Kepler finds circumbinary planet

NASA’s Kepler mission is using the transit technique to search for extrasolar planets (and specifically terrestrial planets in their host star’s habitable zone) in a small region in the solar neighbourhood of the Milky Way.  Kepler is monitoring more than 100,000 stars in the same star field for the 3.5 years of the mission. In February this year the Kepler team announced 1,235 planet candidates, of which 21 have so far been confirmed.  Today the Kepler team announced the discovery of Kepler-16, which orbits not one but two stars  – making it a circumbinary planet. The two stars are a K dwarf, with a mass of 0.7 that of the Sun, and a red dwarf with a mass of about 0.2 solar masses. They orbit each other in 41 days (a=0.22 AU, e=0.16), while Kepler-16 orbits the binary pair in 228 days (a=0.7 AU, e~0.0).  Since both stars are dwarfs, the orbit of Kepler-16 is outside the habitable zone of the system. 

Scale diagram of the Kepler-16 system, from Doyle et al. (2011). Stars marked with A and B, planet marked with b. System centre of mass marked with +.

The planet itself is about 0.33 Jupiter masses and 0.73 Jupiter diameters, with a bulk density of 0.96 g/cm3.  It is thought to be made of half rock and half gas.  The discovery team (Doyle et al. 2011) believe that the planet was formed in the circumbinary disk. Amazingly,  the Kepler team managed to have a representative from Lucasfilm participating in the press conference! (Lucusfilm – makers of Star Wars, home of Tatooine which orbits a binary star… Use the force!)

For more information, see

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5 Responses to Kepler finds circumbinary planet

  1. Pablo says:

    A user named klanjin at @planethunters detected Kepler-16b 4 months ago!

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