Difference between revisions of "Gliese 581"
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| − | '''Gliese 581''', also known as '''HO Librae''' is a red dwarf star around 20.4 [[light year|light years]] away, which is most famous for the | + | '''Gliese 581''', also known as '''HO Librae''', is a red dwarf star around 20.4 [[light year|light years]] away, which is most famous for the discovery of the [[Gliese 581c|first low mass planet within a star's habitable zone]]. In total, four planets have thus been found orbiting the star, two of which may sit within the [[habitable zone]]. |
==The Star== | ==The Star== | ||
Revision as of 08:29, July 24, 2009
Gliese 581, also known as HO Librae, is a red dwarf star around 20.4 light years away, which is most famous for the discovery of the first low mass planet within a star's habitable zone. In total, four planets have thus been found orbiting the star, two of which may sit within the habitable zone.
Contents
The Star
Gliese 581 is a cool, dim, red dwarf in the main sequence with the spectral classification of M3 V. The star is one-third as massive as our own Sun, with around 38 perfect of its diameter, but only around one percent as luminous as our Sun. However much of the light emanating from Gliese 581 is in the infrared, therefore visually, it is only 0.2 percent as bright. The star’s metallicity appears to be between 38 and 62 percent as enriched as our Sun, according to its abundance of iron. Using measurements of Gliese 581’s kinematic characteristics and magnetic activity, the star is calculated to be at least 2 billion years old, possibly as old as 4.3 billion years.[1] More recent measurements of the star showing its brightness only varied slightly suggest it is even older.[2]
Planetary System
There are four known planets in orbit around Gliese 581 with two inside the star’s habitable zone. The first Gliese 581 c is the most widely reported, however Gliese 581 d, discovered later is a much better candidate as a terrestrial, possible life supporting world under current terrestrial climate models.
Gliese 581 b
Gliese 581 b is the first planet discovered and the second closest known to its parent star. The planet was first discovered by a team of French and Swiss astronomers using the HARPS spectrograph and was announced on November 30, 2005. At the time, it was one of the smallest extrasolar worlds discovered and the fifth such world to be found around a red dwarf star.[3]
The planet has a minimum estimated mass of 15.65 times that of Earth. It orbits Gliese 581 in what is commonly called a "torch orbit", being only 0.04 AU (6 million kilometers) away, the orbit is so close that it only takes a little more than 5 days to complete.[1]
Gliese 581 c
On April 25, 2007 the same team of astronomers using the HARPS spectrograph once again announced the discovery of Gliese 581 c (along with Gliese 581 d). When announced Gliese 581 c was the smallest known extrasolar planet around a main sequence star (until Gliese 581 e was found). It is the third closest of the four known worlds.
The planet is calculated to have at least 5.36 times Earth’s mass (maximum of 10.4 times) and is estimated to be 1.5 times the Earth’s diameter. The planet orbits with a mean distance of only 0.07 AU, which takes just under 13 days to complete. At this distance, Gliese 581 c is tidally locked.[1]
Initially the planet was thought to be inside Gliese 581’s habitable zone, the first such terrestrial world outside of our Solar System to be found. However further research indicated that the planet may be too close to the star and would have a Venus like runaway greenhouse effect in its atmosphere that would boil off all the water.[4] Gliese 581 d instead is the better candidate for habitability.
Gliese 581 d
Gliese 581 d was discovered alongside and announced at the same time as Gliese 581 c, and also sits within the habitable zone of Gliese 581 and is now the prime candidate for habitability among the known worlds of the Gliese 581 system. It is the fourth of the four known worlds in distance from its parent star.
The planet has a mass of at least 7.09 (maximum of 13.8) times that of Earth. The planet has a mean orbit of 0.22 AU, which it completes in 66.8 days.[1] In April of 2009 after further studies, the planet was confirmed to be within the habitable zone where liquid water could exist with a greenhouse effect under the right atmospheric conditions.[4] The planet though is thought to be too massive to be made only of rock and it may be an ice world instead at one time and that as the planet migrated close to Gliese 581 the abundant ices have melted into deep worldwide oceans.[5]
Gliese 581 e
The discovery of Gliese 581 e was announced on April 21, 2009. The planet is estimated to have a minimum mass only 1.9 times that of Earth making it the smallest extrasolar world in the system and known overall. It is the closest of the four known worlds in distance from its parent star.
The planet has a mean orbit of only 0.03 AU, which it completes in a mere 3 days. Because of its close distance, the planet is too close to be with Gliese 581’s habitable zone.[1] It is unlikely to have an atmosphere because of the high temperatures and strong radiation it would receive at such a close distance to the star.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 http://exoplanet.eu/star.php?st=Gl+581
- ↑ http://www.astronomy.com/asy/default.aspx?c=a&id=5619
- ↑ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005A%26A...443L..15B&db_key=AST&data_type=HTML&format=&high=438efdb55325468
- ↑ 4.0 4.1 http://arxiv.org/PS_cache/arxiv/pdf/0705/0705.3758v1.pdf
- ↑ http://www.eso.org/public/outreach/press-rel/pr-2009/pr-15-09.html
