NASA engineers are trying to figure out why an orbiting Mars spacecraft went into safe mode this week.

The Mars Reconnaissance Orbiter rebooted its computer Monday, the sixth time it has done so since launching in 2005.

Engineers think the craft may have been hit by a cosmic ray that caused it to mistakenly believe there was a power surge. The orbiter is programmed to go into safe mode when it encounters an unknown event.

An exact cause is still under investigation.

Project managers at NASA's Jet Propulsion Laboratory say it will take several days for the Mars Reconnaissance Orbiter to return to normal science operations.