Gliese 832 c (also known as Gl 832 c or GJ 832 c) was a candidate exoplanet located 16.2 light-years (4.97

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

s) away in the constellation of Grus, orbiting the star Gliese 832, a red dwarf. The existence of the planet was refuted in 2022, when a study found that the radial velocity signal shows characteristics of a signal originating from stellar activity, and not from a planet. It was thought to be in its star's habitable zone and to receive about the same amount of solar flux as Earth. The planet was thought to have a

minimum mass In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets detected by the radial veloci ...

of 5.4 Earth masses.

Characteristics

Mass, radius, and temperature

Gliese 832 c was thought to have a

of approximately 5.4 times that of

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. If it had the same density as Earth, it would have a radius of around 1.75 . The planet was thought to have a relatively high

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

, taking it very near to the predicted inner edge of the habitable zone. The planet's average

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 ...

was predicted to be , but was estimated to vary from at aphelion to at perihelion. However, because of its large mass, it may have a dense atmosphere, which could make it much hotter and more like the planet

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

, or a

mini-Neptune A Mini-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet less massive than Neptune but resembling Neptune in that it has a thick hydrogen–helium atmosphere, probably with deep layers of ice, rock or liquid oceans (mad ...

Host star

The planet orbits an M-type star named Gliese 832, which has one other known planet. The star has a mass of 0.45 and a radius of 0.48 . It has a temperature of 3620 K and is estimated to be about 9.54 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 temperature of 5778 K. The star's

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 ...

, or how bright it appears from Earth's perspective, is 10.19. Therefore, it is too dim to be seen with the naked eye. It is of spectral class M2V.

Orbit

The planet was thought to orbit its host star with about 3% of the Sun's luminosity approximately every 36 days, 10 times shorter than Earth's year, and an orbital radius 0.162 times that of Earth (compared to Mercury's orbital distance of 0.389 AU).

Habitability

The planet is a super-Earth mass planet orbiting in its star's

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 ...

. Although it orbits its star much closer than the Earth orbits the Sun, it orbits a red dwarf, receiving approximately as much energy from it as the Earth does from its star. It is not known whether Gliese 832 c transits its host star, something which would be required in order to detect any atmosphere the planet may have and determine its composition. Its host star (Gliese 832) has 45% of the Sun's mass, and as a result, stars like Gliese 832 have the ability to live up to 50–60 billion years, 5–6 times longer than the Sun will live. The planet is likely tidally locked, with one side of its hemisphere permanently facing towards the star, while the opposite side shrouded in eternal darkness. However, between these two intense areas, there would 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. In the case that Gliese 832 c possesses a Venusian-like atmosphere, which it could have due to its eccentric orbit (and the stellar flux reaching 1.45 ''S''_🜨, high enough to boil any oceans on its surface), the planet would be inhospitable because of a

runaway greenhouse effect A runaway greenhouse effect occurs when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface. A ...

on its surface. Any oceans on its surface would have boiled away due to the dense atmosphere, and as this occurred, the temperature would have risen to around . The

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...

would accumulate in the atmosphere to the point where the surface temperature would rise to around as the planet would have been overwhelmed by water vapor (which is a powerful greenhouse gas). Little amounts of

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

would have been present, as Gliese 832 c was/is probably an

ocean planet An ocean world, ocean planet, panthalassic planet, maritime world, water world or aquaplanet, is a type of planet that contains a substantial amount of water in form of oceans, either beneath the surface, as subsurface oceans, or on the surf ...

. The surface pressure would have also increased to around 100 times Earth's surface pressure (100

kilopascal The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined a ...

s, 100 atm.) because of the amount of water vapor in the atmosphere. The net result would be that Gliese 832 c being a

desert planet A desert planet, also known as a dry planet, an arid planet, or a dune planet, is a theoretical type of terrestrial planet with a surface consistency similar to Earth's hot deserts. History A 2011 study suggested that not only are life-sustaini ...

, rather than an ocean planet.

Discovery and impact

Gliese 832 c was discovered in 2014 by an international team of astronomers led by Robert A. Wittenmyer. It was at the time the newest and closest to earth member of the top three most Earth-like worlds in the

Habitable Exoplanets Catalog Habitability refers to the adequacy of an environment for human living. Where housing is concerned, there are generally local ordinances which define habitability. If a residence complies with those laws it is said to be habitable. In extreme e ...

, but was removed from the catalog in 2022 following its refutation. The planet's discoverers described the planet as "the nearest best habitable world candidate so far". Further research may be done on Gliese 832 c to see if it is suitable for life. Doubts were raised about the existence of Gliese 832 c by a 2015 study, which found that its orbital period is close to the stellar rotation period. The existence of the planet was refuted in 2022, when a study confirmed that the radial velocity signal shows characteristics of a signal originating from stellar activity, and not from a planet. This is similar to claims of super-Earths in the habitable zones of other red dwarfs, such as

Gliese 581 Gliese 581 () is a red dwarf star of spectral type M3V at the center of the Gliese 581 planetary system, about 20 light years away from Earth in the Libra constellation. Its estimated mass is about a third of that of the Sun, and it i ...

and

Kapteyn's Star Kapteyn's Star is a class M1 red subdwarf about 12.83 light-years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With a magnitude of nearly 9 it is visible through binoculars or a te ...

, that were later disproven.

References

External links

Artist's conception of Gliese 832Artist's conception of Gliese 832 compared to the earthThe original study
{{Sky, 21, 33, 33.9752, -, 49, 00, 32.422 Exoplanet candidates Gliese 832