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Image: Spirit robotic arm
NASA / JPL-Caltech
The Spirit rover stretches out its robotic arm to make observations on July 20, in the midst of dust storms sweeping the Red Planet.
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updated 7/24/2007 3:15:26 PM ET 2007-07-24T19:15:26

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.

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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.

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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Photos: Greatest hits from Mars rovers

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  1. Practice run

    JPL engineers Eric Aguilar, left, and Joe Melko monitor the rover's performance on a sandy slope outside JPL's In-Situ Instrument Lab. (NASA / JPL) Back to slideshow navigation
  2. Blastoff to Mars

    A Delta 2 Heavy rocket lifts off from Cape Canaveral Air Force Station in Florida on July 7, 2003. The rocket launched the Opportunity rover toward Mars. (Boeing via AP) Back to slideshow navigation
  3. Look at that!

    Principal rover scientist Steve Squyres points at Martian snapshots displayed on a big screen at NASA's Jet Propulsion Laboratory, beamed back from the Red Planet just after the Spirit rover's landing on Jan. 3, 2004. NASA Administrator Sean O'Keefe, at right, and mission team members watch as the images are added. (NASA) Back to slideshow navigation
  4. Leaving the nest

    NASA's Spirit rover looks back at its own lander platform early Jan. 15, 2004, just after the mission team sent the robot out for its first spin on Martian soil. Spent air bags are crumpled along the sides of the platform. At the top of the image, the view is mirrored by the bottom of the rover's solar arrays. (NASA / JPL) Back to slideshow navigation
  5. Rover's footprint

    This image, taken by NASA's Opportunity rover and released Jan. 28, 2004, shows the "footprint" left by one of the rover's inflated air bags as the spacecraft bounced to its resting place on Martian soil. The circular region of the flowerlike feature is about the size of a basketball. (NASA / JPL) Back to slideshow navigation
  6. In memoriam

    NASA's Spirit rover took this picture of a plaque commemorating the fallen astronauts of the Columbia shuttle mission, which ended in disaster in February 2003. The 6-inch-wide plaque is mounted on the back of Spirit's high-gain antenna. (NASA) Back to slideshow navigation
  7. RAT bites

    This image, taken by the Opportunity rover on Feb. 28, 2004, shows two holes that allowed scientists to peer into Mars' wet past. The rover's Rock Abrasion Tool, or RAT, drilled the holes (indicated by red circles) into rocks in the region dubbed "El Capitan." An analysis of the drilled rock helped scientists determine that this part of Mars was once drenched in water. (NASA / JPL) Back to slideshow navigation
  8. Bedrock beauty

    A mosaic of images from NASA's Opportunity rover shows the rock region dubbed "El Capitan," which lies within a larger outcrop near the rover's landing site. The outcrop represents the first bedrock ever seen up close on Mars. This image was released March 2, 2004. (NASA / JPL) Back to slideshow navigation
  9. Purple Planet

    A false-color image from the Opportunity rover, released Feb. 9, 2004, accentuates the differences between a green-looking slab of Martian bedrock and orange-looking spheres of rock. Scientists likened the "spherules" to blueberries embedded within and scattered around muffins of bedrock. The spherules are thought to have been created by the percolation of mineral-laden water through the bedrock layers. (NASA / JPL / Cornell) Back to slideshow navigation
  10. A scoop of berries

    This microscopic image, taken at the outcrop region dubbed the "Berry Bowl" near the Opportunity rover's landing site, shows spherelike grains of rock or "blueberries." Of particular interest is the blueberry triplet, which indicates these geologic features grew in pre-existing wet sediments. This image was taken March 11, 2004. (NASA / JPL / Cornell) Back to slideshow navigation
  11. A last look back

    The "Lion King" panorama, captured by the Opportunity rover March 24 and 26, 2004, is a wide-angle view of Eagle Crater and the surrounding plains. Opportunity's landing platform is visible in the center, with tracks leading out of the crater. (NASA / JPL / Cornell ) Back to slideshow navigation
  12. Dunes of Mars

    A false-color view from NASA's Opportunity rover, released Aug. 6, 2004, shows the dune field at the bottom of Endurance Crater. The bluish tint indicates the presence of hematite-containing spherules ("blueberries") that accumulate on the flat surfaces of the crater floor. (NASA /JPL / Cornell ) Back to slideshow navigation
  13. Wide-angle walls

    NASA's Opportunity rover captured this view of "Burns Cliff" within Endurance Crater on Mars during the week of Nov. 13-20, 2004. The rover's solar arrays can be seen at the bottom of this true-color mosaic of 46 images. Because of the wide-angle view, the cliff walls appear to bulge out toward the camera. In reality, the walls form a gently curving, continuous surface. (NASA / JPL) Back to slideshow navigation
  14. Martian clouds

    Clouds add drama to the sky above Endurance Crater in this mosaic of frames taken by the navigation camera on NASA's Opportunity rover on the morning of Nov. 16, 2004. The view spans an arc from east on the left to the southwest on the right. These clouds are part of a band that forms near the equator when Mars is near the part of its orbit that is farthest from the sun. (NASA / JPL) Back to slideshow navigation
  15. Farewell to Endurance

    After spending six months studying rocks inside Endurance Crater, NASA's Opportunity rover climbed out Dec. 12, 2004, and used its front hazard-avoidance camera to look back across the stadium-sized crater from the rim. (NASA / JPL) Back to slideshow navigation
  16. Alien junkyard

    NASA's Mars Exploration Rover Opportunity gained this view of its own heat shield during the rover's 325th martian day (Dec. 22, 2004). The main structure from the successfully used shield is to the far left. Additional fragments of the heat shield lie in the upper center of the image. The heat shield's impact mark is visible just above and to the right of the foreground shadow of Opportunity's camera mast. This view is a mosaic of three images taken with the rover's navigation camera. (NASA / JPL) Back to slideshow navigation
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