On 7 September 2011 a paper appeared on the arXiv astrophysics database at Cornell University Library by a team lead by Sarah Ballard of the Harvard Smithsonian Centre for Astrophysics describing the discovery of a new planetary system, Kepler-19. Kepler-19 is 650 light years fro Earth in the constellation of Lyra and was formerly identified as KOI-84 (Kepler Object of Interest 84). If is a fairly sun-like star, with a slightly lower mass and radius as our sun, it is also slightly cooler and dimmer, and only about half as old.
The Kepler Space Telescope was able to detect a regular dimming of this star, which seemed to imply the transit of a planet with a radius 2.2 times that of the Earth, every 9.29 days. However this dimming was not completely regular; it sped up and slowed down by 5 minutes on a 316 day cycle. This implied the presence of another body, either an unseen additional planet or an undetected star, possibly directly behind Kepler-19.
Ballard et al. constructed a computer model of the Kepler-19 system, using the initial Kepler observations and follow-up observations from the Spitzer Space Telescope, which they used to model a number of different scenarios.
They came to the conclusion that the dimming was caused by a planet, dubbed Kepler-19b, passing in front of the star. This planet, as initially suspected has a radius of 2.2 times that of the earth, though its composition and mass are impossible to determine. This planet orbits its star every 9.29 days, at a distance of slightly less than 0.1 AU (1 AU = the distance between the Earth and the sun so Kepler-19b obits its star at slightly less than 10% of the distance between the Earth and the sun).
This Orbit is perturbed by the presence of a second planet, named Kepler-19c and dubbed the 'Invisible Planet' or the 'Phantom Planet' in the media. This planet would have a maximum size of six times that of Jupiter and a maximum orbital time of 160 days, though this is considered unlikely, the most probably scenario being a planet Earth-sized or smaller, orbiting the star at most once every 30 days. It is thought not to orbit in the same plane as Kepler-19b, as it does not appear to transverse the surface of Kepler-19 as seen from the Earth; this is different to our solar system, where all planets orbit in essentially the same plane of axis.
Model of the Kepler-19 system, showing the orbit of Kepler-19b (black), and possible orbits for Kepler-19c (coloured).
See also PSR J1719-1438b. The Diamond Planet, New Exoplanet: TrES-5 and Exoplanets on Sciency Thoughts YouTube.
