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Does Earth have a twin in the galaxy? Our chances of finding an Earthlike planet any time soon may have just shrunk due to a glitch that could limit the lifetime of NASA's exoplanet-hunting spacecraft Kepler.

Since its launch in 2009Movie Camera, Kepler has glimpsed nearly 3000 potential exoplanets in a plethora of configurations around their host stars. This has revolutionised our understanding of the nature of solar systems and planets that lie beyond our own – and spurred the search for alien life.

But on 16 July, Kepler sent down data showing that one of its four reaction wheels, whose spin controls the probe's orientation, had stopped turning. Ground controllers shut down the malfunctioning wheel and the probe briefly stopped gathering usable exoplanet data.

Accurate orientation is critical to Kepler's success. The spacecraft monitors more than 100,000 stars for changes in brightness caused by transits – dips in starlight caused by the passage of an orbiting planet in front of its star, as seen from Earth. The probe tries to keep a given star on the same few pixels of its light detectors for months on end. This avoids variations in the data since not all pixels respond in exactly the same way to light.

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