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 Explorations Program at NASA Headquarters in Washington, D.C.
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 Earth-like clouds also drift across the martian skies.
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 (MER) 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 MER 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.
- Mars Rovers' Top 10 Most Amazing Discoveries
- VIDEO: Mars Rover Team Ponders Mission's End
- SPECIAL REPORT: Mars Rovers
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Ker Than is a science writer and children's book author who joined Space.com as a Staff Writer from 2005 to 2007. Ker covered astronomy and human spaceflight while at Space.com, including space shuttle launches, and has authored three science books for kids about earthquakes, stars and black holes. Ker's work has also appeared in National Geographic, Nature News, New Scientist and Sky & Telescope, among others. He earned a bachelor's degree in biology from UC Irvine and a master's degree in science journalism from New York University. Ker is currently the Director of Science Communications at Stanford University.