A multinational team of astronomers using data from ESO’s HARPS instrument has discovered a new exoplanet in the habitable zone around the nearby dwarf star HD 40307.
This is an artist’s impression of HD 40307g as a water-rich world (PHL / UPR Arecibo)
HD 40307 is a K-type star slightly smaller than our Sun located in the constellation Pictor about 42 light-years away.
HD 40307 was previously known to host three hot super-Earths. Now, the team led by Dr Mikko Tuomi of the University of Hertfordshire’s Center for Astrophysics Research and Dr Guillem Anglada-Escudé of the University of Göttingen has used novel statistical software to detect three additional ones, including one potentially habitable dubbed HD 40307g.
“With Dr Guillem Anglada-Escudé’s new velocity reduction package, we are able to extract more information from the HARPS spectra, and thus make a more precise measurement. This coupled with the innovative Bayesian orbital searching algorithm, primarily written by Dr Mikko Tuomi, allows us to search deeper into the data and to find smaller Earth-sized planets around the nearest stars. This, of course, increases our chances of finding more in that orbital sweet spot that we call the habitable zone – the zone where it is not too cold, nor too hot for liquid water to exist,” said Dr Paul Butler of Carnegie Institute of Washington, senior author of a paper accepted for publication in the journal Astronomy & Astrophysics (arXiv.org version).
HD 40307g is a so-called Super-Earth about 7 times more massive than Earth with a size between 1.9 and 2.5 Earth radii depending on composition, either rocky or water-rich, respectively.
Currently the astronomers don’t know the type and composition of the HD 40307g’s atmosphere, but they predict that average temperatures might be near 48 °F (9 °C) assuming a similar scaled-up terrestrial atmosphere.
This image shows the nearby star HD 40307 (Centre de Données astronomiques de Strasbourg / SIMBAD)
“HD 40307g receives on average about 67% of the light Earth receives from the Sun. It might also experience strong seasonal surface temperature shifts between 1.4° to 126°F (-17° to 52°C) due to its orbital eccentricity. Nevertheless, these extremes are tolerable by most complex life, as we know it.”
HD 40307g is also the closest planet orbiting a Sun-like star, and probably not tidally locked, unlike most of the other listed planets around red dwarf stars.
“The detection of HD 40307g is remarkable example of the use a Bayesian Monte Carlo Markov Chain technique and HARPS-TERRA tools. However, this kind of detection needs independent confirmation by other methods. Meanwhile, this discovery is considered a potentially habitable exoplanet candidate and an interesting target for future observations.”
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Bibliographic information: Mikko Tuomi et al. 2012. Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307. Accepted for publication in the Astronomy and Astrophysics; arXiv: 1211.1617
