![]() ![]() Centre de données astronomiques de Strasbourg. "A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence". This prolonged radiation saturation period may be sterilising, destroying the atmospheres of, or at least delaying the emergence of life for Earth-like planets orbiting inside the habitable zones around K-type dwarf stars. There is also growing evidence that K-type dwarf stars emit dangerously high levels of X-rays and far ultraviolet (FUV) radiation for considerably longer into their early main sequence phase than do either heavier G-type stars or lighter early M-type dwarf stars. For all of these reasons, they may be the most favorable stars to focus on in the search for exoplanets and extraterrestrial life.ĭespite K-stars' lower total UV output, in order for their planets to have habitable temperatures, they must orbit much near to their K-stars hosts, offsetting or reversing any advantage of a lower total UV output. Due to their greater heat, the habitable zones of K-type stars are also much wider than those of M-type stars. ![]() While M-type stars are the most abundant, they are more likely to have tidally locked planets in habitable-zone orbits and are more prone to producing solar flares and cold spots that would more easily strike nearby rocky planets, potentially making it much harder for life to develop. K-type stars emit less total ultraviolet and other ionizing radiation than G-type stars like the Sun (which can damage DNA and thus hamper the emergence of nucleic acid based life). K-type main-sequence stars are about three to four times as abundant as G-type main-sequence stars, making planet searches easier. Some of the nearest K-type stars known to have planets include Epsilon Eridani, HD 192310, Gliese 86, and 54 Piscium. ![]() Like M-type stars, they tend to have a very small mass, leading to their extremely long lifespan that offers plenty of time for life to develop on orbiting Earth-like, terrestrial planets. These stars are of particular interest in the search for extraterrestrial life because they are stable on the main sequence for a very long time (17–70 billion years, compared to 10 billion for the Sun). Main article: Habitability of K-type main-sequence star systems A few examples such as HIP 111288 (K8V) and HIP 3261 (K9V) have been defined and used. Johnson & Morgan 1953, Keenan & McNeil 1989 ), many authors consider the step between K7 V and M0 V to be a single subdivision, and the K8 and K9 classifications are rarely seen. Other primary MK standard stars include: īased on the example set in some references (e.g. those standard stars that have remain unchanged over the years, are: The "anchor points" of the MK classification system among the K-type main-sequence dwarf stars, i.e. The revised Yerkes Atlas system (Johnson & Morgan 1953) listed 12 K-type dwarf spectral standard stars, however not all of these have survived to this day as standards. ![]() Spectral standard stars Properties of typical K-type main-sequence stars Spectral type Well-known examples include Alpha Centauri B (K1 V) and Epsilon Indi (K5 V). These stars are of particular interest in the search for extraterrestrial life due to their stability and long lifespan. They have masses between 0.6 and 0.9 times the mass of the Sun and surface temperatures between 3,900 and 5,300 K. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow/white G-type main-sequence stars. A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence ( hydrogen-burning) star of spectral type K and luminosity class V. ![]()
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