Habitability of orange dwarf systems
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (February 2013)|
Orange dwarf stars, or K-type main-sequence stars, may be candidates for supporting extraterrestrial life. They remain stable in the main phase longer than our Sun, allowing more time for life to form on a planet around an orange dwarf star. These stars are known as "Goldilocks stars" and they emit enough radiation in the non-UV ray spectrum to provide a temperature which allows liquid water to exist on the surface of a planet orbiting around an orange dwarf star in the habitable zone. The planet's habitable zone, at 0.5 to 1 astronomical units (AU), is far enough from the star 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 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 orange dwarfs rather than sun-like stars, given the extra time available for it to evolve. Few planets thus far have been found around orange dwarf stars, but those that have are potential candidates for extraterrestrial life.
A K-type star's habitable zone lies at 0.5 to 1 AU from the star, and receives only a relatively small amount of radiation. 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 forms on the planet. But mathematical models conclude that, 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. On the other hand a planet farther than 0.8 AU from the star may need a larger atmosphere in order to trap heat, and a larger atmosphere requires a larger mass of the planet.
The habitable zone is also very stable, lasting for most of the orange dwarf's main sequence phase. The size of K-type's habitable zone also means that a planet 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 in addition to the possibility of seasons.
Potentially habitable planets around orange dwarfs
A super-Earth orbiting an orange dwarf called HD 85512 b, as well as a planet named HR 7722 c, with ≥24 ± 5 M⊕ (Earth mass) seem to have habitability potential. There may be many more, and the Kepler telescope is currently searching for planets around orange dwarf stars. 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.
- Shiga, David "Orange stars are just right for life" May 6, 2009
- Truong, Phuongmai "Orange Dwarfs Are the Best Suns for Life" 23 Dec 2009"
- Vieru, Tudor "Life Could Easily Develop Around Orange Dwarfs," May 7, 2009
- Merchant, David "Orange Dwarf Stars and Life - Common?" June 18, 2009,
- Zuluaga, J. I., Cuartas P. A., Hoyos, J. H. (2012): "Evolution of magnetic protection in potentially habitable terrestrial planets", ApJ (submitted), arXiv:1204.0275
- "Kepler's Hunt for Earths Shows Progress at Space Conference" Hadhazy, Adam March 9, 2010 12:00 AM
- Fulton, Dylan "XRaDiiX" "Which Stars are a friendly place for life to form" Mar 14 2011,
- Kaltenegger, L.; Udry, S.; Pepe, F. "A Habitable Planet around HD 85512?" 8/2011
- F. Pepe1, C. Lovis1, D. Ségransan1, W. Benz, F. Bouchy, X. Dumusque1, M. Mayor, D. Queloz, N. C. Santos and S. Udry Oct 2011 "The HARPS search for Earth-like planets in the habitable zone"
- Adam Hadhazy Kepler's Hunt for Earths Shows Progress at Space Conference, Popular Mechanics, March 9, 2010