Habitability of binary star systems

Schematic of a binary star system with one planet on an S-type orbit and one on a P-type orbit
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Planets in binary star systems may be candidates for supporting extraterrestrial life.[1] Habitability of binary star systems is determined by many factors from a variety of sources.[2] Typical estimates often suggest that 50% or more of all star systems are binary systems. This may be partly due to sample bias, as massive and bright stars tend to be in binaries and these are most easily observed and catalogued; a more precise analysis has suggested that the more common fainter stars are usually singular, and that up to two thirds of all stellar systems are therefore solitary.[3]

The separation between stars in a binary may range from less than one astronomical unit (au, the "average" Earth-to-Sun distance) to several hundred au. In latter instances, the gravitational effects will be negligible on a planet orbiting an otherwise suitable star, and habitability potential will not be disrupted unless the orbit is highly eccentric (see Nemesis, for example). In reality, some orbital ranges are impossible for dynamical reasons (the planet would be expelled from its orbit relatively quickly, being either ejected from the system altogether or transferred to a more inner or outer orbital range), whilst other orbits present serious challenges for eventual biospheres because of likely extreme variations in surface temperature during different parts of the orbit. If the separation is significantly close to the planet's distance, a stable orbit may be impossible.

Planets that orbit just one star in a binary pair are said to have "S-type" orbits, whereas those that orbit around both stars have "P-type" or "circumbinary" orbits. It is estimated that 50–60% of binary stars are capable of supporting habitable terrestrial planets within stable orbital ranges.[4]

  1. ^ "Earth-Sized 'Tatooine' Planets Could Be Habitable" (Press release). NASA Jet Propulsion Laboratory, California Institute of Technology. April 2017. Archived from the original on 2019-06-19. Retrieved 2018-12-15.
  2. ^ Eggl, Siegfried (2018). "Habitability of Planets in Binary Star Systems". In Deeg, Hans J.; Belmonte, Juan Antonio (eds.). Handbook of Exoplanets. Cham: Springer International Publishing. pp. 1–27. Bibcode:2018haex.bookE..61E. doi:10.1007/978-3-319-30648-3_61-1. ISBN 978-3-319-30648-3.
  3. ^ "Most Milky Way Stars Are Single" (Press release). Harvard-Smithsonian Center for Astrophysics. January 30, 2006. Archived from the original on 2007-08-13. Retrieved 2007-06-05.
  4. ^ V. Quintana, Elisa; J. Lissauer, Jack (2007). "Terrestrial Planet Formation in Binary Star Systems". Extreme Solar Systems. 398: 201. arXiv:0705.3444. Bibcode:2008ASPC..398..201Q.