare-up, which are the first of their kind, are providing important new information about the early evolution of the sun and the process of planet formation. The study, which was conducted by a team of astronomers headed by Joel Kastner of the Rochester Institute of Technology that included David Weintraub from Vanderbilt, is reported in the July 22 issue of the journal Nature.
Last January, Jay McNeil, an amateur astronomer in west Kentucky, discovered a new cloud of dust and gas in the Orion region. Previously, the cloud, now named the McNeil nebula, was not visible from earth. But a new star inside the dark cloud had flared up in brightness, lighting up the surrounding nebula. Looking back at the images taken of this part of the sky revealed that a young star about the size of the sun had burst into visibility last November.
Despite the fact that hundreds of telescopes scan the sky nightly, the discovery of a new star is an extremely rare event, having occurred only twice in the last century. What made this star even more special was that the fact that it appears to be an extremely young star — far less than a million years old — that is about the same mass as the sun. Astronomers know of fewer than a dozen of these stars, which they call FU-Orionis-type. Although this is the third FU-Orionis that has been caught in the act of flaring, it is the first that has occurred in modern times when its behavior could be monitored not only in visible light, but also in radio, infrared and X-ray wavelengths.
”In FU-Orionis stars, these outbursts are very brief,” says Weintraub, associate professor of astronomy. ”They brighten by as much as 100 thousand times in a few months and then fade away over a number of months.”
Knowing that time was short, Kastner and Weintraub submitted an emergency request for viewing time on the orbiting Chandra X-ray observatory. Because X-rays are generated by extremely violent events, they provide a critical window for observing extreme stellar flare-ups of this sort. The astronomers were granted two viewing times in early and late March.
Using Chandra, the astronomers discovered that the star, which has been officially named V1647 Ori, was a very bright X-ray source in early March, but its X-ray brightness had decreased substantially by the end of the month before the star disappeared from view behind the sun. (At the same time, the new star was fading in visible and infrared wavelengths.)
In addition, the astronomers learned that Ted Simon from the Institute for Astronomy in Hawaii had taken some serendipitous X-ray images of the same area in 2002 for another purpose. These showed no X-rays coming from the V1647 Ori’s location at the time, supporting the idea that the recent X-ray production was directly associated with the star’s flare-up.
Kastner and Weintraub propose a novel mechanism to explain their observations. Many stars, including the sun, produce X-rays by a mechanism that depends on the star’s rotation rate and convection depth. But the astronomers calculate that the temperature of the gas that is producing the X-rays at V1647 ORI is substantially higher than can be explained by this traditional mechanism.
Observations of V1647 Ori indicate that it possesses a ”protoplanetary” disk — a thin disk extending out from a star’s equator that contains dust and gas left over from the star’s formation and from which planets form. Kastner and Weintraub argue that the flare was touched off by a sudden avalanche of disk material falling onto the surface of the star and that this was the source of the intense X-rays as well as the other forms of radiation.
If their hypothesis is correct, X-ray observations may help discriminate between young stars that possess protoplanetary disks and those that don’t, Weintraub says.
There is a disagreement among astronomers about whether FU-Orionis stars undergo outbursts of this sort only once, several times or dozens of times before they settle into maturity. Other astronomers who have looked further back in the astronomical records for V1647 Ori have found that it also flared up in 1965, which provides added support for the multiple outburst theories.
Other participants in the study were Michael Richmond at Rochester Institute of Technology, Nicolas Grosso and H. Ozawa at the Laboratoire d’Astrophysique de Grenoble, A. Frank at the University of Rochester, Kenji Hamaguchi at NASA’s Goddard Space Flight Center and Arne Henden at the U.S. Naval Observatory.
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Want to go ice fishing on Jupiter’s moon Europa? There’s no promising you’ll catch anything, but a new set of robotic prototypes could help.
Since 2015, NASA’s Jet Propulsion Laboratory in Pasadena, California, has been developing new technologies for use on future missions to ocean worlds. That includes a subsurface probe that could burrow through miles of ice, taking samples along the way; robotic arms that unfold to reach faraway objects; and a projectile launcher for even more distant samples.
All these technologies were developed as part of the Ocean Worlds Mobility and Sensing study, a research project funded by NASA’s Space Technology Mission Directorate in Washington. Each prototype focuses on obtaining samples from the surface — or below the surface — of an icy moon.
“In the future, we want to answer the question of whether there’s life on the moons of the outer planets — on Europa, Enceladus and Titan,” said Tom Cwik, who leads JPL’s Space Technology Program. “We’re working with NASA Headquarters to identify the specific systems we need to build now, so that in 10 or 15 years, they could be ready for a spacecraft.”
Those systems would face a variety of challenging environments. Temperatures can reach hundreds of degrees below freezing. Rover wheels might cross ice that behaves like sand. On Europa, surfaces are bathed in radiation.
“Robotic systems would face cryogenic temperatures and rugged terrain and have to meet strict planetary protection requirements,” said Hari Nayar, who leads the robotics group that oversaw the research. “One of the most exciting places we can go is deep into subsurface oceans — but doing so requires new technologies that don’t exist yet.”
A hole in the ice
Brian Wilcox, an engineering fellow at JPL, designed a prototype inspired by so-called “melt probes” used here on Earth. Since the late 1960s, these probes have been used to melt through snow and ice to explore subsurface regions.
The problem is that they use heat inefficiently. Europa’s crust could be 6.2 miles deep or it could be 12.4 miles deep (10 to 20 kilometers); a probe that doesn’t manage its energy would cool down until it stopped frozen in the ice.
Wilcox innovated a different idea: a capsule insulated by a vacuum, the same way a thermos bottle is insulated. Instead of radiating heat outwards, it would retain energy from a chunk of heat-source plutonium as the probe sinks into the ice.
A rotating sawblade on the bottom of the probe would slowly turn and cut through the ice. As it does so, it would throw ice chips back into the probe’s body, where they would be melted by the plutonium and pumped out behind it.
Removing the ice chips would ensure the probe drills steadily through the ice without blockages. The ice water could also be sampled and sent through a spool of aluminum tubing to a lander on the surface. Once there, the water samples could be checked for biosignatures.
“We think there are glacier-like ice flows deep within Europa’s frozen crust,” Wilcox said. “Those flows churn up material from the ocean down below. As this probe tunnels into the crust, it could be sampling waters that may contain biosignatures, if any exist.”
To ensure no Earth microbes hitched a ride, the probe would heat itself to over 900 degrees Fahrenheit (482 degrees Celsius) during its cruise on a spacecraft. That would kill any residual organisms and decompose complex organic molecules that could affect science results.
A longer reach
Researchers also looked at the use of robotic arms, which are essential for reaching samples from landers or rovers. On Mars, NASA’s landers have never extended beyond 6.5 to 8 feet (2 to 2.5 meters) from their base. For a longer reach, you need to build a longer arm.
A folding boom arm was one idea that bubbled up at JPL. Unfolded, the arm can extend almost 33 feet (10 meters). Scientists don’t know which samples will be enticing once a lander touches down, so a longer reach could give them more options.
For targets that are even farther away, a projectile launcher was developed that can fire a sampling mechanism up 164 feet (50 meters).
Both the arm and the launcher could be used in conjunction with an ice-gripping claw. This claw could someday have a coring drill attached to it; if scientists want pristine samples, they’ll need to bore through up to eight inches (about 20 centimeters) of Europa’s surface ice, which is thought to shield complex molecules from Jupiter’s radiation.
After deployment from a boom arm or a projectile launcher, the claw could anchor itself using heated prongs that melt into the ice and secure its grip. That ensures that a drill’s bit is able to penetrate and collect a sample.
Wheels for a cryo-rover
In July, NASA will mark a 20-year legacy of rovers driving across Martian desert, harkening back to the July 4, 1997 landing of Mars Pathfinder, with its Sojourner rover.
But building a rover for an icy moon would require a rethink.
Places like Saturn’s moon Enceladus have fissures that blow out jets of gas and icy material from below the surface. They’d be prime science targets, but the material around them is likely to be different than ice on Earth.
Instead, tests have found that granular ice in cryogenic and vacuum conditions behaves more like sand dunes, with loose grains that wheels can sink into. JPL researchers turned to designs first proposed for crawling across the moon’s surface. They tested lightweight commercial wheels fixed to a rocker bogey suspension system that has been used on a number of JPL-led missions.
The next steps
Each of these prototypes and the experiments conducted with them were just starting points. With the ocean worlds study complete, researchers will now consider whether these inventions can be further refined. A second phase of development is being considered by NASA. Those efforts could eventually produce the technologies that might fly on future missions to the outer solar system.
This research was funded by NASA’s Space Technology Mission Directorate’s Game Changing Development Program, which investigates ideas and approaches that could solve significant technological problems and revolutionize future space endeavors.
Caltech manages JPL for NASA.
For more information on Ocean Worlds Europa Technologies, visit:
News Media Contact
Jet Propulsion Laboratory, Pasadena, Calif. | 0.849517 | 3.528098 |
Exploring the influence of galactic winds from a distant galaxy called Makani, UC San Diego’s Alison Coil, Rhodes College’s David Rupke and a group of collaborators from around the world made a novel discovery. Published in Nature, their study’s findings provide direct evidence for the first time of the role of galactic winds — ejections of gas from galaxies — in creating the circumgalactic medium (CGM). It exists in the regions around galaxies, and it plays an active role in their cosmic evolution. The unique composition of Makani — meaning wind in Hawaiian — uniquely lent itself to the breakthrough findings.
“Makani is not a typical galaxy,” noted Coil, a physics professor at UC San Diego. “It’s what’s known as a late-stage major merger — two recently combined similarly massive galaxies, which came together because of the gravitational pull each felt from the other as they drew nearer. Galaxy mergers often lead to starburst events, when a substantial amount of gas present in the merging galaxies is compressed, resulting in a burst of new star births. Those new stars, in the case of Makani, likely caused the huge outflows — either in stellar winds or at the end of their lives when they exploded as supernovae.”
Coil explained that most of the gas in the universe inexplicably appears in the regions surrounding galaxies — not in the galaxies. Typically, when astronomers observe a galaxy, they are not witnessing it undergoing dramatic events — big mergers, the rearrangement of stars, the creation of multiple stars or driving huge, fast winds.
“While these events may occur at some point in a galaxy’s life, they’d be relatively brief,” noted Coil. “Here, we’re actually catching it all right as it’s happening through these huge outflows of gas and dust.”
Coil and Rupke, the paper’s first author, used data collected from the W. M. Keck Observatory’s new Keck Cosmic Web Imager (KCWI) instrument, combined with images from the Hubble Space Telescope and the Atacama Large Millimeter Array (ALMA), to draw their conclusions. The KCWI data provided what the researchers call the “stunning detection” of the ionized oxygen gas to extremely large scales, well beyond the stars in the galaxy. It allowed them to distinguish a fast gaseous outflow launched from the galaxy a few million year ago, from a gas outflow launched hundreds of millions of years earlier that has since slowed significantly.
“The earlier outflow has flowed to large distances from the galaxy, while the fast, recent outflow has not had time to do so,” summarized Rupke, associate professor of physics at Rhodes College.
From the Hubble, the researchers procured images of Makani’s stars, showing it to be a massive, compact galaxy that resulted from a merger of two once separate galaxies. From ALMA, they could see that the outflow contains molecules as well as atoms. The data sets indicated that with a mixed population of old, middle-age and young stars, the galaxy might also contain a dust-obscured accreting supermassive black hole. This suggests to the scientists that Makani’s properties and timescales are consistent with theoretical models of galactic winds.
“In terms of both their size and speed of travel, the two outflows are consistent with their creation by these past starburst events; they’re also consistent with theoretical models of how large and fast winds should be if created by starbursts. So observations and theory are agreeing well here,” noted Coil.
Rupke noticed that the hourglass shape of Makani’s nebula is strongly reminiscent of similar galactic winds in other galaxies, but that Makani’s wind is much larger than in other observed galaxies.
“This means that we can confirm it’s actually moving gas from the galaxy into the circumgalactic regions around it, as well as sweeping up more gas from its surroundings as it moves out,” Rupke explained. “And it’s moving a lot of it — at least one to 10 percent of the visible mass of the entire galaxy — at very high speeds, thousands of kilometers per second.”
Rupke also noted that while astronomers are converging on the idea that galactic winds are important for feeding the CGM, most of the evidence has come from theoretical models or observations that don’t encompass the entire galaxy.
“Here we have the whole spatial picture for one galaxy, which is a remarkable illustration of what people expected,” he said. “Makani’s existence provides one of the first direct windows into how a galaxy contributes to the ongoing formation and chemical enrichment of its CGM.”
This study was supported by the National Science Foundation (collaborative grant AST-1814233, 1813365, 1814159 and 1813702), NASA (award SOF-06-0191, issued by USRA), Rhodes College and the Royal Society. | 0.828727 | 4.185039 |
Gravitation, Astrophysics, and Theoretical Physics
Gravitational physics has grown over the past few decades from a small area of research concerned mainly with mathematical properties of Einstein’s theory of general relativity into a broad field whose theoretical aspects range from astrophysics and cosmology to quantum gravity, one of the most challenging boundaries of our current understanding of the nature of matter and space time. Gravitational physics has also developed a solid experimental side with the building of a variety of gravitational wave detectors and with high-precision tests of gravitational effects on Earth and in orbit; it has found practical applications in the GPS system as well as in the guidance of spacecraft.
The University of Mississippi is at the forefront or modern research in experimental and theoretical gravity, astrophysics and cosmology. Here, researchers actively participate to the LIGO experiment. They study the emission of gravitational waves from astrophysical sources, try to understand the geometrical structure of space-time at the smallest scales, and contribute to the worldwide search for the ultimate theory of quantum gravity.
For more details on the gravitational and high-energy theory research program at The University of Mississippi, see the GR website.
The goal of the LIGO experiment is to detect gravitational waves, explore the fundamental physics of gravity, and develop the emerging field of gravitational-wave astronomy. The University of Mississippi is an institutional member of the LIGO Scientific Collaboration, contributing to the experiment in the areas of data analysis and detector characterization. One of the LIGO detectors is located in southern Louisiana, about four hours drive from The University of Mississippi. As part of their research, senior members of the LIGO Team and graduate students actively participate in commissioning and monitoring the instrument on site.
Theoretical Astrophysics and Classical General Relativity
The University of Mississippi hosts one of the most active groups working on binary systems composed of black holes and/or neutron stars. Our main goal is to use gravitational-wave observations of these binaries to test Einstein’s general relativity, to rule out alternative theories of gravity, and to tell black holes from more exotic alternatives. We are also exploring the astrophysical information carried by the full set of events that will be observed: LIGO will reveal important clues on the evolution of compact binaries and on their relation with gamma-ray bursts; LISA will tell us how the massive black holes lurking at the center of most galaxies were born, and how they grew during cosmic history. From a more theoretical standpoint, we are studying Einstein’s theory of gravity in the most extreme conditions with “numerical experiments” in which we smash black holes at speeds close to the speed of light.
Quantum Gravity and Extra Dimensions
Over the past decades, attempts to formulate a theory of quantum gravity focused largely on loop quantum gravity and superstrings. Loop quantum gravity aims towards a rigorous quantization of gravity as a theory of space-time geometry. Investigations at The University of Mississippi focus mainly on how the quantum geometry of space-time at the smallest scales leads to classical general relativity at macroscopic scales. Specific problems studied here include calculating the macroscopic observational effects of the microscopic quantum geometry, and finding quantum states for gravity, which appear like a classical continuum at large scales. | 0.823566 | 3.978822 |
BICEP Curls: What the recent results mean for inflation, gravitational waves and multiple universes
On March 17th 2014, a press conference was called at Harvard University. Rumours flourished briefly, and then an announcement was made to great excitement. The BICEP2 experiment had detected B-mode polarisation in the cosmic microwave background 1.
In response, a very small number of scientists working in a few very specialised areas went “cool!”, and then started bickering about why it was cool. Parts of the astrophysical and particle physics communities got a bit excited. Most other folk went “huh?”, and then got on with their lives. Here I will do my best to explain to you the significance of the results and what they even mean in the first place.
To begin at the beginning, BICEP2 is a telescope at the South Pole. BICEP stands for Background Imaging of Cosmic Extragalactic Polarisation and BICEP2 is the second generation of this telescope. It images background radiation, as opposed to foreground radiation which would come from sources like nearby stars. Cosmic is in space, extragalactic is further away than our galaxy and polarisation is kind of like direction.
To be more specific, light can be either polarised or unpolarised. It might have a vertical polarisation, which would mean that the light waves oscillate up and down; or it might have a horizontal polarisation which would mean that they oscillate right and left. They might have a spiral polarisation or something weirder or even a combination of all of these. E-modes and B-modes are two kinds of polarisation, or ways in which light can curl. It is these kinds of polarisation that we are interested in for this experiment. E-modes can be produced through a variety of mechanisms, but B-modes can only be produced through gravitational waves.
So BICEP2 was imaging light from further away than our galaxy to see what kind of polarisation it has, if any. To get more specific, it was imaging background light that is especially distant. As far away as any light we can measure in our universe. Since light travels at a finite speed, this far-away light is also the oldest light we can measure. It is primordial light, the “first light” and was created 380,000 years after the big bang.
The early universe, moments after the Big Bang, was very small and compact. The pressures and temperatures were extraordinary. All the matter in the universe was condensed into a sort of superheated plasma. Electrons and quarks were free to move around in this plasma and were not bound to each other in atoms.
Electrons are really great at deflecting photons (particles of light). So if a photon were to exist in the plasma it wouldn’t be able to go anywhere before it got deflected by an electron. It took a while after the big bang (about 380,000 years) before the universe was big enough, the pressures low enough, and the temperatures cool enough for electrons and protons to join as atoms and hence to get out of the way of the photons, so that light could finally get somewhere. The moment this happened light did precisely that. This is the first light. It still exists today as low energy microwaves and, since all of space came out of that plasma, it can be measured throughout all of space.
These microwaves make up what is known as the cosmic microwave background radiation (CMBR) and were first detected accidentally in 1965 by Arno Penzias and Robert Wilson. They were working at Bell Telephone Laboratories trying to explain a noise source they were measuring with their telescope. At first they thought it was caused by pigeon droppings on the telescope dish and they spent a long time cleaning off the droppings. When the noise was still there they realised they had made a discovery, the cosmic microwave background radiation.
It’s surprisingly uniform (incidentally, if you tune an old analogue TV to an unused channel about 1% of what you see is this radiation). We measure the temperature of the radiation and find it to be 2.7 K (-270 °C) everywhere, but only if your thermometer isn’t very sensitive. Later experiments were designed with better thermometers specifically to measure it. The first of these experiments was COBE (the Cosmic Background Explorer) 2 and the most recent experiment was Planck 3. They found that if you have a better thermometer you can detect small differences in the background, fluctuations and small features, but that these fluctuations are tiny.
This brings me to cosmic inflation. The fact that the CMBR was relatively uniform was puzzling to cosmologists. It’s a bit surprising to find that if you look as far as you can in one direction, and then as far as you can in precisely the opposite direction you see the same thing. It’s too far for light to have travelled all the way from one end to the other – light isn’t fast enough to do that – so how does space know that it should look the same in both directions?
Inflation is a theory which tried to resolve this by proposing two things. Firstly, the big bang happened and the universe expanded like crazy at first and then slowed down. Secondly, because of that, for a long time everything in the universe was really close together and light travelled from one end of the universe to the other while it did still have time to do so, and that’s why opposite ends of the universe are the same temperature.
That seemed like a neat solution. However, at the time there wasn’t a great deal of solid evidence to support the theory. In physics if you have a theory but you don’t have any measurements, then you get a whole bunch of different people coming up with their own versions and their own models. It’s only when you start making measurements that you can refine these, put limits on them and start to rule out certain models and theories. The measurement of B-modes is not only direct evidence of inflation, but restricts the form that inflation could have taken.
Heisenberg’s Uncertainty Principle
What about those fluctuations? The CMBR is uniform on the largest scales but fluctuates on the small scale; the more closely you look or the more accurately you measure it, the more you find small features which are not uniformly distributed. Why should it fluctuate at all if there was time for everything to settle down and get to the same temperature before the universe really started expanding?
To understand this you need to know a bit about the Heisenberg Uncertainty Principle. Werner Heisenberg came up with this one (as opposed to Walter White). You may have heard of it in terms of momentum and position; you can measure an object’s momentum as precisely as you like, but to do this you have to sacrifice your precision on your measurement of its position. The same goes the other way around. There are many other pairs of variable like this, where you can measure one infinitely precisely, so long as you don’t know anything at all about the other. That’s typical of quantum physics.
One of those pairs is energy and time. So you can measure how much energy something has, so long as you don’t know precisely over what time period it will have that energy. This is important for inflation because it means that over extremely short time periods energy need not necessarily be conserved; you can get something out of nothing. The “borrowed” energy needs to be paid back, but not immediately. So you can create a particle and an antiparticle out of the vacuum of space. They will quickly combine and annihilate, but temporarily you had nothing, then something, then nothing again. According to quantum theory, this happens all the time and everywhere in the universe.
Since energy and matter are interchangeable and particles count as matter, we can think of this process as fluctuations in energy. You get a little increase in energy as a particle is created and a little decrease as it annihilates. These tiny fluctuations existed at the moment of inflation and, as a result, they still can be seen now in the fluctuations of the CMBR. Those primordial fluctuations caused the formations of stars and galaxies and galactic clusters and all the structure we have in our universe today.
Funnily enough, it turns out that via a similar mechanism you can also get fluctuations in gravitation. The echos of those fluctuations make up part of what the BICEP2 experiment was able to measure.
Gravitational waves and gravitational lensing
Two gravitational effects were indirectly measured by BICEP: gravitational lensing and gravitational waves. Both are relativistic effects. Here’s how it works:
1. Einstein comes along and says we’ve got gravity all wrong – Newton did well to figure things out to begin with, but there’s more to this than meets the eye. Gravity isn’t just what happens because two heavy things find each other attractive – it’s the shape of space itself.
- He says, “get this, heavy stuff bends space.”* He means that if you’ve got a star, the fabric of space itself bends around that star. Just a little, because space is a pretty stiff fabric, but it bends a measurable amount (although Einstein himself thought the effect would be too small to measure). Other heavy stuff then moves around according to the degree to which space is bent. Some guy called John Archibald Wheeler put it like this, “spacetime tells matter how to move; matter tells spacetime how to curve.” 4**
- It doesn’t just work for matter. It turns out that light itself will also follow the curved path if spacetime has been bent out of shape by a star or other massive object.This is known as gravitational lensing because matter acts like a lens, changing the path of the light.
Remember those gravitational fluctuations I was talking about? Turns out they were enough to do some lensing and BICEP was sensitive enough to measure how much lensing they did. That’s not all though, it was also sensitive enough to indirectly measure gravitational waves.
Gravitational waves happen when something moves that is heavy enough to bend spacetime. Only asymmetrical motion will work, otherwise the waves cancel out. What happens is that these heavy things that are bending spacetime move around and cause ripples and wobbles which can propagate a little like water waves on the surface of a pond.
These gravitational waves are tiny and elusive. So far no one has measured them directly, but there is evidence for their existence. The first indirect measurement was carried out by Hulse and Taylor 5. They observed a pair of pulsars (pulsars are a kind of star) which were orbiting their common centre of gravity. As they did so they lost energy, leading Hulse and Taylor to conclude that they must be losing energy through gravitational waves, because no other mechanism seemed possible, and because the system was losing energy in precisely the way that was predicted by Einstein.
The second indirect measurement is the B-modes in the CMBR as measured by BICEP2. E-modes were measured as well, but were a much larger effect and so needed to be subtracted away from the data so that the B-modes could be seen at all. Both were expected but the presence of B-modes can only be explained through gravitational waves. These ripples in spacetime must have caused this kind of polarisation.
Finally, we get to multiple universes. Perhaps you’ve heard the idea that our universe is not necessarily the only one. There could be other universes out there that popped into being just the way that ours did. Of course, they don’t exist in our set of spacetime so most people think it would be impossible for us to detect them or to interact with them, but they could still exist.
This sounds like science fiction, but there are cosmological models which predict that multiple universes can exist. Indeed there are models which say that they must exist. As Professor Marc Kamionkowski said in the press conference on the 17th of March, “You can have inflationary models which don’t imply multiple universes, but most of them do.” He went on to point out that when inflation was first suggested it didn’t make any testable predictions, but now not only do testable predictions exist, they have been tested. Perhaps one day this will be possible for multiple universe theory as well. I’m not holding my breath but it would certainly be impressive.
To properly understand the BICEP2 results you need to first understand a great deal of physics. Really you need to understand electromagnetic theory, quantum theory and the uncertainty principle, relativity, inflationary theory, electroweak and grand unified theories, elements of particle physics and cosmology, statistics, mathematics, telescopes, gravitational waves, gravitational lensing, multiple universe theories, the difference between a theory and a model and all sorts of other things besides. I was at a conference on gravitational waves on the day that this announcement was made. Four days later someone was finally brave enough to say “I think I understand parts of this” and had a go at giving a lecture on it.
However, with that in mind, these measurements are significant and fascinating. They have far-reaching consequences for cosmology, astronomy and particle physics (I haven’t mentioned much about this, but if you’re curious go look up “inflatons”) and they teach us something new about our universe and where we came from. It’s encouraging to have evidence to support inflation and gravitational waves and it is intriguing to hear about multiple universes – even if predictions surrounding them should be made only tentatively and with great care.
Without wishing to detract from any of that I, should also urge a little caution when looking at and interpreting these results, if only because BICEP2 is the first experiment to have detected these B-modes. Until another experiment can independently verify them, the scientific community should not take the measurements as absolute and indisputable evidence. While to my amateurish and inexperienced eyes the evidence is convincing, it is still entirely possible that there is some systematic error that was overlooked. However, the Planck collaboration is due to release results from a similar experiment in October, at which point many people will be a lot happier to label this as a “discovery.”
Until then we wait with baited breath and look forward to all the interesting ideas that the theorists will be busily producing based on what has already been measured. I feel that the BICEP2 group should also be thanked for releasing all of their data and making it freely available online. It would be nice to see more of this in science in general; by doing so, they have allowed the theorists and everyone else to really get to grips with the implications of what is truly a fascinating discovery.
*Not technically an actual, genuine Einstein quote.
**Actual, genuine John Archibald Wheeler quote.
BICEP Curls: What the recent results mean for inflation, gravitational waves and multiple universes by Rebecca Douglas was specialist edited by Sean Leavey and copy edited by Jessica Bownes
- P. A. R. Ade et al, BICEP2 I: Detection of B-mode polarization at degree angular scales, arXiv preprint arXiv:1403.3985 (2014)
- E. L. Wright et al, Interpretation of the COBE FIRAS CMBR spectrum, The Astrophysical Journal. 1994.
- J. M. Lamarre et al. The Planck high frequency instrument, a third generation CMB experiment, and a full submillimeter survey, New Astronomy Reviwews. 2003.
- Kenneth Ford and John Archibald Wheeler, Geons, Blackholes and Quantum Foam: A Life in Physics, W. W. Norton and Company, 1st edn, 2010, p 235
- R.A. Hulse. The discovery of the binary pulsar(PSR 1916 +13). Reviews of Modern Physics, 1994. And also, J.H. Taylor. Binary pulsars and relativistic gravity. Reviews of Modern Physics, 1994 | 0.832629 | 3.791841 |
Crescent ♋ Cancer
Moon phase on 15 June 2007 Friday is New Moon, less than 1 day young Moon is in Gemini.Share this page: twitter facebook linkedin
Moon rises at sunrise and sets at sunset. It's part facing the Earth is completely in shadow.
Lunar disc is not visible from Earth. Moon and Sun apparent angular diameters are ∠1919" and ∠1889".
Next Full Moon is the Strawberry Moon of June 2007 after 15 days on 30 June 2007 at 13:49.
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 03:13 on this date the Moon completes the old and enters a new synodic month with lunation 92 of Meeus index or 1045 from Brown series.
29 days, 8 hours and 51 minutes is the length of new lunation 92. It is 2 hours and 8 minutes shorter than next lunation 93 length.
Length of current synodic month is 3 hours and 53 minutes shorter than the mean length of synodic month, but it is still 2 hours and 16 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠38.7°. At beginning of next synodic month true anomaly will be ∠64.2°. 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°).
2 days after point of perigee on 12 June 2007 at 17:07 in ♉ Taurus. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 9 days, until it get to the point of next apogee on 24 June 2007 at 14:25 in ♎ Libra.
Moon is 373 573 km (232 128 mi) away from Earth on this date. Moon moves farther next 9 days until apogee, when Earth-Moon distance will reach 404 540 km (251 370 mi).
7 days after its ascending node on 8 June 2007 at 00:35 in ♓ Pisces, the Moon is following the northern part of its orbit for the next 5 days, until it will cross the ecliptic from North to South in descending node on 20 June 2007 at 19:32 in ♍ Virgo.
7 days after beginning of current draconic month in ♓ Pisces, the Moon is moving from the beginning to the first part of it.
At 08:31 on this date the Moon is meeting its North standstill point, when it will reach northern declination of ∠28.212°. Next 14 days the lunar orbit will move in opposite southward direction to face South declination of ∠-28.215° in its southern standstill point on 29 June 2007 at 15:41 in ♐ Sagittarius.
The Moon is in New Moon geocentric conjunction with the Sun on this date and this alignment forms Sun-Moon-Earth syzygy. | 0.823901 | 3.105778 |
You are here
Last November, the Ministerial Council of the European Space Agency (ESA) gave the go-ahead for the launch of the Hera mission, for which you are the scientific coordinator. Can you outline the history of this European research project, which has been postponed a number of times?
Patrick Michel: The idea of the project first arose in 2004, when the ESA asked a group of six scientists, including myself, to plan a series of missions aimed at addressing the risk of an asteroid impacting the Earth. Of the six proposals, two were designed to approach such an object as closely as possible in order to characterise its structure using radar or microsatellites. Another of the missions, known as Don Quijote, featured an asteroid deflection trial. At the time, this combined an impactor, called Hidalgo, and an orbiter named Sancho, whose job was to measure the effect of the deflection. Due to lack of funding, Don Quijote was shelved for a few years, before re-emerging as a collaboration, now renamed AIDA, between NASA and the ESA.1
Although in 2016 the European component of the project, initially christened AIM, was unable to obtain the funding it needed from the ESA Ministerial Council, it was nonetheless welcomed by the international community working on small bodies and planetary defence. Encouraged by this support, we therefore conducted another study aimed at optimising the project, now dubbed Hera, before successfully resubmitting it to the Ministerial Council in 2019. So it took us fifteen years to finally make this mission a reality.
Now that the whole AIDA project has been confirmed, what is the main purpose of this international research programme?
P.M.: In its current configuration, the project combines the DART impactor, designed by the US, and the Hera orbiter, which will measure the deflection of the asteroid after the collision. Hera will also carry out a detailed characterisation of the asteroid’s physical properties and composition. The mission will target the binary asteroid Didymos, which is made up of a principal body and a smaller one in orbit around it, informally named Didymoon, which will be impacted by DART.
Targeting a binary body will enable us to instantaneously observe the effects of the deflection, since Didymoon orbits around the main asteroid very slowly in comparison with DART’s impact velocity. In addition, Didymos will pass relatively close to the Earth at the moment of impact, which opens up the possibility of using Earth-based observatories to measure the change in Didymoon’s orbital period around the main asteroid. Although the goal of the DART/Hera mission focuses on planetary defence strategies, the data collected will also be of great interest not only to scientists who study small celestial objects but also to those concerned with potentially exploitable resources in space.
How will Hera fit in with the American part of the mission?
P.M.: The US satellite will launch from California in July 2021 and will reach Didymos in October 2022. Before DART hits the smaller asteroid, Didymoon, the mission will deploy the LICIA CubeSat. This mini-satellite developed by the Italian space agency will be used to view the first seconds of the impact. However, it won’t be able to observe the formation of the crater due to the cloud of dust produced by the collision. At the same time, an international observation campaign using Earth-based radars and optical telescopes will measure the variation in the orbital period of Didymoon caused by the shock. Hera will then take off from French Guiana in 2024, reaching the asteroid in January 2027. The spacecraft will subsequently make a detailed analysis of the effects of the impact.
In what way is this project not only unprecedented but also key to designing an effective planetary defence system?
P.M.: Firstly, Hera will be the first space mission to rendezvous with a binary asteroid, a configuration that makes up 15% of the asteroids that enter the Earth’s neighbourhood. With a diameter of barely 160 metres, Didymos’s moon, Didymoon, will be the smallest such body ever visited. The mission will also be the first to probe an asteroid’s interior: one of the CubeSats accompanying Hera will be equipped with a radar able to analyse Didymoon’s deep structure. Within the Hera team, the scientific expertise for this technique, in which France is a leading player, will be provided by Alain Hérique, a planetary scientist at the IPAG.2
As regards planetary defence, Hera will calculate Didymoon’s mass as well as the properties of the impact crater. Measuring the mass is key to quantifying the momentum transferredFermerQuantity equal to the product of the mass and velocity of a moving body. When two objects collide, the total momentum of both bodies is conserved. by the DART projectile when it hits the asteroid. If no matter is ejected during the impact, only DART’s momentum will be transferred, and the deflection will therefore be minimal. Conversely, if a large amount of matter is released, the deflection will be maximised. To determine the result, we will need to know Didymoon’s momentum. This depends on its mass, which only Hera will be able to measure.
In addition, the amount of matter expelled is also a function of Didymoon’s internal structure. For example, a porous body will absorb the collision, which will reduce the amount of ejected matter and thus the deflection produced. In order to fully assess the effects of the impact, we must ascertain the momentum transferred by the shock, the properties of the crater, and Didymoon’s structure. This information will also enable us to validate the deflection technique as well as the numerical impact simulations so that they can be applied to other scenarios with a higher confidence level. Without this direct data obtained in a real-life situation, we will not be in a position to make any progress in this area.
What significance does this mission have from the point of view of fundamental research?
P.M.: Collisions have been crucial in the formation and evolution of our Solar System. The planets were initially formed by slow-moving shocks in which large amounts of material stuck together. In a second stage, giant impacts gave rise to natural satellites such as the Moon. Today, we are at a stage when asteroid crashes are breaking them up into smaller fragments or are producing craters on every celestial body in the Solar System. Understanding these processes, on scales that are impossible to achieve in the laboratory, will allow us to better define and characterise the history of collisions in our Solar System.
By giving us the opportunity to study a large-scale impact of which DART will record the initial context, and Hera will measure the final conditions, the mission will make it possible to take a giant step forward in our knowledge of crater formation processes in the Solar System. Moreover, to improve our understanding of small bodies, we need to elucidate the mechanisms governing them under their very low-gravity conditions. This fascinating challenge is of interest to a wide range of scientific communities, including those that study the dynamics of granular environments.
As a researcher, you have a special interest in the origins of near-Earth objects (NEOs). What were your scientific contributions in this field?
P.M.: My work helped to show that most of these objects, which are less than a few tens of kilometres in size, result from the clumping together of fragments from collisions between asteroids in the main asteroid belt, located between the orbits of Mars and Jupiter.3 Such aggregates of rocks are sometimes found in unstable regions, which can cause them to shift from circular orbits to more elongated ones where there is a possibility that they cross the Earth’s orbit. Over the past four billion years this population of celestial bodies has remained stable, since its ‘mortality rate’, mainly caused by the Sun’s attraction, is constantly offset by the formation of new objects in the belt.
By analysing the impact craters on the Moon and theoretical models of NEO populations, including those developed in our laboratory, we reckon that there are about 1,000 NEOs with diameters exceeding 1 km, 90% of which have already been identified (which was the goal set for NASA by the US Congress in 1998). Our models have also shed new light on the NEO population. A paper published at the beginning of the year in the journal Icarus4 has drawn up an almost complete inventory of these objects in terms of size, distribution and albedo (reflectivity), all of which tells us about their composition.
How did we first become aware that collisions with celestial objects could be a threat to life on Earth?
P.M.: Until the late 1960s and the Apollo programme’s first lunar exploration missions, the scientific community was convinced that the craters seen on the surface of the Moon were of volcanic origin. Analysis of the samples collected during the Apollo missions finally showed that these were in fact caused by meteorite collisions. One of the very first political acts that acknowledged the hazard associated with the impact of an asteroid was a European resolution adopted in 1996. This inititative was prompted by comet Shoemaker-Levy colliding with Jupiter in July 1994, the first event of this kind to be directly witnessed by humankind.
At an international workshop on NEOs held in Turin (Italy) in 1999, the community of experts on small bodies subsequently set up the well-known Torino Scale. This system, which was meant to be understood by the general public and the media, aimed to provide a measurement of the impact hazard associated with any asteroids threatening the Earth. At the same time, an increasing number of NEOs were discovered, and the initial calculations of their paths, obtained from their estimated orbits (which are still very uncertain when they are carried out on the basis of early observations), sometimes resulted in a non-zero probability of collision with the Earth over shorter or longer time scales.
The discovery in December 2004 of an NEO called Apophis was another turning point in this growing awareness.
P.M.: Trajectory calculations based on the initial observations of the object, which has a diameter of 325 metres, effectively gave a very high chance of collision with the Earth in 2029. Although new radar investigations carried out in 2013 subsequently showed that the asteroid would merely brush by our planet in 2029 and then again in 2036, we suddenly realised that there was no protocol to respond to a disaster of this nature. With a view to setting up an international decision-making process on these issues, I took part in the work of a team commissioned by the UN. This led to the creation of two separate working groups: the first, made up of asteroid specialists, was tasked with predicting the chances of an impact with one of these celestial bodies, while the second brought together the various space agencies in order to organise a possible response to the hazard.
Since 2009, international space agencies and scientific experts have also been meeting at the biennial Planetary Defense Conference to present advances in impact simulation studies, as well as various ideas for missions aimed at deflecting asteroids. On these occasions, a virtual exercise based on a scenario developed by colleagues from the Jet Propulsion Laboratory (California, US) enables us to test our ability to respond to this risk. Since 2012, the European Commission has also been funding consortia — such as NEO-MAPP, of which I am the coordinator — to study this problem.
How can the astrophysics community help predict this type of disaster, which after all remains exceptional?
P.M.: Admittedly, this is the least likely of natural disasters, in comparison with other hazards such as earthquakes, tornadoes and tsunamis. But when one does occur it could have very serious consequences. Unlike earthquakes, we now have the means to predict and prevent an asteroid strike.
To do this, two courses of action must be taken. First, we need to make the most exhaustive inventory possible of objects that exceed 140 metres in diameter, which is the threshold above which an asteroid will affect inhabited areas in whatever region of the world it strikes. In a few decades, it should be possible to achieve this from Earth, using next-generation ground-based telescopes such as the LSST in Chile and Pan-STARRS on the Hawaiian island of Maui. However, within a decade, the American NEOSM mission, which has received encouraging support from the US Congress in its 2020 budget, should be able to do this from space, starting in 2025. Once we’ve completed this catalogue, we should be in a position to determine whether any of these objects pose a direct threat. If, in parallel with this survey, the first attempt at deflecting an asteroid carried out by DART/Hera proves successful, we will have gone a long way towards solving the risk of asteroid collisions.
You are also closely involved in the Hayabusa2 programme, overseen by the Japan Aerospace Exploration Agency (JAXA), and in OSIRIS-REx, funded by NASA. The aim of both these missions is to bring back to Earth samples collected from the near-Earth asteroids Ryugu and Bennu, respectively. Have these two missions yet enabled scientists to find out more about such near-Earth asteroids?
P.M.: Apart from information such as their shape and size, we knew nothing so far about the structure and composition of these objects or about their surface features. All the scientists who, like me, have been lucky enough to take part in these missions have had an extraordinary opportunity to explore two asteroids that were completely uncharted territory located several hundred million kilometres from Earth. Among our most surprising discoveries were the abundance of boulders and the lack of any rock-free areas larger than five metres in diameter.
On one and the same body we also observed extremely varied rock morphologies, whereas we had expected to find a relatively uniform environment. In January 2019, the OSIRIS-REx programme also showed that Bennu was an active object with particles escaping from its surface. A paper published last year in the journal Science5 outlines the different scenarios that could explain this plume of particles, which remains something of a mystery. As well as scientific advances, these missions to small celestial objects are able to capture the general public’s imagination, due to the atmosphere of suspense that surrounds them. This is confirmed by the success of the talks that I give, which aim to get the excitement of these challenging missions across to younger people.
What are we likely to learn from the analysis of the samples that will have returned to Earth by the end of the year for Hayabusa2 and by 2023 for OSIRIS-REx?
P.M.: First of all, we should be able to determine the properties of the basic building blocks present in the early Solar System that gave rise to the formation of the planets. In the various scenarios developed at the J.L. Lagrange laboratory in Nice , we have already shown that a massive asteroid bombardment occurred towards the end of the Earth's formation, around 4.7 billion years ago.
We still don’t know whether the prebiotic material that led to the emergence of life on our planet came from the asteroids. Once we have collected organic materials from the samples returned from Bennu and Ryugu and subjected them to a high-precision analysis in research laboratories, we may be able to find out whether life on Earth was the result of bombardment by meteorites. Measuring the degree of shock in these same samples should also tell us about the intensity of the collisions experienced at the time these asteroids were formed and during the early stages of our Solar System’s history.
To what extent will the findings of missions designed to study near-Earth asteroids help to anticipate their possible impact with the Earth, while implementing effective strategies to prevent such a disaster?
P.M.: By studying NEOs the missions will improve our understanding of these potential enemies, even though personally I prefer to think of them as friends! Thanks to Hayabusa2 and OSIRIS-REx we now know for example that an asteroid with a diameter exceeding 400 metres can have a large number of sizeable rocks evenly distributed over its surface. This characteristic is therefore now taken into consideration when drawing up deflection strategies.
We have also discovered that the density of dark carbonaceous objects like Bennu and Ryugu scarcely exceeds that of water, since these bodies are very porous. So in the event of an impact, a large amount of the energy would be dissipated by the compaction of the porous parts. We therefore believe that the force required to deflect an object of this kind would have to be greater than for a brighter, denser stony asteroid such as Itokawa, investigated in 2005 by the Hayabusa1 mission, and samples of which were brought back to Earth in 2010. However, all this is still uncertain, and the result of DART’s impact is eagerly awaited in order to verify this hypothesis.
Does this mean that the planned defence system will depend not only on the size of the object involved but also on its composition and internal structure?
P.M.: A priori, all this data will have to be taken into consideration before an asteroid is deflected. If the NEOSM mission comes to fruition, it will be possible to characterise the size and density of a potentially threatening object at a very early stage, which will then enable us to calculate the amount of energy needed to deflect it.
That said, the deflection test carried out by the DART/Hera mission will be performed blind, since we have no prior information about the structure and composition of Didymoon. If this first attempt is successful despite the uncertainties, we will then know that the precise nature of the target asteroid is not necessarily a determining factor when it comes to deflecting such an object. Yet in the absence of this real-life test, we are for now completely in the dark.
- 1. Senior researcher at the CNRS, head of the Planetary Science group at the J.L. Lagrange laboratory in Nice (Unité CNRS / Université Côte d’Azur / Observatoire de la Côte d'Azur).
- 2. Institut de planétologie et d'astrophysique de Grenoble (CNRS / Université Grenoble-Alpes).
- 3. “Collision and gravitational reaccumulation: forming asteroid families and satellites”, P. Michel et al., Science, 2001, vol. 294 :1696-1700. https://doi.org/10.1126/science.1065189
- 4. “Debiased albedo distribution for Near Earth Objects”, A. Morbidelli, M. Delbo et al, Icarus, 11 January 2020. On line
- 5. “Episodes of particle ejection from the surface of the active asteroid (101955) Bennu”, D. S. Lauretta, C. W. Hergenrother et al., Science, published 6 December 2019. https://doi.org/10.1126/science.aay3544
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After first studying biology, Grégory Fléchet graduated with a master of science journalism. His areas of interest include ecology, the environment and health. From Saint-Etienne, he moved to Paris in 2007, where he now works as a freelance journalist. | 0.860581 | 3.326669 |
Completion of the first of a total of four Large-Size Telescopes (LST) on La Palma is advancing in leaps and bounds. Scientists and technicians involved in telescope construction have now installed 181 individual mirrors on the telescope. The telescope has a diameter of 23 meters; the entire area of the mirrors is approximately 390 square meters.
An eye for high-energy objects in the cosmos
The task of the telescope mirror is to capture and bundle radiation from the atmosphere. The light is recorded by a camera and electronically analyzed. The light is what is known as Cherenkov radiation, which is generated when high-energy gamma rays from space hit the atmosphere. This method allows high-energy celestial objects to be investigated.
Examples of such celestial bodies include black holes in galactic centers, supernova remnants or pulsars, a special type of neutron star. They emit gamma radiation, sometimes for periods of only a few hours. So-called gamma-ray bursts, the cosmic sources of which remain unknown to this day, often flicker for only a few minutes or even seconds.
Fast reaction times, optimal light yield
In order to observe and classify the routes taken by gamma emissions, scientists need measuring instruments that respond quickly and flexibly – capturing as much as possible of the light that can be analyzed.
The LST is optimally designed to meet these demands: the hexagonal, approximately 1.5-meter wide and 6.6-centimeter thick, individual mirrors weigh only 45 kilograms. Thanks to the lightweight design of the mirrors, the gross weight of the movable telescope dish is a mere 28 tons. This allows the telescope, despite its size, to be rotated and tipped into any position in less than 20 seconds.
The mirrors reflect 94 percent of the incident light – traditional mirrors around 90 percent. To increase light yield even further, the mirrors can be exactly aligned with the angle of incidence of the light source. This is done by a complex control system, allowing each mirror to be moved individually.
The telescope and the mirrors are exposed to extreme weather conditions. A special coating material, consisting of five layers, makes the mirrors especially durable.
The CTA Observatory
The LST prototype is the first of four telescopes of this kind, which will be built over the next few years at the "Roque de los Muchachos" observatory on La Palma in the Canary Islands. Twelve medium-sized telescopes, specialized in Cherenkov radiation (Medium-Sized Telescopes, MST) are also planned.
The second CTA Observatory site is the Paranal facility in Chile. Together, the CTA telescopes therefore provide coverage of both the northern and southern celestial hemispheres. There will be over 100 telescopes across both sites; in Chile, very small telescopes, the Small-Sized Telescopes (SST), are also planned, in addition to LST and MST.
The three telescope models cover different energy ranges, allowing astrophysicists to investigate the origins of cosmic gamma radiation in detail. | 0.860608 | 3.913042 |
A satellite left Earth this week on a mission to open the dark side of the moon to Chinese exploration. The relay satellite can be used to communicate with the far reaches of the moon, allowing controllers on Earth to maintain contact with an expected lunar probe later this year to unexplored territory.
But the pioneering space travel has raised concern that China is also interested in the tiny spots on the moon that never go dark, the polar peaks of eternal light.
Those peaks are vanishingly small, occupying one-one hundred billionth of the lunar surface − roughly equivalent to three sheets of NHL ice on Earth. But their near-ceaseless sunshine gives them great value as a source of solar energy, to power everything from scientific experiments to mining operations.
Their small size could also, scientists have argued, allow one country to take sole occupancy of this unique real estate without falling afoul of the Outer Space Treaty. That agreement stipulates that no state can exert sovereignty in outer space. But it also calls on countries “to avoid interference” with equipment installed by others.
That provides a loophole of sorts, researchers say. The installation of very sensitive equipment on the peaks of eternal light, such as a radio telescope − a 100-metre long uncovered wire used to study transmissions from the sun, and deeper corners of the universe − could use up much of the available space while also providing a rationale to bar others from the area on the grounds that the telescope is too sensitive to be disturbed.
“Effectively a single wire could co-opt one of the most valuable pieces of territory on the moon into something approaching real estate, giving the occupant a good deal of leverage even if their primary objective was not scientific inquiry,” researchers from Harvard University, King’s College London and Georg-August Universitat Gottingen wrote in a 2015 paper.
Such a possibility is not speculative, said Alanna Krolikowski, a scholar at Missouri University of Science and Technology who has written on the peaks. As global interest in lunar exploration rises, “There’s going to be issues like this for sure,” she said. “The poles are the most attractive places on the moon. Everyone wants to go there. And if you want to do things, you need power − and the peaks are the most attractive power source.”
China has chosen the Aitken Basin as the landing site for a lunar probe to the dark side of the moon. The south pole peaks of eternal light lie within the Aitken Basin, a huge impact crater that’s some 2,500 kilometres across.
Chinese researchers have cited the study of radio signals as one of the primary reasons to devote attention to the area.
Indeed, the availability of sunlight is a key consideration for China as it considers building a more permanent establishment on the moon in the future, Pang Zhihao, a retired researcher with the Beijing Institute of Space Science and Technology Information, wrote in a 2013 article for the Beijing News.
“There are two basic requirements for a moon base location: plenty of sunlight and abundant water and ice,” he wrote. He added: “Some areas of the polar region are almost permanently exposed to sunlight, while some are the opposite. So by combining them both, we could get sunlight, water and ice.”
Reached for comment, Prof. Pang said the government has barred him and other scientists from discussing the Chang’e-4 mission without prior permission. Chang’e-4 is the name of China’s planned dispatch of a rover to the dark side of the moon.
Chinese authorities have been careful to position their ambitions as international ones, equipped with instruments developed in Germany, the Netherlands, Saudi Arabia and Sweden.
International observers believe China already possesses the technology to reach the lunar south pole, although it is not alone in its ambitions. Private company Moon Express, based in Cape Canaveral, Fla., has announced plans to install an observatory and research station on the peaks of eternal light. The European Space Agency is developing a lander for the lunar south pole and points out that “maximizing its exposure to the sun is vital.”
A series of discoveries has reinvigorated interest in the moon, including indications that it contains vast quantities of water, as well as other valuable resources.
But in many ways, “China is the story to watch” in the new moon rush, said Leonard David, a journalist who has written about space for more than half a century. “That far side landing they want to do would be historic − nobody has ever done that.”
The peaks of eternal light are valuable even for landing a spacecraft, since they are less vulnerable to temperature swings − which can exceed 200 Celsius degrees in other places − and don’t require stocking battery supplies to power through a 14-day lunar night.
But if any entity moves to occupy such important real estate to the exclusion of others, it will set a dangerous precedent, warned Elvis Martin, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics.
“If you go and grab the peaks of eternal light, you’ve just said to everybody that that’s okay. Then it could be like the scramble for Africa in the European colonial period. People just rush in and grab everything they can.”
That possibility begs a prior solution.
“Some kind of international co-ordination agreement or something is needed before we all get caught in this kind of race for the resources,” he said.
With reporting by Alexandra Li | 0.846463 | 3.247478 |
Skywatchers around the world will get a once-in-a-lifetime chance to see Venus cross in front of the sun today (June 5). The so-called transit of Venus is more than just the last such event for more than a century — it might help shed light on some of the enduring mysteries of our planetary neighbor.
Bizarre stripes on Venus
Strange stripes in the upper clouds of Venus are called "blue absorbers" or "UV absorbers" because they absorb blue and ultraviolet wavelengths of light. These soak up a dramatic amount of energy — nearly half of the total solar energy the world takes in. As such, they seem to play a key role in keeping Venus as hot as it is, with surface temperatures of more than 860 degrees Fahrenheit (460 degrees Celsius).
The Venus Express spacecraft the European Space Agency launched in 2005 is armed with what's called a solar occultation spectrometer "to help us pinpoint the altitude and latitude distribution for these UV absorbers and understand their behavior a bit more now," said David Grinspoon, curator of astrobiology at the Denver Museum of Nature and Science. "However, we have not yet definitively identified it. We think it's a sulfur compound, or it could be a form of elemental sulfur."
The sunlight streaming around Venus during its transit "may help probe Venus' atmosphere," Grinspoon told SPACE.com. "We could ask interesting questions about its concentration of sulfur gas."
The secret of lightning on Venus
Evidence of lightning on the planet was confirmed by Venus Express, even though such weather displays should be impossible there.
"You need rainfall for lightning, and we're not sure if we actually get rainfall on Venus," said Grinspoon, an interdisciplinary scientist on the Venus Express mission. "But in some ways, we don't really understand lightning on Earth very well, so by cracking how lightning works on Venus, we may understand it better here. With Venus Express, we're getting more information at the latitudes lightning's distributed in, which we hope to link with activity in the atmosphere."
The Venus Climate Orbiter Akatsuki, which means "Dawn" in Japanese, was supposed to help capture vital clues about Venusian lightning with a camera dedicated to photographing it. Unfortunately, the Japanese space probe overshot the planet in 2010, although there's a chance it may still get to Venus. "It's a shame Akatsuki didn't make it into orbit around Venus — it was primed to address many questions, this matter of lightning in particular," Grinspoon said.
One of the biggest mysteries of Venus is the "super-rotation" of its atmosphere. Violent winds drive storms and clouds around that world at speeds of more than 220 mph (360 kph), some 60 times faster than the planet rotates.
"Super-rotation is still an unsolved mystery, but we're building more sophisticated 3-D models of cloud motion to simulate it," Grinspoon said. "They could end up helping us better understand how climate works on other planets, including exoplanets and Earth."
While these questions are perplexing, there is one unsolved mystery about the planet that takes the cake.
"The greatest mystery of Venus to me is what happened to its oceans," Grinspoon said.
The long-vanished oceans of Venus are thought to have been culprits of what is called a runaway greenhouse effect. Scientists think that planet's close proximity to the sun heated its water, causing it to build up in Venus' atmosphere as steam. Water is a greenhouse gas, trapping heat from the sun that would have vaporized still more water, a vicious cycle that heated Venus enough to boiled away its oceans.
Ultraviolet light would have then eventually split this atmospheric water into hydrogen and oxygen. The hydrogen escaped into space, the oxygen became trapped in the rocks of the planet, and the end-result was a bone-dry Venus.
Still, the specifics of this event remain uncertain. "How long did the oceans take to dissipate? How did Venus evolve?" Grinspoon asked. "Those are hard questions to answer, and we don't have a time machine to go back and see."
Venus Express is helping answer these questions by monitoring gases in the planet's atmosphere and witnessing hydrogen and oxygen escaping from Venus. "Given that data, we can hopefully extrapolate backward in time and get an idea of what the past was like," Grinspoon said. | 0.871149 | 3.939122 |
Asteroid families more common than believed
Asteroids travel in families, and there are more of them than we thought, according to new measurements from NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft.
Asteroid families are occasionally formed when two asteroids collide. Fragments of the bodies can travel along with one or both of the asteroids through space, creating such a grouping. As time goes on, these families slowly drift apart. Some of these can head toward the Earth, with potentially catastrophic results.
The smaller pieces of stone are generally made of the same materials which compose their parent body. Detecting the makeup of these small objects can be difficult in visible light, but the infrared cameras of the WISE spacecraft made that task easier.
"We're separating zebras from the gazelles. Before, asteroid family members were harder to tell apart because they were traveling in nearby packs. But now we have a better idea of which asteroid belongs to which family," Joseph Masiero of NASA's Jet Propulsion Laboratory, lead author of the study, said.
When images from NEOWISE, the tools aboard the WISE spacecraft meant to discover new asteroids, was examined, researchers discovered 28 new families of asteroids. Thousands of previously-identified asteroids were classified into families for the first time.
Most asteroids stay in stable orbits, mainly between the orbits of Mars and Jupiter, but collisions can send some of these boulders heading on a collision course with Earth. Any such asteroid which travels within 28 million miles of our home world is considered a Near-Earth object, or NEO.
"NEOWISE has given us the data for a much more detailed look at the evolution of asteroids throughout the solar system. This will help us trace the NEOs back to their sources and understand how some of them have migrated to orbits hazardous to the Earth," Lindley Johnson, program executive for the Near-Earth Object Observation Program at NASA Headquarters in Washington, said.
The space observatory took millions of individual images of bodies in the asteroid belt. Masiero's team studied 120,000 of these objects, around one-fifth of the 600,000 known asteroids. Researchers were able to assign about 38,000 of these bodies to families. Where there had only been 48 recognized families of asteroids before the new WISE survey, that list of family names had to be expanded to 76 when research was complete.
The WISE spacecraft was put into hibernation mode in 2011 after photographing the entire sky twice.
The new study appears in the Astrophysical Journal.
Scientists Have Simulated The Asteroid That Caused The Extinction Of The Dinosaurs
Using a supercomputer, scientists simulated the asteroid that hit the Earth and made all the dinosaurs go extinct and left behind the Chicxulub crater. Their results are shocking.
NASA's Hubble Catches Asteroid ATLAS Breaking Off Into House-Sized Lumps Before It Could Come Close Enough To Be Seen Without A Telescope
NASA observes an asteroid shatter as ATLAS loses its brightness, see the spectacle here!
Look! A Massive Asteroid 'Wearing' Face Mask Flying Past Coronavirus-Stricken Earth Next Week Was Caught on Cam
The scientists that took a photograph of 1998 OR2. are currently executing social distancing guidelines as well as wearing face masks at all times while in the facility, which brought about the hilarious surprise. Zoom out to see it yourself!
Another Asteroid To Pass Closely To Earth Is Being Monitored By Nasa; That And Several Others On The Watchlist
Several asteroids will make close quarters visit with Earth this year, see which ones you should look out for in the sky
Asteroid Contact: NASA To Perform 'Checkpoint Rehearsal' As OSIRIS-REx Temporarily Lands To Take Sample Of 'Bennu'
NASA's Spacecraft OSIRIS'REx set to touch-down on Asteroid Bennu to take samples to bring home.
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The Navigation Cameras (Navcam) of the Mars Science Laboratory rover, Curiosity, have been used to examine two aspects of the planetary boundary layer: vertical dust distribution and dust devil frequency. The vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line-of-sight optical depth within Gale Crater and comparing this optical depth to column optical depths obtained using Mastcam observations of the solar disc. The line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere. This suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of Gale Crater and the higher elevation Meridiani Planum. In the case of dust devils, despite an extensive campaign only one optically thick vortex (τ = 1.5 ± 0.5 × 10-3
) was observed compared to 149 pressure events >0.5 Pa observed in REMS pressure data. Correcting for temporal coverage by REMS and geographic coverage by Navcam still suggests 104 vortices should have been viewable, suggesting that most vortices are dustless. Additionally, the most intense pressure excursions observed on other landing sites (pressure drop >2.5 Pa) are lacking from the observations by the REMS instrument. Taken together, these observations are consistent with pre-landing circulation modeling of the crater showing a suppressed, shallow boundary layer. They are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era. | 0.830061 | 3.660155 |
ALMA Resolves Gas Impacted by Young Jets from Supermassive Black Hole
Astronomers obtained the first resolved image of disturbed gaseous clouds in a galaxy 11 billion light-years away by using the Atacama Large Millimeter/submillimeter Array (ALMA). The team found that the disruption is caused by young powerful jets ejected from a supermassive black hole residing at the center of the host galaxy. This result will cast light on the mystery of the evolutionary process of galaxies in the early Universe.
It is commonly known that black holes exert strong gravitational attraction on surrounding matter. However, it is less well known that some black holes have fast-moving streams of ionized matter, called jets. In some nearby galaxies, evolved jets blow off galactic gaseous clouds, resulting in suppressed star formation. Therefore, to understand the evolution of galaxies, it is crucial to observe the interaction between black hole jets and gaseous clouds throughout cosmic history. However, it had been difficult to obtain clear evidence of such interaction, especially in the early Universe.
In order to obtain such clear evidence, the team used ALMA to observe an interesting object known as MG J0414+0534. A distinctive feature of MG J0414+0534 is that the paths of light traveling from it to Earth are significantly distorted by the gravity of another ‘lensing’ galaxy between MG J0414+0534 and us, causing significant magnification.
“This distortion works as a ‘natural telescope’ to enable a detailed view of distant objects,” says Takeo Minezaki, an associate professor at the University of Tokyo.
Another feature is that MG J0414+0534 has a supermassive black hole with bipolar jets at the center of the host galaxy. The team was able to reconstruct the ‘true’ image of gaseous clouds as well as the jets in MG J0414+0534 by carefully accounting for the gravitational effects exerted by the intervening lensing galaxy.
“Combining this cosmic telescope and ALMA’s high-resolution observations, we obtained exceptionally sharp vision, that is 9,000 times better than human eyesight,” adds Kouichiro Nakanishi, a project associate professor at the National Astronomical Observatory of Japan/SOKENDAI. “With this extremely high resolution, we were able to obtain the distribution and motion of gaseous clouds around jets ejected from a supermassive black hole.”
Thanks to such a superior resolution, the team found that gaseous clouds along the jets have violent motion with speeds as high as 600 km/s, showing clear evidence of impacted gas. Moreover, it turned out that the size of the impacted gaseous clouds and the jets are much smaller than the typical size of a galaxy at this age.
“We are perhaps witnessing the very early phase of jet evolution in the galaxy,” says Satoki Matsushita, a research fellow at Academia Sinica Institute of Astronomy and Astrophysics. “It could be as early as several tens of thousands of years after the launch of the jets.”
“MG J0414+0534 is an excellent example because of the youth of the jets,” summarizes Kaiki Inoue, a professor at Kindai University, Japan, and the lead author of the research paper which appeared in the Astrophysical Journal Letters. “We found telltale evidence of significant interaction between jets and gaseous clouds even in the very early evolutionary phase of jets. I think that our discovery will pave the way for a better understanding of the evolutionary process of galaxies in the early Universe.”
Paper and the Research Team
These observation results are presented in K. T. Inoue et al. “ALMA 50-parsec resolution imaging of jet-ISM interaction in the lensed quasar MG J0414+0534” appeared in the Astrophysical Journal Letters on March 27, 2020.
The research team members are:
Kaiki T. Inoue (Faculty of Science and Engineering, Kindai University), Satoki Matsushita (Academia Sinica Institute of Astronomy and Astrophysics), Kouichiro Nakanishi (ALMA Project, National Astronomical Observatory of Japan/School of Physical Sciences, SOKENDAI), and Takeo Minezaki (School of Science, the University of Tokyo) .
This research was supported by JSPS KAKENHI (No. 17H02868, 19K03937); NAOJ ALMA Scientific Grant Number 2018-07A; Ministry of Science and Technology (MoST) of Taiwan, MoST 103-2112-M-001-032-MY3, 106-2112-M-001-011, and 107-2119-M-001-020.
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. | 0.887517 | 4.09765 |
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