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Gliese 876 b: Difference between revisions

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| app_mag = 10.17
| app_mag = 10.17
| dist_ly = 15.3 ± 0.1
| dist_ly = 15.3 ± 0.1
| dist_pc = 4.72 ± 0.04
| dist_pc = 4.70 ± 0.04
| class = M4V
| class = M4V
| mass = 0.334 ± 0.030
| mass = 0.334 ± 0.030

Revision as of 20:54, 21 February 2010

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Gliese 876 b is an extrasolar planet orbiting the red dwarf star Gliese 876 every 61.067 days. Discovered in June 1998, Gliese 876 b was the first planet to be discovered orbiting a red dwarf star. It is the outermost known planet in its planetary system.

Discovery

Gliese 876 b was discovered independently by two different teams, one led by Geoffrey Marcy (with data from Keck Observatory and Lick Observatory)[1] and the other by Xavier Delfosse (at Geneva Observatory).[2] Like the majority of known extrasolar planets, it was discovered by detecting variations in its star's radial velocity as a result of the planet's gravity. This was done by making sensitive measurements of the Doppler shift of the spectral lines of Gliese 876.

Orbit and mass

Gliese 876 b is in a 1:2 orbital resonance with the inner planet Gliese 876 c,[3] which leads to strong gravitational interactions between the two planets.[4] As a result, the orbital elements of the planet change fairly rapidly as the orbits precess.[5] The planet's orbit has a low eccentricity, similar to the planets in our solar system. The semimajor axis of the orbit is only 0.211 AU, less than that of Mercury in our solar system.[6] However Gliese 876 is such a faint star that this puts it in the outer part of the habitable zone.[7]

A limitation of the radial velocity method used to detect Gliese 876 b is that only a lower limit on the planet's mass can be obtained. This lower limit is around 1.93 times the mass of Jupiter.[8] The true mass depends on the inclination of the orbit, which in general is unknown. However in the case of Gliese 876 b, modelling the planet-planet interactions from the 1:2 resonance and combining this with astrometric measurements allows the orientation of the orbit to be fully determined, which reveals the true mass is 2.64 times the mass of Jupiter.[6]

Physical characteristics

Given the planet's high mass, it is likely that Gliese 876 b is a gas giant with no solid surface. Since the planet has only been detected indirectly through its gravitational effects on the star, properties such as its radius, composition, and temperature are unknown. Assuming a composition similar to Jupiter and an environment close to chemical equilibrium, it is predicted that the atmosphere of Gliese 876 b is cloudless, though cooler regions of the planet may be able to form water clouds.[9]

Gliese 876 b lies within the habitable zone of Gliese 876 as defined by the ability of an Earth-mass planet to retain liquid water at its surface. While the prospects for life on a gas giant are unknown, large moons may be able to support a habitable environment. Models of tidal interactions between a hypothetical moon, the planet and the star suggest that large moons should be able to survive in orbit around Gliese 876 b for the lifetime of the system.[10] On the other hand, it is unclear whether such moons could form in the first place.[11]

See also

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Notes


References

  1. ^ Marcy, G.; et al. (1998). "A Planetary Companion to a Nearby M4 Dwarf, Gliese 876". The Astrophysical Journal. 505 (2): L147 – L149. doi:10.1086/311623. {{cite journal}}: Explicit use of et al. in: |author= (help)
  2. ^ Delfosse, X.; et al. (1998). "The closest extrasolar planet. A giant planet around the M4 dwarf GL 876". Astronomy and Astrophysics. 338: L67 – L70. {{cite journal}}: Explicit use of et al. in: |author= (help)
  3. ^ Marcy, G.; et al. (2001). "A Pair of Resonant Planets Orbiting GJ 876". The Astrophysical Journal. 556 (1): 296–301. doi:10.1086/321552. {{cite journal}}: Explicit use of et al. in: |author= (help)
  4. ^ Rivera, E., Lissauer, J. (2001). "Dynamical Models of the Resonant Pair of Planets Orbiting the Star GJ 876". The Astrophysical Journal. 558 (1): 392–402. doi:10.1086/322477.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Butler; Wright, J. T.; Marcy, G. W.; Fischer, D. A.; Vogt, S. S.; Tinney, C. G.; Jones, H. R. A.; Carter, B. D.; Johnson, J. A.; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. doi:10.1086/504701. {{cite journal}}: Explicit use of et al. in: |author= (help) (web version)
  6. ^ a b Cite error: The named reference Correia2010 was invoked but never defined (see the help page).
  7. ^ Jones, B.; et al. (2005). "Prospects for Habitable "Earths" in Known Exoplanetary Systems". The Astrophysical Journal. 622 (2): 1091–1101. doi:10.1086/428108. {{cite journal}}: Explicit use of et al. in: |author= (help)
  8. ^ Rivera, E.; et al. (2005). "A ~7.5 M⊕ Planet Orbiting the Nearby Star, GJ 876". The Astrophysical Journal. 634 (1): 625–640. doi:10.1086/491669. {{cite journal}}: Explicit use of et al. in: |author= (help)
  9. ^ Sudarsky, D.; et al. (2003). "Theoretical Spectra and Atmospheres of Extrasolar Giant Planets". The Astrophysical Journal. 588 (2): 1121–1148. doi:10.1086/374331. {{cite journal}}: Explicit use of et al. in: |author= (help)
  10. ^ Barnes, J., O'Brien, D. (2002). "Stability of Satellites around Close-in Extrasolar Giant Planets". The Astrophysical Journal. 575 (2): 1087–1093. doi:10.1086/341477.{{cite journal}}: CS1 maint: multiple names: authors list (link) (paper incorrectly refers to Gliese 876 b as GJ876c)
  11. ^ Canup, R., Ward, W. (2006). "A common mass scaling for satellite systems of gaseous planets". Nature. 441: 834–839. doi:10.1038/nature04860.{{cite journal}}: CS1 maint: multiple names: authors list (link)

Further reading

Quelle: https://en.wikipedia.org/wiki/Special%3ADiff%2F345499538