This mosaic of frames from the navigation camera on NASA's Mars Exploration Rover Opportunity gives a view to the northeast from the rover's position on its 1,687th Martian day, or sol (Oct. 22, 2008).
When it comes to Mars missions, NASA?s twin rovers Spirit and Opportunity seem to be the robots that never quit.
The two plucky probes were each built for a 90-day romp across the Martian surface, a mission that began when Spirit bounced to a stop on the planet?s expansive Gusev Crater five years ago today. Opportunity touched down on the other side of Mars a few weeks later and now - after half a decade - both rovers are still exploring the red planet after surviving more than 20 times their planned lifetime.
"The American taxpayer was told three months for each rover was the prime mission plan," said Ed Weiler, NASA?s associate administrator for science missions at the agency?s Washington, D.C., headquarters, in a statement. "The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times."
The rovers reportedly cost about $20 million to operate each year since their 2004 arrivals on Mars.
Spirit set down at Gusev Crater on Jan. 3 at 11:35 p.m. EST (8:35 p.m. PST), where it overcame initial computer glitches and went on to scale nearby hills and brave the frigid Martian winter year after year.
Opportunity bounced to a stop inside what scientists later dubbed Eagle crater just after midnight (EST) Jan. 25 in an interplanetary hole-in-one on the vast Martian plains of Meridiani Planum. Since then, the rover has spotted a Martian meteorite, visited the heat shield cast off during its landing and explored ever larger craters as it makes it way toward Endeavour, a monster crater 14 miles (22 km) across.
?We keep setting the bar higher for what these rovers can do," said Frank Hartman, a rover driver at NASA?s Jet Propulsion Laboratory in Pasadena, Calif., which manages the mission. "Once it seemed like a crazy idea to go to Endeavour, but now we're doing it."
Both rovers have weathered glitches from old age, with Opportunity digging its way out of a Martian sand dune that threatened to halt its red planet exploration. Since their mission began, Spirit and Opportunity have returned a veritable feast of information on the composition of Mars? surface and history of water at their local landing sites.
Altogether, the rovers have driven across more than 13 miles (21 km) of Martian terrain, taken some 250,000 photographs and beamed more than 36 gigabytes of data to Earth. They?ve also been the stars of film and television documentaries lauding their unexpected long life.
"These rovers are incredibly resilient considering the extreme environment the hardware experiences every day," said John Callas, NASA?s rover project manager at JPL. "We realize that a major rover component on either vehicle could fail at any time and end a mission with no advance notice, but on the other hand, we could accomplish the equivalent duration of four more prime missions on each rover in the year ahead."
After third winter, new science ahead
Spirit came close to a chilly demise this year as power levels dwindled in the dim Martian winter, mission managers said. But the rover has bounced back after surviving the season, its third winter in the planet?s southern hemisphere, which ended in December.
"This last winter was a squeaker for Spirit," Callas said. "We just made it through."
Scientists plan to send Spirit to a pair of interesting spots about 600 feet (183 meters) away from its current perch atop a rocky plateau called Home Plate, which the rover has been studying since 2006. One target is a mound that may hold the key to determining if Home Plate is the remains of a larger expanse of volcanic material. The other is a depression called Goddard, an immense pit the size of a house.
"Goddard doesn't look like an impact crater," said Steve Squyres, principal investigator for the rover science instruments at Cornell University, in Ithaca, New York. "We suspect it might be a volcanic explosion crater, and that's something we haven't seen before."
Meanwhile, Spirit?s twin Opportunity is chugging along toward Endeavour Crater. The crater is 20 times larger than Opportunity?s last destination, Victoria Crater, which commanded the rover?s attention for nearly two years. The new target sits just seven miles (12 km) from Victoria, but Opportunity must drive much farther to zigzag around obstacles and inspect loose rocks along the way.
?This has turned into humanity's first overland expedition on another planet,? said Squyres. ?When people look back on this period of Mars exploration decades from now, Spirit and Opportunity may be considered most significant not for the science they accomplished, but for the first time we truly went exploring across the surface of Mars."
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