(NEW YORK) -- When the Mars rover Opportunity settled on the Martian surface nine years ago on Friday, mission managers at NASA said they would be pleased if it lasted for 90 days.
Instead, it's been 3,201 days, and still counting. The rover has driven 22.03 miles, mostly at a snail's pace, from one crater to another, stopping for months at a time in the frigid Martian winters. The six motorized wheels, rated to turn 2.5 million times, have lasted 70 million, and are all still working.
"Opportunity is still in very good health, especially considering what it's gone through," said John Callas, manager of NASA's Mars Exploration Rover project. "The surface of Mars is a pretty tough place; there can be temperature fluctuations of a hundred degrees each day. That's pretty hard on the hardware."
When Opportunity and its twin rover, Spirit, reached Mars in January 2004, there was a fair bit of sniping that NASA, with all that 90-day talk, was playing down expectations. It escalated when Steve Squyres of Cornell University, the principal investigator for the missions, said things like, "We're on Sol 300 of a 90-Sol mission." (A Sol is a day on Mars, and lasts 24 hours, 39 minutes.)
Callas and others have insisted that the prediction was based on engineering, not a nod to public relations.
"There was an expectation that airfall dust would accumulate on the rover, so that its solar panels would be able to gather less electricity," said Callas. "We saw that on Pathfinder," a small rover that landed on Mars in 1997. "The cold climate was also expected to be hard on the rovers' batteries, and changes in temperature from night to day would probably pop a circuit or two."
Instead, the temperatures weren't quite as tough as engineers had expected, and the rovers proved tougher. They did become filthy as the red Martian dust settled on them, reducing the sunlight on the solar panels -- but every now and then a healthy gust came along, surprising everyone on Earth by cleaning the ships off.
Spirit, in hilly territory on the other side of the planet, finally got stuck in crusty soil in 2009, and its radio went silent the next year. But Opportunity, though it's had some close calls, is still going.
In its first weeks, NASA said Opportunity found chemical proof that there had once been standing water on the surface of Mars -- good news if you're looking for signs that the planet could once have been friendly to life. Since then, it's been sent to other places, with rocks and soil that are probably older, and with clay that may have been left by ancient rivers.
About 20 NASA staff members still work full-time on Opportunity at the Jet Propulsion Laboratory in Pasadena, Calif. Another 60 split their time between Opportunity and other projects, such as the Curiosity rover that landed last August. About 100 scientists, doing research on Mars, pop in and out.
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