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 data set. 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, told reporters May 15.

”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.”

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 May 22.

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 does not require incredibly precise pointing.

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

“It’s a technical study that the project needs to do to identify what the options are,” he said. “And then we would have to do a scientific study to determine what the benefits of those options might be.”

While just 132 of Kepler’s 2,700 exoplanet candidates have been confirmed to date, mission scientists expect that more than 90 percent will turn out to be the real deal. And the team has had time to go through just half of the spacecraft’s dataset thus far, team members said.

“We have excellent data for an additional two years,” said Kepler principal investigator Bill Borucki of NASA’s Ames Research Center in Mountain View, Calif. “So I think the most interesting, exciting discoveries are coming in the next two years.”


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