Monday, 17 March 2014

The Kepler 210 planetary system.


Since it began its survey of the section of the sky dubbed the Kepler Deep Field in 2009, the Kepler Space Telescope has discovered 2321 probable planets around 1790 stars, and it is thought that the vast majority of these probable planets will turn out to be true planets. The star given the designation KOI 676 (Kepler Object of Interest 676) was identified as a probable planet-host in 2011. It is a K-type Orange Dwarf Star, with 63%of the Sun’s mass, and an effective temperature of 4300K (compared to 5778K for the Sun), and is thought to be about 350 million years old.

In a paper published on the online arXiv database at Cornell University Library on 13 March 2014, and accepted for publication in the journal Astronomy & Astrophysics, Panagiotis Ioannidis and Jürgen Schmitt of the Hamburger Sternwarte at Universität Hamburg, Chrysa Avdellidou of the Centre for Astrophysics and Planetary Science at the School of Physical Sciences at The University of Kent, Canterbury, Carolina von Essen, also of the Hamburger Sternwarte at Universität Hamburg, and Eric Algol of the Department of Astronomy at the University of Washington, describe the discovery of a planetary system about KOI 676.

With the conformation of planets the system is renamed Kepler 210 (i.e. the 210th confirmed planetary system in the Kepler study), and the Star becomes Kepler 210A (when naming objects in other stellar systems stars are given upper case letters and planets lower class letters). Two planets, calculated to be roughly Neptune-sized, were detected making transits of the star on a regular basis, these are named Kepler 210b, which orbits the star once every 2.45 days, and Kepler 210c, which orbits the star every 7.97 days.

These two planets appear to have somewhat eccentric orbits (i.e. they have highly elliptical orbits and get notably closer and further away from the star during each circuit about it), which proved difficult to model based upon the available data about the mass and orbits of the star and planets. Ionnidis et al. tried a variety of models in order to try to explain this, and concluded that the most likely explanation was the presence of a third planet, with a mass of between 30% and 60% that of Jupiter, orbiting the star every 63 days, the gravity of which would perturb the other bodies in the way observed.

This theoretical body is given the designation KOI 676.03, retaining the system’s provisional designation due to its  theoretical, rather than confirmed, status.

The suggested configuration of the Kepler 210 system. The innermost planet is Kepler 210a, the outermost KOI 676.03. The arrow points towards Earth. Scale bars are in AU (Astronomical Units); 1 AU is the average distance between the Earth and the Sun.


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