Kepler-9b 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 currently the largest of the known planets in the Kepler-9 system, and it has a mass roughly half that of Saturn. Kepler-9b and Kepler-9c display a phenomenon called "orbital resonance", where the gravitational pull from each planet alters and stabilizes the orbit of each other. The planet was announced on August 26, 2010.
Characteristics[]
Kepler-9b is a gas giant which has a mass 43 times that of the Earth. It is about half the mass of the planet Saturn. It has a radius of around 0.842 Jupiter radii, or 80% of the radius of Jupiter. It orbits at a distance of 0.14 AU from its star and has an orbital period of 19.22 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-9c, 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.