The National Aeronautics and Space Administration said its decision to keep the robots Spirit and Opportunity in operation, possibly through 2009, is dependent upon the rovers' continued productivity and operability.
The twin rovers landed on Mars in January 2004 on missions originally planned to last only 90 days. In September, Opportunity began descending into Victoria Crater in Mars' Meridiani Planum region. Spirit had climbed onto a volcanic plateau in a range of hills that were on the distant horizon from the landing site.
"After more than three-and-a-half years, Spirit and Opportunity are showing some signs of aging, but they are in good health and capable of conducting great science," said John Callas, rover project manager at NASA's Jet Propulsion Laboratory.
To date, Spirit has driven 4.51 miles and has returned more than 102,000 images. Opportunity has driven 7.19 miles and has returned more than 94,000 images.