Saturday, September 29, 2007

Gliese 581

Star type
g M2.5 V

Distance from Earth
g 20.45 ly

Star Service No.
g NA

g At least two billion years old, possibly around 4.3 billion years old ; as brightness does not vary much, star is probably several billion years old

Radius/Mass/Temp (xSol)
g 38%; 31.5%; 3,480 K

Brightness (xSol)
g 1.3%

g Between 36 to 62 percent as enriched as Sol in elements heavier than hydrogen

Comparison to Sol
g See chart (similar to Proxima)

Picture of star
g See picture above right
g Artist's conceptions of star with its planets

Star system features
g  Hosts vast amounts of cometary debris, at least 10 times more comets than in our own Solar System's Kuiper Belt, possibly because it hosts no Saturn-Jupiter-sized planets

Known planets
g Gliese 581 b: ; mass is 4.9% of Jupiter or 1560% of Earth; orbits in 5.4 days at distance of 0.041 AU
g Gliese 581 c: First low mass extrasolar planet found to be in its star's habitable zone, the more Earth-like planet has at least 5.03 Earth-masses (or 0.0158 Jupiter-masses) and an estimated diameter of at least 1.5 times Earth's if it is rocky, larger if it is composed of mostly ice. It moves around Gliese 581, outside of planet b's orbit, at an average distance of 0.073 AU, in a circular orbit (e=0.28 ± 0.06) which it completes in 12.932 (± 0.007) days. Initially thought to be located within the so-called habitable zone of Gliese 581, “c” almost certainly have a runaway greenhouse effect (surface temperatures of about 500 degress Celsius), and would not be habitable. Some believe the system may have undergone planetary migration and Gliese 581 c may have formed beyond the frost line, with a composition similar to icy bodies like Ganymede. The star would appear to be five times larger in the sky of "c" than the sun does in Earth's sky. Though only 7% as far from its star as Earth is from the Sun, Gliese 581 illuminates this planet about 40% that of the Sun does to the Earth. Intensity of UV, visible and IR radiation would be about 265% as intense as the Sun is to Earth; if ratio of outgoing radiation emissivity to incoming radiation absorption is the sameas Earth's, then average planet surface temperature for "c" would be 95 C. Also see: Speculation about geology/geochemistry of Gliese 581c; comparison to earth illustration.
g Gliese 581 d: Near the outer edge of the habitable zone; “d’ is at least 7.7 Earth-masses (or 0.0243 Jupiter-masses). It revolves around Gliese 581 - outside of planet b's orbit - at an average distance of 0.25 AU, in a roughly circular orbit (e= 0.2 ± 0.09) which it completes in 83.6 (± 0.7) days, not quite a quarter of an Earth year. Although it is possible that this detection is actually caused by a large star spot, the discoverers believe that the host star is too inactive for this possibility to be likely. At first glance, Gliese 581d is a pretty poor candidate in the hunt for life: it receives less than a third of the stellar energy Earth does and may be tidally locked, with a permanent day and night side, meaning the atmosphere would freeze out. New calculations suggests that a greenhouse effect under the right atmospheric conditions may make it possible for liquid water to persist on its surface. With a dense carbon dioxide atmosphere - a likely scenario on such a large planet - the climate is not only stable against collapse, but warm enough to have oceans, clouds and rainfall. The denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth. Also see: Gliese 581d: A Habitable Exoplanet?
g Gliese 581g, or Zarmina's World: Originally this planet was thought to have a mass similar to that of Earth and was close to the center of the habitable zone. For several months, the discovery of the first potential Earth twin outside the Solar System seemed to have been achieved. Unfortunately, later analysis by independent teams has raised serious doubts on this extremely difficult detection. Many now believe that Gliese 581g may not exist at all. Instead, it may simply be a result of noise in the ultra-fine measurements of stellar wobble needed to detect exoplanets in this system.

Habitable zone
g Around 0.11 and 2.8 AUs; in sky of planet, bloated red sun is 10x Sun

Orbital map
g See animation
g No Jupiter-mass planet orbits Gliese 581 with a period of around 10 years or less; star's low metallicity suggests a Jupiter-mass planet could not form around star

View from star
g NA

Nearby stars
(Star systems with 10 light years)
g HN Librae: 4.3 ly
g Gliese 570 ABCD: 5.2 ly
g LP 914-54: 6.8 ly
g Gliese 570 ABCD: 6.9 ly
g L 768-11: 8.2 ly
g Wolf 630 ABC: 8.2 ly
g Hip 72509: 8.2 ly
g BD-12 4523 AB: 8.4 ly
g Wolf 629 AB: 8.6 ly
g CD-25 10553 AB: 8.7 ly

Map locating star system
g See stellar map

Location in Earth sky
g Northeast part of Constellation Libra, the Scales - northeast of Delta Librae, north of Gamma Librae and Graffias (Beta Scorpii), and southwest of Epsilon (Yed Posterior) and Delta (Yed Prior) Ophiuchi, and Mu, Epsilon, and Alpha (Unukalhai) Serpentis

Other names
g HO Librae, Wolf 562, CD-45 13677, BD-07 4003, LHS 394, NSV 7023, Hip 74995, G 151-46, G 152-9, LTT 6112, LPM 564, LFT 1195, Vys/MCC 159

Sci-fi mentions
g A wormhole starting at Neptune opens at Wolf 562 in Geoffrey Landis' short story "Approaching Perimelasma"

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