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Image: NASA's Spirit rover
NASA
NASA's Spirit rover points its instrument-laden robotic arm toward an outcropping in the Columbia Hills nicknamed "Comanche Spur," the focus of Spirit's study as it approaches the two-year mark on Mars.
updated 1/2/2006 3:20:22 PM ET 2006-01-02T20:20:22

The warranty expired long ago on NASA’s twin robots motoring around Mars.

In two years, they have traveled a total of seven miles. Not impressed? Try keeping your car running in a climate where the average temperature is 67 below zero and where dust devils can reach 100 mph.

These two golf cart-sized vehicles were only expected to last three months.

“These rovers are living on borrowed time. We’re so past warranty on them,” says Steven Squyres of Cornell University, the Mars mission’s principal researcher. “You try to push them hard every day because we’re living day to day.”

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The rover Spirit landed on Mars on Jan. 3, 2004, and Opportunity followed on Jan. 24. Since then, they’ve set all sorts of records and succeeded in the mission’s main assignment: finding geologic evidence that water once flowed on Mars.

Part of the reason for their long survival is pure luck. Their lives were extended several times by dust devils that blew away dust that covered their solar panels, restoring their ability to generate electricity.

Like most Earth-bound vehicles, these identical robots have their own personalities.

The overachieving Opportunity dazzled scientists from the start. It eclipsed its twin by making the mission’s first profound discovery — evidence of water at or near the surface eons ago that could have implications for life.

The rock-climbing Spirit went down in the history books by becoming the first robot to scale an extraterrestrial hill. Last summer, it completed a daredevil climb to the summit of Husband Hill — as tall as the Statue of Liberty — despite fears that it might not survive the weather.

Technical hiccups
The rovers haven’t been all get-up and go — technical hiccups have at times limited their activity, even from the start. At one point, Spirit had a balky front wheel, but engineers overcame the problem by driving it in reverse. Last spring, Opportunity got stuck hub-deep in sand while trying to crest a foot-high dune, and was freed after weeks of effort by the Earth-bound engineers.

The six-wheeled travelers, managed by NASA’s Jet Propulsion Laboratory in Pasadena, also are showing signs of aging. In November, a motor on Opportunity’s robotic arm stalled and the arm failed to extend while it was surveying a rock outcrop. The engineers fixed that problem after two weeks.

This mission is the first time any probe has extensively rolled across Mars, whose rocky landscape is a dangerous place for man-made objects to settle and roam.

There have been four previous Mars landings that succeeded. Of those, NASA’s stationary Viking 1 lander operated the longest, from 1976 to 1982. NASA’s Sojourner was the first rover, but it stayed close to its Pathfinder lander.

Spirit and Opportunity parachuted to opposite ends of Mars. Spirit landed in Gusev Crater, a 90-mile-wide depression south of the Martian equator. Opportunity followed three weeks later, touching down on Meridiani Planum on the other side of the planet.

In two years, Spirit has traveled over three miles and beamed back 70,000 images including self-portraits and panoramas of the rust-colored planet’s surface. Opportunity has driven over four miles and transmitted more than 58,000 images.

Three times NASA has extended the rovers’ mission, spending an extra $84 million on top of the $820 million original price tag.

While both rovers have discovered clues of ancient water, they also have found evidence of a violent past that might have prevented some life forms from emerging.

Piecing together a definitive history of Mars is far from over, scientists say, as the rovers head to their next destinations to explore more rocks and minerals.

Spirit recently descended Husband Hill and is driving toward a basin that holds geologic promise. Opportunity is rolling to an enormous depression known as Victoria Crater that is thought to hold more clues about the planet’s past.

“Rock layers are the barcode of Mars history,” said John Grotzinger, a science team member from the Massachusetts Institute of Technology. “Every time we encounter new layers, it’s another piece of the puzzle.”

© 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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