Gliese 581

Gliese 581

Overview
Gliese 581 is a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 with spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 M3V, located 20.3 light years away from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Libra
Libra (constellation)
Libra is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is . It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.-Notable features:]...

. Its estimated mass is about a third of that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, and it is the 89th closest known star system
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...

 to the Sun. Observations suggest that the star has at least six planets: Gliese 581 e
Gliese 581 e
Gliese 581 e or Gl 581 e is an extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra...

, b
Gliese 581 b
Gliese 581 b or Gl 581 b is an extrasolar planet orbiting the star Gliese 581. It is the first planet of six discovered in the system so far, and the second in order from the star.- Discovery :...

, c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, d
Gliese 581 d
Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. It is the third planet discovered in the system and the fifth in order from the star....

, f
Gliese 581 f
Gliese 581 f or Gl 581 f is an unconfirmed planet in the Gliese 581 system, located 20 light years from Earth. It is the fifth planet discovered in the system and the sixth known in order from the star. Its discovery was announced September 29, 2010...

 and g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

. g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

 is thought to be a candidate for habitability.

Gliese 581 has been the subject of a "huge amount of attention" in the quest to discover the first habitable planet
Planetary habitability
Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...

; in 2010, attention focused on unconfirmed planet g, which would have been close to the middle of the star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, but more recently, in a study published in The Astrophysical Journal Letters, planet d "can be considered the first confirmed exoplanet that could support Earth-like life."

The star system first gained attention after Gliese 581 c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, the first low-mass extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...

 found to be near its star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, was discovered in April 2007.
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Encyclopedia
Gliese 581 is a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 with spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 M3V, located 20.3 light years away from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Libra
Libra (constellation)
Libra is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is . It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.-Notable features:]...

. Its estimated mass is about a third of that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, and it is the 89th closest known star system
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...

 to the Sun. Observations suggest that the star has at least six planets: Gliese 581 e
Gliese 581 e
Gliese 581 e or Gl 581 e is an extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra...

, b
Gliese 581 b
Gliese 581 b or Gl 581 b is an extrasolar planet orbiting the star Gliese 581. It is the first planet of six discovered in the system so far, and the second in order from the star.- Discovery :...

, c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, d
Gliese 581 d
Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. It is the third planet discovered in the system and the fifth in order from the star....

, f
Gliese 581 f
Gliese 581 f or Gl 581 f is an unconfirmed planet in the Gliese 581 system, located 20 light years from Earth. It is the fifth planet discovered in the system and the sixth known in order from the star. Its discovery was announced September 29, 2010...

 and g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

. g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

 is thought to be a candidate for habitability.

Gliese 581 has been the subject of a "huge amount of attention" in the quest to discover the first habitable planet
Planetary habitability
Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...

; in 2010, attention focused on unconfirmed planet g, which would have been close to the middle of the star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, but more recently, in a study published in The Astrophysical Journal Letters, planet d "can be considered the first confirmed exoplanet that could support Earth-like life."

The star system first gained attention after Gliese 581 c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, the first low-mass extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...

 found to be near its star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, was discovered in April 2007. It has since been shown that under known terrestrial planet climate models, Gliese 581 c is likely to have a runaway greenhouse effect
Runaway greenhouse effect
A runaway greenhouse effect is not a clearly defined term, but is understood to mean an event analogous to that which is believed to have happened in the early history of Venus, where positive feedback increased the strength of its greenhouse effect until its oceans boiled away...

, and hence is probably too hot to be habitable, analogous to Venus. A subsequently discovered planet Gliese 581 d
Gliese 581 d
Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. It is the third planet discovered in the system and the fifth in order from the star....

, may be just inside or just outside the outer boundary of the habitable zone (depending in part on the greenhouse
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

 properties of its atmosphere), analogous to Mars. The discovery of exoplanet Gliese 581 e
Gliese 581 e
Gliese 581 e or Gl 581 e is an extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra...

, the least-massive planet known around a normal star, was announced in April 2009.

Excitement spiked again in September 2010 with the claimed discovery of Gliese 581 g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

, orbiting between c and d, believed to be the planet with the greatest likelihood of having conditions suitable for liquid water at its surface found to date because it is within the middle of the habitable zone.
However, its existence was later put in "serious doubts" following further analysis.

Star


The name Gliese 581 refers to the catalog number from the 1957 survey Gliese Catalogue of Nearby Stars
Gliese Catalogue of Nearby Stars
The Gliese Catalogue of Nearby Stars is a frequently referenced, modern star catalogue of stars located within 25 parsecs of the Earth.-First edition and supplements:...

of 965 stars located within 20 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....

s of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. Other names of this star include BD-07° 4003 (BD catalogue
Durchmusterung
In astronomy, Durchmusterung or Bonner Durchmusterung , is the usual name for three comprehensive astrometric star catalogues of the whole sky, processed by the Bonn Observatory from 1859 to 1903....

, first known publication) and HO Librae (variable star designation
Variable star designation
Variable stars are named using a variation on the Bayer designation format of an identifying label combined with the Latin genitive of the name of the constellation in which the star lies...

). It does not have an individual name such as Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

or Procyon
Procyon
Procyon is the brightest star in the constellation Canis Minor. To the naked eye, it appears to be a single star, the seventh brightest in the night sky with a visual apparent magnitude of 0.34...

. The star is a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 with spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 M3V, located 20.3 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...

s away from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. It is located about two degrees north of Beta Librae
Beta Librae
Beta Librae is the brightest star in the constellation Libra. It has the traditional name Zubeneschamali and the Latin name Lanx Borealis...

, the brightest star in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Libra
Libra (constellation)
Libra is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is . It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.-Notable features:]...

. Its mass is estimated to be approximately a third that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, and it is the 89th closest known star system
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...

 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, we can estimate an effective temperature of 3200 kelvins and a visual luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...

 of 0.2% of that of the Sun. However, a red dwarf such as Gliese 581 radiates primarily in the near infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

, with peak emission at a wavelength of roughly 830 nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...

s (estimated using Wien's displacement law
Wien's displacement law
Wien's displacement law states that the wavelength distribution of thermal radiation from a black body at any temperature has essentially the same shape as the distribution at any other temperature, except that each wavelength is displaced on the graph...

, which assumes the star radiates as a black body
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...

), so such an estimate will underestimate the star's total luminosity. (For comparison, the peak emission of the Sun is roughly 530 nanometres, 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
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...

 1.3% 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", or, more prosaically, the habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

. The extent of such a zone is not fixed and is highly specific for each planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...

.

Gliese 581 is classified as a variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...

 of the BY Draconis
BY Draconis variable
BY Draconis variables are main sequence variable stars of late spectral types, usually K or M. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in their luminosity due to rotation of the star coupled with star spots, and other...

 type, and has been given the variable star designation HO Librae. This is a star that exhibits variability because of the presence of star spots 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. Gliese 581 emits X-rays.

Planetary system


At least four and possibly six planets are believed to be orbiting Gliese 581. Gliese 581 b
Gliese 581 b
Gliese 581 b or Gl 581 b is an extrasolar planet orbiting the star Gliese 581. It is the first planet of six discovered in the system so far, and the second in order from the star.- Discovery :...

, approximately Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

-sized, was discovered in August 2005 and was the fifth planet to be discovered around a red dwarf star. This inner planet is at least 16 times as mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

ive as Earth (similar to Neptune's mass) and completes a full orbit of Gliese 581 in only 5.4 days.
Another planet, Gliese 581 c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, was discovered in April 2007. In their 2007 paper, Udry et al. asserted that if Gliese 581 c 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
Astronomical transit
The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...

 its sun. With a minimum mass of roughly five times Earth—or one third that of Neptune—Gliese 581 c orbits just inside of the habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

 of its parent star. The mean blackbody surface temperature has been estimated to lie between −3 °C (for a Venus-like albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

) 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
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

. Some astronomers believe the system may have undergone planetary migration
Planetary migration
Planetary migration occurs when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite's orbital parameters, especially its semi-major axis...

 and Gliese 581 c may have formed beyond the frost line
Frost line (astrophysics)
In astronomy or planetary science, the frost line, also known as the snow line or ice line, refers to a particular distance in the solar nebula from the central protosun where it is cool enough for hydrogen compounds such as water, ammonia, and methane to condense into solid ice grains. Depending...

, with a composition similar to icy bodies like Ganymede
Ganymede (moon)
Ganymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...

. Gliese 581 c completes a full orbit in just under 13 days.

Observations of the star also revealed a third planet, Gliese 581 d
Gliese 581 d
Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. It is the third planet discovered in the system and the fifth in order from the star....

, with a mass of roughly 7 Earths, or half a Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

, and an orbit of 66.8 Earth days. It orbits just within the outer limit of the habitable zone of its star, which makes it a potential candidate for being able to support life. (A reanalysis of the radial velocity data has reduced the minimum possible mass of this planet from 7.1 M to 5.6 M.)

4-planet solution (2009)


Discovery of a fourth planet, Gliese 581 e
Gliese 581 e
Gliese 581 e or Gl 581 e is an extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra...

, was announced on 21 April 2009. This planet, at an estimated minimum mass of 1.9 Earths, is currently the lowest mass exoplanet identified around a "normal star" (i.e. excluding pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...

s). It takes 3.15 days to orbit Gliese 581.

Dynamical simulations of the Gliese 581 system assuming that the orbits of planets b to d are coplanar
Coplanarity
In geometry, a set of points in space is coplanar if all the points lie in the same geometric plane. For example, three distinct points are always coplanar; but a fourth point or more added in space can exist in another plane, incoplanarly....

 show that the system becomes unstable if its component masses are more than 1.6 – 2 times the minimum mass. The upper limits on the masses of the planets are found to be 3.1, 30.4, 10.4 and 13.8 Earth masses for planets e, b, c and d respectively.

6-planet solution (2010)


On 29 September 2010, astronomers at Keck Observatory announced the discovery of Gliese 581 f
Gliese 581 f
Gliese 581 f or Gl 581 f is an unconfirmed planet in the Gliese 581 system, located 20 light years from Earth. It is the fifth planet discovered in the system and the sixth known in order from the star. Its discovery was announced September 29, 2010...

 and Gliese 581 g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

, both in nearly circular orbits. The detection was based on analysis of a combination of data sets from the HIRES and HARPS instruments. Nicknamed Zarmina by one of its discoverers, Gliese 581 g has a mass of 3 to 4 Earth-masses, with an orbital period of 37 days, and is at a distance from Gliese 581 that is well within the star's habitable zone. The planet is predicted to be tidally locked, with one side of the planet always facing the star.

The approximate ratios of periods of adjacent orbits are (proceeding outward): 3:5, 2:5, 1:3, 1:2, 2:13.

The parameters listed below come from an orbital fit in which eccentricities were fixed at 0. Allowing eccentricities to vary did not significantly improve the fit.

According to a presentation by F. Pepe at IAU Symposium 276, planet g was not detected in a new analysis of data taken by the HARPS spectrograph, and both planets f and g are listed as unconfirmed at the Extrasolar Planets Encyclopaedia.
Follow up studies published in September 2011 indicate that Gliese f and g do not exist.

Radio signal sent from Earth


A Message From Earth
A Message From Earth
A Message from Earth is a high-powered digital radio signal that was sent on 9 October 2008 towards Gliese 581 c, a large terrestrial extrasolar planet orbiting the red dwarf star Gliese 581. The signal is a digital time capsule containing 501 messages that were selected through a competition on...

 (AMFE) is a high-powered digital radio signal that was sent on 9 October 2008 toward Gliese 581 c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

. The signal is a digital time capsule
Time capsule
A time capsule is an historic cache of goods or information, usually intended as a method of communication with future people and to help future archaeologists, anthropologists, or historians...

 containing 501 messages that were selected through a competition on the social networking site Bebo
Bebo
Bebo is a social networking website launched in July 2005. It is currently owned and operated by Criterion Capital Partners after taking over from AOL in June 2010....

. The message was sent using the RT-70
Yevpatoria RT-70 radio telescope
The Yevpatoria RT-70 radio telescope is an RT-70 radio telescope and planetary radar at the Center for Deep Space Communications, Yevpatoria, Crimea, Ukraine. In the scientific literature is often called Evpatoria planetary radar .With its 70m antenna diameter, it is among the largest single dish...

 radar telescope of Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...

's National Space Agency
National Space Agency of Ukraine
The State Space Agency of Ukraine is the Ukrainian government agency responsible for space policy and programs....

. The signal will reach Gliese 581 in early 2029.

See also

  • Gliese 876
    Gliese 876
    Gliese 876 is a red dwarf star approximately 15 light-years away from Earth in the constellation of Aquarius. As of 2011, it has been confirmed that four extrasolar planets orbit the star...

  • List of extrasolar planets
  • Habitability of red dwarf systems
    Habitability of red dwarf systems
    Determining the habitability of red dwarf systems could help reveal the likelihood of extraterrestrial life, as red dwarfs make up most stars in the Milky Way Galaxy...


External links