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Martian water quest heats up
05/05/2007 12:09 - (SA)
Paris - Detailed thermal imaging of Mars has shown that ice on the red planet is patchy and lurks at varied depths in its soil, a finding that will fine tune the search for water there.
Evidence from orbiting probes and United States rovers found that millions of years ago Mars was covered with water - and there could be substantial quantities lurking as ice.
The big questions are exactly where, and at what depths.
A gamma-ray spectrometer aboard the orbiting Mars Odyssey was the first to indicate that water ice could be lying at relatively shallow depths.
But its pictures are too wide-scale - 500km wide - to locate the ice more precisely or to provide practical tips to shape future explorations.
But a tweaked-up, heat-sensing camera aboard the same spacecraft may have the answer, according to a paper in Nature, the British science journal, on Thursday.
With its infrared eyes, the gadget, called Themis, was able to spot details just 100m across.
Ice 'survives' below the dust
It has now mapped several Martian sites, each at a latitude of 60 to 70 degrees, where surface ice has already been known to exist.
The nature of the soil had a big impact on where the ice could be found, said investigator Joshua Bandfield of Arizona State University.
In dusty areas, ice can survive at several centimetres beneath the surface, apparently insulated by the grains.
But in areas littered with rocks, stable ice - ice unaffected by local seasons - could be found at much greater depths, sometimes "tens of centimetres below the surface", said Bandfield.
The reason: Rocks warmed by the Sun pump a lot of heat into the ground, thwarting the formation of ice at layers very close to the surface.
"These two surface materials - rock and dust - vary widely across the ground, giving underground ice a patchy distribution," Bandfield explains.
Mission depends on promising spot
So far, the evidence for water on Mars is inferred, coming from pictures and other data from US and European orbiters and from two American rovers, Spirit and Opportunity, on the ground.
But in August, Nasa is due to launch a mission that, the agency hopes, will provide the first direct evidence.
It is due to send a non-roving lander, called Phoenix, that will be dropped to a high-latitude site on Mars' northern hemisphere.
There, the scout will scrape away some of the soil, hopefully exposing some ice, which an onboard lab will then analyse to see if it has the potential for harbouring bacterial life.
Choosing the most promising spot will determine whether this mission succeeds.
"The take-home message for the Phoenix lander is that the Themis results show a lot of patchiness in the ground ice, and this should continue down to smaller and smaller scales," Bandfield says.
Phoenix, he warns, "may find ground ice is shallower and much easier to reach in some spots than in others".
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