Researchers report in the Jan. 17 issue of the journal Nature the discovery of a community of various organisms dominated and supported by these methanogens, creatures they say could represent just the sort of life to look for when turning over rocks on Mars.

Unlike other organisms at the bottom of the food chain, methanogens need little of the traditional sustenance that biologists associate with life. They get by without oxygen and no help from sunlight, said the U.S. Geological Survey's Francis H. Chapelle, who led the study along with Derek Lovley of the University of Massachusetts.

Methanogens simply feed off hydrogen in the rocks around an underground hot spring.

"This kind of microbial community has never been found on Earth," Chapelle told SPACE.com, adding that it "may be representative of the kinds of life that initially evolved on the early Earth, and which may presently occur on Mars or Europa."

Idaho is not the only home to methanogens. They cause gas in the digestive tracts of humans. And they're found in oxygen-deprived mud at the bottom of swamps. But they are not seen as essential to supporting other life in these environments, as is the case in Idaho.

Places considered most likely to harbor extraterrestrial life -- pockets of underground water on Mars or an ocean under the frozen crust of Jupiter's moon Europa -- are only presumed to exist, and since they exist below the surface and get no sunlight, any life there would have to have an alternative means of fuel.

The new finding shows that the recipe for life is simpler than previously thought, that sunlight is not needed, and that improves the prospects for finding ET, researchers said.

"Hydrogen may well be an important requirement for extraterrestrial life," Chapelle said.

"If hydrogen is indeed present on Mars in association with liquid water, the kind of metabolism we describe ... may occur on Mars," Chapelle said.

William B. Whitman, a University of Georgia microbiologists who was not involved in the new study, said methanogens were hypothesized to exist in environments like the one studied in Idaho, but that it was unusual that they dominate the community of microbes within which they live.

"This community composition has not been described before," Whitman said.

And what does it say about life as we know it?

"It certainly strengthens the rationale for looking in more kinds of places, especially the subsurface of some of the other planets," Whitman said.

Growing knowledge of Mars and recent findings on Earth bolster notions that the Red Planet may be the best place to look for similar extremophiles, as they are called.

Earlier this week, an international team of researchers said they had discovered organisms clinging to life in frigid, salty soil in Antarctica. Average temperatures in the Quartermain Mountains, where the microorganisms were found, are typically less 22 degrees below zero Fahrenheit (-30 C). Less than a half-inch of precipitation falls each year.

No place on Earth is more like Mars, the researchers said.

The study uncovered fungi and a common bacteria living just below the surface in salt-laden soil, which dramatically lowers the freezing temperature of water by a method not completely understood. The researchers say the same phenomenon may occur on Mars. Other research suggests that soil conditions on parts of Mars could be very similar to the Antarctic dirt.

"The glacial climates of Antarctica would have led to glaciers that produced the same kinds of surfaces that were sampled in Antarctica and that we see on Mars today," said Victor R. Baker of the Lunar and Planetary Lab at the University of Arizona.

The Antarctic finding, led by William C. Mahaney of York University in Canada, will be presented in the journal Icarus. Baker and other geologists helped Mahaney interpret the discovery in the context of the potential for life on Mars.

Whether life exists beyond Earth is the greatest question in the minds of many scientists. No other single question channels more funding for space-related scientific research.

Yet while the prospects for ET seem to grow with each new discovery on Earth, the plain fact is nobody knows if Mars does or ever did harbor life. Solid evidence could come from robotic probes. NASA alone has several planned over the next decade.

Yet many researchers say a human mission to Mars -- which is not even in the planning stages at NASA -- might be required to literally dig up the necessary evidence.

Oxygen-breathing creatures might be wise not to hold their breath for an answer to the ultimate question.