Kepler-9c is a giant extrasolar planet orbiting the star Kepler-9. It is located 2,090 light years away from Earth in the constellation Lyra. It is one of the three known planets in the Kepler-9 system. It is the outermost planet of this system.
This planet is notable for being in a orbital resonance with Kepler-9b, where the gravitational pull from each planet alters and stabilizes the orbit of each other.
The planet was announced on August 26, 2010.
Characteristics[]
The planet is a gas giant, likely mainly composed of hydrogen and helium, and it is slightly smaller and less massive than the planet Saturn. It has a radius of 0.171 Jupiter mass, or 17% the mass of Jupiter, and a radius of 0.823 Jupiter radii. It orbits its host star at a distance of 0.225 AU, and has an orbital period of around 39 days. For comparison, the closest planet to the Sun, Mercury, orbits at a distance of 0.387 AU and takes 87.969 days to complete an orbit.
This, and Kepler-9b, were the first exoplanets confirmed to be in orbital resonance. It is speculated that 9b and 9c may have originally formed very far away from their stars, at the frost line, and migrated inward due to interactions with the remains of the protoplanetary disk. They would have been captured into orbital resonance during this migration.