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Friday, October 1, 2010

Gliese 581 g - Wikipedia, the free encyclopedia

Gliese 581 g

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Gliese 581 g
Extrasolar planet List of extrasolar planets
485014main orbit comparison full 946-710.jpg
The orbits of planets in the Gliese 581 system compared to those of our own solar system
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
Mass (m) 0.31 M
Radius (r) 0.29 R
Temperature (T) 3480 ± 48 K
Metallicity [Fe/H] -0.33 ± 0.12
7 – 11 Gyr
Orbital elements
Semimajor axis (a) 0.146[1] AU
Orbital period (P) 36.6[1] d
Physical characteristics
Minimum mass (m sin i) 3.1 – 4.3[1] M
Radius (r) 1.3 – 2[1] R
Surface gravity (g) 1.1 – 1.7[1] g
Discovery information
Discovery date September 29, 2010
Discoverer(s) Steven S. Vogt et al.
Detection method Radial Velocity
Discovery site Keck Observatory, Hawaii
Discovery status
Database references
Extrasolar Planets

Gliese 581 g (pronounced /ˈɡliːzə/) or Gl 581 g,[2] is an extrasolar planet, orbiting the red dwarf star Gliese 581, approximately 20.5 light-years[3] away from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth in order from the star. The planet was discovered by the Lick-Carnegie Exoplanet Survey after more than a decade's worth of observations. Despite the Gliese 581 system having a "somewhat checkered history of habitable planet claims," [1] results from the study imply that the planet is located in the middle of the "Goldilocks", or habitable zone of its parent star, where the existence of liquid water is considered a strong possibility.[4] The discovery of Gliese 581 g was announced in late September 2010,[1] and is believed to be the first Goldilocks planet ever found, the most Earth-like planet, and the best exoplanet candidate with the potential for harboring life found to date.[5]




The planet was detected by a team of astronomers in the Lick-Carnegie Exoplanet Survey, led by principal investigator Steven Vogt, professor of astronomy and astrophysics at the University of California, Santa Cruz and co-investigator Paul Butler of the Carnegie Institution of Washington. The discovery was made using radial velocity measurements combining 11 years of data from the HIRES instrument of the Keck 1 telescope and the HARPS instrument of ESO's 3.6m telescope at La Silla Observatory.[1][6]

The planet is believed to have a mass of 3.1 to 4.3 times that of the Earth and a radius of 1.3 to 2 times that of Earth. It has an orbital period of just under 37 days, orbiting at a distance of 0.146 AU from its parent star.[1]

The Lick-Carnegie team explained the results of their research in a paper published in the Astrophysical Journal.


The orbits of the Gliese 581 planetary system, with circular orbits, excluding outermost planet f.

In an interview with Lisa-Joy Zgorski of the National Science Foundation, Steven Vogt was asked what he thought about the chances of life existing on Gliese 581 g. 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, my own personal feeling is that the chances of life on this planet are 100%. I have almost no doubt about it."[7]

Despite other planets between Gliese 581g and the parent star not being tidally locked (Gliese 581 d eccentricity is 0.38 [1]) Gliese 581 g's size combined with proximity make it likely to be tidally locked to Gliese 581. Just as our moon always presents the same face to the Earth, the length of Gliese 581 g's sidereal day would then precisely match the length of its year.[1][8] Tidal locking would mean the planet would have no axial tilt and therefore no seasonality in any normal sense of the word. Its mass indicates that it is probably a rocky planet with a definite surface and that it has enough gravity to hold on to an atmosphere, likely one that is denser than Earth's.[1] Researchers have estimated that the global average surface temperature of the planet averages between −31 to −12 degrees Celsius (−24 and 10 degrees Fahrenheit).[9] With one side of the planet always facing the star, temperatures would range from blazing hot in the light side to freezing cold in the dark side, with continuous Earth-like temperatures imaginable along the terminator (the area between the bright and the dark side), informally known as the twilight zone.

Theoretical models of tidally locked worlds predict that under some conditions, volatile compounds such as water and carbon dioxide, if present, might evaporate in the scorching heat of the sunward side, migrate to the cooler night side, and condense to form ice caps. Over time, the entire atmosphere might freeze into ice caps on the night side of the planet. However, the amounts of water and carbon dioxide present on the surface of Gliese 581 g are unknown. Alternatively, an atmosphere massive enough to be stable would circulate the heat more evenly, allowing for a wider habitable area on the surface.[10] For example, Venus has a solar rotation rate approximately 117 times slower than Earth's, producing prolonged days and nights. Despite the uneven distribution of sunlight over time intervals shorter than several months, unilluminated areas of Venus are kept almost as hot as the day side by globally circulating winds.[11]


Scientists have monitored only a relatively small number of stars in the search for exoplanets. The discovery of a potentially habitable planet like Gliese 581 g so early in the search might mean that habitable planets are more widely distributed than had been previously believed. According to Vogt, the discovery "implies an interesting lower limit on the fraction of stars that have at least one potentially habitable planet as there are only ~116 known solar-type or later stars out to the 6.3 parsec distance of Gliese 581."[12] With the discovery of Gliese 581 g, the ratio of systems with habitable planets could be 10–20%[1] with "potentially billions" of Earth-like planets in our Milky Way galaxy alone.[13]

See also

Notes and references

  1. ^ a b c d e f g h i j k l Vogt, Steven S.; Butler, R. Paul; Rivera, Eugenio J.; Haghighipour, Nader; Henry, Gregory W.; Williamson, Michael H. (2010-09-29). "The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the Habitable Zone of the Nearby M3V Star Gliese 581". accepted by the Astrophysical Journal. Retrieved 2010-09-29. 
  2. ^ Borenstein, Seth (2010-09-29). "Could 'Goldilocks' planet be just right for life?". Associated Press. Retrieved September 30, 2010. 
  3. ^ About 193 trillion kilometres
  4. ^ Shiga, David (2010-09-29). "Found: first rocky exoplanet that could host life". New Scientist. Retrieved September 30, 2010. 
  5. ^ "Just-right planet that can support life detected". Reuters, USA. September 29, 2010. Retrieved September 30, 2010. 
  6. ^ Alleyne, Richard (September 30, 2010). "Gliese 581g the most Earth like planet yet discovered". The Daily Telegraph. Retrieved September 30, 2010. 
  7. ^ NSF. Press Release 10-172 - Video. Event occurs at 41:25-42:31. See Overbye, Dennis (2010-09-29). "New Planet May Be Able to Nurture Organisms". The New York Times'. Retrieved September 30, 2010. 
  8. ^ "Astronomers Find Most Earth-like Planet to Date". Science, USA. September 29, 2010. Retrieved September 30, 2010. 
  9. ^ Stephens, Tim (2010-09-29). "Newly discovered planet may be first truly habitable exoplanet". University News & Events. University of California, Santa Cruz. 
  10. ^ Alpert, Mark (2005-11-07). "Red Star Rising". Scientific American. Retrieved 2007–04–25. 
  11. ^ Ralph D Lorenz, Jonathan I Lunine, Paul G Withers, Christopher P. McKay (2001). "Titan, Mars and Earth: Entropy Production by Latitudinal Heat Transport" (PDF). Ames Research Center, University of Arizona Lunar and Planetary Laboratory. Retrieved 2007-08-21. 
  12. ^ Vogt 2010, pp.32-33. For more information, see Turnbull, Margaret C.; Tarter, Jill C. (Mar., 2003). "Target Selection for SETI: 1. A Catalog of Nearby Habitable Stellar Systems". The Astrophysical Journal (Institute of Physics Publishing). 
  13. ^ Berardelli, Phil (2010-09-29). "Astronomers Find Most Earth-like Planet to Date". AAAS. Retrieved September 30, 2010. 

External links

Coordinates: Sky map 15h 19m 27s, −07° 43′ 19″

Press Release 10-172 - Video
Steven Vogt and Paul Butler lead a team that discovered the first potentially habitable exoplanet.

Steven Vogt of UC Santa Cruz and UC Observatories and Paul Butler of the Carnegie Institution of Washington join NSF's Lisa-Joy Zgorski to announce the discovery of the first exoplanet that has the potential to support life.

Credit: National Science Foundation

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