Gliese 581 b

Gliese 581 b

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Gliese 581 b or Gl 581 b is an 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...

 orbiting the 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...

 Gliese 581
Gliese 581
Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...

. It is the first planet of six discovered in the system so far, and the second in order from the star.

Discovery


The planet was discovered by a team of French and Swiss astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

s, who announced their findings on November 30, 2005 as a discovery of one of the smallest 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...

s ever found, with one conclusion being that planets may be more common around the smallest stars. It was the fifth planet found around 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 (after 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...

's planets and Gliese 436 b).

The planet was discovered using the HARPS instrument, with which they found the host star to have a wobble that implied the existence of the planet.

The astronomers published their results in Astronomy and Astrophysics Letters.

Orbit and mass


Gliese 581 b is at minimum about 16 times 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...

's mass, similar to 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...

's mass. It does not transit its star, implying that its inclination is less than 88.1 degrees. Dynamical simulations of the Gliese 581 system assuming that the orbits of the four planets 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 exceed 1.6 – 2 times their minimum masses. This is primarily due to the close separation between planets b and e. For Gliese 581 b, the upper mass limit is 30.4 Earth masses, or about 77% more massive than 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...

.

It is rather close to Gliese 581
Gliese 581
Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...

 and completes a full orbit in only 5.4 day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...

s at a mean distance of about 6 million kilometres (0.041 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

). By comparison, Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

 is at a distance of 58 million kilometres (0.387 AU) and completes an orbit in 88 days.

Characteristics


Gliese 581 b is about 0.04 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

 from its sun. It is likely close to Gliese 436 b
Gliese 436 b
Gliese 436 b is a Neptune-sized extrasolar planet orbiting the red dwarf star Gliese 436. It was among the smallest known transiting planets in mass and radius until the much smaller Kepler discoveries started coming in 2010.-Discovery:...

 in mass, temperature, and (with Gliese 876 d
Gliese 876 d
Gliese 876 d is an extrasolar planet approximately 15 light-years away in the constellation of Aquarius . The planet was the third planet discovered orbiting the red dwarf star Gliese 876. At the time of its discovery, the planet had the lowest mass of any known extrasolar planet apart from the...

) susceptibility to solar effects such as coronal mass ejection
Coronal mass ejection
A coronal mass ejection is a massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space....

. Since Gliese 581 b does not transit, nothing more can be said of it yet. At the least, given that Gliese 581 b orbits alongside five other 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...

, 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...

, 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...

, 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 that Gliese 436 b (thus far) stands alone, their formation must have differed.


See also

  • Gliese 229
    Gliese 229
    Gliese 229 is a red dwarf star about 19 light years away in the constellation Lepus. It has 58% of the mass of the Sun, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s at the stellar equator.The star is known to be a low activity flare star, which means it...

  • Gliese 436 b
    Gliese 436 b
    Gliese 436 b is a Neptune-sized extrasolar planet orbiting the red dwarf star Gliese 436. It was among the smallest known transiting planets in mass and radius until the much smaller Kepler discoveries started coming in 2010.-Discovery:...

  • Gliese 876 b
    Gliese 876 b
    Gliese 876 b is an extrasolar planet orbiting the red dwarf star Gliese 876. It completes one orbit in approximately 61 days. Discovered in June 1998, Gliese 876 b was the first planet to be discovered orbiting a red dwarf star.- Discovery :...

  • Gliese 876 c
    Gliese 876 c
    Gliese 876 c is an extrasolar planet orbiting the red dwarf star Gliese 876, taking about 30 days to complete an orbit. The planet was discovered in April 2001 and is the second planet in order of increasing distance from its star.- Discovery :...

  • Gliese 876 d
    Gliese 876 d
    Gliese 876 d is an extrasolar planet approximately 15 light-years away in the constellation of Aquarius . The planet was the third planet discovered orbiting the red dwarf star Gliese 876. At the time of its discovery, the planet had the lowest mass of any known extrasolar planet apart from the...

  • 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...

  • 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...


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