||It has been suggested that Gliese 581 d, Gliese 581 f and Gliese 581 g be merged into this article. (Discuss) Proposed since July 2014.|
The star Gliese 581.
Digitized Sky Survey photo.
Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||15h 19m 26.8250s|
|Declination||−07° 43′ 20.209″|
|Apparent magnitude (V)||10.56 to 10.58[note 1]|
|B−V color index||1.61|
|Variable type||BY[note 2]|
|Radial velocity (Rv)||−9.5 ± 0.5 km/s|
|Proper motion (μ)||RA: −1233.51 mas/yr
Dec.: −94.52 mas/yr
|Parallax (π)||160.91 ± 2.62 mas|
|Distance||20.3 ± 0.3 ly
(6.2 ± 0.1 pc)
|Absolute magnitude (MV)||11.6|
|Luminosity (bolometric)||0.013 L☉|
|Surface gravity (log g)||4.92±0.10 cgs|
|Temperature||3,480 ± 48 K|
|Metallicity [Fe/H]||−0.33 ± 0.12 dex|
|Age||7 to 11 Gyr|
Gliese 581 (//) is a red dwarf star with spectral type M3V, located about 22 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star to the Sun. Observations suggest that the star has a planetary system consisting of three planets, designated Gliese 581 b, c and e in order of discovery. Additional outer planets which received the designations Gliese 581 d, f and g have been proposed, but the evidence that led to the discovery claims has been shown to be the result of stellar activity mimicking the radial velocity variations due to orbiting planets.
Gliese 581 has been the subject of a "huge amount of attention" in the quest to discover the first habitable extrasolar planet; first for c, and then d and g. Gliese 581 c, the first low-mass extrasolar planet found near a habitable zone, was discovered in April 2007. It has since been shown that under known terrestrial planet climate models, Gliese 581 c is likely to have a runaway greenhouse effect, and hence is probably too hot to be habitable, analogous to Venus. The subsequently-proposed planets Gliese 581 d and Gliese 581 g also received attention as being located within the habitable zone, but their existence has subsequently been refuted.
On 27 November 2012, the European Space Agency announced a debris disk, with at least ten times as many comets as the Solar system. This put constraints on possible planets beyond 0.75 AU.
The name Gliese 581 refers to the catalog number from the 1957 survey Gliese Catalogue of Nearby Stars of 965 stars located within 20 parsecs of the Earth. Other names of this star include BD-07° 4003 (BD catalogue, first known publication) and HO Librae (variable star designation). It does not have an individual name such as Sirius or Procyon. The star is a red dwarf with spectral type M3V, located 20.3 light-years away from Earth. It is located about two degrees north of Beta Librae, the brightest star in the constellation Libra. Its mass is estimated to be approximately a third that of the Sun, and it is the 89th closest known star system to the Sun.
An M-class dwarf star such as Gliese 581 has a much lower mass than the Sun, causing the core region of the star to fuse hydrogen at a significantly lower rate. From the apparent magnitude and distance, we can estimate an effective temperature of 3200 K and a visual luminosity of 0.2% of that of the Sun. However, a red dwarf such as Gliese 581 radiates primarily in the near infrared, with peak emission at a wavelength of roughly 830 nm (estimated using Wien's displacement law, which assumes the star radiates as a black body), so such an estimate will underestimate the star's total luminosity. (For comparison, the peak emission of the Sun is roughly 530 nm, in the middle of the visible part of the spectrum). When radiation over the entire spectrum is taken into account (not just the part that humans are able to see), something known as the bolometric correction, this star has a bolometric luminosity 1.3% of the Sun's total luminosity. A planet would need to be situated much closer to this star in order to receive a comparable amount of energy as the Earth. The region of space around a star where a planet would receive roughly the same energy as the Earth is sometimes termed the "Goldilocks Zone", or, more prosaically, the habitable zone. The extent of such a zone is not fixed and is highly specific for each planetary system.
Gliese 581 is classified as a variable star of the BY Draconis type, and has been given the variable star designation HO Librae. This is a star that exhibits variability because of the presence of star spots combined with the rotation of the star. However, the measured variability is close to the margin of error, and, if real, is most likely a long term variability. Its brightness is stable to 1%. Gliese 581 emits X-rays.
(in order from star)
|e||>1.7 ± 0.2 M⊕||0.02815 ± 0.00006||3.1490 ± 0.0002||0.00 ± 0.06||—||—|
|b||>15.8 ± 0.3 M⊕||0.04061 ± 0.00003||5.3686 ± 0.0001||0.00 ± 0.03||—||—|
|c||>5.5 ± 0.3 M⊕||0.0721 ± 0.0003||12.914 ± 0.002||0.00 ± 0.06||—||—|
|Debris disk||25 ± 12 AU–>60 AU||30° – 70°||—|
Three planets are known to orbit Gliese 581, together with a debris disc. All three of the planets are located close to the star and have near-circular orbits. In order of distance from the star, the planets are designated Gliese 581 e, Gliese 581 b and Gliese 581 c. The letters represent the discovery order, with b being the first planet to be discovered around the star (the letter d was used for a planet that is now no longer thought to be real but an artifact caused by stellar activity). The planets were all discovered with the radial velocity method which gives only lower limits on the planetary masses and no information about their radii. The minimum mass of the middle planet b is comparable to the solar system ice giants Uranus and Neptune, while the inner and outer planets have minimum masses a few times that of the Earth. All three planets orbit closer to the star than the inner edge of the habitable zone.
Gliese 581 e
Gliese 581 e is the innermost planet and with a minimum mass of 1.7 Earth masses is the least massive of the three. Discovered in 2009, it is also the most recent confirmed planet to have been discovered in this system. It takes 3.15 days to complete an orbit. Initial analyses suggested that the planet's orbit is quite elliptical but after correcting the radial velocity measurements for stellar activity, the data now indicates a circular orbit.
Gliese 581 b
Gliese 581 b is the most massive planet known to be orbiting Gliese 581 and was the first to be discovered.
Gliese 581 c
Gliese 581 c is the outermost confirmed planet orbiting Gliese 581. It was discovered in April 2007. In their 2007 paper, Udry et al. asserted that if Gliese 581 c has an Earth-type composition, it would have a radius of 1.5R⊕, which would have made it at the time "the most Earth-like of all known exoplanets". A direct measurement of the radius cannot be taken because, viewed from Earth, the planet does not transit its star. The minimum mass of the planet is 5.5 times that of Earth. The planet initially attracted attention as being potentially habitable, though this has since been discounted. The mean blackbody surface temperature has been estimated to lie between −3 °C (for a Venus-like albedo) and 40 °C (for an Earth-like albedo), however, the temperatures could be much higher (about 500 degrees Celsius) due to a runaway greenhouse effect akin to that of Venus. Some astronomers 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. Gliese 581 c completes a full orbit in just under 13 days.
On 27 November 2012, the European Space Agency announced that the Herschel space observatory had discovered a comet belt "at 25 ± 12 AU to more than 60 AU". It must have "at least 10 times" as many comets as does the Solar system. This likely rules out Saturn-mass planets beyond 0.75 AU. However another (undiscovered) planet further out, say a Neptune-mass planet at 5 AU, might be required to keep the comet belt replenished.
History of detections
The first discovery of a planet around the star was Gliese 581 b, which was discovered in August 2005 and was the fifth planet to be discovered around a red dwarf. Further observations of the star resulted in the detection of two further planets, Gliese 581 c and Gliese 581 d, with a mass of roughly 7 Earths and an orbit of 66.8 Earth days.
The next discovery was the inner planet Gliese 581 e, which was announced on 21 April 2009. This planet, at a minimum mass of 1.9 Earths, was at the time the least massive confirmed exoplanet identified around a main-sequence star.
On 29 September 2010, astronomers at Keck Observatory proposed two additional planets, Gliese 581 f and Gliese 581 g, both in nearly circular orbits based on analysis of a combination of data sets from the HIRES and HARPS instruments. Nicknamed Zarmina by one of its discoverers, the predicted mass of Gliese 581 g was between 3 to 4 Earth-masses, with an orbital period of 37 days. The orbital distance was calculated to be well within the star's habitable zone though the planet was expected to be tidally locked, with one side of the planet always facing the star.
According to a presentation by F. Pepe at IAU Symposium 276, planet g was not detected in a new analysis of data taken by the HARPS spectrograph, and both planets f and g are listed as unconfirmed at the Extrasolar Planets Encyclopaedia. Follow up studies published in September 2011, 2012 and in 2013 indicate that Gliese f and g do not exist, though the first such study was disputed by other groups.
Radio signal sent from Earth
A Message From Earth (AMFE) is a high-powered digital radio signal that was sent on 9 October 2008 toward Gliese 581 c. The signal is a digital time capsule containing 501 messages that were selected through a competition on the social networking site Bebo. The message was sent using the RT-70 radar telescope of Ukraine's National Space Agency. The signal will reach Gliese 581 in early 2029.
- Gliese 581 is classified as a BY Draconis variable in the General Catalogue of Variable Stars. This catalog gives a maximum magnitude of 10.56 and minimum of magnitude 10.58 for a relatively low 20 mmag (0.020 magnitudes) variability. For full data see data description and "The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars". Sternberg Astronomical Institute. Retrieved 2009-04-27.
- In 1994 Edward Weis concluded that Gliese 581, like half the 43 dwarf M stars he studied over a multi-year period, showed long term variability (and page 1137, Fig 1 shows Gliese 581 had magnitude 10.58 in 1982 and between 10.57 and 10.56 from 1985 to 1990). Bonfils noted in 2005 that Gliese 581 "has been classified as a variable star (HO Lib), but its variability (Weis 1994) is only marginally significant. If real it would be on a time scale of several years, with short term variability being at most ∼0.006 mag." Measurements by MOST showed short term variability of about 5 mmag (half a percent) over a period of a few weeks.
- The radial velocity method allows the determination of the minimum mass which is the product of the true mass with the sine of the orbital inclination, denoted m sin i. In general the inclination is unknown. For a given inclination, the true mass is therefore the minimum mass multiplied by 1/sin i.
- GJ 581 , SIMBAD. Retrieved 2008-08-21.
- Lopez-Morales, M.; et al. (2006). "Limits to Transits of the Neptune-mass planet orbiting Gl 581". Publications of the Astronomical Society of the Pacific 118 (849): 1506–1509. arXiv:astro-ph/0609255. Bibcode:2006PASP..118.1506L. doi:10.1086/508904. "V* HO Lib ... BY Draconis" (page 2 of pre-print submitted 9 September 2006)
- "General Catalogue of Variable Stars Query results". Sternberg Astronomical Institute. Retrieved 2009-04-27.
- Bonfils, X.; et al. (2005). "The HARPS search for southern extra-solar planets VI: A Neptune-mass planet around the nearby M dwarf Gl 581". Astronomy and Astrophysics Letters 443 (3): L15–L18. arXiv:astro-ph/0509211. Bibcode:2005A&A...443L..15B. doi:10.1051/0004-6361:200500193.
- Weis, E. W. (1994). "Long term variability in dwarf M stars". American Astronomical Society 107 (3): 1138. Bibcode:1994AJ....107.1135W. doi:10.1086/116925.
- Bonfils page L15
- Matthews, J. M.; et al. (2007). "MOST Exoplanet System Photometry". p. 80. Retrieved 2009-04-27.
- van Leeuwen, F. (2007). "HIP 74995". Hipparcos, the New Reduction. Centre de données astronomiques de Strasbourg. Retrieved 2008-08-16.
- From apparent magnitude and parallax.
- "Star: Gliese 581". Extrasolar Planets Encyclopaedia. "Mass 0.31 MSun, Age 8+3
- Bean, J. L; Benedict, G. F.; Endl, M. (2006). "Metallicities of M Dwarf Planet Hosts from Spectral Synthesis". Astrophysical Journal Letters 653 (1): L65–L68. arXiv:astro-ph/0611060. Bibcode:2006ApJ...653L..65B. doi:10.1086/510527.
- Selsis 3.4-page 1382 "lower limit of the age that, considering the associated uncertainties, could be around 7 Gyr", "preliminary estimate", "should not be above 10-11 Gyr"
- "Entry 5594-1093-1". The Hipparcos and Tycho Catalogues. Centre de données astronomiques de Strasbourg. ID I/239.
- Claire Connelly (2012-07-20). "SUPER EARTH: Scientists discover life-supporting planet 'right at Earth's front door'". Herald Sun (Melbourne, Australia). Retrieved 2014-07-11.
- "The One Hundred Nearest Star Systems". Research Consortium on Nearby Stars, Georgia State University. 1 January 2009. Retrieved 2010-06-04.
- Roman Baluev (2013). "The impact of red noise in radial velocity planet searches: Only three planets orbiting GJ581?". Monthly Notices of the Royal Astronomical Society 429 (3): 2052–2068. arXiv:1209.3154. Bibcode:2013MNRAS.429.2052B. doi:10.1093/mnras/sts476.
- Carlisle, Camille (3 July 2014). "The Planet That is No More". Sky & Telescope.com. Retrieved 4 July 2014.
- Robertson, Paul; Mahadevan, Suvrath; Endl, Michael; Roy, Arpita (3 July 2014). "Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581". Science (journal). arXiv:1407.1049. doi:10.1126/science.1253253.
- Quenqua, Douglas (8 July 2014). "Earthlike Planets May Be Merely an Illusion". New York Times. Retrieved 8 July 2014.
- "First Habitable Exoplanet? Climate Simulation Reveals New Candidate That Could Support Earth-Like Life". ScienceDaily. 16 May 2011. Retrieved 2011-05-16.
- Vogt, S. S.; et al. (2010). "The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the Habitable Zone of the Nearby M3V Star Gliese 581". arXiv:1009.5733 [astro-ph.EP].
- ESA Herschel (27 November 2012). "Do missing Jupiters mean massive comet belts?".
- Udry, S; et al. (2007). "The HARPS search for southern extra-solar planets XI: Super-Earths (5 and 8 M⊕) in a 3-planet system". Astronomy and Astrophysics Letters 469 (3): L43–L47. arXiv:0704.3841. Bibcode:2007A&A...469L..43U. doi:10.1051/0004-6361:20077612.
- Selsis, F.; et al. (2007). "Habitable planets around the star Gl 581?". Astronomy and Astrophysics 476 (3): 1373–1387. arXiv:0710.5294. Bibcode:2007A&A...476.1373S. doi:10.1051/0004-6361:20078091.
- Dragomir, D.; et al. (2012). "A Search for Transits of GJ 581e and Characterization of the Host Star Variability Using MOST Space Telescope Photometry". The Astrophysical Journal 759 (1): 2f. arXiv:1211.0577. Bibcode:2012ApJ...759....2D. doi:10.1088/0004-637X/759/1/2.
- Schmitt, J. H. M. M; Fleming, T. A; Giampapa, M. S. (1995). "The X-Ray View of the Low-Mass Stars in the Solar Neighborhood". Astrophysical Journal 450 (9): 392–400. Bibcode:1995ApJ...450..392S. doi:10.1086/176149.
- J.-F. Lestrade et al. (2012). "A DEBRIS Disk Around The Planet Hosting M-star GJ581 Spatially Resolved with Herschel". Astronomy and Astrophysics. arXiv:1211.4898. Bibcode:2012A&A...548A..86L. doi:10.1051/0004-6361/201220325.
- Mayor, M.; et al. (2009). "The HARPS search for southern extra-solar planets XVIII: An Earth-mass planet in the GJ 581 planetary system". Astronomy and Astrophysics 507: 487. arXiv:0906.2780. Bibcode:2009A&A...507..487M. doi:10.1051/0004-6361/200912172.
- von Bloh, W.; et al. (2007). "The Habitability of Super-Earths in Gliese 581". Astronomy and Astrophysics (Astronomy & Astrophysics) 476 (3): 1365–1371. arXiv:0705.3758. Bibcode:2007A&A...476.1365V. doi:10.1051/0004-6361:20077939.
- von Bloh, W.; et al. (2008). "Habitability of Super-Earths: Gliese 581c & 581d". Proceedings of the International Astronomical Union (International Astronomical Union) 3 (S249): 503–506. arXiv:0712.3219. doi:10.1017/S1743921308017031.
- "New 'super-Earth' found in space". BBC News. 25 April 2007. Retrieved 2008-10-20.
- Rincon, P.; Amos, J. (21 April 2009). "Lightest exoplanet is discovered". BBC News. Retrieved 2009-04-21.
- "The astrophysicist who discovered Zarmina describes life on "second Earth"". 1 October 2010. Retrieved 2010-10-01.
- "Keck Observatory discovers the first Goldilocks exoplanet" (Press release). Keck Observatory. 29 September 2010. Retrieved 2010-09-29.
- Ron Cowen (13 October 2010). "Existence of habitable exoplanet questioned". Science News. Retrieved 2010-10-14.
- "Notes for star Gl 581". The Extrasolar Planets Encyclopaedia. Retrieved 2010-10-11.
- T. Forveille, X. Bonfils, X.Delfosse, R. Alonso, S. Udry, F. Bouchy, M. Gillon, C. Lovis, V. Neves, M. Mayor, F. Pepe, D. Queloz, N.C. Santos, D. Segransan, J.M. Almenara, H. Deeg, M. Rabus (2011-09-12). "The HARPS search for southern extra-solar planets XXXII. Only 4 planets in the Gl 581 system". arXiv:1109.2505 [astro-ph.EP].
- investigation into the radial velocity variability of GJ 581 - On the significance of GJ 581g
- Grossman, Lisa (18 January 2011). "New Study Finds No Sign of ‘First Habitable Exoplanet'". Wired.
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