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Gliese 581b
Extrasolar planet List of extrasolar planets
Planet Gliese 581 b.png
Artist's conception of Gliese 581 b as a hot-Neptune.
Parent star
Star Gliese 581
Constellation Libra
Right ascension (α) 15h 19m 26s
Declination (δ) −07° 43′ 20″
Apparent magnitude (mV) 10.55
Distance 20.3 ± 0.3 ly
(6.2 ± 0.1 pc)
Spectral type M3V
Orbital elements
Semimajor axis (a) 0.041[1] AU
(6.1 Gm)
    6.6 mas
Eccentricity (e) 0[1]
Orbital period (P) 5.36874 ± 0.00019[1] d
(0.0146986 y)
    (128.85 h)
Orbital speed (υ) 84 km/s
Inclination (i) ≥30[1]°
Time of periastron (T0) 2,454,712.62 ± 0.062[1] JD
Semi-amplitude (K) 12.48 ± 0.23[1] m/s
Physical characteristics
Minimum mass (m sin i) 15.65[1] M
Discovery information
Discovery date August 22, 2005
announced November 30, 2005
Discoverer(s) X. Bonfils, T. Forveille, X. Delfosse,
S. Udry, M. Mayor, C. Perrier,
F. Bouchy, F. Pepe, D. Queloz,
J.-L. Bertaux
Detection method Doppler Spectroscopy
Discovery status Published
Database references
Extrasolar Planets
An extrasolar neptune compared to Jupiter (right) and Earth (left).

Gliese 581 b or Gl 581 b is an extrasolar planet orbiting the star Gliese 581.



The planet was discovered by a team of French and Swiss astronomers, who announced their findings on November 30, 2005 as a discovery of one of the smallest extrasolar planets 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 star (after Gliese 876'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 a Letter to the Editor of Astronomy and Astrophysics.[2]

Orbit and mass

Gliese 581 b is at minimum about 16 times the Earth's mass, similar to Neptune's mass. It does not transit its star, implying that its inclination is less than 88.1 degrees.[3] Dynamical simulations of the Gliese 581 system assuming that the orbits of the four planets are coplanar 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.[1]

It is rather close to Gliese 581 and completes a full orbit in only 5.4 days at a mean distance of about 6 million kilometres (0.041 AU). By comparison, Mercury is at a distance of 58 million kilometres (0.387 AU) and completes an orbit in 88 days.


Gliese 581 b is about 0.04 AU from its sun. It is likely close to Gliese 436 b in mass, temperature, and (with Gliese 876 d) susceptibility to solar effects such as coronal mass ejection. 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 three other planets and that Gliese 436 b (thus far) stands alone, their formation must have differed.


  1. ^ a b c d e f g h M. Mayor, X. Bonfils, T. Forveille, X. Delfosse, S. Udry, J.-L. Bertaux, H. Beust, F. Bouchy, C. Lovis, F. Pepe, C. Perrier, D. Queloz, N. C. Santos (2009). "The HARPS search for southern extra-solar planets XVIII. An Earth-mass planet in the GJ 581 planetary system". arΧiv:0906.2780 [astro-ph].  
  2. ^ Bonfils, X.; Forveille, T.; Delfosse, X.; Udry, S.; Mayor, M.; Perrier, C.; Bouchy, F.; Pepe, F. et al. (2005). "The HARPS search for southern extra-solar planets". Astronomy and Astrophysics 443: L15–L18. doi:10.1051/0004-6361:200500193.   edit
  3. ^ Mercedes Lopez-Morales, Nidia I. Morrell, R. Paul Butler, Sara Seager (2006). "Limits to Transits of the Neptune-mass planet orbiting Gl 581". arΧiv:0609255v1 [astro-ph].  

See also

External links

Coordinates: Sky map 15h 19m 26s, −07° 43′ 20″



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