Kepler ends successful mission
NASA/Kepler mission; Starry background: Imageman/Shutterstock
When NASA’s Kepler space telescope launched in March 2009, astronomers had no proof that any star other than the sun harbored an Earth-sized planet (with a diameter within 25 percent of Earth’s). By May 2013, when the telescope suffered a mechanical failure that ended its planet hunt, Kepler scientists had discovered 10 such worlds and identified hundreds of yet-to-be-confirmed Earth-sized candidates.
Kepler’s death blow came when the second of four wheels used to orient the telescope failed. The spacecraft requires three wheels to home in on a patch of sky and search for planets that block out some of the light of their stars. Mission engineers tried to repair the wheels but gave up in August (