View source for Kepler-186f

{{Infobox person
| name                     = Kepler-186f
| image                    = Kepler186f-ArtistConcept-20140417.jpg
| caption                  = Artist's depiction of Kepler-186f ''(foreground)'' as a rocky [[Earth]]-like planet in the [[habitable zone]], with the [[Kepler-186]] system visible in the background ''(bottom left)''. The actual appearance and composition of the exoplanet is not currently known.
<!-- DISCOVERY           -->
| discoverer               = [[Elisa Quintana]]
| discovery_site           = [[Kepler space telescope]]
| discovered               = 17 April 2014
| discovery_method         = Transit
<!-- DESIGNATIONS        -->
<!-- ORBITAL             -->
| apsis                    = astron
| semimajor                = 0.432 ± 0.01 [[astronomical unit|AU]]<ref name=NASAExoplanet>{{cite web|url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=Kepler-186+f|title=Kepler-186 f|work=NASA Exoplanet Archive|access-date=19 July 2016}}</ref>
| eccentricity             = 0.04<ref name=NASAExoplanet/>
| period                   = 129.9444 ± 0.0012 [[day|d]]<ref name=NASAExoplanet/><br />0.355772 [[year|y]]
| inclination              = 89.9<ref name=NASAExoplanet/>
| star                     = [[Kepler-186]]
<!-- PHYS CHARS          -->
| mean_radius              = 1.17 ± 0.08<ref name="NASAExoplanet" /> {{Earth radius|link=y}}
| mass                     = {{val|1.44|2.33|1.12}}<ref name="SCI-20140418" /> {{Earth mass|link=y}}
| surface_grav             = 1.17 (est.) [[g-force|g]]
| single_temperature       = [[Planetary equilibrium temperature|''T''<sub>eq</sub>]]: {{convert|188|K|C F}}
<!-- ATMOSPHERE          -->
<!-- NOTES               -->
}}
'''Kepler-186f'''<ref name="SCI-20140418">{{Cite journal| doi = 10.1126/science.1249403| title = An Earth-Sized Planet in the Habitable Zone of a Cool Star|url=http://www.nasa.gov/sites/default/files/files/kepler186_main_final.pdf |journal = [[Science (journal)|Science]]| volume = 344| issue = 6181| pages = 277–280| date = 2014-04-18 | arxiv=1404.5667 |author-link1=Elisa Quintana| last1 = Quintana | first1 = E. V. |display-authors=etal. |bibcode = 2014Sci...344..277Q | pmid=24744370| s2cid = 1892595 |archive-url=https://web.archive.org/web/20140418183443/https://www.nasa.gov/sites/default/files/files/kepler186_main_final.pdf|archive-date=April 18, 2014}}</ref><ref name="NASA-20140417">{{cite web |last1=Johnson |first1=Michele |last2=Harrington |first2=J.D. |title=NASA's Kepler Discovers First Earth-Size Planet in The 'Habitable Zone' of Another Star |url=http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star |date=17 April 2014 |publisher=[[NASA]] |url-status=live |archive-date=2014-04-17 |archive-url=https://web.archive.org/web/20140417193242/http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star/ }}</ref> (also known by its [[Kepler object of interest]] designation ''KOI-571.05'') is an Earth-sized [[exoplanet]] orbiting within the [[habitable zone]] of the [[red dwarf]] [[star]] [[Kepler-186]],<ref name="NYT-20140417">{{cite news |last=Chang |first=Kenneth |title=Scientists Find an 'Earth Twin', or Maybe a Wife
|url=https://www.nytimes.com/2014/04/18/science/space/scientists-find-an-earth-twin-or-maybe-a-cousin.html |date=17 April 2014 |work=[[The New York Times]] }}</ref><ref name="AP-20140417">{{cite news |last=Chang |first=Alicia |title=Astronomers spot most Earth-like planet yet |url=http://apnews.excite.com/article/20140417/DAD832V81.html |date=17 April 2014 |agency=Associated Press |url-status=live |archive-date=2014-04-18 |archive-url=https://web.archive.org/web/20140418172427/http://apnews.excite.com/article/20140417/DAD832V81.html }}</ref><ref name="BBC-20140417">{{cite news |last=Morelle |first=Rebecca |author-link=Rebecca Morelle |title='Most Earth-like planet yet' spotted Helper the Kepler |url=https://www.bbc.co.uk/news/science-environment-27054366 |date=17 April 2014 |work=[[BBC News]] |url-status=live |archive-date=2014-04-18 |archive-url=https://web.archive.org/web/20140418172858/http://www.bbc.co.uk/news/science-environment-27054366 }}</ref> the outermost of five such planets discovered around the star by [[NASA]]'s [[Kepler space telescope]]. It is located about {{Convert|580|ly|pc|abbr=off|lk=on}} from [[Earth]] in the constellation of [[Cygnus (constellation)|Cygnus]].<ref name="Gaia DR2 Specific4Distances">{{cite journal |title=Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2 |journal=The Astronomical Journal |last1=Bailer-Jones |first1=C. A. L. |last2=Rybizki |first2=J. |last3=Fouesneau |first3=M. |last4=Mantelet |first4=G. |last5=Andrae |first5=R. |display-authors=1 |volume=156 |issue=2 |pages=58 |date=August 2018 |doi=10.3847/1538-3881/aacb21 |bibcode=2018AJ....156...58B |arxiv=1804.10121|s2cid=119289017 |doi-access=free }}[http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ5d5b5b10086b&-out.add=.&-source=I/347/gaia2dis&-c=298.65273597008%20%2b43.95498841816,eq=ICRS,rs=2&-out.orig=o &nbsp;Distance to Kepler 186, after taking into account light extinction]</ref>

Kepler-186f orbits its star at a distance of about {{convert|0.43|AU|abbr=on}} from its host star with an orbital period of roughly 130 [[days]], and a mass and radius around 1.44 and 1.17 times that of Earth, respectively. As one of the more promising candidates for habitability, it was the first planet with a radius similar to Earth's to be [[Discovery (observation)|discovered]] in the habitable zone of another star. However, key components still need to be found to determine its habitability for life, including an [[atmosphere]], and its composition and if [[liquid water]] can exist on its surface.

Analysis of three years of data was required to find its signal.<ref name="SETI-2014">{{cite web |last=Quintana |first=Elisa |title=Kepler 186f – First Earth-sized Planet Orbiting in Habitable Zone of Another Star |publisher=[[SETI Institute]] |date=17 April 2014 |url=http://www.seti.org/seti-institute/kepler-186f-first-earth-sized-planet-orbiting-in-habitable-zone-of-another-star |url-status=dead |archive-date=18 April 2014 |archive-url=https://archive.today/20140418060439/http://www.seti.org/seti-institute/kepler-186f-first-earth-sized-planet-orbiting-in-habitable-zone-of-another-star |access-date=18 April 2014 }}</ref> NASA's Kepler space telescope detected it using the [[transit method]] (in which the dimming effect that a planet causes as it crosses in front of its star is measured), along with four additional planets orbiting much closer to the star (all modestly larger than Earth).<ref name="AP-20140417" />  The results were presented initially at a conference on 19 March 2014<ref name="EBI-2014">{{cite web |author=Staff |title=EBI – Search for Life Beyond the Solar System 2014 – Exoplanets, Biosignatures & Instruments |url=https://www.regonline.com/builder/site/tab1.aspx?EventID=1261706 |date=16 March 2014 |work=EBI2014 |url-status=dead |archive-date=18 April 2014 |archive-url=https://web.archive.org/web/20140418174129/https://www.regonline.com/builder/site/tab1.aspx?EventID=1261706 |access-date=18 April 2014 }} See session 19 March 2014 – Wednesday 11:50–12:10 – Thomas Barclay: The first Earth-sized habitable zone exoplanets.</ref> and some details were reported in the media at the time.<ref name="DSC-20140320">{{cite web |last=Klotz |first=Irene |title=Scientists Home in on Earth-Sized Exoplanet |url=http://news.discovery.com/space/alien-life-exoplanets/scientists-home-in-on-earth-sized-exoplanet-140320.htm |date=20 March 2014 |publisher=[[Discovery Communications]] |url-status=live |archive-date=2014-04-18 |archive-url=https://web.archive.org/web/20140418172250/http://news.discovery.com/space/alien-life-exoplanets/scientists-home-in-on-earth-sized-exoplanet-140320.htm }}</ref> The planet was announced on 17 April 2014,<ref name="NASA-20140417" /> simultaneously with publication of a [[scientific paper]] in ''[[Science (journal)|Science]]''.<ref name="SCI-20140418" />

== Physical characteristics ==
=== Mass, radius and temperature ===
The only physical property directly derivable from the observations (besides the orbit) is the size of the planet relative to the central star, which follows from the amount of occultation of stellar light during a transit. This ratio was measured to be 0.021,<ref name="SCI-20140418" /> giving a planetary radius of 1.17 ± 0.08 times that of [[Earth]].<ref name="NASA-20140417" /><ref name="AP-20140417" /> The planet is about 11% larger in radius than Earth (between 4.5% smaller and 26.5% larger), giving a volume about 1.37 times that of Earth (between 0.87 and 2.03 times as large).

A very wide range of possible [[mass]]es can be calculated by combining the [[radius]] with [[density|densities]] derived from the possible types of [[matter]] from which planets can be made. For example, it could be a rocky [[terrestrial planet]] or a lower density [[ocean planet]] with a thick atmosphere. A massive [[hydrogen]]/[[helium]] (H/He) atmosphere is thought to be unlikely in a planet with a radius below 1.5 {{Earth radius}}. Planets with a radius of more than 1.5 times that of Earth tend to accumulate the thick atmospheres which make them less likely to be habitable.<ref name="guardian-2014apr17">{{cite news |agency=Press Association |url=https://www.theguardian.com/science/2014/apr/17/planet-earth-like-discovered-kepler-186f |title=NASA Kepler telescope discovers planet believed to be most Earth-like yet found |work=The Guardian |location=London |date=17 April 2014 |url-status=live |archive-date=2014-04-18 |archive-url=https://web.archive.org/web/20140418030811/http://www.theguardian.com/science/2014/apr/17/planet-earth-like-discovered-kepler-186f }}</ref> Red dwarfs emit a much stronger [[extreme ultraviolet]] (XUV) flux when young than later in life. The planet's primordial atmosphere would have been subjected to elevated [[photoevaporation]] during that period, which would probably have largely removed any H/He-rich envelope through [[Hydrodynamic escape|hydrodynamic mass loss]].<ref name="SCI-20140418" />

Mass estimates range from 0.32 {{Earth mass}} for a pure [[water]]/ice composition to 3.77 {{Earth mass}} if made up entirely of [[iron]] (both implausible extremes). For a body with radius 1.11 {{Earth radius}}, a composition similar to that of Earth (i.e., 1/3 iron, 2/3 [[Silicate minerals|silicate rock]]) yields a mass of 1.44 {{Earth mass}},<ref name="SCI-20140418" /> taking into account the higher density due to the higher average [[pressure]] compared to Earth.{{citation needed|date=May 2016}} That would make the force of gravity on the surface 17% higher than on Earth.

The estimated [[equilibrium temperature]] for Kepler-186f, which is the surface temperature without an atmosphere, is said to be around {{convert|188|K|C F}}, somewhat colder than the equilibrium temperature of [[Mars]].<ref>{{cite web|url=http://phl.upr.edu/projects/habitable-exoplanets-catalog|title=The Habitable Exoplanets Catalog – Planetary Habitability Laboratory @ UPR Arecibo|website=phl.upr.edu}}</ref>

=== Host star ===
{{Main|Kepler-186}}
The planet orbits [[Kepler-186]], an [[Stellar classification#Class M|M-type]] [[red dwarf]] [[star]] which has a total of five known planets. The star has a mass of 0.54 {{solar mass}} and a radius of 0.52 {{solar radius}}. It has a temperature of 3755 [[Kelvin scale|K]] and is about 4&nbsp;billion years old,<ref name="NASAExoplanet" /> about 600 million years younger than the [[Sun]], which is 4.6&nbsp;billion years old<ref>{{cite web |url=http://www.universetoday.com/18237/how-old-is-the-sun/ |title=How Old is the Sun? |author=Fraser Cain |date=16 September 2008 |publisher=Universe Today |access-date=19 February 2011}}</ref> and has a temperature of {{convert|5778|K|C F}}.<ref>{{cite web |url=http://www.universetoday.com/18092/temperature-of-the-sun/ |title=Temperature of the Sun |author=Fraser Cain |date=15 September 2008 |publisher=Universe Today |access-date=19 February 2011}}</ref>

The star's [[apparent magnitude]], or how bright it appears from Earth's perspective, is 14.62. This is too dim to be seen with the naked eye, which can only see objects with a [[magnitude (astronomy)|magnitude]] up to at least 6.5 – 7 or lower.<ref>{{cite web|title=What's my naked-eye magnitude limit?|url=https://www.skyandtelescope.com/astronomy-resources/astronomy-questions-answers/naked-eye-magnitude-limit/|first=Roger W.|last=Sinnott|publisher=[[Sky and Telescope]]|date=19 July 2006|access-date=17 April 2019}}</ref>

=== Orbit ===
Kepler-186f orbits its star with about 5% of the Sun's luminosity with an orbital period of 129.9 days and an orbital radius of about 0.40<ref name="NASAExoplanet" /> times that of Earth's (compared to {{convert|0.39|AU|e6km e6mi|abbr=unit|lk=on}} for [[Mercury (planet)|Mercury]]). The habitable zone for this system is estimated conservatively to extend over distances receiving from 88% to 25% of Earth's illumination (from {{convert|0.23|to|0.46|AU|e6km e6mi|abbr=unit}}).<ref>{{cite web|url=http://www.hpcf.upr.edu/~abel/phl/hec_plots/hec_orbit/hec_orbit_Kepler-186_f.png|access-date=6 April 2023|website=hpcf.upr.edu|title=Kepler 186 f}}</ref> Kepler-186f receives about 32%, placing it within the conservative zone but near the outer edge, similar to the position of [[Mars]] in the Solar System.<ref name="SCI-20140418" />
{{clear left}}

== Habitability ==
[[File:Kepler186f-ComparisonGraphic-20140417.jpg|thumb|300px|left|Size comparison of Kepler-186f (artist's impression) with Earth along with their projected [[habitable zone]]s]]
{{See also||Habitability of red dwarf systems}}
Kepler-186f's location within the habitable zone does not necessarily mean it is habitable; this is also dependent on its atmospheric characteristics, which are unknown.<ref name="Clark-2014">{{cite web |last=Clark | first=Stephen |title=Earth's 'cousin' planet lies 500 light-years away |work= Spaceflight Now |date=17 April 2014 |url=http://www.spaceflightnow.com/news/n1404/17kepler/ |url-status=live |archive-date=2014-04-18 |archive-url=https://web.archive.org/web/20140418183648/http://www.spaceflightnow.com/news/n1404/17kepler/ }}</ref> However, Kepler-186f is too distant for its atmosphere to be analyzed by existing telescopes (e.g., [[NESSI]]) or next-generation instruments such as the [[James Webb Space Telescope]].<ref name="AP-20140417" /><ref name="NPR-303806575">{{cite web |last=Greenfieldboyce |first=Nell |url=https://www.npr.org/blogs/thetwo-way/2014/04/17/303806575/scientists-spot-a-planet-that-looks-like-earths-cousin |title=Scientists Spot A Planet That Looks Like 'Earth's Cousin' |publisher=National Public Radio |date=17 April 2014 |url-status=live |archive-date=2014-04-18 |archive-url=https://web.archive.org/web/20140418054531/http://www.npr.org/blogs/thetwo-way/2014/04/17/303806575/scientists-spot-a-planet-that-looks-like-earths-cousin }}</ref> A simple climate model – in which the planet's inventory of volatiles is restricted to nitrogen, carbon dioxide and water, and clouds are not accounted for – suggests that the planet's surface temperature would be above {{convert|273|K|C F}} if at least 0.5 to 5 [[Bar (unit)|bars]] of CO<sub>2</sub> is present in its atmosphere, for assumed N<sub>2</sub> partial pressures ranging from 10 bar to zero, respectively.<ref name="arXiv-4368" />

The star hosts four other planets discovered so far, although Kepler-186 b, c, d, and e (in order of increasing orbital radius), being too close to their star, are considered too hot to have liquid water. The four innermost planets are probably [[tidally locked]], but Kepler-186f is in a higher orbit, where the star's [[Tidal force|tidal effects]] are much weaker, so the time could have been insufficient for its spin to slow down significantly. Because of the very slow evolution of red dwarfs, the age of the Kepler-186 system was poorly constrained, although it is likely to be greater than a few billion years.<ref name="arXiv-4368" /> Recent results have placed the age at around 4&nbsp;billion years.<ref name="NASAExoplanet" /> The chance that it is tidally locked is approximately 50%.<ref>{{Cite web |last=Ross |first=Hugh |date=2019-04-15 |title=Earth, an Extraordinary Magnet for Life |url=https://reasons.org/explore/blogs/todays-new-reason-to-believe/earth-an-extraordinary-magnet-for-life |access-date=2023-03-06 |website=Reasons to Believe |language=en-US}}</ref> Since it is closer to its star than Earth is to the Sun, it will probably rotate much more slowly than Earth; its day could be weeks or months long (see [[Exoplanet#Tidal effects on rotation rate, axial tilt and orbit|Tidal effects on rotation rate, axial tilt and orbit]]).<ref name="SETI-video">{{cite web |author=Staff |title=Kepler 186f – A Planet in the Habitable Zone (video) |url=http://www.seti.org/hangout/planet-in-habitable-zone |work=Hangout On-Air |publisher=[[SETI Institute]] |date=17 April 2014 |url-status=dead |archive-date=18 April 2014 |archive-url=https://web.archive.org/web/20140418175837/http://www.seti.org/hangout/planet-in-habitable-zone |access-date=2014-04-18 }}</ref>

Kepler-186f's [[axial tilt]] (obliquity) is likely very small, in which case it would not have tilt-induced seasons like Earth's.  Its orbit is probably close to circular,<ref name="SETI-video" /> so it will also lack eccentricity-induced seasonal changes like those of [[Mars]]. However, the axial tilt could be larger (about 23 degrees) if another undetected non-transiting planet orbits between it and Kepler-186e; planetary formation simulations have shown that the presence of at least one additional planet in this region is likely. If such a planet exists, it cannot be much more massive than Earth as it would then cause orbital instabilities.<ref name="arXiv-4368">{{cite journal|last1=Bolmont|first1=Emeline|last2=Raymond|first2=Sean N.|last3=von Paris|first3=Philip|last4=Selsis|first4=Franck|last5=Hersant|first5=Franck|last6=Quintana|first6=Elisa V.|last7=Barclay|first7=Thomas|title=Formation, tidal evolution and habitability of the Kepler-186 system|journal=The Astrophysical Journal|date=27 August 2014|volume=793|issue=1|pages=3  |arxiv=1404.4368 |bibcode=2014ApJ...793....3B|doi=10.1088/0004-637X/793/1/3|s2cid=118709918}}</ref>

One review essay in 2015 concluded that Kepler-186f, along with the exoplanets [[Kepler-442b]] and [[Kepler-62f]], were likely the best candidates for being potentially habitable planets.<ref name=centauridreams>{{cite web|url=http://www.centauri-dreams.org/?p=32470|title=A Review of the Best Habitable Planet Candidates|author=Paul Gilster, Andrew LePage|date=2015-01-30|publisher=Centauri Dreams, Tau Zero Foundation|access-date=2015-07-24}}</ref>

In June 2018, studies suggest that Kepler-186f may have seasons and a climate similar to those on Earth.<ref name="CNET-20180629">{{cite web |last=Mack |first=Eric |title=Two Earth-like exoplanets (Kepler 186f and Kepler 62f) now even better spots to look for life – Two of the earliest Earth-ish exoplanet finds are now more exciting targets in the search for habitable worlds beyond this rock. |url=https://www.cnet.com/news/earth-size-planets-kepler-186f-62f-now-even-better-spots-to-look-for-life/ |date=29 June 2018 |work=[[CNET]] |access-date=29 June 2018 }}</ref><ref>{{Cite journal|last1=Shan|first1=Yutong|last2=Li|first2=Gongjie|date=2018-05-16|title=Obliquity Variations of Habitable Zone Planets Kepler-62f and Kepler-186f|journal=The Astronomical Journal|volume=155|issue=6|pages=237|doi=10.3847/1538-3881/aabfd1|issn=1538-3881|arxiv=1710.07303|bibcode=2018AJ....155..237S|s2cid=59033808 |doi-access=free }}</ref>

== Follow-up studies ==
[[File:Kepler-186f 39x27 CMYK-1.jpg|thumb|NASA Exoplanet Exploration Program "travel poster" for Kepler-186f<ref>{{Cite web |title=Where the Grass is Always Redder - NASA Science |url=https://science.nasa.gov/resource/where-the-grass-is-always-redder/ |access-date=2024-11-09 |website=science.nasa.gov |date=23 March 2016 |language=en-US}}</ref>]]

=== Target of SETI investigation ===
As part of the [[SETI Institute]]'s [[search for extraterrestrial intelligence]], the [[Allen Telescope Array]] had listened for radio emissions from the Kepler-186 system for about a month as of 17 April 2014. No signals attributable to extraterrestrial technology were found in that interval; however, to be detectable, such transmissions, if radiated in all directions equally and thus not preferentially towards the Earth, would need to be at least 10 times as strong as those from [[Arecibo Observatory]].<ref name="SETI-2014" /> Another search, undertaken at the [[crowdsourcing]] project [[SETILive|SETI-Live]], reports inconclusive but optimistic-looking signs in the radio noise from the Allen Array observations.<ref name="sci20.134555">{{cite web |first=Hontas |last=Farmer |title=A better than 50/50 chance Kepler-186f has technological life |date=18 April 2014 |url=http://www.science20.com/quantum_gravity/blog/a_better_than_5050_chance_kepler186f_has_technological_life-134555 |work=Science 20 |url-status=live |archive-date=2014-04-28 |archive-url=https://web.archive.org/web/20140428092144/http://www.science20.com/quantum_gravity/blog/a_better_than_5050_chance_kepler186f_has_technological_life-134555 }}</ref> The more well known [[Seti@Home|SETI @ Home]] search does not cover any object in the Kepler field of view.<ref name="seti.1491559">See the fourth question at {{cite web |last=Kevvy |first=Mr. | title=The (Preliminary and Premature) Green Bank SERENDIP Fundraiser – Help SETI@Home Build a New (non-Arecibo) Receiver! |work=SETI@home |date=20 March 2014 | url=http://setiathome.berkeley.edu/forum_thread.php?id=74362&postid=1491559 |url-status=live |archive-date=2014-05-04 |archive-url=https://web.archive.org/web/20140504144955/http://setiathome.berkeley.edu/forum_thread.php?id=74362&postid=1491559 }}</ref> Another follow-up survey using the [[Green Bank Telescope]] has not reviewed Kepler 186f.<ref name="arxiv=1302.0845v1">{{cite journal |first1=Andrew P.V. |last1=Siemion |first2=Paul  |last2=Demorest |first3=Eric |last3=Korpela |first4=Ron J. |last4=Maddalena |first5=Dan |last5=Werthimer |first6=Jeff |last6=Cobb |first7=Glen |last7=Langston |first8=Matt |last8=Lebofsky |first9=Geoffrey W. |last9=Marcy | first10=Jill |last10=Tarter |author-link1=Andrew Siemion |title=A 1.1 to 1.9&nbsp;GHz SETI Survey of the Kepler Field: I. A Search for Narrow-band Emission from Select Targets |journal=The Astrophysical Journal |volume=767 |issue=1 |pages=94  |date=2013 |arxiv=1302.0845 |bibcode=2013ApJ...767...94S |doi=10.1088/0004-637X/767/1/94 |s2cid=119302350 }}</ref> Given the interstellar distance of {{convert|151|pc|ly|disp=flip}}, the signals would have left the planet many years ago.

=== Future technology and observations ===
At approximately {{convert|580|ly|pc}} distant, Kepler-186f is too far and its star too faint for current telescopes or the next generation of planned telescopes to determine its mass or whether it has an atmosphere. However, the discovery of Kepler-186f demonstrates conclusively that there are other Earth-sized planets in habitable zones. The Kepler spacecraft focused on a single small region of the sky but next-generation planet-hunting space telescopes, such as [[Transiting Exoplanet Survey Satellite|TESS]] and [[CHEOPS]], will examine nearby stars throughout the sky. Nearby stars with planets can then be studied by the [[James Webb Space Telescope]] and future large ground-based telescopes to analyze atmospheres, determine masses and infer compositions.<ref name="SETI-video" /> Additionally the [[Square Kilometer Array]] would significantly improve radio observations over the [[Arecibo Observatory]] and [[Green Bank Telescope]].<ref name="arxiv=1302.0845v1" />

== Previous names ==
As the [[Kepler telescope]] observational campaign proceeded, an initially identified system was entered in the [[Kepler Input Catalog]] (KIC), and then progressed as a candidate host of planets to a [[Kepler Object of Interest]] (KOI). Thus, [[Kepler-186]] started as ''KIC 8120608'' and then was identified as ''KOI-571''.<ref name="arXiv-6534">{{cite journal |title=Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems |journal=  The Astrophysical Journal|volume= 784 |issue= 1|page=45 |date=27 February 2014 |arxiv=1402.6534 |bibcode=2014ApJ...784...45R |doi=10.1088/0004-637X/784/1/45 |last=Rowe |first=Jason F. |s2cid= 119118620|display-authors=etal}}</ref> Kepler-186f was mentioned when known as KOI-571-05 or KOI-571.05 or using similar nomenclatures in 2013 in various discussions and publications before its full confirmation.<ref name="multi_ref">{{cite web|first=Paul |last=Glister |url=http://www.centauri-dreams.org/?p=29448 |title=Earth-Sized Planets in Habitable Zone Common |work=Centauri Dreams |date=5 November 2013 |url-status=live |archive-date=19 April 2014 |archive-url=https://web.archive.org/web/20140419083016/http://www.centauri-dreams.org/?p=29448 }} See comment by "Holger 16 November 2013 at 14:21".<br />
'''^''' {{cite web|author=redakce ["editor"] |url=http://www.exoplanety.cz/2013/08/06/koi-571/ |title=Kepler (asi) našel obyvatelnou planetu o velikosti Země |language=cs |trans-title=Kepler (probably) found a habitable planet the size of Earth |publisher=exoplanety.cz |date=6 August 2013 |url-status=live |archive-date=20 August 2013 |archive-url=https://web.archive.org/web/20130820192548/http://www.exoplanety.cz/2013/08/06/koi-571/ }}<br />
'''^''' {{cite web|url=http://zauberdersterne.wordpress.com/2013/08/19/kepler-erster-kandidat-einer-habitablen-exoerde/ |title=Kepler: Erster Kandidat einer habitablen Exoerde Veröffentlicht |language=de |trans-title=Kepler: First candidate of a habitable Exoplanet Published |work=Zauber der Sterne [Magic of the stars] |date=19 August 2013 |url-status=live |archive-date=27 September 2013 |archive-url=https://web.archive.org/web/20130927042529/http://zauberdersterne.wordpress.com/2013/08/19/kepler-erster-kandidat-einer-habitablen-exoerde/ }}<br />
'''^''' {{cite journal |first1=Timothy |last1=Bovaird |first2=Charles H. |last2=Lineweaver  |title=Exoplanet Predictions Based on the Generalised Titius-Bode Relation |journal=  Monthly Notices of the Royal Astronomical Society|volume=435 |issue=2 |pages=14–15 |date=1 August 2013 |arxiv=1304.3341 |bibcode=2013MNRAS.435.1126B |doi=10.1093/mnras/stt1357 |doi-access=free |s2cid=15620163 }}</ref>

== Comparison ==
The nearest-to-Earth-size planet in a habitable zone previously known was [[Kepler-62f]] with 1.4 Earth radii. Kepler-186f orbits an M-dwarf star, while Kepler-62f orbits a K-type star. A study of atmospheric evolution in Earth-size planets in habitable zones of [[Stellar classification#Class G|G-Stars]] (a class containing the Sun, but not Kepler-186) suggested that 0.8–1.15 R<sub>🜨</sub> is the size range for planets small enough to lose their initial accreted hydrogen envelope but large enough to retain an outgassed secondary atmosphere such as Earth's.<ref name="arXiv-2765">{{cite journal |first1=H. |last1=Lammer |first2=A. |last2=Stökl |first3=N.V. |last3=Erkaev |first4=E.A. |last4=Dorfi |first5=P. |last5=Odert |first6=M. |last6=Güdel |first7=Yu.N. |last7=Kulikov |first8=K.G. |last8=Kislyakova |first9=M. |last9=Leitzinger |title=Origin and Loss of nebula-captured hydrogen envelopes from "sub"- to "super-Earths" in the habitable zone of Sun-like stars |journal=Monthly Notices of the Royal Astronomical Society |volume=439 |issue=4 |pages=3225 |date=13 January 2014  |arxiv=1401.2765 |bibcode=2014MNRAS.439.3225L |doi=10.1093/mnras/stu085  |doi-access=free |s2cid=118620603 }}</ref>

{| class="wikitable" style="margin:0.5em auto; width:450px;"
! [[Exoplanet|Notable Exoplanets]] – [[Kepler (spacecraft)|Kepler Space Telescope]]
|-
| style="font-size:88%" | [[File:KeplerExoplanets-NearEarthSize-HabitableZone-20150106.png|450px]]
{{center|Confirmed small exoplanets in [[habitable zone]]s.<br />([[Kepler-62e]], [[Kepler-62f]], Kepler-186f, [[Kepler-296e]], [[Kepler-296f]], [[Kepler-438b]], [[Kepler-440b]], [[Kepler-442b]])<br />(Kepler Space Telescope; 6 January 2015).<ref name="NASA-20150106">{{cite web |last1=Clavin |first1=Whitney |last2=Chou |first2=Felicia |last3=Johnson |first3=Michele |title=NASA's Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones |url=http://www.jpl.nasa.gov/news/news.php?release=2015-003 |date=6 January 2015 |work=[[NASA]] |access-date=6 January 2015 }}</ref>}}
|}

== In popular culture ==
* Along with five other exoplanets, Kepler-186f was included in ''[[Civilization: Beyond Earth]]''{{'}}s exoplanet [[Downloadable content|DLC]] as a playable map.<ref>{{cite web|title=Civilization: Beyond Earth|work=[[Steam (service)|Steam]]|url=http://store.steampowered.com/app/304010/}}</ref>
* Dutch rock band {{ill|The Hubschrauber|nl|vertical-align=sup}} named their 2017 album ''Kepler-186f'' after this exoplanet.<ref>{{cite web
 |url=http://nos.nl/op3/artikel/2154853-nijmeegse-band-schiet-album-naar-de-maan.html |title=Nijmeegse band schiet album naar de maan |date=25 January 2017 |website=NOS op 3 |publisher=[[Nederlandse Omroep Stichting]] |access-date=31 July 2017 |quote=Vernoemd naar de eerst ontdekte planeet waar misschien wel menselijk leven mogelijk is |language=nl}}; {{Google translation|en|nl|http://nos.nl/op3/artikel/2154853-nijmeegse-band-schiet-album-naar-de-maan.html|'google translated here'}}</ref>
*Kepler-186f is the location of a future earth colony in the short story [[Take Us to Your Chief: and Other Stories|"Stars"]] by [[Drew Hayden Taylor]].
*In season 2 of the 2020 [[Animaniacs]] reboot, Kepler 186f, alongside [[Pegasi 51b]] & the fictional WB-1, is referenced in the song "Yakko's Big Idea"
*In season 12 of [[The Big Bang Theory]] episode "The Conjugal Configuration", Kepler 186F is shown on a poster in Neil deGrasse Tyson's office.