Saturday science subject: Mars' wet past

Using a radar instrument co-built by NASA and the Italian Space Agency and mounted on the European Space Agency's Mars Express spacecraft, scientists have managed to gauge the amount of frozen water that covers the Martian south pole. As the Scientific American reports, the deposits at the pole are 2.3 miles (3.7km) thick and are made up of at least 90% frozen water. If the ice were to melt, it would reportedly cover the planet in 36 feet (11m) of water. Jeffrey Plaut of NASA's Jet Propulsion Laboratory, the researcher who led the study, says his team is currently examining the planet's north pole. He estimates that the ice deposits there are comparable to those on the south pole. However, Plaut believes these results don't account for the amount of water that once covered the red planet:
Plaut said the amount of water in the Martian past may have been the equivalent of a global layer hundreds of meters deep, while the polar deposits represent a layer of perhaps tens of meters.

"We have this continuing question facing us in studies of Mars, which is: where did all the water go?" Plaut said.

"Even if you took the water in these two (polar) ice caps and added it all up, it's still not nearly enough to do all of the work that we've seen that the water has done across the surface of Mars in its history."

The Scientific American says that geological artifacts like channels suggest that Mars was once "very wet". According to Plaut, the frozen water at the poles only accounts for maybe 10% of the water that was once on Mars. He says that perhaps more water exists below the surface, or that most of the water simply evaporated into space over time.
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