NASA's planet-hunting Kepler spacecraft has been crippled by the failure of one of the reaction wheels that keep it pointed, the space agency is announcing this afternoon, according to astronomers close to the situation.
If engineers cannot restore the wheel or find some other way to keep the spacecraft's telescope pointed, it could spell a premature end to one of the most romantic and successful of NASA's missions: the search for Earth-like planets in habitable orbits around other stars. Just last month, astronomers reported that Kepler had found two planets only slightly larger than Earth orbiting in the "Goldilocks" zone, where liquid water is possible, of a star 1,200 light-years from here. More planet candidates, even smaller and closer to being Earth-like, lurk in the pipeline, astronomers say, but they have not yet been confirmed.
Kepler was launched in March 2009. Its mission was to determine the fraction of stars in the galaxy that harbor Earth-like planets by carrying out a survey of some 150,000 stars in the constellations of Cygnus and Lyra, looking for the dips in starlight caused by planets passing, or transiting, in front of their suns. To date, the spacecraft has identified 115 planets and has a list of 2,740 other candidates.
Since Earth transits only once a year, two more years would have given astronomers a chance to see more transits of the planets they are looking for. Without the extra time, the data will be noisy, astronomers say, and so the answer will be a little more uncertain than it might have been.
"It was one of those things that was a gift to humanity," said one astronomer who spoke on condition of anonymity because NASA had not yet made the news public. "We're all going to lose for sure."
In January engineers noticed that one of the reaction wheels that keep the spacecraft pointed was experiencing too much friction. They shut the spacecraft down for a couple of weeks to give it a rest, in the hopes that the wheel's lubricant would spread out and solve the problem. But when they turned it back on, the friction was still there. Until now, the problem had not interfered with observations, which are scheduled to go on until at least 2016.
Kepler was launched with four reaction wheels, but one failed last year after showing signs of erratic friction. Three wheels are required to keep Kepler properly and precisely aimed. Loss of the wheel has robbed it of the ability to detect Earth-size planets, although project managers hope to remedy the situation. The odds, astronomers said, are less than 50-50.science
This article originally appeared in The New York Times.