Editing Red dwarf (section)

==Planets==
[[File:AU MIc M-dwarf artist's conception.jpg|thumb|Illustration depicting [[AU Mic]], an M-type (spectral class M1Ve) red dwarf star less than 0.7% the age of the Sun. The dark areas represent huge sunspot-like regions.]]
Many red dwarfs are orbited by [[exoplanet]]s, but large [[Jupiter]]-sized planets are comparatively rare. Doppler surveys of a wide variety of stars indicate about 1 in 6&nbsp;stars with twice the mass of the Sun are orbited by one or more of Jupiter-sized planets, versus 1 in 16 for Sun-like stars and the frequency of close-in giant planets (Jupiter size or larger) orbiting red dwarfs is only 1 in 40.<ref name="Mawet">{{cite conference|last1=Mawet|first1=Dimitri|last2=Jovanovic|first2=Nemanja|last3=Delorme|first3=Jacques-Robert|last4=Wizinowich|first4=Peter L.|last5=Wallace|first5=James K.|last6=Bond|first6=Charlotte Z.|last7=Chun|first7=Mark R.|last8=Cetre|first8=Sylvain|last9=Lilley|first9=Scott J.|last10=Hall|first10=Donald N. B.|last11=Echeverri|first11=Daniel |title=Adaptive Optics Systems VI |display-authors=3|editor-last=Schmidt|editor-first=Dirk|editor2-last=Schreiber|editor2-first=Laura|editor3-last=Close|editor3-first=Laird M.|chapter=Keck Planet Imager and Characterizer (KPIC): status update|publisher=SPIE|date=2018-07-10|page=6 |chapter-url=https://authors.library.caltech.edu/87801/1/1070306.pdf<!--If terms of use conflict -"https://web.archive.org/web/20200702221850/https://www.astro.caltech.edu/~dmawet/research/exoplanets-around-m-stars.html"-->|doi=10.1117/12.2314037|isbn=9781510619593 |quote=<span style="font-family:LatinModern;">Close separations {{nowrap|(< 1 AU)}} have been extensively probed by Doppler and transit surveys with the following results: the frequency of close-in giant planets (1−10&nbsp;{{mvar|M}}{{sub|Jup}}) is only {{nowrap|2.5 ± 0.9%}}, consistent with core accretion plus migration models.</span>}}</ref> On the other hand, [[microlensing]] surveys indicate that long-orbital-period [[Neptune]]-mass planets are found around one in three red dwarfs.<ref name="JAJohnson">{{cite magazine |last=Johnson |first=J.A. |date=April 2011 |title=The stars that host planets |magazine=[[Sky & Telescope]] |pages=22–27}}</ref> Observations with [[HARPS]] further indicate 40% of red dwarfs have a "[[super-Earth]]" class planet orbiting in the habitable zone where liquid water can exist on the surface.<ref>{{cite web |url=http://www.spaceref.com/news/viewpr.html?pid=36565 |title=Billions of rocky planets in habitable zones around red dwarfs |publisher=[[European Southern Observatory]] |date=28 March 2012 |access-date=2019-07-10 |df=dmy-all }}{{Dead link|date=February 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Computer simulations of the formation of planets around low-mass stars predict that Earth-sized planets are most abundant, but more than 90% of the simulated planets are at least 10% water by mass, suggesting that many Earth-sized planets orbiting red dwarf stars are covered in deep oceans.<ref name="AlibertBenz">
{{cite journal
|first=Yann |last=Alibert
|year=2017
|title=Formation and composition of planets around very low mass stars
|journal=Astronomy and Astrophysics |volume=539 |pages=8
|issue=12 October 2016
|doi=10.1051/0004-6361/201629671 |bibcode=2017A&A...598L...5A |arxiv=1610.03460|s2cid=54002704
}}</ref>

At least four and possibly up to six exoplanets were discovered orbiting within the [[Gliese 581 planetary system|Gliese&nbsp;581 planetary system]] between 2005 and 2010. One planet has about the mass of [[Neptune]], or 16&nbsp;[[Earth mass]]es ({{Earth mass|link=y}}). It orbits just {{Convert|6|e6km|AU|lk=on}} from its star, and is estimated to have a surface temperature of {{cvt|150|C|K F|lk=on}}, despite the dimness of its star. In 2006, an even smaller exoplanet (only {{Earth mass|5.5}}) was found orbiting the red dwarf [[OGLE-2005-BLG-390L]]; it lies {{convert|390|e6km|AU}} from the star and its surface temperature is {{cvt|−220|C|K F}}.

In 2007, a new, potentially [[planetary habitability|habitable]] exoplanet, {{nowrap|[[Gliese 581c]]}}, was found, orbiting [[Gliese 581]]. The minimum mass estimated by its discoverers (a team led by [[Stephane Udry]]) is {{Earth mass|5.36}}. The discoverers estimate its radius to be 1.5&nbsp;times that of Earth ({{Earth radius|link=y}}). Since then [[Gliese 581d]], which is also potentially habitable, was discovered.

Gliese&nbsp;581c and d are within the [[habitable zone]] of the host star, and are two of the most likely candidates for habitability of any exoplanets discovered so far.<ref>{{cite web |url=http://www.space.com/scienceastronomy/070424_hab_exoplanet.html |title=Major discovery: New planet could harbor water and life |author=Than, Ker |date=24 April 2007 |publisher=SPACE.com |access-date=2019-07-10}}</ref> [[Gliese 581g]], detected September 2010,<ref>{{cite web |url=http://www.physorg.com/news204999128.html |title=Scientists find potentially habitable planet near Earth |publisher=Physorg.com |access-date=2013-03-26}}</ref> has a near-circular orbit in the middle of the star's habitable zone. However, the planet's existence is contested.<ref>{{cite journal |author=Tuomi, Mikko |date=2011 |title=Bayesian re-analysis of the radial velocities of Gliese&nbsp;581. Evidence in favour of only four planetary companions |journal=Astronomy & Astrophysics |volume=528 |pages=L5 |arxiv=1102.3314 |doi=10.1051/0004-6361/201015995 |bibcode=2011A&A...528L...5T|s2cid=11439465 }}</ref>

On 23&nbsp;February 2017 NASA announced the discovery of seven Earth-sized planets orbiting the red dwarf star [[TRAPPIST-1]] approximately 39&nbsp;light-years away in the constellation Aquarius. The planets were discovered through the transit method, meaning we have mass and radius information for all of them. [[TRAPPIST-1e]], [[TRAPPIST-1f|f]], and [[TRAPPIST-1g|g]] appear to be within the habitable zone and may have liquid water on the surface.<ref>{{cite web |url=https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around |website=www.nasa.gov |title=NASA telescope reveals record-breaking exoplanet discovery |date=2017-02-22 |df=dmy-all}}</ref>