Mercury Probe Shuts Down During Key Flyby

A spacecraft en route to map the innermost planet in our solar system shut down during a key pass by Mercury on Tuesday, missing about half of its planned investigations, officials said Wednesday.

The primary purpose of Tuesday's flyby was to use the planet's gravity so the probe, known as MESSENGER, could slip into orbit in 2011. However, the spacecraft's temporary shutdown did not impact its overall mission.

"These things do happen," project manager Peter Bedini told Discovery News. "The MESSENGER flew by the planet and got the gravity assist. That was the highest priority."

"We know that we will be returning to Mercury and will be able to observe the innermost planet in exquisite detail," added lead scientist Sean Solomon with the Carnegie Institution in Washington, D.C.

MESSENGER flew 142 miles above Mercury at 5:55 p.m. EDT on Tuesday, its third and final pass before settling into orbit. Scientists had hopes to use the flyby to image unusual surface features spotted during two previous passes.

During its approach, MESSENGER was able to capture previously unseen portions of Mercury's surface. In addition to the two previous MESSENGER flybys, NASA's Mariner 10 spacecraft passed by Mercury three times in 1974 and 1975.

But four minutes prior to closest approach, MESSENGER put itself into a safe mode that suspended its instruments.

The probe was in Mercury's shadow at the time and was operating on battery power. Engineers believe MESSENGER shut down as a precaution when automated systems attempted to switch to an alternative power configuration.

"The spacecraft said, 'This doesn't look right,' and it ceased the onboard command sequence and puts the instruments on hold," Bedini said.

MESSENGER resumed normal operations at 12:30 a.m. EDT on Wednesday. Engineers, meanwhile, are assessing what happened to better understand how the spacecraft operates.

"We're still learning how to drive," Bedini said.