Lisa Grossman, physical sciences reporter
(Image: NASA/Kepler mission/Wendy Stenzel)
NASA's planet-hunting Kepler telescope has put its search for alien Earths on hold while it rests a stressed reaction wheel.
The injured wheel normally helps to control the telescope's orientation, keeping it pointed continuously at the same patch of sky. Kepler stares at the thousands of stars in its field of view to watch for the telltale blinks that occur when a planet crosses in front of its star. It has found nearly 3000 potential planets outside our solar system since its launch in 2009, transforming the field of exoplanet research and raising hopes of someday finding alien life.
When it launched, Kepler had four reaction wheels: three to control its motion along each axis, and one spare. But last July, one wheel stopped turning. If the spacecraft loses a second wheel, the mission is over.
So when another wheel started showing signs of elevated friction on 7 January, the team decided to play it safe. After rotating the spacecraft failed to fix the problem, NASA announced yesterday that they're placing Kepler in safe mode for 10 days to give the wheel a chance to recover.
The hope is that the lubricating oil that helps the wheel's ball bearings run smoothly around a track will redistribute itself during the rest period.
The telescope can't take any science data while in safe mode. But if the wheel recovers on its own, Kepler's extended mission will run until 2016, leaving it plenty of time to make up for the lost days.
"Kepler is a statistical mission," says Charlie Sobeck, Kepler's deputy project manager at NASA's Ames Research Centre in Mountain View, California. "In the long run, as long as we make the observations, it doesn't matter a lot when we make the observations."
Despite the high stakes, the team doesn't seem too worried.
"Each wheel has its own personality, and this particular wheel has been something of a free spirit," Sobeck says. "It's had elevated torques throughout the mission. This one is typical to what we've seen in the past, and if we had four good wheels we probably wouldn't have taken any action."
"I prefer to picture the spacecraft lounging at the shore of the cosmic ocean sipping a Mai Tai so that she'll be refreshed and rejuvenated for more discoveries," wrote Kepler co-investigator Natalie Batalha in an email.
The team will check up on the wheel on 27 January and return to doing science as soon as possible.
There are two exoplanet missions currently being considered for after Kepler is finished, says Doug Hudgins at NASA Headquarters in Washington, DC. One, TESS (Terrestrial Exoplanet Survey Satellite), would scan the entire sky for planets transiting the stars nearest to the sun. The other, FINESSE (Fast Infrared Exoplanet Spectroscopy Survey Explorer), would take spectra of planets as they passed in front of their stars as a way to probe their atmospheres.
The missions are being evaluated now, and NASA will probably select one this spring, Hudgins says. The winner will launch in 2017.
If Kepler goes down with its reaction wheel, that won't affect which mission wins, he adds. "That's a straight-up competition based on the merits of the two concept study reports."
NASA planet-hunter is injured and resting
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NASA planet-hunter is injured and resting
