There is much more water on Mars than anyone had thought -- possibly twice as much as in Greenland's ice sheet, scientists said Thursday.
NASA's Mars Reconnaissance Orbiter spotted ice in five recently formed meteorite craters midway between the northern pole and the equator, researchers said in a report in the journal Science. That's the farthest south the underground ice sheet has been found.
The spacecraft's instruments were able to confirm that the bluish material inside the crater was, indeed, ice.
"Buried ice on Mars is much more extensive than we had thought," Shane Byrne, an astronomer at the University of Arizona, said at a news briefing Thursday at the Jet Propulsion Lab in La Canada Flintridge. "It's also a lot purer than we had thought."
Scientists had expected that the ice on Mars would be heavily mixed with dirt, but the ice was found to be 99% uncontaminated, according to the scientific team.
The findings, announced Thursday, reveal Mars to be wetter and to possess a more complex climate history than scientists expected.
Scientists believe that water once flowed across the planet, but most thought the surface had been largely dry and parched, with planet-wide dust storms, for billions of years. They had long known that water ice and carbon dioxide ice accumulated at the poles in winter, but until now, they had no idea how far from the poles the underground ice sheet extended.
The Mars Reconnaissance Orbiter was launched in 2005 to probe the history of water on the planet. The new finding was made with the orbiter's high resolution camera, which is able to distinguish objects less than a yard across.
According to Ken Edgett, part of the team that built and operates the camera, the meteorite craters appeared in the first half of 2008. Some were small, allowing the ice to fade away over the course of the Martian summer. (Because Mars is so dry, ice does not melt into water before evaporating. Instead it sublimates directly to a gas.)
The largest crater was 18 feet across. The ice exposed in that one lasted long enough that the spacecraft's spectrometer was able to see "this beautiful water ice signature," said Selby Cull, a planetary scientist at Washington University in St. Louis.
"There was no doubt about it," she added.
Byrne said the large amount of water on Mars, which he said could be double the size of the Greenland ice sheet, indicates the planet had a warmer and more humid climate as recently as 10,000 years ago. That's relatively recent in geological terms.
Still, Byrne said, the climate wouldn't have been warm or wet enough to support life as we know it.
The discovery might have been made 30 years ago when Viking 2 landed in the same general area, scientists said, but the lander didn't dig deep enough into the soil to find the ice.