An artist's conception shows the Kepler-10 system, home to two rocky planets. In the foreground is Kepler-10c, a planet that weighs 17 times as much as Earth and is more than twice as large in size.

An artist's conception shows the Kepler-10 system, home to two rocky planets. In the foreground is Kepler-10c, a planet that weighs 17 times as much as Earth and is more than twice as large in size. Planet formation theorists are challenged to explain how such a massive world could have formed.

For more information about the Kepler mission, visit http://www.nasa.gov/kepler.

More information about exoplanets and NASA's planet-finding program is at http://planetquest.jpl.nasa.gov.

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