Gliese 581 planetary system
The orbits of planets in the Gliese 581 planetary system compared to those of the Solar System
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| Age | 7–11 billion years |
|---|---|
| Location | Libra constellation |
| Right ascension | 15h 19m 26.8250s |
| Declination | −07° 43′ 20.209″ |
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Populations
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| Known stars | 1 |
| Known planets | 3–5 |
The Gliese 581 planetary system is the gravitationally bound system comprising Gliese 581 and the objects that orbit it. The system is known to consist of at least three planets (possibly up to five) along with a debris disc discovered using the radial velocity method. The system's notability is due primarily to early exoplanetology discoveries, between 2008 and 2010, of possible terrestrial planets orbiting within its habitable zone and the system's relatively close proximity to the Solar System at 20 light years away. Though its observation history is controversial due to false detections and conjecture, and with the radial velocity method yielding little information about the planets themselves beyond their mass.
The confirmed planets are believed to be located close to the star with near-circular orbits. In order of distance from the star, these are Gliese 581e, Gliese 581b, and Gliese 581c. The letters represent the discovery order, with b being the first planet to be discovered around the star.
The first announcement of a planet around the star was Gliese 581b discovered by astronomers at the Observatory of Geneva in Switzerland and Grenoble University in France. Detected in August 2005 and using extensive data from the ESO/HARPS spectrometer it was the fifth planet to be discovered around a red dwarf. Further observations by the same group resulted in the detection of two more planets, Gliese 581c and Gliese 581d. The orbital period of Gliese 581d was originally thought to be 83 days but was later revised to a lower value of 67 days. The revised orbital distance would place it at the outer limits of the habitable zone, the distance at which it is believed possible for liquid water to exist on the surface of a planetary body, given favourable atmospheric conditions. Gliese 581d was estimated to receive about 30% of the intensity of light the Earth receives from the Sun. By comparison, sunlight on Mars has about 40% of the intensity of that on Earth, though if high levels of carbon dioxide are present in the planetary atmosphere, the greenhouse effect could keep temperatures above freezing.
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