Habitability of K-type main-sequence star systems

K-type main-sequence stars may be candidates for supporting extraterrestrial life. These stars are known as "Goldilocks stars" as they emit enough radiation in the non-UV ray spectrum[1] to provide a temperature that allows liquid water to exist on the surface of a planet; they also remain stable in the main phase longer than the Sun,[2] allowing more time for life to form on a planet around a K-type main-sequence star.[3] The planet's habitable zone, ranging from 0.1–0.4 to 0.3–1.3 astronomical units (AU),[4] depending on the size of the star, is often far enough from the star so as not to be tidally locked to the star, and to have a sufficiently low solar flare activity not to be lethal to life. In comparison, red dwarf stars have too much solar activity and quickly tidally lock the planets in their habitable zones, making them less suitable for life. The odds of complex life arising may be better on planets around K-type main-sequence stars than around Sun-like stars, given the extra time available for it to evolve.[5] Few planets thus far have been found around K-type main-sequence stars, but those that have are potential candidates for extraterrestrial life.[2]

Habitable zone

A K-type star's habitable zone approximately ranges between 0.1–0.4 to 0.3–1.3 AU from the star. Here, exoplanets will receive only a relatively small amount of ultraviolet radiation, especially so towards the outer edge. This is favorable to support life, as it means that there is enough radiated energy to allow liquid water to exist on the surface, but not so much radiation as to destroy life.[4]

The habitable zone is also very stable, lasting for most of the K-type main-sequence star's main sequence phase.[6]

Potentially habitable planets around K-type main-sequence stars

A super-Earth orbiting a K-type main-sequence star called HD 85512 b appears to have habitability potential.[7][8] The super-Earth HD 40307 g around the K2.5V star HD 40307 also orbits in the CHZ, although it has a reasonably elliptical orbit (e=0.22). There may be many more, and the Kepler telescope (now retired) was one of the main sources of information of these exoplanets.[9] Kepler-62 is an example of a discovery by Kepler of a system consisting of a K-type dwarf with potentially habitable planets orbiting it.

See also

References
  1. Grossman, Lisa. "Sun may not be a 'Goldilocks' star". Science News. Retrieved 16 April 2014.
  2. Shiga, David. "Orange stars are just right for life". New Scientist. Retrieved 16 April 2014.
  3. Vieru, Tudor. "Life Could Easily Develop Around Orange Dwarfs". Softpedia. Retrieved 16 April 2014.
  4. Merchant, David. "Orange Dwarf Stars and Life – Common?". Retrieved 16 April 2014.
  5. Loeb, Abraham (2017). "Reduced biodiversity of life around Proxima Centauri and TRAPPIST-1". The Astrophysical Journal Letters. 846 (L21): L21. arXiv:1707.07007. Bibcode:2017ApJ...846L..21L. doi:10.3847/2041-8213/aa8860.
  6. "Kepler's Hunt for Earths Shows Progress at Space Conference" Hadhazy, Adam March 9, 2010 12:00 AM
  7. Kaltenegger, L; S. Udry; F. Pepe (2011). "A Habitable Planet around HD 85512?". arXiv:1108.3561v1 [astro-ph.EP].
  8. Pepe, F.; Lovis, C.; Ségransan, D.; Benz, W.; Bouchy, F.; Dumusque, X.; et al. (3 October 2011). "The HARPS search for Earth-like planets in the habitable zone". Astronomy & Astrophysics. 534: A58. arXiv:1108.3447. Bibcode:2011A&A...534A..58P. doi:10.1051/0004-6361/201117055.
  9. Adam Hadhazy Kepler's Hunt for Earths Shows Progress at Space Conference, Popular Mechanics, March 9, 2010
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