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Under Close Scrutiny, Mars Gives Up Signs of a Watery History
New observations by teams around the world have been yielding more and more evidence that the Red Planet once bore significant quantities of water—and may hold it still in hidden reservoirs.
The martian surface bears well-known channels and signs of water-based erosion, suggesting that liquid water may once have been available at the planet's surface in quantities sufficient to support life. Now the European Space Agency's MARSIS radar probe has found that Mars' northern polar ice cap, 1.8 kilometers thick, is composed of nearly pure water—and MARSIS has also discovered places where water ice could extend as much as a full kilometer below the surface. There are also intriguing hints of icelike material in a broad, buried basin recently discovered in the northern Chryse Planitia lowlands.
"We have no convincing evidence yet of subsurface liquid water," said Jeffrey Plaut, one of the principal investigators in the MARSIS project. "However, we can certainly say that we have seen significant amounts of subsurface water in the form of ice. The search for liquid water will begin in earnest next year."
Meanwhile, France's Observatory for Mineralogy, Water, Ice and Activity has discovered two different kinds of hydrated mineral while mapping the planet's surface. Both imply the existence of surface water at some time in Mars' past. One, a claylike mineral known as phyllosilicate, likely was formed more than 3.8 billion years ago, but the other, hydrated sulfate, would have required less time.
