NASA hasn't given up on resurrecting its planet-hunting Kepler space telescope, but even if the observatory can't be saved, scientists expect it already has accomplished its goal of finding a habitable, Earth-like planet. They just don't know it yet.
"We have quite a bit of data that needs to be fully processed," said William Borucki, lead Kepler scientist at NASA's Ames Research Center in Moffett Field, Calif.
"With what we've seen -- so many Earth-size planets and a number of planets in the habitable zone already, we're really pretty positive that we will get the Earth-sized planets in the habitable zone around stars like the sun. I'm very optimistic that the data we have will allow us to accomplish that," Borucki said.
ANALYSIS: Kepler's Planet-Hunting Mission May Be Over
After four years in orbit, Kepler's hunt for planets beyond the solar system was suspended last week due to a problem with the telescope's steering system. The spacecraft uses spinning wheels to keep itself steady enough to capture slight changes in the amount of light coming from distant target stars, some of which may be due to a planet passing by relative to the telescope's line of sight.
Kepler needs at least three so-called reaction wheels to have a steady enough gaze for planet-hunting. Two have failed.
Engineers are mulling options for reviving the telescope, which so far has found 132 confirmed planets and identified another 2,700 contenders. Scientists are most interested in planets about the same size of Earth that orbit their parent stars about where Earth circles the sun. At that distance, surface temperatures likely would be suitable for liquid water, if any exists. Water is believed to be necessary for life.
"There are planets that we believe are (in the data) that we haven't found yet," Borucki said, estimating that the analysis and follow-up confirmations will keep the Kepler team busy for at least two years.
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In a conference call with reporters last week, NASA managers said there was a reasonable chance Kepler could be revived.
Options include trying to coax one or both of the failed wheels back into service by running them backwards, for example. If that were successful, Kepler would need to fight the destabilizing pressure of sunlight on the observatory by firing its maneuvering thrusters occasionally, limiting its mission lifetime.
"Like with any stuck wheel ... we could try jiggling it, we could try commanding it back and forth in both directions, we can try forcing it through whatever the resistance is that's holding it up," said deputy project manager Charles Sobeck, who is also with Ames.
NASA expects it will take a few weeks to assess the options and decide what recovery attempts to make.
Not everyone was so optimistic, however.
"I think ‘The mission is not over' means ‘the mission is over.' Might be other things it can do. But, kids, I think the mission is over," astronomer Mike Brown, with the California Institute of Technology, wrote on Twitter.
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Just before Kepler's shutdown, another team of astronomers unveiled a new method to comb through Kepler data for planets that uses quirky aspects of Einstein's theory of relativity.
Though precise and repeated measurement of a star's light is still needed, the new technique looks for a slight brightening of light from target stars. Kepler data typically is analyzed for light dips as planets pass across the face of their parent stars, relative to Kepler's line of sight.
The brightening is a manifestation of a planet tugging on its parent star, which causes photons of light to squeeze together, concentrating the energy and temporarily brightening the star. The technique does not require a planet to transit its parent star's face, but the effects may be too subtle for hunting for anything other than massive planets orbiting close to their parent stars.