|Discovery date 12/22/2011 (announced)|
Discovery site Kepler telescope
|Discoverer(s) Charpinet et al.|
Discovery status Published
Kepler-70c (formerly called KOI-55.02; sometimes listed as KOI-55 c) is a planet discovered orbiting the sdB star Kepler-70. It orbits its host along with another planet, Kepler-70b, both of which orbit very close to their host star. Kepler-70c completes one orbit around its star in just 8.232 hours. It is also the one of the hottest exoplanets as of mid-2013. It has a high density, suggesting that it is largely composed of metals.
Kepler-70b passes 240,000 km away from Kepler-70c during their closest approach. This is currently the closest recorded approach between planets. Such orbital configuration is relatively stable due to orbital resonance between planets and small hill spheres of planets due to proximity of the star.
According to the main author of the paper in Nature which announced the discovery of the two planets, Stephane Charpinet, the two planets "probably plunged deep into the star’s envelope during the red giant phase, but survived.” However, this is not the first sighting of planets orbiting a post-red giant star - numerous pulsar planets have been observed, but no planet has been found with such a short period around any star, whether or not on the main sequence.
The two planets were most likely gas giants which spiraled inward toward their host star, which subsequently became a red giant, vaporizing much of the planets except for parts of their solid cores, which are now orbiting the sdB star. According to the Extrasolar Planets Encyclopedia, the star left the red giant stage 18.4 million years ago.