* Astronomy

Scientists on Thursday said they had found evidence that Mars was once latticed by an underground water system, proving that the Red Planet has had a long and complex relationship with one of the potential ingredients for life.
Writing in the British journal Nature, researchers focussed on questions thrown up by NASA's Martian rover, Opportunity, in its exploration of a vast sloping plain called Meridiani Planum.
Opportunity found sulphate-rich sediments that some experts claimed were the remains of seas that once washed over the planet.

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Liquid or gas flowed through cracks penetrating underground rock on ancient Mars, according to a report based on some of the first observations by NASA's Mars Reconnaissance Orbiter. These fluids may have produced conditions to support possible habitats for microbial life.
These ancient patterns were revealed when the most powerful telescopic camera ever sent to Mars began examining the planet last year. The camera showed features as small as approximately one metre across. Mineralisation took place deep underground, along faults and fractures. These mineral deposits became visible after overlying layers were eroded away throughout millions of years.
Dr. Chris Okubo, a geologist at the University of Arizona , Tucson , discovered the patterns in an image of exposed layers in a Martian canyon named Candor Chasma. The image was taken in September 2006 by the High Resolution Imaging Science Experiment camera aboard the orbiter.

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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.
Some scientists have proposed that the Red Planet lost its water and CO2 to space as the solar wind stripped molecules from the top of the planet's atmosphere. Measurements by Russia's Phobos-2 probe to Mars in 1989 hinted that the loss was quite rapid.
Now the European Space Agency's Mars Express spacecraft has revealed that the rate of loss is much lower. Stas Barabash of the Swedish Institute of Space Physics in Kiruna led a team that used data from Mars Express's ASPERA-3 instrument (Analyser of Space Plasmas and Energetic Atoms).
Its measurements suggest the whole planet loses only about 20 grams per second of oxygen and CO2 to space, only about 1% of the rate inferred from Phobos-2 data.
If this rate has held steady over Mars's history, it would have removed just a few centimetres of water, and a thousandth of the original CO2.

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NASA photographs have revealed bright new deposits seen in two gullies on Mars that suggest water carried sediment through them sometime during the past seven years.

"These observations give the strongest evidence to date that water still flows occasionally on the surface of Mars" - Michael Meyer, lead scientist for NASA's Mars Exploration Program, Washington.

Liquid water, as opposed to the water ice and water vapour known to exist at Mars, is considered necessary for life. The new findings heighten intrigue about the potential for microbial life on Mars. The Mars Orbiter Camera on NASA's Mars Global Surveyor provided the new evidence of the deposits in images taken in 2004 and 2005.

"The shapes of these deposits are what you would expect to see if the material were carried by flowing water. They have finger-like branches at the downhill end and easily diverted around small obstacles" - Michael Malin of Malin Space Science Systems, San Diego.


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A new gully deposit in a crater in the Centauri Montes Region.
Credit: NASA/JPL/Malin Space Science Systems

Malin is principal investigator for the camera and lead author of a report about the findings published in the journal Science.
The atmosphere of Mars is so thin and the temperature so cold that liquid water cannot persist at the surface. It would rapidly evaporate or freeze. Researchers propose that water could remain liquid long enough, after breaking out from an underground source, to carry debris downslope before totally freezing. The two fresh deposits are each several hundred meters or yards long.
The light tone of the deposits could be from surface frost continuously replenished by ice within the body of the deposit. Another possibility is a salty crust, which would be a sign of water's effects in concentrating the salts. If the deposits had resulted from dry dust slipping down the slope, they would likely be dark, based on the dark tones of dust freshly disturbed by rover tracks, dust devils and fresh craters on Mars.
Mars Global Surveyor has discovered tens of thousands of gullies on slopes inside craters and other depressions on Mars. Most gullies are at latitudes of 30 degrees or higher. Malin and his team first reported the discovery of the gullies in 2000. To look for changes that might indicate present-day flow of water, his camera team repeatedly imaged hundreds of the sites. One pair of images showed a gully that appeared after mid-2002. That site was on a sand dune, and the gully-cutting process was interpreted as a dry flow of sand.


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New Gully Deposit in a Crater in Terra Sirenum
Before-and-after views of a Mars site where a gully flowed. In the expanded view, on the left, the site as it appeared in 2001. On the right, the same site in 2005.
Credit: NASA/JPL/Malin Space Science Systems

Today's announcement is the first to reveal newly deposited material apparently carried by fluids after earlier imaging of the same gullies. The two sites are inside craters in the Terra Sirenum and the Centauri Montes regions of southern Mars.

"These fresh deposits suggest that at some places and times on present-day Mars, liquid water is emerging from beneath the ground and briefly flowing down the slopes. This possibility raises questions about how the water would stay melted below ground, how widespread it might be, and whether there's a below-ground wet habitat conducive to life. Future missions may provide the answers" - Michael Malin .

Besides looking for changes in gullies, the orbiter's camera team assessed the rate at which new impact craters appear. The camera photographed approximately 98 percent of Mars in 1999 and approximately 30 percent of the planet was photographed again in 2006. The newer images show 20 fresh impact craters, ranging in diameter from 2 meters to 148 meters that were not present approximately seven years earlier. These results have important implications for determining the ages of features on the surface of Mars. These results also approximately match predictions and imply that Martian terrain with few craters is truly young.


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A colourised view of a new crater on the upper north flank of the Martian volcano Ulysses Patera.
Credit: NASA/JPL/Malin Space Science Systems

Mars Global Surveyor began orbiting Mars in 1997. The spacecraft is responsible for many important discoveries. NASA has not heard from the spacecraft since early November. Attempts to contact it continue. Its unprecedented longevity has allowed monitoring Mars for over several years past its projected lifetime.

Source Nasa