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Extrasolar planet List of extrasolar planets
Parent star
Star KOI-55
Constellation Cygnus
Right ascension (α) 19h 45m 25s
Declination (δ) +41° 5′ 34″
Apparent magnitude (mV) 14.87 [1]
Distance 3849 ± 310 ly
(1180 ± 95 [2] pc)
Spectral type sdB
Mass (m) 0.496 ± 0.002 M
Radius (r) 0.203 ± 0.007 R
Temperature (T) 27730 ± 270 K
Orbital elements
Semimajor axis (a) 0.006 AU
(0.897 Gm)
Orbital period (P) 0.2401 ± 0.000004 d
Inclination (i) ~65°
Physical characteristics
Minimum mass (m sin i) 0.440 M
Radius (r) 0.759 [note 1][2] R
Density (ρ) 5500 kg m−3
Stellar flux (F) 640000
Discovery information
Discovery date 12/22/2011 (announced) [3]
Discoverer(s) Charpinet et al.[3]
Discovery method Reflection/emission modulations
Discovery site Kepler telescope
Discovery status Published
Other designations
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

Kepler-70b (formerly called KOI-55.01;[3] sometimes listed as KOI-55 b) is a planet discovered orbiting the subdwarf B star (sdB) Kepler-70. It orbits its host along with another planet, Kepler-70c, both of which orbit very close to their host star. Kepler-70b completes one orbit around its star in just 5.76 hours, one of the shortest orbital periods of any exoplanetary system yet discovered, only second to PSR 1719-14 b with a period of 2.2 hours. It is also the hottest exoplanet as of mid-2013, with a surface temperature of 7143 K.[4] Its density is 5500 kg/m3 which is not much different from Earth.[5]

Kepler-70c passes 240,000 km away from Kepler-70b during their closest approach. This is currently the closest recorded approach between planets.

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.”[6] 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.[6] According to the Extrasolar Planets Encyclopedia, the star left the red giant stage 18.4 million years ago.[2]

See also[edit]


  1. ^ Assuming an albedo of 0.1.

External links[edit]


  1. ^ "SIMBAD query result". SIMBAD. Retrieved 1 January 2012. 
  2. ^ a b c "Notes for Planet KOI-55 b". Extrasolar Planet Database. Retrieved 1 January 2012. 
  3. ^ a b c Charpinet, S. et al. (December 21, 2011), "A compact system of small planets around a former red-giant star", Nature 480 (7378): 496–499, Bibcode:2011Natur.480..496C, doi:10.1038/nature10631, PMID 22193103 
  4. ^ "HEC Top 10 Lists of Exoplanets". Retrieved 11 November 2014. 
  5. ^ "Kepler mission discoveries". Retrieved 23 May 2013. 
  6. ^ a b "Two More Earth-Sized Planets Discovered by Kepler, Orbiting Former Red Giant Star". Universe Today. Retrieved 1 January 2012.