View source for Gliese 667 Cc

{{Short description|Goldilocks super-Earth orbiting Gliese 667 C}}
{{Infobox planet
| name                     = Gliese 667 Cc
| image                    = [[File:Gliese 667 Cc sunset.jpg|225px]]
| caption                  = An artist's impression of Gliese 667 Cc
<!-- DISCOVERY           -->
| discovered               = 2011 (mentioned), 2012 (announced)
| discovery_method         = [[Methods of detecting extrasolar planets#Radial velocity|Radial velocity]] ([[European Southern Observatory]])
<!-- DESIGNATIONS        -->
<!-- ORBITAL             --> 
| apsis                    = astron
| semimajor                = 0.1251 (± 0.03) [[astronomical unit|AU]]
| eccentricity             = 0.133 (± 0.098)
| period                   = 28.155 (± 0.017) [[day|d]]
| inclination              = >30
| semi-amplitude           = 1.5
| star                     = [[Gliese 667C]]
<!-- PHYS CHARS          --> 
| mean_radius              = ~1.7<ref name=sloane>{{Cite journal |last1=Sloane |first1=Stephen A. |last2=Guinan |first2=Edward F. |last3=Engle |first3=Scott G. |date=June 2023 |title=Super-Earth GJ 667Cc: Age and XUV Irradiances of the Temperate-zone Planet with Potential for Advanced Life |journal=Research Notes of the AAS |language=en |volume=7 |issue=6 |pages=135 |doi=10.3847/2515-5172/ace189 |doi-access=free |bibcode=2023RNAAS...7..135S |issn=2515-5172}}</ref> {{Earth radius|link=y}}
| mass                     = >3.7<ref name=sloane/> {{Earth mass|link=y}}
| single_temperature       = {{cvt|277|K|C F}}<ref name=sloane/>
<!-- ATMOSPHERE          --> 
<!-- NOTES               --> 
}}
'''Gliese 667 Cc''' (also known as '''GJ 667 Cc''', '''HR 6426 Cc''', or '''HD 156384 Cc''')<ref>{{cite simbad
 | title=HD 156384 Cc
 | access-date=2015-10-31
}}</ref> is an [[exoplanet]] orbiting within the [[habitable zone]] of the [[red dwarf]] star [[Gliese 667 C]], which is a member of the [[Gliese 667]] triple star system, approximately {{Convert|23.62|ly|pc e12km|abbr=off|lk=on}} away in the constellation of [[Scorpius (constellation)|Scorpius]]. The exoplanet was found by using the [[Doppler spectroscopy|radial velocity method]], from [[radial velocity|radial-velocity]] measurements via observation of [[Doppler shift]]s in the [[spectrum]] of the [[planet]]'s parent star. Gliese 667 Cc is sometimes considered as the first confirmed exoplanet with a high prospect for [[Planetary habitability|habitability]].<ref>{{Cite web|url=http://phl.upr.edu/library/notes/falsestarts|title=False Starts: Potentially Habitable Exoplanets - Planetary Habitability Laboratory @ UPR Arecibo|access-date=2020-11-15|archive-date=2021-10-18|archive-url=https://web.archive.org/web/20211018065612/http://phl.upr.edu/library/notes/falsestarts|url-status=dead}}</ref><ref>{{Cite magazine |title=The Ugly Battle Over Who Really Discovered the First Earth-Like Planet |url=https://www.wired.com/2014/11/exoplanets/ |access-date=2024-11-04 |magazine=Wired |language=en-US |issn=1059-1028}}</ref>

== Physical characteristics ==

===Mass, radius and temperature===
Gliese 667 Cc is a [[super-Earth]], an exoplanet with a mass and radius greater than that of Earth, but smaller than that of the [[giant planet]]s [[Uranus]] and [[Neptune]]. It is heavier than Earth with a minimum mass of about 3.7 Earth masses.<ref name="NASA">{{cite web|url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=GJ+667+C+c|title=GJ 667 C c|work=NASA Exoplanet Archive|access-date=2 August 2016|archive-date=13 November 2021|archive-url=https://web.archive.org/web/20211113212122/https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=GJ+667+C+c|url-status=live}}</ref> The [[equilibrium temperature]] of Gliese 667 Cc is estimated to be {{cvt|277.4|K|C F}}.<ref name="PHL">{{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|access-date=2014-01-09|archive-date=2018-02-11|archive-url=https://web.archive.org/web/20180211104253/http://phl.upr.edu/projects/habitable-exoplanets-catalog|url-status=live}}</ref> It is expected to have a radius of around 1.5 {{Earth radius}}, dependent upon its composition.

=== Host star ===
{{main|Gliese 667 C}}
The planet orbits a [[red dwarf]] ([[Stellar Classification#Class M|M-type]]) [[star]] named [[Gliese 667 C]], orbited by a total of two planets. The star is part of a [[trinary star system]], with Gliese 667 A and B both being more massive than the smaller companion. Gliese 667 C has a mass of 0.31 {{solar mass}} and a radius of 0.42 {{solar radius}}. It has a temperature of 3,700 [[Kelvin scale|K]], but its age is poorly constrained, estimates place it greater than two billion years old. In comparison, the [[Sun]] is 4.6 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 |archive-date=18 August 2010 |archive-url=https://web.archive.org/web/20100818191941/http://www.universetoday.com/18237/how-old-is-the-sun/ |url-status=live }}</ref> and has a surface temperature of 5,778 K.<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 |archive-date=29 August 2010 |archive-url=https://web.archive.org/web/20100829025937/http://www.universetoday.com/18092/temperature-of-the-sun/ |url-status=live }}</ref> This star is radiating only 1.4% of the Sun's luminosity from its outer atmosphere. It is known to have a system of two planets: claims have been made for up to seven, but these may be in error due to failure to account for correlated noise in the radial velocity data. Since red dwarfs emit little [[ultraviolet]] light, the planets likely receive minimal amounts of ultraviolet radiation.

Gliese 667 Cc is the second confirmed planet out from Gliese 667 C, orbiting towards the inner edge of the habitable zone.<ref name="PHL2">{{cite web|url=http://phl.upr.edu/press-releases/anearbystarwiththreepotentiallyhabitableworlds|website=phl.upr.edu|title=A Nearby Star with Three Potentially Habitable Worlds|access-date=2021-04-08|archive-date=2019-09-05|archive-url=https://web.archive.org/web/20190905024436/http://phl.upr.edu/press-releases/anearbystarwiththreepotentiallyhabitableworlds|url-status=dead}}</ref> From its surface, the star would have an angular diameter of 1.24 degrees and would appear to be 2.3 times<ref name="Apparentsize" group="note"><math>\begin{smallmatrix}\frac {h} {{h}_{\odot}}={\left( \frac{{{T}_{\odot}}_{\rm eff}} {{T}_{\rm eff}} \right)^2} *\frac{\sqrt{L}} {a}\end{smallmatrix}</math>.{{citation needed|date=March 2012}}
where <math>\begin{smallmatrix}{h}\end{smallmatrix}</math> is the [[apparent diameter]] of the star from the surface of the planet in orbit (GJ667Cc in this case), <math>\begin{smallmatrix}{{h}_{\odot}}\end{smallmatrix}</math> is the apparent diameter of the Sun (sol) from the surface of Earth, <math>\begin{smallmatrix}{{T}_{\odot}}_{\rm eff}\end{smallmatrix}</math> is the effective temperature of the Sun (sol), <math>\begin{smallmatrix}{{T}_{\rm eff}}\end{smallmatrix}</math> the effective temperature of the star, <math>\begin{smallmatrix}{L}\end{smallmatrix}</math> is the luminosity of the star as a fraction of the Sun's luminosity and <math>\begin{smallmatrix}{a}\end{smallmatrix}</math> is the distance of the planet from the star in AU.<!--used this formula rather than the simpler h=1/d*a or angular diameter = 2arcsin*(1/2dact/D) because the diameter comes from a different source paper and is not consistent with luminosity, temperature and distance figures which all come from the same paper by Anglada-Escudé, Guillem et al., 2012-->
</ref> the visual diameter of the Sun as it appears from the surface of the Earth. Gliese 667 C would have a visual area 5.4 times greater than that of the Sun but would still only occupy 0.003 percent of Gliese 667 Cc's sky sphere or 0.006 percent of the visible sky when directly overhead.

The [[apparent magnitude]] of the star is 10.25, giving it an [[absolute magnitude]] of about 11.03. It is too dim to be seen from Earth with the naked eye, and even smaller telescopes cannot resolve it against the brighter light from Gliese 667 A and B.

=== Orbit ===
The orbit of Gliese 667Cc has a [[semi-major axis]] of 0.1251 [[astronomical unit]]s, making its year 28.155 Earth-days long. Based on its host star's bolometric luminosity, GJ 667 Cc would receive 90% of the light Earth does; however, a good part of that electromagnetic radiation would be in the invisible infrared part of the spectrum.

== Habitability ==
{{see also|Habitability of red dwarf systems}}

Based on black body temperature calculation, Gliese 667 Cc should absorb a similar, but slightly higher, amount of overall [[electromagnetic radiation]] than Earth, making it a little warmer ({{cvt|277.4|K|C F|disp=sqbr}}) and consequently placing it slightly closer to the "hot" inner edge of the habitable zone than Earth ({{cvt|254.3|K|C F|disp=sqbr}}).<ref name="Anglada-Escudé">{{cite journal|title=A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone |url=http://www.eso.org/public/archives/releases/sciencepapers/eso1328/eso1328a.pdf |date=2013-06-07 |author=Anglada-Escudé, Guillem |display-authors=etal |journal=[[Astronomy & Astrophysics]] |doi=10.1051/0004-6361/201321331 |access-date=2013-06-25 |arxiv=1306.6074 |bibcode=2013A&A...556A.126A |volume=556 |pages=A126 |s2cid=14559800 |url-status=dead |archive-url=https://web.archive.org/web/20130630214924/http://www.eso.org/public/archives/releases/sciencepapers/eso1328/eso1328a.pdf |archive-date=2013-06-30 }}</ref> According to the Planetary Habitability Laboratory (PHL), Gliese 667 Cc is (as of July 2018) the fourth-most Earth-like exoplanet located in the conservative [[habitable zone]] of its parent [[star]].<ref>{{cite web|url=http://phl.upr.edu/projects/habitable-exoplanets-catalog|archive-url=https://web.archive.org/web/20160109001847/http://phl.upr.edu/projects/habitable-exoplanets-catalog|url-status=dead|archive-date=9 January 2016|title=Habitable Exoplanets Catalog|date=9 January 2016}}</ref>

Its host star is a [[red dwarf]], with about a third as much mass as the Sun. As a result, stars like Gliese 667 C may live up to 100–150 billion years, 10–15 times longer than the Sun's lifespan.<ref name="Adams2004">{{cite conference
 | last=Adams | first=Fred C.
 | author2=Laughlin, Gregory|author3= Graves, Genevieve J. M.
 | title=Red Dwarfs and the End of the Main Sequence
 | book-title=Gravitational Collapse: From Massive Stars to Planets
 | pages=46–49
 | publisher=Revista Mexicana de Astronomía y Astrofísica
 | bibcode=2004RMxAC..22...46A
}}</ref> This, however, does not equate to a longer period of favorable conditions for life. A 2017 paper employed [[bayesian inference]] to show that if Earth is assumed to be typical of a habitable planet, then there must be some constraint that prohibits habitability and the evolution of life on planets that orbit stars of less than 0.65 {{solar mass}}.<ref>{{cite journal |last1=Waltham |first1=D |title=Star Masses and Star-Planet Distances for Earth-like Habitability. |journal=Astrobiology |date=January 2017 |volume=17 |issue=1 |pages=61–77 |doi=10.1089/ast.2016.1518 |pmid=28103107 |pmc=5278800 |bibcode=2017AsBio..17...61W }}</ref> Given that Gliese 667 Cc orbits a star of mass 0.31 {{solar mass}}, its chances of habitability may be considerably smaller than estimates based purely on how Earth-like the planet is. 

Furthermore, the planet is likely tidally locked, with one side of its hemisphere permanently facing towards the star, and the opposite side being dark and cold. However, between these two intense areas, there could be a sliver of habitability—called the [[terminator line]], where the temperatures may be suitable (about {{cvt|273|K|C F|disp=sqbr}}) for liquid water to exist. Additionally, a much larger portion of the planet may be habitable if it supports a thick enough atmosphere to transfer heat to the side facing away from the star.

However, in a 2013 paper, it was revealed that Gliese 667 Cc is subject to tidal heating 300 times that of Earth. This in part is due to its small eccentric orbit around the host star. Because of this, the chances of habitability are very likely to be lower than originally estimated.<ref>{{Cite journal |doi = 10.1088/0004-637X/780/2/124|title = Dynamical Evolution and Spin-Orbit Resonances of Potentially Habitable Exoplanets. The Case of Gj 667C|journal = The Astrophysical Journal|volume = 780|issue = 2|pages = 124|year = 2013|last1 = Makarov|first1 = Valeri V.|last2 = Berghea|first2 = Ciprian|arxiv = 1311.4831|s2cid = 118700510}}</ref><ref>http://www.centauri-dreams.org/?p=32470 {{Webarchive|url=https://web.archive.org/web/20170619071911/https://www.centauri-dreams.org/?p=32470 |date=2017-06-19 }} See the GJ 667 Cc section.</ref>

==Discovery==
Gliese 667 Cc was first announced in a pre-print made public on 21 November 2011 by the [[European Southern Observatory]]'s [[High Accuracy Radial Velocity Planet Searcher]] (HARPS) group using the radial velocity method (Doppler method).<ref>European Southern Observatory. ''Press information: The HARPS search for southern extra-solar planets.'' 11.24.2011. [http://www.eso.org/public/archives/releases/sciencepapers/eso1214/eso1214a.pdf] {{Webarchive|url=https://web.archive.org/web/20200601135110/http://www.eso.org/public/archives/releases/sciencepapers/eso1214/eso1214a.pdf|date=2020-06-01}}</ref> The announcement of a refereed journal report came on 2 February 2012 by researchers at the [[University of Göttingen]] and the [[Carnegie Institution for Science]] and backing up the ESO HARPS group discovery.<ref>University of Göttingen. ''Presseinformation: Wissenschaftler entdecken möglicherweise bewohnbare Super-Erde - Göttinger Astrophysiker untersucht Planeten in 22 Lichtjahren Entfernung.'' Nr. 17/2012 - 02.02.2012. [http://www.uni-goettingen.de/de/3240.html?cid=4110 Announcement on university homepage, retrieved 2012-02-02] {{Webarchive|url=https://web.archive.org/web/20190915140339/http://www.uni-goettingen.de/de/3240.html?archive=true&archive_source=presse&archive_id=4110 |date=2019-09-15 }}</ref>

==See also==
{{commons category}}
*[[KELT-4Ab]], another exoplanet in a triple star system
*[[LTT 1445]] is a triple M-dwarf system with three planets orbiting LTT 1445A
*[[List of potentially habitable exoplanets]]

== References ==
{{Reflist|2}}

== Notes ==
{{reflist|group=note}}
{{Gliese-667}}
{{exoplanets}}
{{Astrobiology}}
{{Extraterrestrial life}}
{{2012 in space}}
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{{Sky|17|18|57.16483|-|34|59|23.1416|22.1}}

[[Category:Exoplanets detected by radial velocity]]
[[Category:Exoplanets discovered in 2012]]
[[Category:Exoplanets in the Gliese Catalog|6]]
[[Category:Gliese 667]]
[[Category:Super-Earths in the habitable zone]]
[[Category:Super-Earths]]
[[Category:Scorpius]]
[[Category:Articles containing video clips]]