Habitability of K-type main-sequence star systems

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K-type main-sequence stars may be candidates for supporting extraterrestrial life. They remain stable in the main phase longer than the Sun,[1] allowing more time for life to form on a planet around a K-type main-sequence star. These stars are known as "Goldilocks stars" and they emit enough radiation in the non-UV ray spectrum[2] to provide a temperature that allows liquid water to exist on the surface of a planet orbiting around a K-type main-sequence star in the habitable zone.[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 far enough from the star, in part, 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 intelligent 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.[citation needed] Few planets thus far have been found around K-type main-sequence stars, but those that have are potential candidates for extraterrestrial life.[1]

Habitable zone[edit]

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] But some mathematical models have concluded that,[5] even under the highest attainable dynamo-generated magnetic field strengths, exoplanets with masses like that of the Earth which are closer than 0.8 AU, probably lose a significant fraction of their atmospheres by the erosion of the exobase's atmosphere by CME bursts and XUV emissions. A planet farther than 0.8 AU from the star may need a larger atmosphere in order to trap heat,[6] and such a larger atmosphere is less likely around smaller massed planets.[7] On the other hand, with a colder planet with a larger polar ice cap there would likely be less removal of carbon dioxide from the atmosphere, as there would be fewer exposed rocks to react with at all latitudes, and therefore there could be a stronger greenhouse effect allowing even Earth sized or smaller planets to be warm enough to sustain life in the outer habitable zone.

The habitable zone is also very stable, lasting for most of the K-type main-sequence star's main sequence phase.[8] The size of K-type's habitable zones also means that a planet, even if it's orbiting a late K-type main-sequence star so long as it lies towards the middle-outer edge, can lie far enough away in the star's habitable zone so as not be tidally locked to its host star. This is further beneficial to the emergence of life, as it means that the planet can possess rotation, which can help to average out heat distribution longitudinally around a planet with in addition axial tilt there is the possibility of seasons and greater sharing of heat across latitudes.[9]

Potentially habitable planets around K-type main-sequence stars[edit]

A super-Earth orbiting a K-type main-sequence star called HD 85512 b,[10] as well as a planet named HR 7722 c, with ≥24 ± 5 M⊕ (Earth mass) seem to have habitability potential.[11] There may be many more, and the Kepler telescope is currently searching for planets around K-type main-sequence stars.[12] 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[edit]


  1. ^ a b Shiga, David. "Orange stars are just right for life". New Scientist. Retrieved 16 April 2014. 
  2. ^ Grossman, Lisa. "Sun may not be a 'Goldilocks' star". Science News. Retrieved 16 April 2014. 
  3. ^ Vieru, Tudor. "Life Could Easily Develop Around Orange Dwarfs". Softpedia. Retrieved 16 April 2014. 
  4. ^ a b Merchant, David. "Orange Dwarf Stars and Life – Common?". Retrieved 16 April 2014. 
  5. ^ Zuluaga, J. I., Cuartas P. A., Hoyos, J. H. (2012): "Evolution of magnetic protection in potentially habitable terrestrial planets", ApJ (submitted), arXiv:1204.0275
  6. ^ Swanson, Molly. "Planet Atmospheres & Weather". Aero Space Web. Retrieved 16 April 2014. 
  7. ^ Strobel, Nick. "Planetary Science – Atmospheres". Retrieved 16 April 2014. 
  8. ^ "Kepler's Hunt for Earths Shows Progress at Space Conference" Hadhazy, Adam March 9, 2010 12:00 AM
  9. ^ XRaDiiX. "Which Stars are friendly place for life to form.Lets see...". Retrieved 16 April 2014. 
  10. ^ Kaltenegger, L; S. Udry; F. Pepe (2011). "A Habitable Planet around HD 85512?". v1. arXiv:1108.3561. 
  11. ^ 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. 
  12. ^ Adam Hadhazy Kepler's Hunt for Earths Shows Progress at Space Conference, Popular Mechanics, March 9, 2010