HD 40307 g

HD 40307 g is an exoplanet orbiting in the habitable zone of HD 40307. It is 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 Observatory's HARPS apparatus[1][4][5] by a team of astronomers led by Mikko Tuomi at the University of Hertfordshire and Guillem Anglada-Escude of the University of Göttingen, Germany.[6]

HD 40307 g
Approximate size comparison of HD 40307 g with Earth.
Discovery
Discovered byMikko Tuomi et al.
Discovery siteLa Silla Observatory, Chile
Discovery dateOctober 28, 2012
radial velocity, using HARPS
Orbital characteristics
0.600 AU (89,800,000 km)
Eccentricity0.22[1]
197.8 ± 9.0[1] d
Semi-amplitude0.95 ± 0.3[1]
StarHD 40307
Physical characteristics
Mean radius
2.39[2] R⊕
Mass7.09[2] M⊕
Temperature277.6[3]
    NASA Exoplanet Exploration Program "travel poster" for HD 40307 g

    Composition theories

    The codiscoverer Hugh Jones, of the University of Hertfordshire in England, surmised: "The longer orbit of the new planet means that its climate and atmosphere may be just right to support life."[4]

    However, another astronomer, Rory Barnes of the University of Washington, had already studied the orbits of the planets b, c, and d. First, Barnes had presumed b to take on too much tidal heating for it to be terrestrial, instead predicting a "mini-Neptune". He thought that b, c, and d had all migrated inward,[7] which extrapolates to e and f as well, which are further out, but not by much. It is possible that HD 40307 g has also migrated into where it is now. The discoverers of HD 40307 g did not try to refute Barnes, on the nature of b and its extrapolation to the other planets. The composition of g is unsettled.[8] Lead author Mikko Tuomi, also of the University of Hertfordshire, stated "If I had to guess, I would say 50-50 ... But the truth at the moment is that we simply do not know whether the planet is a large Earth or a small, warm Neptune without a solid surface."[4]

    See also

    References
    1. 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". Astronomy. 549: A48. arXiv:1211.1617. Bibcode:2013A&A...549A..48T. doi:10.1051/0004-6361/201220268.
    2. PHL's Exoplanets Catalog - Planetary Habitability Laboratory @ UPR Arecibo
    3. "HEC: Data of Potential Habitable Worlds". University of Puerto Rico at Arecibo (Planetary Habitability Laboratory). November 12, 2012.
    4. Wall, Mike (November 7, 2012). "'Super-Earth' Alien Planet May Be Habitable for Life". Space.com. Retrieved November 8, 2012.
    5. Tate, Karl (November 7, 2012). "Super-Earth Planet: Potentially Habitable Alien World Explained (Infographic)". Space.com. Retrieved November 8, 2012.
    6. Murrin, Marc (November 8, 2012). "Astronomers discover a potentially habitable Super-Earth HD 40307g (Infographic)". tech-stew.com. Archived from the original on November 10, 2012. Retrieved November 8, 2012.
    7. 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): 1006–1011. arXiv:0901.1698. Bibcode:2009ApJ...695.1006B. doi:10.1088/0004-637X/695/2/1006.
    8. University of Toronto astronomer Ray Jayawardhana, author of Strange New Worlds: The Search for Alien Planets and Life beyond Our Solar System. Paraphrased in Dan Vergano (November 7, 2012). "Habitable zone 'Super Earth' candidate planet detected". Cite journal requires |journal= (help)

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