HD 40307 b
|Extrasolar planet||List of extrasolar planets|
|Right ascension||(α)||05h 54m 04.2409s|
|Declination||(δ)||−60° 01′ 24.498″|
|Distance||41.8 ± 0.3 ly
(12.83 ± 0.09 pc)
|Radius||(r)||0.716 ± 0.010 R☉|
|Temperature||(T)||4977 ± 59 K|
|Metallicity||[Fe/H]||−0.31 ± 0.03|
|Age||1.2 (≥ 0.2) Gyr|
|Semimajor axis||(a)||0.04680.04450.0492 AU|
|Orbital period||(P)||4.3115 ± 0.0006 d|
|Minimum mass||(m sin i)||4.03.34.8 M⊕|
|Discovery date||June 16, 2008|
|Discoverer(s)||Mayor et al.|
|Discovery method||radial velocity, using HARPS|
|Discovery site||La Silla Observatory, Chile|
HD 40307 b is an extrasolar planet orbiting the star HD 40307, located 42 light-years away in the direction of the southern constellation Pictor. The planet was discovered by the radial velocity method, using the European Southern Obervatory's HARPS apparatus, in June 2008. It is the second smallest of the planets orbiting the star, after HD 40307 e. The planet is of interest as this star has relatively low metallicity, supporting a hypothesis that different metallicities in protostars determine what kind of planets they will form.
As with many other extrasolar planets, HD 40307 b was discovered by measuring variations in the radial velocity of the star it orbits. These measurements were made by the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph at the Chile-based La Silla Observatory. The discovery was announced at the astrophysics conference that took place in Nantes, France between 16 and 18 June 2008. HD 40307 b was one of three found here at the time.
Orbit and Mass
HD 40307 b is the second lightest planet discovered in the system, with at least 4.2 times the mass of the Earth. The planet orbits the star HD 40307 every 4.3 Earth days, corresponding of its location at approximately 0.047 astronomical units from the star. The eccentricity of the planet's orbit was found to not differ significantly from zero, meaning that there is insufficient data to distinguish the orbit from an entirely circular one.
The star around which HD 40307 b orbits has a low metallicity, compared to other planet-bearing stars. This supports a hypothesis concerning the possibility that the metallicity of stars during their births may determine whether a protostar's accretion disk forms gas giants or terrestrial planets.
With a lower mass bound of 4.2 times the mass of the Earth, HD 40307 b is presumably too small to be a jovian planet. This concept was challenged in a 2009 study, which stated that if HD 40307 b is terrestrial, the planet would be highly unstable and would be affected by tidal heating in a manner greater than Io, a volcanic satellite of planet Jupiter; restrictions that seem to bind terrestrial planets, however, do not restrict ice giant planets like Neptune or Uranus.
HD 40307 b, c, and d are presumed to have migrated into their present orbits.
- "HD 40307". SIMBAD. Centre de Données astronomiques de Strasbourg. 2008. Retrieved 18 June 2008.
- HD 40307, database entry, Geneva-Copenhagen Survey of Solar neighbourhood, J. Holmberg et al., 2007, CDS database V/117A, accessed November 19, 2008; described in The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ~14 000 F and G dwarfs, B. Nordström, M. Mayor, J. Andersen, J. Holmberg, F. Pont, B. R. Jørgensen, E. H. Olsen, S. Udry, and N. Mowlavi, Astronomy and Astrophysics 418 (May 2004), pp. 989–1019, Bibcode: 2004A&A...418..989N, doi:10.1051/0004-6361:20035959.
- HD 40307, entry, CDS database J/A+A/450/735; described in Effective temperature scale and bolometric corrections from 2MASS photometry, E. Masana, C. Jordi, and I. Ribas, Astronomy and Astrophysics 450, #2 (May 2006), pp. 735–746. Bibcode: 2006A&A...450..735M. doi:10.1051/0004-6361:20054021.
- M. Mayor, S. Udry, C. Lovis, F. Pepe, D. Queloz, W. Benz, J.-L. Bertaux, F. Bouchy, C. Mordasini, D. Segransan (2009). "The HARPS search for southern extra-solar planets. XIII. A planetary system with 3 Super-Earths (4.2, 6.9, & 9.2 Earth masses)". Astronomy and Astrophysics 493 (2): 639–644. arXiv:0806.4587. Bibcode:2009A&A...493..639M. doi:10.1051/0004-6361:200810451.
- Tuomi, Anglada-Escude, Gerlach, Jones, Reiners, Rivera, Vogt, Butler, Mikko, Guillem, Enrico, Hugh R. R., Ansgar, Eugenio J., Steven S., R. Paul (2012). "Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307". arXiv:1211.1617v1 [astro-ph].
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- Bryner, Jeanna (June 16, 2008). "3 super-Earths found around one star". MSNBC. Retrieved 2008-10-30.
- "Notes for Planet HD 40307 b". Extrasolar Planets Encyclopaedia. Paris Observatory. 2008. Retrieved 2008-10-30.
- Barnes, R., Jackson, B., Raymond, S., West, A., Greenberg, R. (2009). "The HD 40307 Planetary System: Super-Earths or Mini-Neptunes?". The Astrophysical Journal 695 (2): 1006. arXiv:0901.1698. Bibcode:2009ApJ...695.1006B. doi:10.1088/0004-637X/695/2/1006.
- Characterizing Extrasolar Planets, Timothy M. Brown, chapter 3, Extrasolar Planets: XVI Canary Islands Winter School of Astrophysics, edited by Hans Deeg, Juan Antonio Belmonte, and Antonio Aparicio, Cambridge, UK: Cambridge University Press, 2007, ISBN 0-521-86808-4.
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