Based on a telltale chemical signature for the water samples that distinguished them from water at the glacier's surface, the researchers determined that their samples came from the thin layer of water that is found underneath many glaciers. This water is produced mainly by the melting of the bottom of the glacier due to geothermal heat and friction from the lazy creep of the glacier. Microbes thawed from ice squeezed out from the glacier's underbelly also flourished in the lab in later experiments.

"Now we say, 'Duh, yeah we should have expected that,'" said teammember microbiologist Julia Foght of the results -- given the fact that prospering microbes have over the past few years been turning up in all sorts of places previously thought impossible. Studies of scalding hot water, the insides of rocks and sea ice have all exposed more of the mind-boggling microbes known as extremophiles.

On Earth, researchers are increasingly realizing that wherever you look for life you find it. Many people are hoping that a similar conclusion will apply on Mars -- at least if the looking occurs in places where liquid water once existed, or even better, still exists. But planners are still struggling with where such areas will most likely be. Skidmore said the glacier research points to the bases of Martian polar caps, particularly the larger northern cap, as good targets in the search for life because conditions similar to those he studied could be found there.

The most critical condition is, of course, liquid water. Scientists are still debating whether there is currently liquid water under the Martian caps, but there is strong evidence that such water existed in the geological past because the caps were once thicker and would have trapped more ice-melting heat given off by the planet.

Volcanic activity is also a possibility for today and the past. Water beneath the cap could have delivered a record of life to the edges as it trickled -- or if volcanoes were involved -- was spewed out. If so, said Skidmore, then the accessible ice either at the current cap's margin, or buried in ice just below the surface of the historical margins, might hold preserved extraterrestrial microbes. This could offer an alternative to the daunting task of creating a probe capable of digging to the bottom of the ice cap, which is thought to be 2 to 2 and a half miles (3 to 4 kilometers) thick, he said.

"This definitely advances our knowledge along the right path for justifying this kind of approach for Mars exploration," said Jack Farmer, an astrobiologist at Arizona State University in Tempe, of the University of Alberta study. "That's why I'm particularly excited about it," he said. Farmer and other researchers have also advocated the fringes of glaciers as targets in the search for life.