Those Other Martian Rovers Celebrate 9 Years on the Red Planet

Curiosity can look up to its older, wiser cousins.

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An artist's rendering of the Spirit rover on Mars (NASA/JPL)

On January 3, 2004, a vehicle the size of a golf cart, standing on six wheels and weighing about a fifth of a ton, landed on the surface of Mars. The rover -- official name: Mars Exploration Rover-A; given name: Spirit -- had begun its mission to the Red Planet. Three weeks later, another vehicle -- a twin of the first, officially named MER-B and actually called Opportunity -- made its own Martian arrival. On the other side of the planet.

The robotic pair would join four other rovers -- the USSR's Prop-M rovers, Britain's Beagle 2, and the United States's Sojourner -- in exploring the surface of mars. And they would go on to traverse Mars -- seeking, in particular, signs of past water activity -- for much longer than their human benefactors initially intended. While Spirit's primary surface mission was originally planned to last at least 90 sols (90 Martian days), that mission was extended several times -- lasting, ultimately, about 2,208 sols. Which is to say, about six years. (After getting stuck in some soft Martian sand, and despite NASA's "free Spirit" campaign, Spirit finally lost contact with Earth in March 2010.) And Opportunity, bless its robotic little heart, is still exploring the planet. Powered by solar panels and, you have to assume, just a little bit of moxie.

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So, yes. Though Curiosity, having spent less than a year on the Red Planet, gets much of the public attention when it comes to NASA's Martian rovings, its cousins are accomplished in their own rights. The two robots of the Mars Exploration Rover Mission helped to confirm that Mars, despite its current state of ruddy aridity, was once warmer and wetter than it is now. Spirit, for its part, found an ancient hydrothermal system -- a place where heat energy and liquid water may have created conditions that would have been capable of supporting life as we know it. And Opportunity is, at the moment, exploring clay deposits on the rim of Mars's Endeavor Crater.

Together, the two rovers have covered 26.82 miles so far, with Opportunity clocking in at 22.02 miles (and counting). They have surpassed everyone's -- even their creators' -- expectations of them, and gotten us closer to understanding whether, and how, Mars might have once supported life. Here's a timeline of where the rovers have roved -- and what the rovers have accomplished -- during their sojourn on Mars:

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While Opportunity, Live Science notes, "is showing some signs of its advanced age, such as an arthritic arm," the robot overall "remains in good health and continues to return interesting data to its handlers back on Earth." Nine years old -- ancient, in Mars rover years -- and still going strong. And humans are going along for the ride. As Cornell's Steve Squyres, rover mission principal investigator, recently said of Opportunity's extended adventures: "Every day is a gift at this point."