Nuovo Pianeta Abitabile (Italian) - New Habitable Planet (English) - Gliese 581 - INDEX

NASA -- larger image

Gliese 581 is a dim red dwarf star, like Gliese
623 A (M2.5V) and B (M5.8Ve) at lower right.
(See a Digitized Sky Survey field image around
Gliese 581 at the NStars Database.)
 


 
• System Summary

  Also known as HO Librae, this dim star lies around 20.4 light-years from Sol. It is located in the northeast part (15:19:26.8-07:43:20.2, ICRS 2000.0) 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. Like other red dwarf stars, however, it is not visible to the naked eye. On November 30, 2005, a team of French and Swiss astronomers announced the discovery of a Neptune-class planet in a very close "torch" orbit around Gliese 581 (ESO press release and Bonfils et al, 2005, in pdf -- details below). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

  This star was probably first designated as BD-07 4003 and added to a catalogue that was originally published in 1863 by Friedrich Wilhelm August Argelander (1799-1875) on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896). This catalogue became famous as the Bonner Durchmusterung ("Bonn Survey") and is typically abbreviated as BD. It was later expanded and extended during the early 20th Century with the Cordoba (observed from Argentina) then the Cape Photographic Durchmusterung (observed from South Africa).

  Its high proper motion was probably discovered photographically, and it was designated as Wolf 562 by Max (Maximilian Franz Joseph Cornelius) Wolf (1863-1932). Wolf was a pioneer of astrophotography who discovered hundreds of variable stars and asteroids, and about 5,000 nebulae by analyzing photographic plates and developing the "dry plate" in 1880 and the "blink comparator" in 1900 with the Carl Zeiss optics company in Jena, Germany. Today, many astronomers refer to this star by its earliest designation as Gl 581 in the first Gliese Catalogue of Nearby Stars (CNS, now ARICNS database) of Wilhelm Gliese (1915-93), who was a longtime astronomer at the Astronomiches Rechen-Institut at Heidelberg (even when it was at Berlin).

  The Star

  Gliese 581 is a cool and dim, main sequence red dwarf (M2.5 V). The star has almost a third (31 +/- 2 percent) of Sol's mass, possibly 29 percent of its diameter, and a bit more than one percent (around 0.013) of its visual luminosity (Bonfils et al, 2005, in pdf). The star appears to be only around 47 to 56 percent as enriched as Sol in elements heavier than hydrogen ("metals") ((Bean et al, 2006; Ken Crosswell, 2006; and Bonfils, et al, 2005). Its kinematic characterisitcs, magnetic activity, and sub-Solar metallicity indicate that that Gliese 581 is at least two billion years old. Gliese 851 is a variable star with the designation "HO Librae" and NSV 7023. Some other useful star catalogue designations include: HO Lib, Gl 581, Hip 74995, BD-07 4003, G 151-46, G 152-9, LHS 394, LTT 6112, LPM 564, LFT 1195, Vys/MCC 159, and Wolf 562.
   

  Planet b

  JPL, NASA
  
  
  
  Larger image.
  
  
  
  It is not yet known whether
  planetary candidate "b" is
  rocky or gaseous -- like
  Neptune.
   

  
   

  On November 30, 2005, a team of French and Swiss astronomers announced the discovery of a Neptune-class planet in a very close "torch" orbit around this star using the HARPS spectrograph on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile (ESO press release) and Bonfils et al, 2005, in pdf). Planet "b" has around 16.6 times the Earth's mass. with a semi-major axis of 0.041 AUs (around 6 million kilometers), it orbits so close to its host star that its orbital period last only only 5.366 days. As a result, the planet must be very hot, about 147 degrees Celsius (420° Kelvin), and its presence would have disturbed the development and orbit of a nearby earth-type in the habitable zone (center around 0.05 AUs). Other measurements of the star suggest that no Jupiter-mass planet orbits Gliese 581 with a period of around 10 years or less. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)