Scientists searching for extraterrestrial life might want to start digging under a Martian mountain three times as high as Mount Everest.

Liquid water likely once sloshed beneath the 15-mile-high Olympus Mons, and may still be there today. Because the mountain is volcanic, the water could be warm and friendly to life.

"Olympus Mons is a favored place to find ongoing life on Mars," said geophysicist Patrick McGovern of Houston's Lunar and Planetary Institute, lead author of a study in *Geology *in February. "An environment that's warm and wet, and protected from adverse surface conditions, is a great place to start looking."

Other recent discoveries have hinted that life may exist — or may once have existed — on Mars. Scientists have gathered many indications that liquid water once flowed on the planet. And over the years, they have found tantalizing, but equivocal, evidence of life in Martian meteorites and on the Martian surface. In January, researchers documented methane burps on Mars, which could indicate microbial activity. But so far, it's all about "if" and "could be." The new research suggests Olympus Mons could be a good place to hunt for more definitive evidence.

Using computer simulations, McGovern and Julia Morgan of Rice University determined that the volcano's strange asymmetry — it has a gently sloped northwest flank and a much steeper southeast side — is the result of what lies beneath it: lava spread unevenly on a slippery surface such as clay, which is deposited by water.* *

"In order for the volcano to have that unusual shape, you need some sort of low-friction base," McGovern said.

The same phenomenon happens in some Hawaiian volcanoes that have a clay foundation, McGovern said. And the European Space Agency's Mars Express spacecraft has already detected clay on Mars.

Olympus Mons is about 340 miles wide, so clay beneath it "would correspond to a huge amount of water," said geochemist Jennifer Blank of the SETI Institute, who was not involved in the study.

And unlike the long-suspected water ice that the Phoenix lander sampled for the first time, if water does exist under Olympus Mons, it could be piping hot. Because the volcano doesn't show impact craters on a planet that bears many such scars, it was probably actively coating its surface with fresh lava just 10 million or 20 million years ago.

"On our time scale, that's pretty close to current," McGovern said.

Despite a apparent lack of more-recent eruptions, the researchers speculate that the volcano could still be warm on the inside. If they are right, and the environment beneath Olympus Mons is hot, wet and dark, it would mirror the conditions that many scientists believe gave rise to life on Earth.

"Some of the most primitive life forms on Earth are thermophiles," Blank said. "And they're underground. They don't need light."

*Citation: "Volcanic spreading and lateral variations in the structure of Olympus Mons, Mars." By Patrick J. McGovern, Julia K.

Morgan. Geology Vol. 37, February 2009. *

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Image: NASA