Whether or not NASA's Kepler spacecraft can bounce back from the malfunction that has stalled its search for alien planets, the mission's place in history is assured, scientists say.

Kepler has spotted more than 2,700 potential exoplanets to date, with many more waiting to be plucked from the mission's huge dataset. Its discoveries have opened the eyes of scientists and the public alike, revealing that the Milky Way galaxy abounds with an incredible diversity of alien worlds.

"Kepler has opened up the next set of questions in exoplanets," Paul Hertz, astrophysics director at NASA Headquarters in Washington, D.C., told reporters Wednesday (May 15). [7 Greatest Kepler Planet Discoveries (So Far)]

"Before we flew Kepler, we didn't know that Earth-sized planets in habitable zones were common throughout our galaxy," Hertz added. "We didn't know that virtually every star in the sky had planets around them. Now we know that."

An uncertain future

The Kepler spacecraft launched in March 2009, kicking off a 3.5-year prime mission to determine how common Earth-like planets are throughout the galaxy.

The observatory spots alien worlds by detecting the tiny brightness dips caused when they pass in front of their parent stars from the instrument's perspective. To stay locked onto its 150,000-plus target stars, Kepler needs three functioning reaction wheels, gyroscope-like devices that allow the spacecraft to maintain its position in space.

Kepler has four such wheels. But one, known as No. 2, failed in July 2012. And No. 4 has now failed as well, NASA officials announced Wednesday.

Mission engineers will try to bring the two failed wheels back into service over the coming weeks. If they cannot recover at least one wheel, Kepler's planet-hunting days are almost certainly over, though the observatory may get a new mission that doesn't require incredibly precise pointing.

Mapping out a new mission would likely take months, Hertz said.

Originally posted here:

NASA's Planet-Hunting Kepler Telescope Will Have Long Legacy, Despite Big Glitch