No missions are currently planned to land near the areas that Payne and Farmer are studying. To bolster their case that a mission could be fruitful, they have begun studying similar subglacial volcanoes on Earth in an effort to determine whether life survives such harsh conditions here.

Their terrestrial studies focus on Iceland, where two large plates of the Earth's crust meet, creating a host of geophysical conditions similar to those on Mars. Next summer, they plan to lead a trip to the small frozen country.

"We're interested in looking at the ice just overlying a pocket of water and the water itself," Payne explains. Finding life in such a spot in Iceland would serve as a biological roadmap to Mars.

Payne and Farmer say a Mars mission could easily access the subglacial volcanic lakes on the fringes of the north polar ice cap on Mars. And one of the tools needed to explore one of these ice-covered volcanoes is already being developed.

But a cryobot would have to make it to the surface of Mars, and in the right location, before it could explore a subglacial lake.

The right location would be an area of current or past volcanic activity, with uneven terrain that makes mission managers nervous. Pinpoint landings are not possible. Instead, managers target a landing ellipse, which can be several miles long. The failed Mars Polar Lander, which was to explore Mars' south pole in 1999, had a landing ellipse that was 125 miles (200 kilometers) long and 12.5 miles (20 kilometers) wide.

Mission planners like to target a large, flat expanse where no slope exceeds 10 percent.

Beyond the difficulties of touching down on uneven terrain, putting spacecraft in the polar regions requires more fuel to get into the proper orbital position prior to landing. It also requires more power to operate a spacecraft in the polar regions, since there is less Sun and solar power is less useful.

All this costs more money, says Alfred McEwen, a researcher at the University of Arizona's Lunar and Planetary Lab. "But that doesn't make them less interesting."

McEwen called the idea of searching for life in subglacial lakes interesting and appealing.

"We don't know if there are or were subglacial lakes or any other near-surface environments with long-lived liquid water," he said. But he adds that it is important to maintain multiple hypotheses like this in the continuing effort to understand Mars.

So for now, Payne and Farmer will have to content themselves with a study of Iceland and pictures from above the Red Planet. Theirs is one of many efforts designed to increase knowledge about extremophiles, as well as Martian geology, so that mission planners can eventually decide what sorts of robots to send to Mars and where and how to deploy them.

A gamma-ray spectrometer aboard the orbiting satellite will map the amounts of some 20 different elements on the surface of Mars or just beneath it. If the instrument finds hydrogen in the soil, that would indicate water or water ice exists below, possibly as shallow as three feet (1 meter), say scientists associated with the mission. A similar technique was used by the Lunar Prospector to map water near the Moon's surface, but no such comprehensive analysis has been done on Mars.

Mission managers are searching for "compelling landing zones with the fewest hazards," NASA officials say. "We are thinking about localities where there is evidence of surface processes involving what we might call 'past' water on Mars," said Jim Garvin, Mars program scientist at NASA headquarters.

Not exactly a fishing expedition, but one small step in the grand search to find out if life is unique to Earth or not.