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The Mars Exploration Rover Mission
In early 2004, the Mars Exploration Rovers (MERs) Spirit and Opportunity made history when they landed successfully on Mars. Part of NASA’s long-term Mars Exploration Program, the mission succeeded beyond even the hopes of its creators, with Spirit and Opportunity proving hardier than anyone could have imagined, overcoming obstacles some thought signaled the end of the mission.
Spirit landed in Gusev crater, a 100-mile-wide basin thought to have once held a body of water. On the opposite side of Mars, Opportunity landed on the Meridiani Planum, a flat plain that when viewed from orbit seemed to be covered in hematite—an iron compound that forms in water. The landing sites were chosen to help the rovers achieve their primary scientific mission: to examine rocks and soils for evidence that liquid water once flowed and pooled on the Martian surface. Mars today is too cold and its atmosphere too thin for liquid surface water to exist. But there are signs that water—on Earth an essential ingredient in the formation of life—may have once made Mars a place where life was possible.
Over the next several days the rovers raised their camera masts and antennas with which they communicate with Earth, and unfolded themselves. After they took a good look around with their Panoramic Cameras (Pancams) and sent those images home to Earth, scientists decided on the best direction for the rovers to head in. Finally, the MERs rolled off their landers onto the dusty red surface of Mars to begin their explorations. (Go to http://mars.jpl.nasa.gov/mer/gallery/video/animation.html for an exceptional animation of the rover’s journey, landing, and initial investigations.)
Rolling along on its six wheels, a rover travels about 20 inches a minute. (They’re capable of going about five times faster, but slower is safer.) Navigational and hazard-avoidance cameras help the rovers make their way around. Like all good field geologists, the rovers have excellent tool kits so they can conduct “hands-on” investigations. These and other high-tech instruments helped the rovers determine the mineral composition of a rock. In turn, scientists used that information to study how the rock was formed and if water played a role in its formation.
Designed to operate for a minimum of 90 Martian days (a Martian day is 24.6 hours) on solar power, they have lasted much longer. When the solar cells on the rovers’ solar panels were compromised by dust, the solution came from an unlikely source. Dust devils—miniature tornados that occur mostly around early afternoon on Mars—engulfed the rovers, scouring away grit and cleaning the solar panels.
But even with the panels fully operational, no one expected the rovers to last through the Martian winter—after all, winter on Mars offers precious little sun. Ingenious engineers came up with the idea of parking the rovers on hills, their panels angled to catch what little sun was available. Because the rovers “live” on sunlight, catching more of it kept them “alive.”
And there were other obstacles too. Five months after it landed, Opportunity found itself with all six of its wheels stuck in a soft dune. Engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, worked for 5 weeks to maneuver the rover out of the distant sand trap over 108 million miles away.
Despite all the obstacles, however, the MERs have made some exciting discoveries. They’ve provided indisputable proof that water once flowed on Mars. Shortly after it landed, Opportunity found ripple marks and layered bedrock in a crater, geographical evidence of a shallow ancient sea. Spirit took longer to find evidence of water on its side of the planet, but then discovered--high on a hill no one thought the golf cart-sized rover would be able to climb--rocks with some of the highest sulfur content ever found on Mars. (The sulfate salts found were deposited by water.) And large amounts of hematite were confirmed, in the form of “blueberries”--BB-sized pellets of water-formed rock.
The robot explorers are still on the job, beaming back images that help scientists delve into the mysteries of the red planet’s past and to predict whether of not Mars might be able to sustain life in the future.
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