Gliese 667 Cc (also known as GJ 667Cc, HR 6426Cc, or HD 156384Cc) is an exoplanet orbiting within the

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kast ...

of the red dwarf star

Gliese 667 C Gliese 667 (142 G. Scorpii) is a triple- star system in the constellation Scorpius lying at a distance of about from Earth. All three of the stars have masses smaller than the Sun. There is a 12th-magnitude star close to the other three ...

, which is a member of the

Gliese 667 Gliese 667 (142 G. Scorpii) is a triple-star system in the constellation Scorpius lying at a distance of about from Earth. All three of the stars have masses smaller than the Sun. There is a 12th-magnitude star close to the other three, ...

triple star system, approximately away in the constellation of

Scorpius Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation that pre-dates the Gr ...

. The exoplanet was found by using the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

, from radial-velocity measurements via observation of Doppler shifts in the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

of the

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

's parent star.

Physical characteristics

Mass, radius and temperature

Gliese 667 Cc is a

super-Earth A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to ...

, an exoplanet with a mass and radius greater than that of Earth, but smaller than that of the

giant planet The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. The ...

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...

and Neptune. It is heavier than Earth with a minimum mass of about 3.7 Earth masses. The

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...

of Gliese 667 Cc is estimated to be . It is expected to have a radius of around 1.5 , dependent upon its composition.

Host star

The planet orbits a red dwarf ( M-type) star named

, 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 and a radius of 0.42 . It has a temperature of 3,700 K, but its age is poorly constrained, estimates place it greater than two billion years old. In comparison, the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

is 4.6 billion years old and has a surface temperature of 5,778 K. 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 Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

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. From its surface, the star would have an angular diameter of 1.24 degrees and would appear to be 2.3 times

\begin\frac  = *\frac \end

. where

\begin\end

is the

apparent diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...

of the star from the surface of the planet in orbit (GJ667Cc in this case),

\begin\end

is the apparent diameter of the Sun (sol) from the surface of Earth,

\begin_\end

is the effective temperature of the Sun (sol),

\begin\end

the effective temperature of the star,

\begin\end

is the luminosity of the star as a fraction of the Sun's luminosity and

\begin\end

is the distance of the planet from the star in AU. 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 Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

of the star is 10.25, giving it an

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...

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 The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits ...

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

Based on black body temperature calculation, GJ 667 Cc should absorb a similar, but slightly higher, amount of overall electromagnetic radiation than Earth, making it a little warmer () and consequently placing it slightly closer to the "hot" inner edge of the habitable zone than Earth (). According to PHL, Gliese 667 Cc is (as of July 2018) the fourth-most Earth-like exoplanet located in the conservative

of its parent star. 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 have the ability to live up to 100–150 billion years, 10–15 times longer than the Sun's lifespan. 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 ) 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 may be lower than originally estimated.

History

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 The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision echelle planet-finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. ...

(HARPS) group using the radial velocity method (Doppler method). The announcement of a refereed journal report came on 2 February 2012 by researchers at the

University of Göttingen The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded ...

and the

Carnegie Institution for Science The Carnegie Institution of Washington (the organization's legal name), known also for public purposes as the Carnegie Institution for Science (CIS), is an organization in the United States established to fund and perform scientific research. Th ...

and backing up the ESO HARPS group discovery.University of Göttingen. ''Presseinformation: Wissenschaftler entdecken möglicherweise bewohnbare Super-Erde - Göttinger Astrophysiker untersucht Planeten in 22 Lichtjahren Entfernung.'' Nr. 17/2012 - 02.02.2012
Announcement on university homepage, retrieved 2012-02-02
/ref>

Potentiality of survival

According to astrobiologists, there is a slight potential chance of eventual

survival Survival, or the act of surviving, is the propensity of something to continue existing, particularly when this is done despite conditions that might kill or destroy it. The concept can be applied to humans and other living things (or, hypotheti ...

for humans to sustain on a usually Earth-like exoplanet within a directly hostile environment.

In fiction

Gliese 667 Cc features in the story "The Audience" by

Sean McMullen Sean Christopher McMullen (born 21 December 1948 in Sale, Victoria) is an Australian science fiction and fantasy author. Biography McMullen is one of Australia's leading science-fiction and fantasy authors and has written over 70 stories and 1 ...

in the June 2015 issue of '' Analog Science Fiction and Fact''. In the ''

Alien vs. Predator ''Alien vs. Predator'' (also known as ''Aliens versus Predator'' and ''AVP'') is a science-fiction action horror media franchise created by comic book writers Randy Stradley and Chris Warner. The series is a crossover between, and part of, th ...

'' franchise, Gliese 667 Cc was the first planet to be terraformed, being done so by the Weyland Corporation in 2039. It is also mentioned in the 2015 novel ''Not Alone'' by Craig A. Falconer. This planet is also featured in Allen Steele's 2016 novel ''Arkwright''. Gliese 667 Cc is also the setting of the 2020 video game '' In Other Waters''.

References

Notes

{{Sky, 17, 18, 57.16483, -, 34, 59, 23.1416, 22.1 Exoplanets detected by radial velocity Exoplanets discovered in 2012 6 Gliese 667 Near-Earth-sized exoplanets in the habitable zone Super-Earths Scorpius (constellation) Articles containing video clips