Wednesday, 18 July 2012

Two planets found orbiting the Sun-like star HD 207832

HD 207832 is a Sun-like G-type Dwarf Star 177 light years from Earth in the constellation of Piscis Austrinus. It is slightly smaller than the Sun, with a mass 94% of the Sun's and an effective surface temperature of 5710 K (compared to 5778 K for the Sun).

In a paper published on the online arXiv database at Cornell University Library on 11 July 2012, and accepted for publication in the Astrophysical Journal, a team of scientists led by Nader Haghighipour of the Institute for Astronomy and NASA Astrobiology Institute at the University of Hawaii-Manoa describe the discovery of two planets orbiting HD 207832, during a study with the High Resolution Echelle Spectrometer at the Keck Observatory. The planets were found using the radial velocity technique, which detects planets by the effect their mass (and therefore gravity) has on the motion of the star.

The first of these new planets, HD 207832b, has a mass 56% of that of Jupiter (or 187% of that of Saturn), and orbits the star every 162 days at a distance of 0.57 AU (i.e. 57% of the distance at which the Earth orbits the Sun). 

The second of these planets, HD 207832c, has a mass 73% of that of Jupiter, and orbits the star every 1156 days (3.2  Earth years) at a distance of 2.112 AU.

Diagrammatic representation of the HD 207832 System, showing the orbits of the two planets, and the orbits of the inner four planets of our own Solar System for comparison. The Visual Exoplanet Catalogue.

Since HD 207832 is an essentially Sun-like star, we would expect the distribution of any planets around it to follow the same pattern as in our own Solar System. Our current models of planetary system formation suggest that planets as large as HD 207832b and HD 207832c should not form close into a Sun-like star, but rather further out within the system. This suggests that the planets of the HD 207832 System have migrated inwards for some reason, though the cause of this is not apparent.

Haghighipour et al. tried to construct a computer model of the HD 207832 System, to determine if any other planets might be present in the inner system. They found that there could potentially be a planet as large as the Earth inside the orbit of HD 207832b; although there is no actual evidence to suggest such a planet exists.

See also Two Hot Jupiters found in the Beehive ClusterTwo new more planets discovered in the Gliese 676 systemThe peculiar planets of Kepler-36HATSouth network discovers its first planet and Exoplanets on Sciency Thoughts YouTube.

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