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The planet-hunting days of NASA's prolific Kepler space telescope, which has discovered more than 2,700 potential alien worlds to date, may be over.
The second of Kepler's four reaction wheels — devices that allow the observatory to maintain its position in space — has failed, NASA officials announced Wednesday (May 15).
If one or both of those failed wheels cannot be brought back, the telescope likely cannot lock onto target stars precisely enough to detect orbiting planets, scientists have said.
The $600 million Kepler spacecraft spots exoplanets by flagging the tiny brightness dips caused when they pass in front of their host stars from the instrument's perspective. The mission's main goal is to determine how common Earth-like alien planets are throughout the Milky Way galaxy.
Kepler needs three functioning reaction wheels to stay locked onto its more than 150,000 target stars. The observatory had four wheels when it launched in March 2009 — three for immediate use, and one spare.
One wheel (known as number two) failed in July 2012, giving Kepler no margin for error. And now wheel number four has apparently given up the ghost as well, after showing signs of elevated friction for the past five months or so.
"This is something that we've been expecting for a while, unfortunately," NASA science chief John Grunsfeld told reporters today.
Grunsfeld is a former astronaut who flew on five space shuttle missions, including three that serviced or upgraded NASA's Hubble Space Telescope in Earth orbit. But in-space repair is not an option for Kepler, which circles the sun rather than Earth and is currently about 40 million miles (64 million kilometers) from our planet.
Originally Posted by Jim Colyer
