This week NASA announced the discovery of a planetary system by the Kepler Space Telescope. This has been named Kepler-18; it was formerly identified as KIC 8644288 (where KIC is Kepler Input Catalogue, a catalogue of all the stars in the Kepler field of vision). The system has a single star, which is similar to our sun; it has 97% of the sun's mass, and a volume of 110% that of the sun, it's surface temperature is slightly cooler.
The system has three (known) planets, named Kepler-19b (closest to the star), Kepler-18c and Kepler-18d. Kepler-19b is a rocky planet, 3.4 times the size of the Earth, Kepler-18c and Kepler-18d are larger, Neptune-like worlds, six and seven times the size of the earth respectively. Both these planets are less massive than Neptune, but have slightly larger volumes, suggesting they have larger gaseous envelopes and smaller rocky cores.
All three planets orbit within the orbital radius or Mercury (it is likely that there are other planets further out and harder to detect). Kepler-18b has a year of only 3.5 of our days. Kepler-18c and Kepler-18d are locked in an orbital resonance with orbits of roughly 7.6 and 14.9 (Earth) days respectively. The orbital resonance is caused by an exchange of orbital momentum between the planets as they pass each other; this also means the orbits are not quite constant. At any given time one of these planets will be running ahead of its average orbit and the other behind. Each time they pass they exchange energy, so that the one that was running slow speeds up, and the one that was running fast slows down.
A diagrammatic representation of the Kepler-18 system comparing the sizes of the star, planets and planetary orbits to those of our solar system.
The discovery was announced this week at a joint meeting of the American Astronomical Society's Division of Planetary Science and the European Planetary Science Conference and published in a paper on the on-line arXiv archive at Cornell University Library, by a team led by William Cochran of the McDonald Observatory at the University of Texas, and is scheduled for publication in the Astrophysical Journal Suplement Series.
Following initial identification of the system with the Kepler Space Telescope the team made follow up observations with the Shane and Nickel Telescopes at the Lick Observatory, the United Kingdom Infrared Telescope, the Wisconsin-Indiana-Yale National Optical Astronomy Observatory, the Hale Telescope at the Palomar Observatory, the Keck 1 HIRES spectrometer and the Spitzer Space Telescope. This enabled the scientists not only to build up a more complete picture of the Kepler-18 system, but also to confirm that the dimming of the star due to planets passing in front of it (how the system was detected) did indeed occur at a checkable electromagnetic wavelengths, considered a good way to determine that this has been caused by a planet and not some other phenomenon.
See also Just how big is Iota Draconis b? Kepler-16 (AB)b; the first planet discovered in a binary star system and Exoplanets on Sciency Thoughts YouTube.
