Kepler-11 c

Kepler-11c is an exoplanet discovered in the orbit of the Sun-like star Kepler-11 by the Kepler space telescope, a NASA telescope aiming to discover Earth-like planets. It is the second planet from its star, and is most likely a water planet with a thin hydrogen–helium atmosphere. Kepler-11c orbits Kepler-11 every 10 days, and has an estimated density twice that of pure water. It is estimated to have a mass thirteen times that of Earth and a radius three times that of Earth. Kepler-11c and its five sister planets form the first discovered system with more than three transiting planets. The Kepler-11 system also holds the record of being the most compact and the flattest system discovered. Kepler-11c and the other Kepler-11 planets were announced to the public on February 2, 2011, and was published in Nature a day later.

==Name and discovery== Kepler-11c's name is divided into two parts: it is named for Kepler-11, the star around which it orbits. As planets with discoveries that are announced at the same time are sorted by distance, Kepler-11c's "c" is because it was the second-closest planet from its host star at the time of discovery (Kepler-11b is the closest). Kepler-11, the host star, was named for the Kepler satellite, a NASA telescope that searches for terrestrial planets by measuring small fluctuations in the light of stars that occurs when celestial bodies transit, or cross in front of, the star with respect to Earth. Kepler-11 was flagged as home to a potential transit event by the satellite, and was given the designation KOI-157. After further observations, Kepler-11c's existence was confirmed by the observation of an orbital resonance effect between Kepler-11b and Kepler-11c. Along with the other five planets in orbit around Kepler-11, Kepler-11c was announced on February 2, 2011 at a press conference. Its findings were published on February 3 in the journal Nature. The Kepler-11 system is the first known to host more than three transiting planets.