Kepler's quest for an Earth-like planet orbiting a sun-like star has been put on hold, NASA said, after the spacecraft sensed it was facing in the wrong direction and put itself in 'safe mode.'
This file artist's rendering shows the Kepler space telescope. NASA scientists are attempting to repair the spacecraft after it apparently lost its long-distance planet-hunting abilities. Kepler has been collecting data for 4 years, scientists hope it will be able to continue to do so.
AP Photo/NASA, File
EnlargeThe planet-hunting Kepler spacecraft?s dramatic, some would say romantic, quest for an Earth-like exoplanet orbiting a star in its habitable zone has suddenly been put on hold, NASA officials said Tuesday, while engineers try to figure out what caused the craft to lose its ability to point itself at its distant targets.
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The spacecraft is essentially hibernating, NASA said at a hastily called briefing late Wednesday afternoon, having put itself into "safe mode" on Sunday after sensing it was pointing in the wrong direction.
Controllers discovered the glitch Tuesday during their twice-a-week touch-base with the craft, currently some 40 million miles away in an Earth-like orbit around the sun.
When the craft is in safe mode, thrusters control its orientation, rather than the fast-spinning ?reaction wheels? that normally provide stability. The craft uses these wheels to maintain the exquisite pointing precision needed to relentlessly stare at stars long enough to detect the telltale dimming imposed by a planet as its orbit carries it in front of the star.
As controllers tried to restart the craft's reaction wheels Tuesday, one of the wheels woke up, then balked. This left the craft with two functioning wheels. It needs three to resume observing the patch of sky that for four years it has scanned for Earth-like planets in Earth-like orbits around sun-like stars.
While the malfunction is serious, NASA officials were not ready Wednesday to declare the mission over.
"The loss of the reaction wheel is not good news," said Charles Sobeck, Kepler's deputy project manager at NASA's Ames Research Center in Mountain View, Calif.
The goal now is to place the craft in an operating mode that reduces the use of its thrusters in order to preserve fuel and "take the time to figure out what to do next," he said.
Kepler was launched in March 2009 as a kind of planetary census taker. The mission's aim is to observe the same 170,000 stars in a hunt for rocky planets orbiting in their stars' habitable zones ? roughly defined as a distance that leaves a planet's surface not too hot or not too cold, but just right for liquid water to persist on its surface. Liquid water is a key prerequisite for organic life.
To date, Kepler has found Earth-mass planets. And it has found larger, super-Earths orbiting in their star's habitable zones. The Kepler team has yet to uncover its ultimate planets. But after bagging more than 2,700 planet-candidates so far, finding the first "just right" extra-solar planet isn't far off, says William Borucki, the mission's lead scientist.
"I'm absolutely delighted that we've got all this data," he said at the briefing. "The mission was designed for four years. It operated four years. It gave us excellent data for four years. On the other hand, I would have been even happier if it continues another four years."
The discoveries the additional data would have yielded "would have been in some sense frosting on the cake," he acknowledged. "But we have an excellent cake."
If Kepler can't be revived, analyzing the 2,700 planet-candidates in the queue so far will keep the team busy for at least two more years, he noted.
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