Mars probes unravel watery mysteries

By Andrea Thompson

updated 4:55 p.m. ET May 21, 2009

NASA's intrepid rover Opportunity spent two years exploring the geology of Mars' Victoria Crater, often perched perilously on the crater's edge.

The results of that effort are now detailed in Friday's issue of the journal Science. They've given scientists a clear view of some of the processes that have sculpted the Martian surface, including evidence that water shaped much of the entire region where the crater is found.

Another separate study, detailed in Thursday's issue of the journal Nature, looked at the question of how liquid water might have formed on early Mars. The research shows that even though the planet's surface temperature could have been well below freezing, water might still have flowed there if enough minerals were dissolved in it.

Opportunity, trundling across the Martian surface for more than five years now, arrived at Victoria crater 952 Martian days into its journey on the planet.

The rover had previously explored the Eagle and Endurance craters, about 3.7 miles (6 kilometers) away from Victoria. Mission scientists chose Victoria as the next crater to explore because "it was the biggest crater we could possibly find," said Steve Squyres of Cornell University, and the lead scientist for the Mars Exploration Rover Project.

The science team hoped that Victoria's depth — of about 400 feet (120 meters) — might shed more light on the geology of the Meridiani Planum region, an area about the size of Oklahoma.

Scientists had already seen distinctive sediment layers in Endurance, as well as evidence that water had been an active ingredient in shaping those layers. But Victoria offered a different perspective of the region because it is deeper than Endurance and sits slightly higher, offering a chance to peek at different layers of the ground.

During its two-year expedition there, Opportunity drove to the edges of promontories along Victoria's serrated edge, allowing it to look across to the next ridge and image the layers of sediment. The rover also drove down into the crater to get a look at what was inside.

What it found were layers of the same sulfate-rich sandstone that Opportunity had found at Endurance, with evidence that water had weathered away minerals in the rocks, then evaporated, leaving behind salts that eventually solidified into rock once again.

The findings show that water acted at both the Endurance and Victoria sites, suggesting that it did so across the whole Meridiani region. Squyres told Space.com that this was probably "the most significant finding" of the Victoria expedition.

Opportunity also found "gorgeous, striking evidence" of dune structures preserved in the rocks, Squyres said. There had been some signs of dunes at Endurance, but "Victoria really enabled us to nail that problem," he said.

While driving up to the crater and around it, the rover also saw clusters of meteorites that Squyres and the other mission scientists think could be fragments of the impactor that created the crater.

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