His team first grew test tube cultures of various methanogens (organisms that thrive on methane rather than oxygen) in simulated Mars soil. Derived from altered volcanic ash, the soil approximates the composition, grain size, density, and magnetic properties of Martian soil. They then exposed the methanogens to various Martian conditions in a so-called Andromeda Chamber donated by NASA's Jet Propulsion Laboratory in Pasadena, California.

Methanogen cultures were frozen, put into the chamber, and then the temperature was raised to Mars-like conditions and the pressure kept much lower than on Earth. Mars' thin atmosphere creates but a fraction of the air pressure of Earth.

So far, the tests indicate "low levels of methane production," Kral and his colleagues say, meaning the organisms are metabolizing.

There is no solid evidence for life on the Red Planet, but the new research builds on other recent discoveries that point to conditions being possible. Earlier this year, scientists announced strong evidence for vast amounts of water ice just below the surface of Mars. Water is thought to be a key ingredient for life.

Mars' atmosphere contains large amounts of carbon dioxide with almost no oxygen. Assuming that hydrogen and some water are present under the surface, the basic requirements for methanogen growth are met on Mars. And even if hydrogen is not present, carbon monoxide is, and some methanogens can use this instead of hydrogen.

A separate study released in January found methanogens living in complete darkness 660 feet (200 meters) underground here on Earth. They eat hydrogen, breathe carbon dioxide, and form the root of an ecosystem unlike any previously known on Earth.

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