There may be life in the old girl yet. There's a slim chance that NASA's hugely successful planet-hunter, the Kepler space telescope, may recover from a recent glitch that ended its planet-hunting activities. Even if it doesn't, the telescope may still have a role – uncovering more details of the planets it has found so far.
Launched in 2009
Until recently, the mission had been edging closer to its ultimate goal of finding a planet the same size as Earth in a sunlike star's habitable zone, the region where liquid water – and maybe life – can exist. In April, for instance, the Kepler team revealed a pair of habitable worlds orbiting a star slightly cooler than our sun.
Two wheels down
Then in May the team announced that one of the telescope's four reaction wheels had stopped turning. The telescope needs at least three of these wheels to keep its gaze steady, and one had already been switched off last year as it was not spinning smoothly. With only two functional wheels left, it looked like it was curtains for Kepler.
But Kepler's researchers haven't given up yet. After giving the hobbled telescope a rest, the team started exploratory tests on 18 July to see if either of the malfunctioning wheels could be coaxed back into service.
Now they report that both broken wheels responded. However, one can spin in only one direction, and both wheels appear to be plagued by friction, which makes the spacecraft vibrate and can keep it from getting precise observations.
There's a slim chance that Kepler could resume the search for Earth-like worlds if one wheel can be reactivated – but for this to happen, the amount of friction must stay constant, says deputy project manager Charlie Sobeck, at NASA's Ames Research Center in Moffett Field, California. "We don't yet know whether the friction levels are stable, but this is the only option we have for a three-wheel mission to point accurately," he says.
It looks unlikely, though. "The fact that there is friction indicates that there's probably something wrong internal to the wheel," Sobeck adds – and that would mean the amount of friction is likely to be unpredictable.
Fallback options
As a fallback, the Kepler team has already started examining ideas for what the telescope could do with just two wheels and its thrusters to stabilise its gaze. It may be possible for Kepler to get a clear view of a planetary system for short periods – hours or days at a time – says Sobeck. That's not enough time to discover new planets, but it could look at known planet candidates and perhaps tell us more about their characteristics. Another possibility is to reassign Kepler to look for near-Earth asteroids.
Or Kepler could switch to an alternative planet-hunting technique called microlensing, says Sobeck.
"The discussion is ongoing internally and in the wider community," says Sobeck, who adds that the Kepler team is preparing to invite fellow scientists to suggest possible new tasks for the craft.
"We have to wait and see how the wheels will perform," says exoplanet research Sara Seager of the Massachusetts Institute of Technology. Even if the wheels can't be fixed, she holds out hope that the four years of Kepler data may reveal an Earth-sized, habitable planet, as there is still a year and a half's worth of information awaiting analysis. The software that sifts through the results has been improving as well, so those archives may yet hold a surprise or two. "The Kepler database remains a gold mine," she says.
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