Ancient water may lie hidden within the largest volcano on Mars, researchers now say, and they speculate that such a setup could also harbor life.

While there is no firm evidence that Mars does or ever has hosted life, one of the prerequisites would be water. The surface of the red planet is bone dry, but several studies have shown liquid water may once have flowed on Mars and could still exist in pockets below the surface.

The Martian volcano Olympus Mons is about three times the height of Mount Everest, with gentle slopes that sprawl across more than 150 miles of the planet surface.

The widespread volcanic material suggests the presence of water-formed clay which can reduce friction — an effect seen on Earth at volcanoes in Hawaii.

"What we were analyzing was the structure of Olympus Mons, why it's shaped the way it is," said Patrick McGovern, a geophysicist at the NASA-affiliated Lunar and Planetary Institute in Houston. "What we found has implications for life — but implications are what go at the end of a paper."

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NASA's hard-digging Phoenix lander uncovered water ice last year on Mars. So some researchers think it's reasonable to suspect water that may lie trapped underneath the largest volcano in the solar system, although many suspect that it remains ice-locked.

McGovern and Julia Morgan, a Rice University geologist, used computer models to simulate how Olympus Mons might have formed.

They concluded that only ancient clay sediments could account for the volcano's asymmetric shape. And where there's sediment, water must have been involved at some point.

The European Space Agency's Mars Express spacecraft has in recent years found abundant evidence of clay on Mars. This supports a previous theory that where Olympus Mons now stands, a layer of sediment once rested that may have been hundreds of meters thick.

What may be trapped underneath is of great interest, said the researchers. Fluids embedded in an impermeable, pressurized layer of clay sediment would allow the kind of slipping motion that would account for Olympus Mons' spread-out northeast flank — and may still exist in deep, trapped pockets within the volcano.

"This deep reservoir, warmed by geothermal gradients and magmatic heat and protected from adverse surface conditions, would be a favored environment for the development and maintenance of thermophilic organisms," McGovern and Morgan write in this month's issue of the journal Geology. Such primal organisms already thrive deep in Earth's ocean near geothermal vents.

Finding a source of heat would be the main challenge.

"We'd love to have the answer to that question," McGovern said, noting evidence of methane on Mars is considered by some to be another possible marker for life. Spacecraft have yet to detect a true thermal event on Mars, such as a magma flow or active volcano.

"What we need is 'ground truth' — something reporting from the surface saying, 'Hey, there's a Marsquake,' or 'Hey, there's unusual emissions of gas,'" McGovern added. "Ultimately, we'd like to see a series of seismic stations so we can see what's moving around the planet."

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