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HD 40307 b

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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 HARPS apparatus, in June 2008; it is the smallest of three "Super-Earths", planets somewhat larger than the Earth, discovered orbiting the star. 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.

Discovery

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.[1] HD 40307 b was one of three "Super-Earth" exoplanets found orbiting the star HD 40307.[2]

Orbit and Mass

While HD 40307 b is considered a "Super-Earth" planet, it is the lightest planet discovered in the system, with at least 4.2 times the mass of the Earth.[3] The planet orbits the star HD 40307 every 4.3 Earth days,[2] corresponding of its location at approximately 0.047 astronomical units from the star.[4] 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.[3]

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.[3]

Characteristics

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.[2] However, as the planet was discovered via radial velocity measurements rather than by transit or by imaging, more specific characteristics, such as its radius, composition, and surface temperature cannot be determined.[5]

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.[6]

See also

References

  1. ^ "Trio of 'super-Earths' discovered". BBC news. 2008-06-16. Retrieved 2008-06-16. {{cite news}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ a b c Bryner, Jeanna (June 16, 2008). "3 super-Earths found around one star". MSNBC. Retrieved 2008-10-30. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
  3. ^ a b c M. Mayor, S. Udry, C. Lovis, F. Pepe, D. Queloz, W. Benz, J.-L. Bertaux, F. Bouchy, C. Mordasini, D. Segransan. "The HARPS search for southern extra-solar planets. XIII. A planetary system with 3 Super-Earths (4.2, 6.9, & 9.2 Earth masses)".  Submitted to Astronomy & Astrophysics. Bibcode:2008arXiv0806.4587M. Retrieved 2008-06-30. {{cite journal}}: Italic or bold markup not allowed in: |journal= (help)CS1 maint: multiple names: authors list (link)
  4. ^ "Notes for Planet HD 40307 b". Extrasolar Planets Encyclopaedia. Paris Observatory. 2008. Retrieved 2008-10-30.
  5. ^ 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 0521868084.
  6. ^ Barnes, J., O'Brien, D. (2002). "Stability of Satellites around Close-in Extrasolar Giant Planets". The Astrophysical Journal. 575 (2): 1087–1093. doi:10.1086/341477.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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