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Gone With the Galactic Wind: 10 Years of Chandra
When NASA launched its Chandra X-ray observing telescope into orbit in 1999, astronomers didn’t know much about the galactic winds made of wispy, multi-million-degree gas clouds that stream out from normal galaxies like our own, because they are “diffuse, gentle and unspectacular” compared to far more dramatic emanations of starbursts, recalls astronomer Q. Daniel Wang of the University of Massachusetts Amherst.
But direct observation by the Chandra orbiting telescope have changed all that and led to “the first characterization of the spatial, thermal, chemical and kinetic properties of the gas in our galaxy,” Wang states. Chandra data show, among other things, that though seemingly as ephemeral as fog, the outflowing hot gas from normal galaxies exerts a very powerful feedback force on the surroundings, preventing or slowing the infall of intergalactic gas due to gravity. “This discovery is a new key to our understanding of how galaxies work, especially how they lose mass and energy, that was not possible before Chandra,” he adds.
The astronomer catalogs the new knowledge in an article published this week in the early online edition of Proceedings of the National Academy of Sciences. Because his group has made extensive use of Chandra data, he was asked to write a review celebrating the instrument’s 10-year anniversary.
As Wang explains, galaxies like our own are made of visible stars and gas but investigating this matter and its properties using only visible light reveals only a small fraction of material actually present. “The hot gas is very hard to detect because of its low density, hence weak radiation, compared to black holes and neutron stars that accrete from their companions, which tend to overwhelm X-ray emissions from a galaxy,” he adds.
“By X-raying galaxies, we can see the invisible, and with the Chandra instrument we can detect gas that emits or absorbs X-rays, as well as such exotic objects as black holes and neutron stars that tend to emit primarily in X-rays.” X-ray tomography by the high-spectral resolution Chandra instrument has given astronomers the unprecedented opportunity to examine the amount, distribution and composition of the hot gas against bright background sources.
It has also helped to yield clues to the mystery of why there is not enough hot gas present inside or in the immediate vicinity of galaxies as predicted by current theory, in particular elements synthesized and ejected by stars. In fact, says Wang, “we find that the bulk of energy expected from the supernovae is missing as well. We conclude that this missing energy is gone with the wind, a galactic wind that blows matter to much larger regions around galaxies than previously understood.”
“Indeed, we find direct evidence for such winds and outflows in nearby galaxies. This uses another well-known capability of the Chandra, the exquisite spatial resolution, which allows us to detect discrete X-ray sources and to remove them cleanly when mapping X-ray emission in and around galaxies. The outflows are called galactic feedback, which can have profound impact on the ecosystem of the galaxies.”
“These results, compared with detailed simulations, now enable us to study how the feedback regulates the formation and evolution of galaxies,” Wang says.
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|Image Credit: NASA/CXC Source: University of Massachusetts Amherst Permalink: http://www.sflorg.com/comm_center/unv_space/p1004_42.html Time Stamp: 3/12/2010 at 7:07:01 PM UTC|
Scientist Explains Whistler Turbulence in Space
Gusty winds streaming off our Sun are called solar wind and this wind propagates outwardly and develops in complicated structures, i.e. turbulence, in space and time all across the interplanetary space. The behavior of the solar wind is quite unpredictable and has long been a subject of comprehensive research because it governs numerous processes that directly impacts planet Earth.
These include geomagnetic storm, hazardous cosmic particles, space weather etc. Understanding the behavior of solar wind is therefore very critical. In situ spacecraft measurements, theory and modeling are trying to find out a fundamental question; how energy from the solar wind is transferred across many different scales (like packets or eddies of various shapes and sizes) in the interplanetary space. Unfortunately, owing to its complex nature, the problem of solar wind turbulence continues to remain one of the unresolved issues in space physics.
What is remarkably complicated is the multitude of length and time scales on which turbulence is happening throughout the interplanetary space. At very high (higher than ion cyclotron) frequency, the magnetized solar wind plasma excites whistler waves (that sounds like whistles and were first discovered by World War I radio operators) whose behavior is far more complicated than ever thought. Unfortunately their dynamics is poorly understood in the context of solar wind turbulence that transfers energy from large scale down to the scales where the wind heats up the local plasma in the interplanetary space.
A new fluid model developed by Professor Dastgeer Shaikh at the Physics Department and Center for Space Plasma and Aeronomic Research at The University of Alabama in Huntsville (UAHuntsville), links turbulence in solar wind to the transfer of energy in space and might help shed light on this mysterious process.
Dr. Shaikh discovered that the transfer of energy in solar wind occurs much quicker than predicted by earlier theories and that density of these waves do not affect the manner in which energy is transferred across the small scale high frequency whistler turbulence in the solar wind plasma. “Earlier researchers have ignored the effect of density fluctuations on whistler wave turbulence and this step was very crucial for us to take in a forward direction if are to understand the solar wind turbulence,” he said.
“Unfortunately we are not yet well equipped to measure the role of density fluctuations in the regime where whistler waves play a critical role in converting the solar wind energy into heat,” said Dr Shaikh, who added that his work is therefore very important to test observationally by in situ measurements. “Since density does not modify the general consensus of solar wind turbulence, that follows a universal power law, we like to believe that they interact weakly with the wave magnetic field at such a high frequency,” he said.
Dr. Shaikh is a leading scientist in the field of whistler and solar wind turbulence at UAHuntsville. His results agree with the spacecraft observations that measured the solar wind energy law 20 years ago. The research results of Dr. Shaikh are to appear in Monthly Notices of the Royal Astronomical Society.
|Source: University of Alabama Huntsville Permalink: http://www.sflorg.com/comm_center/unv_space/p1003_41.html Time Stamp: 3/12/2010 at 6:48:09 PM UTC|
Aussie galaxy survey to lead to "new physics"
astronomers have released the first set of data from the first
project to look at the effects of “dark energy”
halfway back in the Universe's lifetime.
|Image Caption: Time goes from top to bottom. The "bullseyes" show where there have been two sources of pressure waves in the early universe, the waves traveling outwards like the ripples on a pond. Galaxies prefer to grow at the center and edge of the bullseye. Their preferred separation is the radius of the bullseye (the scale bar). Image Credit: Sam Moorefield, Swinburne University Source: University of Queensland Permalink: http://www.sflorg.com/comm_center/unv_space/p986_40.html Time Stamp: 12/10/2009 at 4:38:37 PM UTC|
Life on Mars theory boosted by new methane study
Scientists have ruled out the possibility that methane is delivered to Mars by meteorites, raising fresh hopes that the gas might be generated by life on the red planet, in research published tomorrow (Wednesday 9 December 2009) in Earth and Planetary Science Letters.
Methane has a short lifetime of just a few hundred years on Mars because it is constantly being depleted by a chemical reaction in the planet's atmosphere, caused by sunlight. Scientists analyzing data from telescopic observations and unmanned space missions have discovered that methane on Mars is being constantly replenished by an unknown source and they are keen to uncover how the levels of methane are being topped up.
Researchers had thought that meteorites might be responsible for Martian methane levels because when the rocks enter the planet's atmosphere they are subjected to intense heat, causing a chemical reaction that releases methane and other gases into the atmosphere.
However, the new study, by researchers from Imperial College London, shows that the volumes of methane that could be released by the meteorites entering Mars' atmosphere are too low to maintain the current atmospheric levels of methane. Previous studies have also ruled out the possibility that the methane is delivered through volcanic activity.
This leaves only two plausible theories to explain the gas's presence, according to the researchers behind today's findings. Either there are microorganisms living in the Martian soil that are producing methane gas as a by-product of their metabolic processes, or methane is being produced as a by-product of reactions between volcanic rock and water.
Co-author of the study, Dr Richard Court, Department of Earth Science and Engineering at Imperial College London, says:
"Our experiments are helping to solve the mystery of methane on Mars. Meteorites vaporising in the atmosphere are a proposed methane source but when we recreate their fiery entry in the laboratory we get only small amounts of the gas. For Mars, meteorites fail the methane test."
The team say their study will help NASA and ESA scientists who are planning a joint mission to the red planet in 2018 to search for the source of methane. The researchers say now that they have discovered that meteorites are not a source of Methane on Mars, ESA and NASA scientists can focus their attention on the two last remaining options.
Co-author, Professor Mark Sephton, Department of Earth Science and Engineering at Imperial College London, adds:
"This work is a big step forward. As Sherlock Holmes said, eliminate all other factors and the one that remains must be the truth. The list of possible sources of methane gas is getting smaller and excitingly, extraterrestrial life still remains an option. Ultimately the final test may have to be on Mars."
The team used a technique called Quantitative Pyrolysis-Fourier Transform Infrared Spectroscopy to reproduce the same searing conditions experienced by meteorites as they enter the Martian atmosphere. The team heated the meteorite fragments to 1000 degrees Celsius and measured the gases that were released using an infrared beam.
When quantities of gas released by the laboratory experiments were combined with published calculations of meteorite in-fall rates on Mars, the scientists calculated that only 10 kilograms of meteorite methane was produced each year, far below the 100 to 300 tonnes required to replenish methane levels in the Martian atmosphere.
This research was funded by a grant from the Science Technology Facilities Council.
Imperial College London
Time Stamp: 12/8/2009 at 3:30:54 PM UTC
Researchers make rare meteorite find using new camera network in Australian desert
Researchers have discovered an unusual kind of meteorite in the Western Australian desert and have uncovered where in the Solar System it came from, in a very rare finding published today in the journal Science.
Meteorites are the only surviving physical record of the formation of our Solar System and by analyzing them researchers can glean valuable information about the conditions that existed when the early Solar System was being formed. However, information about where individual meteorites originated, and how they were moving around the Solar System prior to falling to Earth, is available for only a dozen of around 1100 documented meteorite falls over the past two hundred years.
Dr Phil Bland, the lead author of today's study from the Department of Earth Science and Engineering at Imperial College London, said: "We are incredibly excited about our new finding. Meteorites are the most analyzed rocks on Earth but it's really rare for us to be able to tell where they came from. Trying to interpret what happened in the early Solar System without knowing where meteorites are from is like trying to interpret the geology of Britain from random rocks dumped in your back yard."
The new meteorite, which is about the size of cricket ball, is the first to be retrieved since researchers from Imperial College London, Ondrejov Observatory in the Czech Republic, and the Western Australian Museum, set up a trial network of cameras in the Nullarbor Desert in Western Australia in 2006.
The researchers aim to use these cameras to find new meteorites, and work out where in the Solar System they came from, by tracking the fireballs that they form in the sky. The new meteorite was found on the first day of searching using the new network, by the first search expedition, within 100m of the predicted site of the fall. This is the first time a meteorite fall has been predicted using only the data from dedicated instruments.
The meteorite appears to have been following an unusual orbit, or path around the Sun, prior to falling to Earth in July 2007, according to the researchers' calculations. The team believes that it started out as part of an asteroid in the innermost main asteroid belt between Mars and Jupiter. It then gradually evolved into an orbit around the Sun that was very similar to Earth's. The other meteorites that researchers have data for follow orbits that take them back, deep into the main asteroid belt.
The new meteorite is also unusual because it is composed of a rare type of basaltic igneous rock. The researchers say that its composition, together with the data about where the meteorite comes from, fits with a recent theory about how the building blocks for the terrestrial planets were formed. This theory suggests that the igneous parent asteroids for meteorites like today's formed deep in the inner Solar System, before being scattered out into the main asteroid belt. Asteroids are widely believed to be the building blocks for planets like the Earth so today's finding provides another clue about the origins of the Solar System.
The researchers are hopeful that their new desert network could yield many more findings, following the success of their first meteorite search.
Dr Bland added: "We're not the first team to set up a network of cameras to track fireballs, but other teams have encountered problems because meteorites are small rocks and they're hard to find in vegetated areas. Our solution was quite simple - build a fireball network in a place where it's easy to find them. The Nullarbour Desert is ideal because there's very little vegetation and dark rocks show up really easily on the light desert plain.
"It was amazing to find a meteorite that we could track back to its origin in the asteroid belt on our first expedition using our small trial network. We're cautiously optimistic that this find could be the first of many and if that happens, each find may give us more clues about how the Solar System began," said Dr Bland.
The researchers' network of cameras takes a single time-lapse picture every night to record any fireballs in the sky. When a meteorite falls, researchers can then use complex calculations to uncover what orbit the meteorite was following and where the meteorite is likely to have landed, so that they can retrieve it.
|Source: Imperial College London Permalink: http://www.sflorg.com/comm_center/unv_space/p927_38.html Time Stamp: 9/17/2009 at 7:26:28 PM UTC|
Earthshine reflects Earth’s oceans and continents from the dark side of the Moon
Researchers from the University of Melbourne and Princeton University have shown for the first time that the difference in reflection of light from the Earth’s land masses and oceans can be seen on the dark side of the moon, a phenomenon known as earthshine.
Sally Langford from the
University of Melbourne’s School of Physics who conducted
the study as part of her PhD, says that the brightness of the
reflected earthshine varied as the Earth rotated, revealing the
difference between the intense mirror-like reflections of the
ocean compared to the dimmer land.
The paper is published in this week’s edition of the international journal Astrobiology.
|Source: University of Melbourne Permalink: http://www.sflorg.com/comm_center/unv_space/p896_37.html Time Stamp: 4/7/2009 at 3:21:05 AM UTC|
Astrophysicist Helps Map the Milky Way’s Four Spiral Arms
Iowa State University’s Martin Pohl is part of a research team that has developed the first complete map of the Milky Way galaxy’s spiral arms.
The map shows the inner part of the Milky Way has two prominent, symmetric spiral arms, which extend into the outer galaxy where they branch into four spiral arms.
“For the first time these arms are mapped over the entire Milky Way,” said Pohl, an Iowa State associate professor of physics and astronomy. “The branching of two of the arms may explain why previous studies – using mainly the inner or mainly the outer galaxy – have found conflicting numbers of spiral arms.”
The new map was developed by Pohl, Peter Englmaier of the University of Zurich in Switzerland and Nicolai Bissantz of Ruhr-University in Bochum, Germany.
As the sun and other stars revolve around the center of the Milky Way, researchers cannot see the spiral arms directly, but have to rely on indirect evidence to find them. In the visible light, the Milky Way appears as an irregular, densely populated strip of stars. Dark clouds of dust obscure the galaxy’s central region so it cannot be observed in visible light.
The National Aeronautics and Space Administration’s Cosmic Background Explorer satellite was able to map the Milky Way in infrared light using an instrument called the Diffuse IR Background Experiment. The infrared light makes the dust clouds almost fully transparent.
Englmaier and Bissantz used the infrared data from the satellite to develop a kinematic model of gas flow in the inner galaxy. Pohl used the model to reconstruct the distribution of molecular gas in the galaxy. And that led to the researchers’ map of the galaxy’s spiral arms.
The Milky Way is the best studied galaxy in the universe because other galaxies are too far away for detailed observations. And so studies of the galaxy are an important reference point for the interpretation of other galaxies.
Astrophysicists know that the stars in the Milky Way are distributed as a disk with a central bulge dominated by a long bar-shaped arrangement of stars. Outside this central area, stars are located along spiral arms.
In addition to the two main spiral arms in the inner galaxy, two weaker arms exist. These arms end about 10,000 light-years from the galaxy’s center. (The sun is located about 25,000 light-years from the galactic center.) One of these arms has been known for a long time, but has always been a mystery because of its large deviation from circular motion. The new model explains the deviation as a result of alternations to its orbit caused by the bar’s gravitational pull. The other, symmetric arm on the far side of the galaxy was recently found in gas data.
The discovery of this second arm was a great relief for Englmaier: “Finally it is clear that our model assumption of symmetry was correct and the inner galaxy is indeed quite symmetric in structure.”
Other scientific groups are already interested in using the new map for their research. A group from France, for example, hopes to use it in their search for dark matter.
|Source: Iowa State University Permalink: http://www.sflorg.com/comm_center/unv_space/p819_36.html Time Stamp: 1/5/2009 at 3:31:14 PM UTC|
Embargo Till: 18:00 UTC December 31, 2008
Hubble Telescope to Get Last Tuneup During International Year of Astronomy
From troubled beginnings nearly 18 years ago, the Hubble Space Telescope has revolutionized astronomy and its stunning images have stirred the imaginations of people around the globe.
But as the International Year of Astronomy dawns, the renowned telescope is preparing for its final chapter, starting with the scheduled May 12 launch of the space shuttle Atlantis for NASA's fifth and final service mission to the telescope.
The repairs will provide Hubble with a future as bright, though perhaps not nearly as long, as its past, said Julianne Dalcanton, a University of Washington associate professor of astronomy who for nearly a decade has used the telescope for a major part of her research.
Dalcanton is the author of a review article in the Jan. 1 edition of Nature that recounts the storied history of Hubble and its many contributions to astronomy, most of which could not have been achieved by ground-based telescopes.
She attributes Hubble's success to the fact that it orbits nearly 350 miles above the Earth, far removed from the atmosphere and ambient light that limit the effectiveness of ground-based telescopes, and says the upcoming servicing mission will likely allow Hubble to add to its already rich legacy of scientific discovery.
That legacy includes helping to revolutionize astronomers' understanding of phenomena called black holes and their role in forming galaxies; more detailed observations of pulsating stars called Cepheids that enhanced the ability to judge the huge distances involved in stellar astronomy; and, most recently, producing an image, the first direct evidence, of a planet orbiting a star outside our solar system.
"One of the things Hubble has done is enhance the precision with which we can carry out research," Dalcanton said. "And the images produced have really spurred public interest. Those pictures are on screen savers throughout the world."
Hubble was launched on April 24, 1990, as a joint venture of NASA, the European Space Agency and the Space Telescope Science Institute. But the mission got off to a rocky start when it was discovered that an error had been made in fabricating the main mirror and its images were often fuzzy at best. The problem was corrected on NASA's first service mission in 1993 and the telescope has been wildly successful ever since.
One of the biggest successes, Dalcanton believes, is the democratization of Hubble's data. Astronomers place requests for the telescope to make specific observations, and if their project is accepted the data is returned to them to continue their work. But after one year, the data becomes available for anyone to use for any type of study.
"You don't have to be at Harvard or CalTech. You can be at a small Midwestern liberal arts teaching college and still have the opportunity to work with Hubble data," she said.
Asked what Hubble's greatest contribution is, Dalcanton was hard pressed to single one out from among the telescope's many accomplishments. She suspects the answers might vary greatly among astronomers who have different research goals.
The upcoming service mission, among other things, will replace gyroscopes and heat shields, upgrade instruments and add "some spiffy new capabilities that will allow us to make much deeper observations."
Dalcanton is pleased that she and others will have at least another five years or so to work with Hubble. The telescope eventually will be replaced by the James Webb Space Telescope, though the Webb telescope will focus more on the infrared part of the spectrum and won't produce the same type of images that Hubble has.
"It's a great telescope and I'm happy to be part of it," she said. "Like any tool, the more you use it the more you are able to get the best out of i
|Source: University of Washington Permalink: http://www.sflorg.com/comm_center/unv_space/p814_35.html Time Stamp: 12/31/2008 at 18:00:00 UTC|
PS3s Help Astrophysicists Solve Black Hole Mystery
Using only the computing power of 16 Sony Playstation 3 gaming consoles, scientists at The University of Alabama in Huntsville and the University of Massachusetts, Dartmouth, have solved a mystery about the speed at which vibrating black holes stop vibrating.
It may be the first time this kind of research has been conducted exclusively on a PS3 cluster: A related 2007 UMass Dartmouth/UAHuntsville project using a smaller PS3 cluster also used a "traditional" supercomputer to run its simulations.
The biggest advantage of the console cluster — the PS3 Gravity Grid — at UMass Dartmouth was the cost saving, said Dr. Lior Burko, an assistant physics professor at UAHuntsville. "If we had rented computing time from a supercomputer center it would have cost us about $5,000 to run our simulation one time. For this project we ran our simulation several dozens of times to test different parameters and circumstances, so you can see how much that would have cost us.
"You can build a cluster like this for perhaps $6,000, and then you can run the simulation as many times as you like at no additional cost."
"Science budgets have been significantly dropping over the last decade," said UMass Dartmount Physics Professor Gaurav Khanna, who built the PS3 cluster. "Here's a way that people can do science projects less expensively."
Khanna recently launched a website which includes step-by-step instructions for building a supercomputing PS3 cluster.
The PS3 cluster was well suited to this type of astrophysical research, which requires a large number of mathematical calculations but has low demands for RAM memory, Burko said. "Not every kind of job would be suitable for that system, but it is exactly the kind of computation that we did."
The current price for supercomputing time through a center like the National Science Foundation's TeraGrid or the Alabama Supercomputing Center is about $1 per CPU hour. Each PS3 has a powerful Cell processor. The 16-unit PS3 grid can complete a 5,000-CPU-hour (and $5,000) simulation run in about a day. That is a speed comparable to a rented supercomputer.
Published in the journal, "Classical and Quantum Gravity," the new research resolved a dispute over the speed at which black holes stop vibrating after they first form or are perturbed by something like swallowing some matter.
"Think of a bell," said Burko. "A bell rings, but eventually it gets quiet. The energy that goes out with the sound waves is energy that the bell is losing. A black hole does exactly that in gravitational waves instead of sound waves. A black hole that is wobbling is emitting gravitational waves. When those vibrations die down you get a quiet black hole."
(Most black holes are "quiet," which means the only things astronomers can measure are their mass and how fast they spin.)
Khanna and Burko used a high resolution computer simulation to "perturb" a simulated spinning black hole, then watched as it returned to its quiet state. They found that the speed at which black holes go quiet was the faster of the two competing theories.
|Source: University of Alabama Huntsville Permalink: http://www.sflorg.com/comm_center/unv_space/p800_34.html Time Stamp: 12/22/2008 at 2:35:20 PM UTC|
Researchers Interpret Asymmetry in Early Universe
The Big Bang is widely considered to have obliterated any trace of what came before. Now, astrophysicists at the California Institute of Technology think that their new theoretical interpretation of an imprint from the earliest stages of the universe may also shed light on what came before.
"It's no longer completely crazy to ask what happened before the Big Bang," comments Marc Kamionkowski, Caltech's Robinson Professor of Theoretical Physics and Astrophysics. Kamionkowski joined graduate student Adrienne Erickcek and senior research associate in physics Sean Carroll to propose a mathematical model explaining an anomaly in what is supposed to be a universe of uniformly distributed radiation and matter.
Their investigations turn on a phenomenon called inflation, first proposed in 1980, which posits that space expanded exponentially in the instant following the Big Bang. "Inflation starts the universe with a blank slate," Erickcek describes. The hiccup in inflation, however, is that the universe is not as uniform as the simplest form of the theory predicts it to be. Some parts of it are more intensely varied than others.
Until recently, measurements of the Cosmic Microwave Background (CMB) radiation, a form of electromagnetic radiation that permeated the universe 400,000 years after the Big Bang, were consistent with inflation--miniscule fluctuations in the CMB seemed to be the same everywhere. But a few years ago, some researchers, including a group led by Krzysztof Gorski of NASA's Jet Propulsion Laboratory, which is managed by Caltech, scrutinized data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP). They discovered that the amplitude of fluctuations in the CMB is not the same in all directions.
"If your eyes measured radio frequency, you'd see the entire sky glowing. This is what WMAP sees," Kamionkowksi describes. WMAP depicts the CMB as an afterglow of light from shortly after the Big Bang that has decayed to microwave radiation as the universe expanded over the past 13.7 billion years. The probe also reveals more pronounced mottling--deviations from the average value--in the CMB in one half of the sky than the other.
"It's a certified anomaly," Kamionkowski remarks. "But since inflation seems to do so well with everything else, it seems premature to discard the theory." Instead, the team worked with the theory in their math addressing the asymmetry.
They started by testing whether the value of a single energy field thought to have driven inflation, called the inflaton, was different on one side of the universe than the other. It didn't work--they found that if they changed the mean value of the inflaton, then the mean temperature and amplitude of energy variations in space also changed. So they explored a second energy field, called the curvaton, which had been previously proposed to give rise to the fluctuations observed in the CMB. They introduced a perturbation to the curvaton field that turns out to affect only how temperature varies from point to point through space, while preserving its average value.
The new model predicts more cold than hot spots in the CMB, Kamionkowski says. Erickcek adds that this prediction will be tested by the Planck satellite, an international mission led by the European Space Agency with significant contributions from NASA, scheduled to launch in April 2009.
For Erickcek, the team's findings hold the key to understanding more about inflation. "Inflation is a description of how the universe expanded," she adds. "Its predictions have been verified, but what drove it and how long did it last? This is a way to look at what happened during inflation, which has a lot of blanks waiting to be filled in."
But the perturbation that the researchers introduced may also offer the first glimpse at what came before the Big Bang, because it could be an imprint inherited from the time before inflation. "All of that stuff is hidden by a veil, observationally," Kamionkowski says. "If our model holds up, we may have a chance to see beyond this veil."
The study appears December 16 in the journal Physical Review D. It was supported by the Department of Energy and by Caltech's Moore Center for Theoretical Cosmology and Physics.
|Source: California Institute of Technology Permalink: http://www.sflorg.com/comm_center/unv_space/p799_33.html Time Stamp: 12/16/2008 at 3:24:43 PM UTC|
Study Provides Possible Explanation for Migration of Volcanic Activity on Mars
Picture a ball. It's an ordinary ball in every way except that it is roughly 4,300 miles in diameter and is moving through the cold of space some 35 million miles from Earth, and hurtling around the sun in just less than two Earth years. This is Mars.
After a first glance at the Martian surface, one may quickly notice two striking global-scale features. The first is the three-mile elevation difference between the northern lowlands and southern highlands, known as the Crustal Dichotomy, which got the name because the highlands and lowlands are underlain by thick and thin crust, respectively. The second feature is the vast area of high elevation with numerous volcanoes near the equator covering a quarter of the Martian surface, known as the Tharsis Rise.
For a moment consider the tectonic plates that make up the crust of the Earth, including the way they move around the planet, rising from below as molten rock and dipping back down under the surface to melt and complete the chain. Earth is the only planet known to scientists that has this mechanism for moving huge sections of the planet's surface great distances. This movement accounts for, among other things, the chain of land masses that form the Hawaiian Islands. As the Pacific Plate moves over a plume of molten rock, the islands formed, one after another.
This is not the case on Mars, which appears to have a single plate that encapsulates the entire planet like the shell of an egg. But Shijie Zhong, associate professor of physics at the University of Colorado at Boulder, thinks this shell-like plate might be moving, driven by a powerful, single plume of hot material affecting the area of the thickened crust of the Crustal Dichotomy. This would explain the migration of volcanic activity in the Tharsis Rise region of the formation of Tharsis, he said.
The possibility of a large-scale, horizontal motion of the outer shell of Mars or similar terrestrial planets and moons has not been previously demonstrated, Zhong said. Using three-dimensional numerical models to simulate the slow churning of Mars' interior in response to the cooling of the planet, Zhong shows in the Dec. 14 issue of Nature Geoscience that a single plume of hot material rising through the planet's interior led to the earliest volcanism in the highlands region of the Crustal Dichotomy, simultaneously triggering rotation of the outer shell. As the shell moved southward over the stationary plume -- like a sheet of cardboard over a candle -- it shifted the location of the volcanism and created the Tharsis Rise.
Zhong said a very specific set of circumstances had to fall into place to get rotation of the outer shell to occur. First, he said an area of thickened crust needed to form on the planet's surface. "It is almost universally accepted that the Crustal Dichotomy with the thickened crust in the highlands formed in the first few hundred million years of Mars' existence, and the Tharsis Rise was only formed a few hundred million years later," said Zhong.
Scientists know this because the Tharsis region is nearly devoid of impact sites, unlike the pockmarked surface of the Crustal Dichotomy. "You don't see so many craters," said Zhong. "It's been resurfaced."
Within this smooth environment, obvious features pop from the surface. Volcanoes, in a straight line, mark the Tharsis Rise. One, Olympus Mons -- a still active volcano -- reaches 15 miles into the Martian sky.
"All the faulting, tectonics and volcanics on Mars in the last 4 billion years happen here, in the Tharsis Rise region," said Zhong.
The second condition is the one-plume convection in the mantle. For the last 10 years, Zhong and his collaborators have studied physical mechanisms for one-plume convection to explain hemispherically asymmetric structures known to have existed for terrestrial planets, including the Crustal Dichotomy and Tharsis Rise on Mars, Supercontinents Pangea and Rodinia on Earth, and mare basalts on the Moon.
Zhong's theory is that a single plume of hot material is jetting from the core of Mars out toward the surface. Where it breaks through, on the Tharsis Rise, it causes volcanoes. But it is the affect that the rising, super-heated material has on the neighboring Crustal Dichotomy's thickened shell that makes the shell of Mars move relative to the underlying mantle and the plume.
"The mechanism I'm describing here is a path to unify the two major features of Mars: the Tharsis Rise and the Crustal Dichotomy," said Zhong.
|Source: University of Colorado at Boulder Permalink: http://www.sflorg.com/comm_center/unv_space/p793_32.html Time Stamp: 12/14/2008 at 6:28:44 PM UTC|