How the rovers changed our view of Mars

By Ker Than

updated 3:15 p.m. ET July 24, 2007

Talk about a tough act to follow. The robotic rovers Spirit and Opportunity have been exploring Mars' rocky landscape for more than 1,200 Martian days — much longer than any previous robot to touch down on the Red Planet.

Originally designed to last only three months, Spirit and Opportunity have continued functioning for 14 times that duration. They have survived to see not just one, but three, landing anniversaries. The hardy rovers have helped scientists make numerous amazing discoveries, the most notable of which was that liquid water once existed there, encouraging the continued search for signs of life on the Red Planet.

"They've spectacularly surpassed all expectations for what they were going to do," said Michael Meyers, lead scientist for the Mars Exploration Program at NASA Headquarters in Washington.

The robots' sojourn on Mars has not been trouble-free, however, and they have more than once overcome obstacles that could have ended the mission. Opportunity, in particular, has proven to be an especially tough trooper. It dug itself out of a sandy "purgatory dune" in the summer of 2005. Now, both rovers are struggling to survive one of the most severe episodes of dust-storm darkening ever observed on Mars.

The rovers' knack for overcoming obstacles and exceeding expectations are legendary and has endeared them to the dozens of researchers who have used data beamed back by the pair to reveal many of Mars' secrets.

The rovers' leading scientific achievements include snapping images of twisted rocks and smooth pebbles shaped by water; cooperating to create the first temperature profile of Mars' atmosphere; and revealing that Earthlike clouds also drift across the Martian skies.

Greatest hits from the rovers The scientists behind the Mars rovers have produced a long list of discoveries since the robots bounced to the Red Planet’s surface in January 2004. Here’s just a sampling: Rover reveals Mars was wet enough for life First solar eclipse seen from Mars Dust devils caught on Mars Rover discovers an alien meteorite on Mars Earth spotted from Martian surface Rover finds evidence of volcanic blast Oohs and ahs over Martian rocks and clouds Gasp! Even the dirt points to water on Mars More from MSNBC’s ‘Return to the Red Planet’ From Space.com: Top 10 rover discoveries MSNBC.com

Given the rovers' track record, scientists are optimistic that the rolling robots will successfully weather the latest Martian dust storms.

"These are hardy robust vehicles that are very capable, so I think given time we'll get through this," said John Callas, project manager for the Mars Exploration Rovers project.

Scientists predict, however, that it could be weeks before Mars' dust-clogged air clears.

"In order for us to really resume full scientific operations, even at a reduced rate, we need to have the dust opacity drop by a bit from what we've been seeing," said the rover team’s lead scientist, Steve Squyres of Cornell University. "How long it will take to drop to that level, we cannot predict."

Before the dust storms began, Opportunity was poised to descend into Victoria Crater and Spirit was investigating silica-rich soil that could provide even more evidence of Mars' water-rich past.

"As soon as conditions allow, we'll pick that up again," Callas said.

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