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HD 40307 b

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HD 40307 b
Exoplanet List of exoplanets
Parent star
Star HD 40307
Constellation Pictor
Right ascension (α) 05h 54m 04.2409s[1]
Declination (δ) −60° 01′ 24.498″[1]
Apparent magnitude (mV) 7.17[1]
Distance 41.8 ± 0.3 ly
(12.83 ± 0.09[1] pc)
Spectral type K2.5V[1]
Mass (m) 0.75+0.03
[2] M
Radius (r) 0.716 ± 0.010[3] R
Temperature (T) 4977 ± 59[4] K
Metallicity [Fe/H] −0.31 ± 0.03[4]
Age 1.2 (≥ 0.2)[2] Gyr
Orbital elements
Semi-major axis (a) 0.0468+0.0492
[5] AU
Eccentricity (e) 0.20+0.25
Orbital period (P) 4.3115 ± 0.0006[4] d
Semi-amplitude (K) 1.94+2.25
[5] m/s
Physical characteristics
Minimum mass (m sin i) 4.0+4.8
[5] M
Discovery information
Discovery date June 16, 2008
Discoverer(s) Mayor et al.
Discovery method radial velocity, using HARPS
Discovery site La Silla Observatory, Chile
Discovery status Confirmed[5]
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

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.[5] 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.[6] HD 40307 b was one of three found here at the time.[7]

Orbit and mass[edit]

HD 40307 b is the second lightest planet discovered in the system, with at least 4.2 times the mass of the Earth.[5] The planet orbits the star HD 40307 every 4.3 Earth days,[7] corresponding of its location at approximately 0.047 astronomical units from the star.[8] 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.[4]

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.[4]

The Arizonan astronomer Rory Barnes's mathematical model, in 2009, found that "Planet b’s orbit must be more than 15◦ from face-on";[9] however it cannot be much more.[5]


HD 40307 b. Artist impression

HD 40307 b does not transit[5] and has not been imaged. More specific characteristics, such as its radius, composition, and possible surface temperature cannot be determined.[10]

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.[7] 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.[9]

As strong tidal forces often result in the destruction of larger natural satellites in planets orbiting close to a star, it is unlikely that HD 40307 b hosts any satellites.[11]

HD 40307 b, c, and d are presumed to have migrated into their present orbits.[9]

See also[edit]


  1. ^ a b c d e "HD 40307". SIMBAD. Centre de Données astronomiques de Strasbourg. 2008. Retrieved 18 June 2008. 
  2. ^ a b 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, Bibcode2004A&A...418..989N, doi:10.1051/0004-6361:20035959.
  3. ^ 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. Bibcode2006A&A...450..735M. doi:10.1051/0004-6361:20054021.
  4. ^ a b c d e M. Mayor; S. Udry; C. Lovis; F. Pepe; D. Queloz; W. Benz; et al. (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. Bibcode:2009A&A...493..639M. arXiv:0806.4587Freely accessible. doi:10.1051/0004-6361:200810451. 
  5. ^ a b c d e f g h i Tuomi, Mikko; Anglada-Escude, Guillem; Gerlach, Enrico; Jones, Hugh R. R.; Reiners, Ansgar; Rivera, Eugenio J.; Vogt, Steven S.; Butler, R. Paul (2012). "Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307". arXiv:1211.1617v1Freely accessible [astro-ph]. 
  6. ^ Mayor; et al. (2008-06-16). "Trio of 'super-Earths' discovered". BBC news. Retrieved 2008-06-16. 
  7. ^ a b c Bryner, Jeanna (June 16, 2008). "3 super-Earths found around one star". MSNBC. Retrieved 2008-10-30. 
  8. ^ "Notes for Planet HD 40307 b". Extrasolar Planets Encyclopaedia. Paris Observatory. 2008. Retrieved 2008-10-30. 
  9. ^ a b c 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. Bibcode:2009ApJ...695.1006B. arXiv:0901.1698Freely accessible. doi:10.1088/0004-637X/695/2/1006. 
  10. ^ 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.
  11. ^ Barnes, J.; O'Brien, D. (2002). "Stability of Satellites around Close-in Extrasolar Giant Planets". The Astrophysical Journal. 575 (2): 1087–1093. Bibcode:2002ApJ...575.1087B. arXiv:astro-ph/0205035Freely accessible. doi:10.1086/341477. 

External links[edit]

Coordinates: Sky map 05h 54m 04.2409s, −60° 01′ 24.498″