Malfunction May End Kepler Spacecraft’s Hunt for Planets

Kepler, the NASA spacecraft that has identified more than 2,700 planets orbiting distant stars, is malfunctioning and may be abandoned, the U.S. space agency said.

A second “reaction wheel,” one of four that keep the spacecraft’s camera stable as it examines stars for telltale signs of orbiting planets, has failed, the National Aeronautics and Space Administration said yesterday in a statement. Without at least three wheels, “it’s unlikely that the spacecraft will be able to return to the high-pointing accuracy that enables its high-precision photometry,” the agency said.

Kepler, launched in 2009, has made several discoveries, including two planets found last month that may have the best chance of any to date of being Earth-like and harboring life. The planets, orbiting a star 2,000 light years away also named Kepler, sit in the “habitable zone” of their sun where temperatures may allow for liquid water.

“We’ve known for a while that this day would come,” William Welsh, an astronomer at San Diego State University who has used Kepler data in his research, said in a telephone interview. “Nevertheless, it is a sad day because it could mean Kepler’s ability to take data on planets, or find new planets, may be at an end.”

The faulty reaction wheel was discovered May 14 when Kepler’s mission managers tried to communicate with the craft and found it in “safe mode.” Kepler’s solar panels were facing the sun and it was slowly spinning in space. NASA was able to place the satellite in a “loosely pointed, thruster-controlled state” while engineers try to determine how they might fix it.

Spacecraft Stable

“The spacecraft is stable and safe, if still burning fuel,” NASA said. “In its current mode, our fuel will last for several months.”

The first wheel malfunction occurred last year, according to NASA.

The Kepler spacecraft is essentially a huge camera, parked in orbit around the sun slightly behind Earth, that stares at a single patch of sky containing about 160,000 stars, Welsh said. It watches for tiny flickers of light as planets transit their suns, causing distant eclipses.

The reaction wheels keep the camera stable. “Think of a tripod that only has two legs instead of three,” said Jerome Orosz, another San Diego State astronomer.

It’s possible that NASA could “unstick” the malfunctioning wheel, Welsh said, which could extend Kepler’s mission for months or years.

Top Achievement

If not, Kepler has completed its “primary” mission, which was intended to last three and a half years, the space agency said. It has been in an “extended mission phase” since November, NASA said in the statement.

Welsh said Kepler has answered the question that led to its launch: How common are small planets about the size of Earth?

“We now know that small planets and Earth-size planets are really common, and there’s lots and lots of them,” he said, calling Kepler “incredibly successful.”

Even if the spacecraft has to be abandoned, there are “substantial quantities of data” already collected that haven’t yet been analyzed, NASA said.

“The string of scientific discoveries is expected to continue for years to come,” the agency said.

NASA seldom repeats its missions and is unlikely to replace Kepler, Orosz said. The next step in planet finding, he and Welsh said, will be spacecraft capable of identifying planets orbiting stars near our own, and measuring their atmospheres for chemicals that may indicate the presence of life, such as water, oxygen and carbon dioxide.

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