NASA's Opportunity rover landed on Mars' Meridiani Planum on January 25, 2004. It was designed to last just 90 days on the surface, but more than a decade later it's still rolling along. And now, having driven its 25th mile on Mars, Opportunity now holds the record for distance driving on another planet.
"Opportunity has driven farther than any other wheeled vehicle on another world," said Mars Exploration Rover Project Manager John Callas. "This is so remarkable considering Opportunity was intended to drive about one kilometer [0.62 miles] and was never designed for distance."
The previous off-world driving record was secured in 1973 by the Soviet Lunokhod 2 rover. Lunokhod 2, the payload of the Luna 3 mission that landed on the Moon's LeMonnier crater on January 14, 1973. The rover moved during the lunar day, stopping occasionally to recharge its batteries with solar panels, and hibernated during the lunar nights, relying on a radioactive heat source for warmth.
Over the course of its four-month drive, Lunokhod 2 covered about 23 miles. It helped that this rover wasn't subject to the seven minute one-way communications delay between the Earth and Mars—the Soviet drivers guided the rover in near-real time using images sent back from its cameras as guides—while the lunar day provided two solid weeks of solar power. The rover finally went silent in June of 1973, but its laser retroreflector is still used for laser ranging from the Earth.
"The Lunokhod missions still stand as two signature accomplishments of what I think of as the first golden age of planetary exploration, the 1960s and '70s," said Steve Squyres, the principal investigator for NASA's twin Mars Exploration rovers Opportunity and its twin Spirit. "We're in a second golden age now, and what we've tried to do on Mars with Spirit and Opportunity has been very much inspired by the accomplishments of the Lunokhod team on the moon so many years ago. It has been a real honor to follow in their historical wheel tracks."
Opportunity, which is currently exploring Endeavour Crater, carved a conservative path around Mars. Drivers planned the rover's route from images, uploading a series of drive commands then waiting to see at the next data transfer time how the rover fared.
And it's worth noting that no other off-Earth vehicle has come anywhere close to completing an otherworldly marathon. Seriously, just check out this (rather lengthy) graphic from NASA's Mars Exploration program:
NASA's first Mars rover, the microwave-sized Sojourner, was part of the agency's 1997 Mars Pathfinder mission. This first free-range rover was designed to roam for about seven days, going no further than 1,640 feet from the lander; any further and communications would degrade. This little rover ended up lasting 85 days, covering hundreds of square feet within range of the lander before ceasing operations on September 25, 1997.
Spirit, Opportunity's twin, went silent in 2010 after getting stuck at a site called Troy. The rover's energy levels dropped and NASA never managed to regain communications with its Martian proxy. The rover's odometer stopped when it died, reading 4.8 miles.
Despite being a shorter departure, no Moon rovers have come close to an off-world marathon. Lunokhod 2's twin, Lunokhod 1, reached the Moon as the payload of the Luna 17 lander and covered 34,580 feet in about 10 months on the surface. NASA also sent rovers to the Moon as part of the last three Apollo missions, though they were driven by astronauts seated at the controls. On Apollo 15 the Lunar Roving Vehicle covered 17.2 miles in 3 hours, 2 minutes; on Apollo 16 the LRV covered 16.5 miles in 3 hours 26 minutes; and Apollo 17 saw the the rover travel 22.3 miles in 4 hours 26 minutes.
None of these rovers are still moving, which means NASA's Curiosity is currently the only challenger to Opportunity's record. This massive rover has enough power in its radioisotopic thermoelectric to last for at least another decade, so unless the rover physically falls apart it will probably cover a lot of Martian ground. But for the moment, its odometer reads a little over one mile.
10 and a half years later, NASA's Opportunity rover is just short of rolling the 26.2 miles needed to complete a marathon. Making it that far means reaching its next major investigation site, which is fittingly being called "Marathon Valley" by the Mars Exploration team.
Marathon Valley is a site mission scientists suspect has several exposed clay minerals surrounded by steep slopes, an arrangement that could shed new light on Mars's geologic history. Because at the end of the day, as Callas said, "how much exploration and discovery we have accomplished over that distance" is more impressive than the distance covered. Here's to many more miles of science!