Scientists are searching for Earth-like planets with the Kepler space telescope. It works by detecting periodic variations in the brightness of stars caused by orbiting exoplanets passing in front of them.
In February 2011 the Kepler team announced they had found 54 planets thought to be suitable for life because they lie in their stars' habitable zones. Five of these planets are Earth-sized.
The telescope's discoveries also include the Kepler-11 solar system - six large exoplanets circling an eight billion year-old star, 2,000 light years from Earth.
Image: An illustration of Kepler (credit: NASA/Kepler mission/Wendy Stenzel)
Launched in 2009, the Kepler space telescope's mission is to find Earth-like worlds orbiting distant stars. In this clip, NASA's William Borucki explains how it will work.
Kepler is a space observatory launched by NASA to discover Earth-like planets orbiting other stars. The spacecraft, named in honor of the 17th-century German astronomer Johannes Kepler, was launched in March 2009.
The Kepler mission is "specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets."Kepler's only instrument is a photometer that continually monitors the brightness of over 145,000 main sequence stars in a fixed field of view. This data is transmitted to Earth, then analyzed to detect periodic dimming caused by extrasolar planets that cross in front of their host star.
Kepler is a project under NASA's Discovery Program of relatively low-cost, focused science missions. Construction and initial operation were managed by NASA's Jet Propulsion Laboratory, with Ball Aerospace responsible for developing the Kepler flight system. The Ames Research Center is responsible for the ground system development, mission operations (from December 2009), and science data analysis.
The Kepler observatory is currently in active operation, with the first main results announced on 4 January 2010. As expected, the initial discoveries were all short-period planets. As the mission continued, additional longer-period candidates were found – as of December 2011, there are a total of 2,326 candidates. Of these, 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars. The Kepler team estimated that 5.4% of all stars host Earth-size planet candidates, and that 17% of all stars have multiple planets.
In December 2011, two of the Earth-sized candidates, Kepler-20e and Kepler-20f, were confirmed as planets orbiting a Sun-like star, Kepler-20.
The Kepler mission began with a planned mission lifetime of at least 3.5 years; in 2012, the mission was extended to 2016.
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