NASA is calling off attempts to return its planet-hunting Kepler space telescope to its primary mission following a pointing system failure that cannot be repaired.
The telescope was launched in 2009 to hunt for Earth-like planets properly positioned from their parent stars for liquid surface water, which is believed to be a key ingredient for life.
Operations have been on hold since May when the telescope's positioning system failed. The observatory relies on a trio of spinning reaction wheels to keep its gaze fixed on about 100,000 target stars. It works by detecting slight changes in the amount of light coming from the stars, some of which are caused by planets passing by, or transiting, relative to the telescope's line of sight.
PHOTOS: Exquisite Exoplanetary Art
Kepler has four reaction wheels, but lost use of one of them in July 2012, leaving it with no spare. A second wheel failed in May. Engineers have been testing the spacecraft to see if either broken wheel can be unjammed, but to no avail. NASA announced on Thursday it was calling off those efforts.
"The wheels are sufficiently damaged that they cannot sustain spacecraft pointing control for any extended period of time," Charles Sobeck, Kepler deputy project manager at NASA's Ames Research Center in California, told reporters during a conference call on Thursday.
NASA is now soliciting ideas for other missions for Kepler that do not require such precise pointing.
NEWS: Time Really Flies on These Kepler Planets
Options include searching for asteroids, comets, supernovas and other celestial objects.
"At this time, we don't know if any of these concepts are practical," said Kepler lead scientist William Borucki, also with Ames.
Kepler scientists also still have about two years of archived data to analyze. So far, the telescope is credited with finding 135 confirmed extrasolar planets and has identified another 3,548 candidate planets.
"We expect many more discoveries," Borucki said. "The Kepler mission is in no way done."
An artist rendering pf Kepler-62f, one of the 135 planets found by the Kepler space telescope. Image: NASA