Scientists initially thought the remote-controlled machines would last only three months in Mars' freezing climate, said John Callas, rover project manager at the National Aeronautics and Space Administration's Jet Propulsion laboratory in Pasadena, Calif.
"These rovers are incredibly resilient considering the extreme environment the hardware experiences every day," Callas said, noting information sent by the rovers have proved water existed on Mars billions of years ago.
No one knows how long the rovers will continue to operate. Spirit can only drive backward because of a stuck wheel, while Opportunity's robotic arm misfires because of a broken electrical wire, the BBC reported Saturday.
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