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Habitability of K-type main-sequence star systems
K-type main-sequence stars may be candidates for supporting extraterrestrial life. They remain stable in the main phase longer than the Sun, 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 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. The planet's habitable zone, ranging from 0.1–0.4 to 0.3–1.3 astronomical units (AU), 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 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. Few planets thus far have been found around K-type main-sequence stars, but those that have are potential candidates for extraterrestrial life.〔
==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.〔
The habitable zone is also very stable, lasting for most of the K-type main-sequence star's main sequence phase.〔"Kepler's Hunt for Earths Shows Progress at Space Conference" Hadhazy, Adam March 9, 2010 12:00 AM〕
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.〔(【引用サイトリンク】title=Which Stars are friendly place for life to form.Lets see... )〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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