Europeans fix radar antenna over Mars

Could subsurface water exist as liquid?
Planetary geologists have speculated for decades about exactly how warm it gets beneath the Martian surface, as the planet’s interior heat seeps toward the frigid surface. Some theories had suggested a region of "warm enough" rubble somewhere between the impervious bedrock and the frozen top layers, where water could migrate from the polar ice caps to the warmer equatorial regions. Other geologists told MSNBC.com they believed the layers would be frozen all the way to bedrock.

”We utilized similar models of the subsurface to get an idea of how deep we might detect liquid water,” Plaut explained. “These models depend on the existence (at least locally) of a saturated cryosphere, below which the temperature and the water abundance is sufficient for a groundwater deposit.

“Whether the water is part of a globally connected aquifer tied in with the polar deposits is not really important,” he continued. “The first question is, is the water there? The next would be, how did it get there?”

Tag-team radars
Next year, MARSIS could be joined by yet another ground-penetrating radar system in Martian orbit: the Shallow Radar, or SHARAD, experiment aboard NASA's Mars Reconnaissance Orbiter, which is due for launch in August.

Like MARSIS, SHARAD combines U.S.-built and Italian-built hardware.

”The two differences are depth and vertical resolution,” he pointed out. “MARSIS was designed to probe deep, SHARAD to probe shallow. The advantage MARSIS has is that its low frequencies are the best for deep penetration. The advantage that SHARAD has is that higher frequencies can be used to obtain higher resolution of layers in the vertical dimension.

“One might expect that the shallow zone that SHARAD will investigate is less likely to contain liquid water than deeper zones, simply because it is colder near the surface. On the other hand, if the deep subsurface is devoid of water, SHARAD will better explore the shallow zones which we know contain water ice,” based on spectral observations from other instruments.

MARSIS will also observe the Martian ionosphere, and may even be able to detect ionization trails of meteors. SHARAD, which operates at frequencies about 10 times higher than MARSIS, will not be able to detect anything of interest along those lines.

Some scientists not involved with MARSIS have expressed concerns to MSNBC.com that the radar will not be able to penetrate nearly as deeply as is hoped, due to attenuation from iron-bearing minerals in the Martian soil. In the worst case, the visible depth may only be a tenth as deep as hoped. But even the skeptics expect the radar to see unexpected and unusual geologic features when it begins its observational program.

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