HD 40307 g
Exoplanet candidate in the constellation of Pictor
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HD 40307 g is an exoplanet candidate suspected to be 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]
Approximate size comparison of HD 40307 g with Earth. | |
| Discovery | |
|---|---|
| Discovered by | Mikko Tuomi et al. |
| Discovery site | La Silla Observatory, Chile |
| Discovery date | October 28, 2012 |
| radial velocity, using HARPS | |
| Orbital characteristics | |
| 0.600 AU (89,800,000 km) | |
| Eccentricity | 0.22[1] |
| 197.8 ± 9.0[1] d | |
| Semi-amplitude | 0.95 ± 0.3[1] |
| Star | HD 40307 |
| Physical characteristics | |
| 2.39[2] R🜨 | |
| Mass | 7.09[2] M🜨 |
| Temperature | 277.6[3] |
The existence of the planet was disputed in 2015, as more Doppler spectroscopy data has become available.[7]
Planetary characteristics
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,[8] 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.[9] 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]