Mars' aging twin rovers will explore the red planet for at least two more years under an extension approved by NASA.
It is the fifth time the space agency has continued the activities of the solar-powered, six-wheel robots, which landed on opposite ends of the planet in 2004.
The extension means Spirit and Opportunity will conduct science experiments through 2009 provided they stay healthy. The rovers weathered a giant dust storm earlier this year that at one point drastically reduced their power and scaled back their operations.
Spirit is currently exploring a plateau called Home Plate for evidence of volcanism. Last month, Opportunity reached its first stop inside a huge Martian crater and began studying the rock layers. Spirit has driven 4.5 miles while Opportunity has clocked 7.2 miles to date.
The price tag of the original mission, managed by NASA's Jet Propulsion Laboratory, was $820 million. NASA previously granted four extensions totaling about $106 million. The latest extension will cost at least $20 million.