Astronaut Steve Bowen works outside the International Space Station's Quest airlock during Monday's spacewalk. Bowen's spacewalk was unexpectedly extended by a computer malfunction. NASA TV hide caption

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Astronauts aboard the space shuttle Discovery, seen here lifting off from Kennedy Space Center in Florida, are preparing to dock with the International Space Station Saturday. Stan Honda/AFP/Getty Images hide caption

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Space shuttle Discovery lifts off at Kennedy Space Center in Cape Canaveral, Fla., on Thursday for the final time. The world's most traveled spaceship is heading toward the International Space Station with a crew of six on a journey that marks the beginning of the end of the shuttle era. Chris O'Meara/AP hide caption

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Discovery leaves the International Space Station on June 11, 2008. NASA hide caption

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Scientists from NASA's Kepler mission discovered 54 planets in so-called "habitable zones" in the Milky Way. The SETI Institute turned its telescopes toward those planets to listen. AP hide caption

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Commander Scott Kelly and Flight Engineer Paolo Nespoli look on as Flight Engineer Cady Coleman plays the flute for NPR. Courtesy of NASA TV hide caption

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