Ice at the poles—of Mars….

WASHINGTON (Reuters) – A spacecraft orbiting Mars has scanned huge deposits of water ice at its south pole so plentiful they would blanket the planet in 36 feet of water if they were liquid, scientists said on Thursday.
The scientists used a jointNASA-Italian Space Agency radar instrument on the European Space Agency Mars Express spacecraft to gauge the thickness and volume of ice deposits at the Martian south pole covering an area larger than Texas.
The deposits, up to 2.3 miles thick, are under a polar cap of white frozen carbon dioxide and water, and appear to be composed of at least 90 percent frozen water, with dust mixed in, according to findings published in the journal Science.
Scientists have known that water exists in frozen form at the Martian poles, but this research produced the most accurate measurements of just how much there is.
They are eager to learn about the history of water on Mars because water is fundamental to the question of whether the planet has ever harbored microbial or some other life. Liquid water is a necessity for life as we know it.
Characteristics like channels on the Martian surface strongly suggest the planet once was very wet, a contrast to its present arid, dusty condition.
Jeffrey Plaut of NASA’s Jet Propulsion Laboratory in Pasadena, California, who led the study, said the same techniques are being used to examine similar ice deposits at the Martian north pole.
Radar observations made in late 2005 and early 2006 provided the data on the south pole, and similar observations were taken of the north pole in the past several months, Plaut said.
Plaut, part of an international team of two dozen scientists, said a preliminary look at this data indicated the ice deposits in at the north pole are comparable to those at the south pole.
SEARCH FOR LIFE
“Life as we know it requires water and, in fact, at least transient liquid water for cells to survive and reproduce. So if we are expecting to find existing life on Mars we need to go to a location where water is available,” Plaut said.
“So the polar regions are naturally a target because we certainly know that there’s plenty of H2O there.”
Some of the new information even hints at the possible existence of a thin layer of liquid water at the base of the deposits.
But while images taken by NASA’s Mars Global Surveyor spacecraft made public in December suggested the presence of a small amount of liquid water on the surface, researchers are baffled about the fate of most of the water. The polar deposits contain most of the known water on Mars.
Plaut said the amount of water in the Martian past may have been the equivalent of a global layer hundreds of meters deep, while the polar deposits represent a layer of perhaps tens of meters.
“We have this continuing question facing us in studies of Mars, which is: where did all the water go?” Plaut said.
“Even if you took the water in these two (polar) ice caps and added it all up, it’s still not nearly enough to do all of the work that we’ve seen that the water has done across the surface of Mars in its history.”
Plaut said it appears perhaps 10 percent of the water that once existed on Mars is now trapped in these polar deposits. Other water may exist below the planet’s surface or perhaps some was lost into space through the atmosphere, Plaut said.