Los Angeles ? Scientists plan to put one of the twin Mars rovers to sleep and limit the activities of the other robot to fulfill a NASA order to cut $4 million from the program’s budget, mission team members said Monday.

The solar-powered rovers Spirit and Opportunity have dazzled scientists and the public with findings of geologic evidence that water once flowed at or near the surface of Mars long ago.

Both rovers were originally planned for three-month missions at a cost of $820 million, but are now in their fourth year of exploration. It costs NASA about $20 million annually to keep the rovers running.

The latest directive from NASA to cut $4 million means Spirit will be forced into hibernation in the coming weeks, said principal investigator Steve Squyres of Cornell University.

“It’s very demoralizing for the team,” Squyres said.