Gliese 581 () is a
red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
star of
spectral type
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
M3V at the center of the Gliese 581 planetary system, about 20
light years
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
away from
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 ...
in the
Libra constellation
Libra is a constellation of the zodiac and is located in the Southern celestial hemisphere. Its name is Latin for weighing scales. Its old astronomical symbol is (♎︎). It is fairly faint, with no first magnitude stars, and lies between Vi ...
. Its estimated mass is about a third of that of 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 ...
, and it is the 89th closest known star to the Sun. Gliese 581 is one of the oldest, least active M dwarfs known. Its low stellar activity improves the likelihood of its planets retaining significant
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
s, and lessens the sterilizing impact of
stellar flare
The asterisk ( ), from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star.
Computer scientists and mathematicians often voc ...
s.
History of observations
Gliese 581 is known at least from 1886, when it was included in
Eduard Schönfeld
Eduard Schönfeld (22 December 18281 May 1891) was a German astronomer.
Education
Schönfeld was born at Hildburghausen, in the Duchy of Saxe-Meiningen, where he had a distinguished career at the gymnasium. On leaving the gymnasium, he desired t ...
's ''Southern (SD)''—the fourth part of the '. The corresponding designation is BD -7 4003.
Characteristics
![SunGliese581](https://upload.wikimedia.org/wikipedia/commons/c/cd/SunGliese581.png)
The name ''Gliese 581'' refers to the catalog number from the 1957 survey ''
Gliese Catalogue of Nearby Stars
The ''Gliese Catalogue of Nearby Stars'' (, English ) is a star catalogue listing stars located within 25 parsecs (81.54 ly) of the Sun.
First edition and supplements
In 1957 German astronomer Wilhelm Gliese published his first star catalogue ...
'' of 965 stars located within 20
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 of the
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 ...
. Other names of this star include ''BD-07° 4003'' (
BD catalogue, first known publication) and ''HO Librae'' (
variable star designation
In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the conste ...
). It does not have an individual name such as ''
Sirius
Sirius is the list of brightest stars, brightest star in the night sky. Its name is derived from the Ancient Greek language, Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinisation ...
'' or ''
Procyon
Procyon () is the brightest star in the constellation of Canis Minor and usually the eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Minoris, which is Latinized ...
''.
The star is a
red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
with
spectral type
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
M3V, located 20.4
light-years away from
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 ...
. It is located about two degrees north of
Beta Librae
Beta Librae (β Librae, abbreviated Beta Lib, β Lib), formally named Zubeneschamali , is (despite its 'beta' designation) the brightest star in the zodiac constellation of Libra. From parallax measurements, its distance can be estimated ...
, the brightest star in the
Libra constellation
Libra is a constellation of the zodiac and is located in the Southern celestial hemisphere. Its name is Latin for weighing scales. Its old astronomical symbol is (♎︎). It is fairly faint, with no first magnitude stars, and lies between Vi ...
. Its mass is estimated to be approximately a third that of 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 ...
, and it is the 89th closest known
star system to the Sun.
An M-class dwarf star such as Gliese 581 has a much lower mass than the Sun, causing the core region of the star to fuse hydrogen at a significantly lower rate. From the apparent magnitude and distance, astronomers have estimated an effective temperature of 3200 K and a visual
luminosity
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
of 0.2% of that of the Sun.
However, a red dwarf such as Gliese 581 radiates primarily in the
near infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...
, with peak emission at a wavelength of roughly 830
nm (estimated using
Wien's displacement law
Wien's displacement law states that the black-body radiation curve for different temperatures will peak at different wavelengths that are inversely proportional to the temperature. The shift of that peak is a direct consequence of the Planck r ...
, which assumes the star radiates as a
black body
A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...
), so such an estimate will underestimate the star's total luminosity.
(For comparison, the peak emission of the Sun is roughly 530 nm, in the middle of the visible part of the spectrum.) When radiation over the entire spectrum is taken into account (not just the part that humans are able to see), something known as the bolometric correction, this star has a
bolometric luminosity
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a ...
1.2% of the
Sun's total luminosity A planet would need to be situated much closer to this star in order to receive a comparable amount of energy as the Earth. The region of space around a star where a planet would receive roughly the same energy as the Earth is sometimes termed the "
Goldilocks 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. Ka ...
", or, more prosaically, 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. Kas ...
. The extent of such a zone is not fixed and is highly specific for each
planetary system. Gliese 581 is a very old star. Its slow rotation makes it very inactive, making it better suited than most red dwarfs for having habitable planets.
Gliese 581 is classified as a
variable star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...
of the
BY Draconis type, and has been given the variable star designation HO Librae. This is a star that exhibits variability because of the presence of
star spot
Starspots are stellar phenomena, so-named by analogy with sunspots.
Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...
s combined with the rotation of the star. However, the measured variability is close to the margin of error, and, if real, is most likely a long term variability.
Its brightness is stable to 1%. Gliese 581 emits X-rays.
Planetary system
The Gliese 581 planetary system is the gravitationally bound system comprising the star Gliese 581 and the objects that orbit it. The system is known to consist of at least three planets discovered 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 ...
, along with a
debris disk
A debris disk (American English), or debris disc (Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris di ...
. The system's notability is due primarily to early
exoplanetology discoveries, between 2008 and 2010, of possible
terrestrial planets
A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, ...
orbiting within its
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. Kas ...
and the system's relatively close proximity to the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
at 20 light years away. However, its observation history is controversial due to false detections and conjecture and with the radial velocity method yielding little information about the planets themselves beyond their mass.
The confirmed planets are believed to be located close to the star with near-circular orbits. In order of distance from the star, these are
Gliese 581e
Gliese 581e or Gl 581e is an extrasolar planet orbiting within the Gliese 581 system, located approximately 20.4 light-years away from Earth in the Libra constellation. It is the third planet discovered in the system (fourth if the disputed plane ...
,
Gliese 581b
Gliese 581b or Gl 581b is an extrasolar planet orbiting within the Gliese 581 system. It is the first planet discovered of three confirmed in the system so far, and the second in order from the star.
Discovery
The planet was discovered by a tea ...
, and
Gliese 581c
Gliese 581c (Gl 581c or GJ 581c) is a planet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a ...
. The letters represent the discovery order, with b being the first planet to be discovered around the star.
Observation history
The first announcement of a planet around the star was
Gliese 581b
Gliese 581b or Gl 581b is an extrasolar planet orbiting within the Gliese 581 system. It is the first planet discovered of three confirmed in the system so far, and the second in order from the star.
Discovery
The planet was discovered by a tea ...
discovered by astronomers at the
Observatory of Geneva in Switzerland and
Grenoble University
The Université Grenoble Alpes (UGA, French: meaning "''Grenoble Alps University''") is a public research university in Grenoble, France. Founded in 1339, it is the third largest university in France with about 60,000 students and over 3,000 resea ...
in France. Detected in August 2005 and using extensive data from the ESO/
HARPS
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. ...
spectrometer it was the fifth planet to be discovered around a red dwarf.
Further observations by the same group resulted in the detection of two more planets,
Gliese 581c
Gliese 581c (Gl 581c or GJ 581c) is a planet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a ...
and
Gliese 581d
Gliese 581d (often shortened to Gl 581d or GJ 581d) is a proposed extrasolar planet orbiting within the Gliese 581 system, approximately 20.4 light-years away in the Libra constellation. It is the third planet claimed in the system and (assumi ...
.
The orbital period of Gliese 581d was originally thought to be 83 days but was later revised to a lower value of 67 days.
The revised orbital distance would place it at the outer limits of the habitable zone, the distance at which it is believed possible for
liquid water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...
to exist on the surface of a planetary body, given favourable atmospheric conditions. Gliese 581d was estimated to receive about 30% of the intensity of light the Earth receives from the Sun. By comparison, sunlight on Mars has about 40% of the intensity of that on Earth, though if high levels 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 transpar ...
are present in the planetary atmosphere, the greenhouse effect could keep temperatures above freezing.
The next discovery was the inner planet
Gliese 581e
Gliese 581e or Gl 581e is an extrasolar planet orbiting within the Gliese 581 system, located approximately 20.4 light-years away from Earth in the Libra constellation. It is the third planet discovered in the system (fourth if the disputed plane ...
, also by the Observatory of Geneva and using data from the HARPS instrument, was announced on 21 April 2009.
This planet, at a minimum mass of 1.9 Earths, was at the time the least massive confirmed exoplanet identified around a main-sequence star.
On 29 September 2010, astronomers using the
Keck Observatory
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when co ...
proposed two additional planets,
Gliese 581f
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 is ...
and
Gliese 581g
Gliese 581g , unofficially known as Zarmina (or Zarmina's World), was a candidate exoplanet postulated to orbit within the Gliese 581 system, twenty light-years from Earth. It was discovered by the Lick–Carnegie Exoplanet Survey, and was the si ...
, both in nearly circular orbits based on analysis of a combination of data sets from the HARPS and
HIRES Hires may refer to:
* High Resolution Fly's Eye, ultra-high-energy cosmic ray observatory
* High Resolution Echelle Spectrometer or High Resolution Echelle Spectrograph, W. M. Keck Observatory's spectrometer
* Hires Big H, restaurant chain headquar ...
instruments. The proposed planet Gliese 581f was thought to be a 7 Earth-mass planet in a 433-day orbit and too cold to support liquid water. The candidate planet Gliese 581g attracted more attention: nicknamed Zarmina's World by one of its discoverers,
the predicted mass of Gliese 581g was between 3 and 4 Earth-masses, with an orbital period of 37 days. The orbital distance was calculated to be well within the star's habitable zone, though the planet was expected to be tidally locked with one side of the planet always facing the star.
In an interview with Lisa-Joy Zgorski of the
National Science Foundation
The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...
, Steven Vogt was asked what he thought about the chances of life existing on Gliese 581g. Vogt was optimistic: "I'm not a biologist, nor do I want to play one on TV. Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say that ... the chances of life on this planet are 100%. I have almost no doubt about it."
Two weeks after the announcement of the discovery of and , astronomer
Francesco Pepe
Francesco, the Italian (and original) version of the personal name " Francis", is the most common given name among males in Italy. Notable persons with that name include:
People with the given name Francesco
* Francesco I (disambiguation), sev ...
of the Geneva Observatory reported that in a new analysis of 179 measurements taken by the
HARPS
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. ...
spectrograph over 6.5 years, neither planet ''g'' nor planet ''f'' was detectable, and the relevant measurements were included in a paper uploaded to the arXiv preprint server, though still unpublished in a refereed journal. The non-existence of Gliese 581f was accepted relatively quickly: it was shown that the radial velocity variations that led to the claimed discovery of Gliese 581f were instead associated with the stellar activity cycle rather than an orbiting planet. Nevertheless, the existence of planet g remained controversial: Vogt responded in the media that he stood by the discovery and questions arose as to whether the effect was due to the assumption of circular rather than eccentric orbits or the statistical methods used.
Bayesian analysis found no clear evidence for a fifth planetary signal in the combined HIRES/HARPS data set, though other studies led to the conclusion that the data did support the existence of planet g, albeit with strong degeneracies in the parameters as a result of the first eccentric harmonic with the outer planet Gliese 581d.
Using the assumption that the noise present in the data was correlated (red noise rather than white noise), Roman Baluev called into question not only the existence of planet g, but Gliese 581d as well, suggesting there were only three planets (Gliese 581b, c, and e) present.
On 27 November 2012, the European Space Agency announced that the Herschel space observatory had discovered a
comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
belt "at 25 ± 12 AU to more than 60 AU".
It must have "at least 10 times" as many comets as does the Solar system. This likely rules out Saturn-mass planets beyond 0.75 AU. However another (undiscovered) planet further out, say a Neptune-mass planet at 5 AU, might be required to keep the comet belt replenished.
A different objection against the existence of Gliese 581d was offered in a 2014 study whose authors argued that
Gliese 581d
Gliese 581d (often shortened to Gl 581d or GJ 581d) is a proposed extrasolar planet orbiting within the Gliese 581 system, approximately 20.4 light-years away in the Libra constellation. It is the third planet claimed in the system and (assumi ...
is "an artifact of stellar activity which, when incompletely corrected, causes the false detection of the planet ''g''."
This remains controversial, with one 2015 paper agreeing with the 2014 analysis
and another disagreeing with it.
Planets
![GJ581orbits](https://upload.wikimedia.org/wikipedia/commons/6/68/GJ581orbits.svg)
Ongoing analysis of the system has produced several models for the orbital arrangement of the system. There is no current consensus and 3-planet, 4-planet, 5-planet and 6-planet models have been proposed to address the available radial velocity data. Most of these models predict, however, that the inner planets are close in with circular orbits, while outer planets, particularly Gliese 581d, should it exist, are on more elliptical orbits.
Models of the habitable zone of Gliese 581 show that it extends from about 0.1 to 0.5 AU taking in part of the orbit of Gliese 581d. The first three planets orbit closer to the star than the inner edge of the habitable zone, with planets d and g orbiting within it.
Confirmed planets
= Gliese 581e
=
Gliese 581e is the innermost planet and, with a minimum mass of 1.7 Earth masses, is the least massive of the three. Discovered in 2009, it is also the most recent confirmed planet to have been discovered in this system.
It takes 3.15 days to complete an orbit. Initial analyses suggested that the planet's orbit is quite elliptical but after correcting the radial velocity measurements for stellar activity, the data now indicate a circular orbit.
= Gliese 581b
=
Gliese 581b is the most massive planet known to be orbiting Gliese 581 and was the first to be discovered.
= Gliese 581c
=
Gliese 581c is the third planet orbiting Gliese 581. It was discovered in April 2007.
In their 2007 paper, Udry et al. asserted that if Gliese 581c has an Earth-type composition, it would have a radius of 1.5R
🜨, which would have made it at the time "the most Earth-like of all known exoplanets".
A direct measurement of the radius cannot be taken because, viewed from Earth, the planet does not
transit
Transit may refer to:
Arts and entertainment Film
* ''Transit'' (1979 film), a 1979 Israeli film
* ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world
* ''Transit'' (2006 film), a 2006 ...
its star. The minimum mass of the planet is 5.5 times that of Earth. The planet initially attracted attention as being potentially habitable, though this has since been discounted.
The mean blackbody surface temperature has been estimated to lie between −3 °C (for a Venus-like
albedo
Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...
) and 40 °C (for an Earth-like albedo),
however, the temperatures could be much higher (about 500 degrees Celsius) due to a runaway greenhouse effect akin to that of
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 fa ...
.
Some astronomers believe the system may have undergone
planetary migration
Planetary migration occurs when a planet or other body in orbit around a star interacts with a disk of gas or planetesimals, resulting in the alteration of its orbital parameters, especially its semi-major axis. Planetary migration is the most l ...
and Gliese 581c may have formed beyond the
frost line
The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the groundwater in soil is expected to freeze. The frost depth depends on the climatic conditions of an area, the heat transfer properties of the s ...
, with a composition similar to icy bodies like
Ganymede. Gliese 581c completes a full orbit in just under 13 days.
Unconfirmed planets
= Gliese 581g
=
Gliese 581g, unofficially known as Zarmina's World,
is an unconfirmed (and disputed)
exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
claimed to orbit within the Gliese 581 planetary system, twenty light-years from Earth. It was discovered by the
Lick–Carnegie Exoplanet Survey
The Lick–Carnegie Exoplanet Survey (LCES) is a search for exoplanets using the Keck I optical telescope of the W. M. Keck Observatory in Hawaii. The survey is sponsored by NASA and the National Science Foundation. The survey comprises a decade of ...
, and is the sixth
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 ...
found orbiting the
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
(Gliese 581 f was found to be an artifact);
however, its existence could not be confirmed by the
European Southern Observatory (ESO) /
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) survey team, and its existence remains controversial. It is thought to be near the middle of 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. Kas ...
of its
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
.
That means it could sustain
liquid water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...
—a necessity for all known
life
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
—on its surface, if there are favorable
atmospheric conditions on the planet.
Gliese 581g was claimed to be detected by astronomers of the
Lick–Carnegie Exoplanet Survey
The Lick–Carnegie Exoplanet Survey (LCES) is a search for exoplanets using the Keck I optical telescope of the W. M. Keck Observatory in Hawaii. The survey is sponsored by NASA and the National Science Foundation. The survey comprises a decade of ...
. The authors stated that data sets from both
High Resolution Echelle Spectrometer (HIRES) and HARPS were needed to sense the planet; however, the ESO/HARPS survey team could not confirm its existence. The planet remained unconfirmed as consensus for its existence could not be reached. Additional reanalysis only found evidence for four
planets
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 young ...
, but the discoverer,
Steven S. Vogt, did not agree with those conclusions; another study by
Guillem Anglada-Escudé
Guillem Anglada-Escudé (born in Ullastrell, Barcelona in 1979), is a Catalan astronomer. In 2016, he led a team of astronomers under the Pale Red Dot campaign, which resulted in the confirmation of the existence of Proxima Centauri b, the close ...
later supported the planet's existence. In 2012, a reanalysis by Vogt supported its existence.
A new study in 2014 concluded that it was a false positive;
however, in 2015, a reanalysis of the data suggested that it could still exist. The planet is thought to be
tidally locked
Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked bo ...
to its star. If the planet has a dense
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, it may be able to circulate heat. The actual
habitability
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 ...
of the planet depends on the composition of its surface and the atmosphere. It is thought to have
temperatures
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied on ...
around −37 to −11 °C (−35 to 10 °F). By comparison,
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 ...
has an average
surface temperature of 15 °C (59 °F)—while
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
has an average surface temperatures of about −63 °C (−81 °F). The planet has, according to Vogt, a "100%"
chance of supporting life, but this is disputed.
= Gliese 581d
=
Gliese 581d is an exoplanet that is currently disputed due to inaccurate analysis caused by noise and stellar activity,
and is considered disproven by the
NASA Exoplanet Archive
The NASA Exoplanet Archive is an online astronomical exoplanet catalog and data service that collects and serves public data that support the search for and characterization of extra-solar planets (exoplanets) and their host stars. It is part of ...
. This remains controversial, with one 2015 paper agreeing with the 2014 analysis
and another disagreeing with it.
A 2019 paper on planets orbiting nearby
M-dwarfs lists GJ 581 d (although they designate it GJ 581 e).
The planet's mass is thought to be 6.98
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 ...
s and its radius, assuming an Earth-like composition, is thought to be 2.2R
🜨, making it 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 ...
. Its orbital period is thought to be 66.87 days long, with a semi-major axis of 0.21847 AU, with an unconstrained eccentricity. Analysis suggests that it orbits within the 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. Kas ...
, where the temperatures are just right to support life.
SETI
The Gliese 581 system has been the target of both
SETI
The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other p ...
and Active SETI searches for extraterrestrial life.
A Message from Earth
Gliese 581c (Gl 581c or GJ 581c) is a planet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a ...
(AMFE) is a high-powered digital radio signal that was sent on 9 October 2008, toward Gliese 581c. The signal is a digital time capsule containing 501 messages that were selected through a competition on the social networking site Bebo. The message was sent using the Yevpatoria RT-70 radio telescope radar telescope of the National Space Agency of Ukraine. The signal will reach Gliese 581 in early 2029.
Using optical SETI,
Ragbir Bhathal claimed to have detected an unexplained pulse of light from the direction of the Gliese 581 system in 2008.
In 2012, the International Centre for Radio Astronomy Research at Curtin University in Perth, Gliese 581 was precisely targeted by Australian Long Baseline Array using three radio telescope facilities across Australia and the Very Long Baseline Interferometry technique, however no candidate signals were found.
Debris disk
At the outer edge of the system is a massive debris disk containing more comets than the Solar System. The debris disc has an inclination between 30° and 70°.
If the planetary orbits lie in the same plane, their masses would be between 1.1 and 2 times the minimum mass values.
[The radial velocity method allows the determination of the minimum mass which is the product of the true mass with the sine of the orbital inclination, denoted m sin i. In general the inclination is unknown. For a given inclination, the true mass is therefore the minimum mass multiplied by 1/sin i.]
See also
*
Habitability of red dwarf systems
The habitability of red dwarf systems is presumed to be determined by a large number of factors from a variety of sources. Modern evidence indicates that planets in red dwarf systems are unlikely to be habitable, due to their low stellar flux, ...
*
Lists of exoplanets
These are lists of exoplanets. Most of these were discovered by the Kepler space telescope. There are an additional 2,054 potential exoplanets from Kepler's first mission yet to be confirmed, as well as 978 from its " Second Light" mission and ...
*
Gliese 876
Gliese 876 is a red dwarf approximately 15 light-years away from Earth in the constellation of Aquarius. It is one of the closest known stars to the Sun confirmed to possess a planetary system with more than two planets, after Gliese 1061 ...
Notes
References
External links
Major Discovery: New Planet Could Harbor Water and LifeSpace.com
Solstation.com
''Extrasolar Planets Encyclopaedia'': Gl 581AstronomyCast: Gliese 581All Wet? Astronomers Claim Discovery of Earth-like Planet Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it i ...
Position of Gliese 581 marked on local space(Top right corner)
''The Geochemical Society''
Washington University in St. Louis
Washington University in St. Louis (WashU or WUSTL) is a private research university with its main campus in St. Louis County, and Clayton, Missouri. Founded in 1853, the university is named after George Washington. Washington University is r ...
Extrasolar Planet Interactions
by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona
Earth-like planet found that may support life
Ctv.ca
* ttp://video.foxnews.com/v/1301110758001/earths-twin-discovered/ Earth's Twin Discovered?
{{DEFAULTSORT:Gliese 581
0581
074995
M-type main-sequence stars
BY Draconis variables
Librae, HO
Durchmusterung objects
Libra (constellation)
Planetary systems with three confirmed planets
TIC objects