Keeping it clean at Mars' South Pole

The white patch in this image, which was taken from the Mars Global Surveyor spacecraft, shows Mars' south polar ice cap.

Though we can't say you'd want to drink it, the water frozen in Mars' south polar ice cap is pretty pure, a new study suggests.

Scientists have known that both poles of Mars are hidden beneath caps of layered ice. But they're only just learning how much ice there is and what it's made of.

The ice cap on Mars' south pole is the largest reservoir of water on Mars today and the largest in the inner solar system, except for what's on Earth.

Maria Zuber of Massachusetts Institute of Technology and her colleagues wanted to find out how clean the ice cap's frozen water was. Since they couldn't scoop up the ice and study it directly, they used a variety of measurements to figure out how dense the ice was.

They used gravity measurements from the Mars Reconnaissance Orbiter, which is currently looking for evidence of water on the Red Planet, as well as information about the ice cap's volume, which had been collected on previous missions to Mars.

Because they knew the ice cap's size and how strong its gravity was, the researchers could calculate the ice's density. They determined that a cubic meter of the ice probably weighs about 1,220 kilograms.

This is the density you'd expect for an ice block that contained about 15 percent dust. That's a far cry from the ice cubes in your freezer, but for ice that forms in nature, it's pretty clean.

These findings appear in the 21 September issue of the journal Science, which is a special issue about the Mars Reconnaissance Orbiter.

###