Watering Pole

Ice thickness at the Martian South Pole. Credit: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS

Wednesday, March 21st, 2007--

Researchers looked deep into the Martian South Pole and found enough frozen water to cover the red planet in 36 feet of water, according to a recent study in the journal Science.

An ice cube the size of Texas may sound big, but it's not big enough to account for all the water that researchers think used to exist on the planet, leaving scientists still wondering where all the Martian water went.

To get a precise estimate of the ice, researchers analyzed data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), which flies aboard an orbiting satellite called Mars Express. MARSIS is the first radar to probe Mars. "Like any radar, it sends out pulses of radio waves and then waits and listens and detects the echoes that come back," says Jeffrey Plaut, a researcher at the Jet Propulsion Laboratory at the California Institute of Technology and lead author on the study.

When the radio waves hit the surface of Mars, some bounce back to the radar and others permeate the ice, bouncing back only after they hit another barrier--in this case, the crust of Mars. Researchers use the delay of the radio waves to calculate the depth of the ice. From the waves' energy loss, researchers can predict the composition of the ice: more energy is lost in dirty ice than pure frozen water.

This data may give scientists insight into Mars' climate history. At the Martian poles, the ice is layered. Darker layers correspond to dustier times on Mars. "Then, as conditions change, there may not be as much dust in the atmosphere, perhaps it was a period with very few dust storms, and the ice that gets deposited is cleaner," Plaut explains. These layers show up as white. "We're trying to understand how this layering is related to the climate history of Mars."

One puzzler from the data is that there are spots deep under the surface of Mars where the reflected radar waves are brighter than those reflected at the surface of the planet. These bright spots, in theory, could be explained by liquid water trapped below the surface. Is a Martian fish fry right around the corner? Not likely. The bright spots could also be explained by different properties of the ice. Plus, Plaut says, it is unlikely that liquid water exists in such a cold area.

The radar data also revealed that under the weight of the ice, Mars barely buckles. Compared to earth--which would sag under equivalent ice--Mars is firm. Plaut says this means Mars is probably colder inside and "more mature." In planetary speak, the temperature of the planet relates to its maturity. Plaut says: "Mars has lost a larger fraction of its heat. Its interior is a little bit colder, not quite dead, but not as active as the interior of Earth."

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--Flora Lichtman