— A radar instrument that could spot liquid water under the Red Planet's surface is set to deploy on Saturday from NASAs Mars Reconnaissance Orbiter (MRO). If all goes according to plan, it should be able to start peeking beneath the Martian surface by the end of September.
Having tightened its orbit around the Red Planet with a series of aerobraking manoeuvres, MRO is now preparing to begin its science observations (see Spy probe closes in on the red planet).
These will include radar measurements using MRO's Shallow Subsurface Radar (SHARAD), which will scrutinise layers of subsurface rock to search for buried water.
Mission controllers will try to deploy the instrument at 1600 GMT on Saturday. It will then take 12 to 16 hours for the team to complete tests that will determine whether it deployed properly.
The tube containing the radar antenna for a similar instrument on Europe's Mars Express spacecraft, called MARSIS, did not straighten out properly when first deployed, which delayed observations.
But Jim Graf, project manager for MRO at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, US, says SHARAD will avoid such problems because it is only 10 metres long, while MARSIS spans 40 metres.
SHARAD's tube will not have as much pent-up energy when it deploys, which should prevent the kind of overextension that caused a kink in one of the MARSIS arms, he says. "Our design is much less energetic," he told New Scientist.
MRO's radar is operating at shorter wavelengths, which means it can penetrate about 1 kilometre below the surface, while MARSIS can probe five times as far. But it has much better vertical resolution, so it can see layers just 10 metres thick, compared to 50 to 100 metres for MARSIS.
SHARAD will look for signs of solid and liquid water beneath the surface, says Jeff Plaut of JPL, one of the scientists in charge of the instrument.
It will investigate gullies that could have been formed by liquid water seeping out from just beneath the surface, he says (see Landslips, impacts and eroding ice revealed on Mars).
Despite the frigid surface temperatures of Mars, it is thought to have a hot interior like the Earth, Plaut says. Some of this heat could make its way towards the surface to keep pockets of subsurface water warm enough to stay liquid, he says.
Another place he wants to investigate is an area near the equator that could be a frozen sea. Scientists have not been able to determine from orbital images whether the jumbled slabs seen there are made of rock or frozen water, but SHARAD should be able to tell the difference, Plaut says.
"I think it might really help solve that particular mystery," he told New Scientist. "Rock is much more reflective than ice."
The MRO team hopes to make observations with SHARAD and the spacecraft's other instruments for about a week starting on 29 September. After that, Mars will be too close to the Sun as seen from Earth for reliable communications, so further observations will not be possible until early November.
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