NASA's Kepler spacecraft has spotted 503 new potential alien worlds, some of which may be capable of supporting life as we know it.

"Some of these new planet candidates are small and some reside in the habitable zone of their stars, but much work remains to be done to verify these results," Kepler mission manager Roger Hunter, of NASA's Ames Research Center in Moffett Field, Calif., wrote in an update last Friday (June 7).

The latest haul brings Kepler's tally of exoplanet candidates to 3,216. Just 132 of them have been confirmed by follow-up observations to date, but mission scientists expect at least 90 percent will end up being the real deal. [7 Greatest Kepler Discoveries (So Far)]

The new finds were pulled from observations Kepler made during its first three years of operation, from May 2009 to March 2012, researchers said. The telescope hasn't done any planet hunting since being hobbled by a failure in its orientation-maintaining system last month.

Uncertain future

The $600 million Kepler spacecraftlaunched in March 2009, kicking off a 3.5-year mission to determine how common Earth-like planets are throughout the Milky Way galaxy.

Kepler spots exoplanetsby detecting the tiny brightness dips caused when they pass in front of their stars' faces from the instrument's perspective. The observatory does this precision work by staying locked onto 150,000-plus target stars using three gyroscope-like devices called reaction wheels.

Kepler launched with four functioning reaction wheels three for immediate use and one spare. But one wheel, known as number two, failed in July 2012. And a second (number four) gave up the ghost last month, robbing the spacecraft of its precision pointing ability.

If at least one of the failed wheels cannot be recovered, Kepler's planet-hunting days are almost certainly over and a new mission will have to be drawn up for the spacecraft.

Engineers have identified a number of tests that could help gauge the likelihood of bringing back the balky wheels, Hunter said. They're currently developing these commands on the Kepler testbed at Ball Aerospace in Boulder, Colo., where the spacecraft was built.

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Ailing NASA Telescope Spots 503 New Alien Planet Candidates