The Mars rover Curiosity has temporarily stopped science observations while NASA checks out an electrical problem.
The space agency said Wednesday the voltage change was first discovered on Sunday and engineers think it might be some kind of short.
The six-wheel, nuclear-powered rover halted work as a precaution.
So far, there's no sign that the problem is related to a computer reboot earlier this month that put Curiosity in safe mode.
Curiosity landed in a Martian crater in August 2012 and has spent the last several months driving toward its ultimate destination, Mount Sharp.
Despite the trouble, "the vehicle is safe and stable, fully capable of operating in its present condition, but we are taking the precaution of investigating what may be a soft short," said Mars Science Laboratory Project Manager Jim Erickson at NASA's Jet Propulsion Laboratory, Pasadena, Calif.