Not surprisingly, the mantra, "Follow the Water," has become a primary driver in NASA's new Mars Program. Water in liquid form is regarded as essential for life.

But how can we explore for life on Mars when liquid water is unstable at the surface today due to an atmospheric density that is only ~1/1000 of Earth's? This is a challenge we must overcome if we are to mount a successful search for life on Mars.

While many scientists believe that liquid water could be present on Mars today at a depth of several kilometers beneath the surface, we simply do not yet have the technology to drill to those depths from the simple robotic platforms we will be sending.

At best, we can hope to drill a few meters to perhaps tens of meters with current technologies. But what If there was shallow ground water on Mars within a few meters of the surface?

Then small rovers and landers could probably drill and find it. This would better than having to postpone exploring for deep subsurface water (and life) until human astronauts could go to Mars and run deep drilling rigs. Humans will probably not go to Mars for at least another twenty years. That's a long time to wait! So can we do in the meantime?

Scientists are confident that there's water on Mars' polar caps. But that water is perpetually frozen and unavailable for biology. But there could be special geological exceptions where that water could exist as a liquid and those potential "oases" (within the otherwise frozen deserts of the polar regions) are important targets for astrobiology in the next two decades.

There is also speculation that very young channels and debris aprons found on many north-facing slopes at high latitudes formed when liquid water seeped out from the subsurface.

To be liquid at those latitudes requires that near surface water be both saline and warm, but probably still within the range for life. Unfortunately all of the seep sites discovered so far are on slopes inaccessible to landers and rovers.

One way to have liquid water under the polar caps at shallow depths would be through subglacial volcanism. Such volcano-ice interactions could be going on beneath the North polar cap of Mars today, or even within the adjacent permafrost around the margins of the ice cap.

On Earth, subglacial volcanic eruptions are often associated with outbursts of water that create a variety of distinctive geological features.

On Mars, such outbursts of liquid water could carry microbes and their byproducts to the surface where they could be incorporated into ground ice and preserved. Such deposits could be easily accessed by rovers in upcoming missions.

Meredith Payne and Jack Farmer from Arizona State University have been focusing their recent research efforts on finding such environments on Mars.

They have studied all available Viking and Mars Orbiter Camera images taken on and near the North polar cap searching for the tell-tell signs of subglacial volcanic eruptions.

This search has produced several potential sites of probable recent volcano-ice interactions and was reviewed and compared with similar features in Iceland during a poster presentation on Wednesday June 27 at Earth Systems Processes in Edinburgh, Scotland.

"We are presently working to merge all Viking, MOC and Mars Laser Altimeter (topographic) data into a spatially correlated base map for each area," Farmer said. "This effort will allow us to make detailed geologic maps and establish age relationships between major rock units and terrain types. We have been updating our mapping effort as new MOC and MOLA data become available."

These correlated data sets will allow Payne and Farmer to refine hypotheses concerning the origin of these features and test them through comparisons with remote sensing of analogous landforms in Iceland of known origin.

"Discoveries in the last two decades have greatly extended the known range of terrestrial habitats where life survives," Farmer explained.

"Viable microbial communities have been found living in deep (-2800 m) geothermal groundwater at 349 K and pressures >300 bar�.Furthermore, microbes have been postulated to exist in basaltic rocks in rinds of altered volcanic glass. All of these conditions could exist in polar regions of Mars today where subglacial volcanism has occurred."

Payne and Farmer will soon begin fieldwork in Iceland to better understand the processes associated with subglacial volcanism and the habitats for life created by such processes.

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