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Johannesburg Centre,
Astronomical Society of Southern Africa
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Snipperts from the Astronomical
Press
Date: Thu, 9 Mar 2000 16:30:23 -0500 (EST) VIEW INSIDE MARS REVEALS RAPID COOLING AND BURIED CHANNELS Some of Mars' best kept secrets, long buried beneath the surface of the red planet, were recently revealed by instruments on NASA's Mars Global Surveyor spacecraft. New observations of Mars reveal that the planet's flat northern lowlands were an early zone of high heat flow that later may have been the site of rapid water accumulation, according to a view of the Martian interior generated using data from Mars Global Surveyor (MGS). Elevation and gravity measurements, which have been used to probe beneath the surface of Mars, indicate a period of rapid cooling early in Martian history, and evidence for large, buried channels that could have formed from the flow of enormous volumes of water. This global view of the Martian interior was generated from gravity measurements with the Radio Science experiment and elevation measurements from the Mars Orbiter Laser Altimeter (MOLA) instruments. Gravity and topography measurements were combined to reveal the structure of the crust on Mars, which preserves the record of melting of the interior and the heat loss from the planet over time. "The crustal thickness map shows that, as for Earth, Mars has two distinct crustal provinces," explained Dr. Maria Zuber of the Massachusetts Institute of Technology, Cambridge, MA, and lead author of a study to be published in the March 10 issue of Science. Beneath the rough southern highlands and Tharsis volcanic province the crust, estimated at 50 miles thick, thins progressively from the South pole toward the North. In contrast, the northern lowlands and Arabia Terra region of the southern highlands have a crust of uniform thickness, about 22 miles deep. The crustal structure accounts for the elevation of the Martian northern lowlands, which controlled the northward flow of water early in Martian history, producing a network of valleys and outflow channels. The new gravity-field data suggest that the transport of water continued far into the northern plains. The gravity shows features interpreted as channels buried beneath the northern lowlands emanating from Valles Marineris and the Chryse and Kasei Valles outflow regions. The features are about 125 miles wide and over a thousand miles long, with characteristics that can be explained by water flow on the surface or in a submarine environment, later buried by sediments. The large size of these channels implies that any bodies of water in the northern lowlands could have accumulated rapidly. The now-buried channels may represent the means for filling an early ocean. The gravity and topography also provide information on the cooling of Mars over time, which bears on the early climate and history of water. "The observations suggest that the northern lowlands was a location of high heat loss from the interior early in Martian history, probably due to a period of vigorous convection and possibly plate recycling inside of Mars," said Dr. Sean Solomon, Director of the Department of Terrestrial Magnetism of the Carnegie Institution in Washington, DC, and a co-author of the study. The high heat-loss zone corresponds to the part of Mars proposed to have been the site of an ancient ocean. The rapid transport of heat to the surface in this region would have released onto the surface and into the atmosphere gases and water or ice trapped in the interior. The time of rapid interior heat loss may correspond to the period when Mars had a warmer climate, liquid water flowed on the surface, and the planet's surface was shielded from the solar wind by a global magnetic field. During the ongoing Mars Global Surveyor mapping mission the Radio Science and MOLA experiments will continue to collect data on a near-continuous basis through the end of the mission in February 2001. The MOLA instrument was designed and built by the Laser Remote Sensing Branch of the Laboratory for Terrestrial Physics at NASA's Goddard Space Flight Center, Greenbelt, MD. The Radio Science experiment is implemented from the Center for Radio Astronomy of Stanford University, Palo Alto, CA. The Mars Global Surveyor mission is managed for NASA's Office of Space Science, Washington, DC, by the Jet Propulsion Laboratory, Pasadena, CA, a division of the California Institute of Technology. Maps of the interior of Mars may be viewed at: http://svs.gsfc.nasa.gov/imagewall/MOLA/mola_images.html Information about the MGS Radio Science investigation can be found at: http://nova.stanford.edu/projects/mgs/dmwr.html Information about the MOLA investigation can be found at: http://ltpwww.gsfc.nasa.gov/tharsis/mola.html The MGS home page is: The Power of Jupiter Date: Wed, 8 Mar 2000 9:54:43 Powerful tidal forces from Jupiter have molded two of the solar system's most bizarre worlds, fiery Io and icy Europa. Images released this week reveal new details of tidal action on the two moons. FULL STORY at:- http://spacescience.com/headlines/y2000/ast08mar_1.htm Date: Tue, 7 Mar 2000 14:10:23 -0500 (EST) With a new technique that uses ripples on the Sun's visible surface to probe its interior, scientists are able to see right through the Sun to observe active regions on its far side, the side facing away from the Earth. With a far-side preview, scientists may be able to have a week's advance warning of potential bad weather in space. SOHO is a cooperative project between the European Space Agency and NASA.
Date: Wed, 8 Mar 2000 15:30:20 -0500 (EST) New high-resolution images from NASA's Mars Global Surveyor spacecraft comparing the ice caps at the North and South poles show the difference between the two regions is in the "cheese." The North polar cap has a relatively flat, pitted surface that resembles cottage cheese, while the South polar cap has larger pits, troughs and flat mesas that give it a holey Swiss-cheese appearance. "Looking like pieces of sliced and broken Swiss cheese, the upper layer of the Martian South polar residual cap has been eroded, leaving flat-topped mesas into which are set circular depressions," said Dr. Peter Thomas of Cornell University, Ithaca, NY, and lead author of the paper. "Nothing like this has ever been seen anywhere on Mars except within the South polar cap, leading to some speculation that these landforms may have something to do with the carbon dioxide thought to be frozen in the South polar region." In a paper to be published March 9, 2000, in the journal Nature, members of the Mars Global Surveyor imaging team have described some of the newly discovered differences in polar terrain. "The unusual shapes of the landforms on the North and South polar caps suggest that these regions have had different climates and histories for thousands or perhaps even millions of years," said Thomas. "We are discovering them for the first time because Mars Global Surveyor is working to provide high-resolution views of the tremendously diverse terrain on Mars over all Martian seasons." "These landforms may be telling us what the South polar cap is made of," says Dr. Andrew Ingersoll of the California Institute of Technology, Pasadena, CA and one of the authors of the paper. "The North residual cap -- the part that survives the summer is made of water ice. The South residual cap seems to be made of frozen carbon dioxide, otherwise known as dry ice, but we don't know if this is a veneer a few meters thick or a solid block that extends down 2 or 3 kilometers. These images may help us decide." The North polar cap is covered mainly by pits, cracks, small bumps and knobs that give it a cottage-cheese look. The pits that have developed on the surface are spaced close together relative to the very different depressions in the South polar cap. These pits probably developed slowly over successive spring and summer seasons. "The polar images demonstrate again that understanding Mars' complicated history requires studying many areas in detail, just as understanding the Earth does," Thomas said. "If we discovered that both polar caps are mostly water, it would leave a mystery about why there is so little carbon dioxide on Mars. Earth has a lot of carbon dioxide, but creatures living in the ocean have turned it into limestone rocks. Without oceans or life, Mars should have a lot more carbon dioxide on its surface than we seem to be finding," explained Ingersoll. Mars Global Surveyor is managed by the Jet Propulsion Laboratory (JPL), Pasadena, CA, for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology. The new images can be seen at: |
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