A little more than half of scientists' planned observations during the Messenger spacecraft's flyby of the planet Mercury were lost Tuesday when the probe sensed a problem, shut down its scientific instruments and went into "safe mode."
The $426 million mission remains on track to enter orbit around Mercury in 2011, scientists said Wednesday. But much of what they had hoped to learn during the last of three scheduled flybys will have to wait for that orbital phase.
"It isn't the outcome everyone expected or wanted," said Eric Finnegan, systems manager for the mission. But Messenger gathered a wealth of data during the first half of the flyby, he said.
Mission managers said it was unclear what caused Messenger's onboard computers to shut down all seven scientific instruments four minutes before the spacecraft's closest approach to Mercury. But it appeared to occur five minutes after Messenger switched to battery power as it flew into Mercury's shadow and lost access to electrical power through its solar panels.
Evidently, the computers saw something in the configuration that "didn't match what the spacecraft thought it should," so they shut everything down to await instructions, Finnegan said.
Nearly an hour later, when Messenger emerged from behind Mercury, engineers at the Johns Hopkins University's Applied Physics Laboratory near Laurel realized that the spacecraft was in safe mode, with all instruments shut down.
Finnegan said it was six hours more before they got the spacecraft out of safe mode and that it would be early Saturday before Messenger resumes its science observations of Mercury.
The good news from mission control was that all of the scientific data gathered before the glitch occurred has been downloaded safely. Messenger took several days of measurements of Mercury's thin atmosphere and magnetic "tail," and carried out intensive photography.
"That includes imaging ... 5 percent of the planet that hadn't been seen," Finnegan said. "Now, 95 percent of the planet's surface has been imaged at fairly high resolution." Those photos have begun to be posted on the Internet. Some had scientists at APL "oohing and aahing," he said. What was lost, he said, were targeted observations of geological features spotted during earlier flybys.
