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Alien Planets Beyond the Solar SystemNASA's Kepler space telescope launched in March 2009 to hunt for Earth-size alien planets that may be capable of supporting life as we know it.
The $600 million mission's future is in doubt after the second of the observatory's four orientation-maintaining reaction wheels failed in May 2013. (Kepler needs at least three working reaction wheels to stay locked onto its 150,000-plus target stars.)
Whether or not Kepler can continue hunting for alien worlds, the mission has been a spectacular success, researchers say, flagging more than 2,700 potential alien planets thus far. And more discoveries will keep rolling in for years to come as team members pore through the spacecraft's data.
Here are some of Kepler's greatest finds to date.
FIRST STOP: A Rocky Exo-world
Kepler-10b: The First Unquestionably Rocky Alien PlanetSlide 2 of 15
Kepler-10b: The First Unquestionably Rocky Alien PlanetKepler-10b is the first "unquestionably rocky" exoplanet, scientists said upon announcing its discovery in January 2011. The scorching-hot world, which is about 1.4 times the size of Earth, lies about 560 light-years away.
NEXT: 'Tatooine Planet' with twin SunsSlide 3 of 15
Kepler-16b: The First 'Tatooine Planet'Slide 4 of 15
Kepler-16b: The First 'Tatooine Planet'The gas giant Kepler-16b is the first exoplanet ever found with two suns in its sky. Like Tatooine — the home world of Luke Skywalker in the "Star Wars" films — Kepler-16b orbits a pair of stars rather than a singleton like our own sun. The planet was spotted in September 2011; Kepler has since found others like it.
NEXT: Alien Planet Smaller Than EarthSlide 5 of 15
Kepler-20e: The First Alien World Smaller than EarthSlide 6 of 15
Kepler-20e: The First Alien World Smaller than EarthKepler-20e is the first alien world ever found smaller than Earth; it's about 0.87 times the width of our planet. Kepler-20e and its sibling Kepler-20f, which is 1.03 times the size of Earth, were announced in December 2011.
NEXT: A Truly Habitable World?Slide 7 of 15
Kepler-22b: Kepler's First Possibly Habitable PlanetSlide 8 of 15