Look for life in pools of water in the polar regions of Mars, say scientists.
Liquid water is the key for life, they say, but over most of Mars the atmospheric pressure is too low for water to exist in that state.
Now, an assessment of all the available satellite data suggests that there may be pools of open water at the poles, or small lakes just under the ice.
A research project is already underway that will gather as much information as possible on Mars' polar regions, and look for lakes so that future landers can be targeted on them.
Open water
Scientists believe that liquid water is the key to finding habitable environments on the Red Planet today.
Indeed, "Follow the Water" has become a motto for Mars explorers looking for life. But the atmospheric pressure on Mars, a thousandth of that on Earth, is too low to allow liquid water to exist on the surface.
Many scientists believe that liquid water could be present on Mars at a depth of several kilometres but, with current unmanned spacecraft technology, it is only possible to drill down a few metres at most.
The answer to finding the water may be to look at Mars' polar caps. They contain a lot of water but it is usually frozen and therefore unavailable for biology.
Viking missions
But Meredith Payne and Jack Farmer, from Arizona State University, US, believe that sometimes there could be pools of open water at the poles.
They have studies all of the polar images returned by the Viking Orbiter missions in the 1970s and the current Mars Global Surveyor mission, and have identified several sites of possible recent volcano-ice interactions that could result in water.
Jack Farmer is encouraged by the discoveries made on Earth over the past few decades that life can exist in a far greater range of extreme environments than had been once thought.
"These discoveries have greatly extended the known range of terrestrial habitats where life survives," said Farmer. "All of these conditions could exist in polar regions of Mars today where subglacial volcanism has occurred."
Close-up studies will now be made of the regions to see if there are further indications that water could be present. If it is found, the locations would be prime candidates for future landers.