Kepler-10c

Kepler-10c is an exoplanet orbiting the G-type star Kepler-10, located around 608 light-years away in Draco. Its discovery was announced by the Kepler space telescope team in May 2011, although it had been seen as a planetary candidate since January 2011, when Kepler-10b was discovered. The team confirmed the observation using data from NASA's Spitzer Space Telescope and a technique called BLENDER that ruled out most false positives. Kepler-10c was the third transiting planet to be confirmed statistically (based on probability rather than actual observation), after Kepler-9d and Kepler-11g. The Kepler team considers the statistical method that led to the discovery of Kepler-10c as what will be necessary to confirm many planets in Kepler's field of view.

Kepler-10c orbits its host star every forty-five days at a quarter of the average distance between the Sun and Earth. Initial observations showed that it has a radius more than double that of Earth, and suggested a higher density, suggesting a mainly rocky composition with around 5–20% ices by mass. For comparison, the Earth's oceans represent only 0.02% of our planet's mass, with an additional amount potentially a few times this stored in the mantle. However, in 2017, more careful analysis using both HARPS and HIRES data revealed that Kepler-10c is not a large terrestrial planet, but instead a typical volatile-rich planet of about seven Earth masses.