Planetary scientists who have been using two extraordinary rovers to tour the surface of Mars for more than three years are deeply dismayed by a $4-million budget cut that they say would force them to shut down one of the robotic explorers and curtail the activities of the other.

“It’s very demoralizing for the team,” said Steve W. Squyres, a professor of astronomy at Cornell University who is principal investigator for the rover program, in an interview with the Associated Press.

The twin rovers, which were designed for three-month missions, have been exploring Mars since January 2004. They cost NASA about $20-million a year to operate. NASA’s Jet Propulsion Laboratory, which oversees the rovers, said it would appeal the order to trim the rover budget. And CNN reported late Monday evening that a spokesman for the NASA administrator, Michael Griffin, had said that “shutting down one of the rovers is not an option.”

If the cut is not rescinded, it will require the rover Spirit to be put in hibernation and limit Spirit’s twin, Opportunity, to receiving orders every other day, instead of daily. —Lawrence Biemiller