The Mars rovers Spirit and Opportunity are now entering their seventh year of operation.
The little robot vehicles have traveled a total of 16 miles on the Martian surface.
What was supposed to have been a three-month mission has stretched way beyond the warranty period.
NASA engineers worry that Spirit might be stuck in the sand as the Martian winter approaches.
But they say even if Spirit's roving days are over, it still can beam back useful data from a fixed position.
