NASA’s Kepler Space Telescope has in recent months returned a veritable treasure trove of confirmed and as-of-yet unconfirmed exoplanets. The impressive haul is estimated at a preliminary 1235 planetary candidates (!), the most interesting of which to date has proven to be the Kepler 10 and 11 planetary systems, but more fascinating finds are likely to be announced in the coming weeks and months. These results will serve to double the repository of known extra-solar planets and possibly reveal, for the first time, an Earth-like planet orbiting within the habitable zone of its star.
In the above image I have attempted to illustrate the orbital configuration of these two planetary systems, with Earth and Jupiter included for reference. Kepler 10 is a G-type star in the constellation Draco, with a mass of 0.895 solar masses, or M☉. Its single known planetary companion, Kepler 10b is the first confirmed rocky extra-solar planet, but at 8.8 g cm-3 it is significantly denser than the Earth, comparable to that of refined iron, and approximately 4.6 times more massive. It’s low semi-major axis means that it also completes an orbit of Kepler 10 in around 20 hours at an average distance of only 0.016 AU, or 2 519 230 kilometres. This proximity would result in an extremely harsh radiative environment and an average surface temperature of around 1833 °K (1560 °C), which is roughly the melting point of steel, and much to hot for any form of life as we know it. Nevertheless, the discovery of Kepler 10b has been triumphantly lauded by scientists responsible for the operation of the Kepler Space Telescope at NASA’s Ames Research Centre as the accurate detection of a planet of this size, orbiting in such close proximity to it’s parent star, is a testament to the effectiveness of the space telescope, and increases the likelihood that Kepler will return more significant findings of a similar planets.
Kepler 11 is a 8 billion year-old G-type star in the northern constellation Cygnus with a mass roughly similar to that of our Sun. Around Kepler 11 is a remarkable family of 6 closely packed planets, denoted Kepler 11b through g. This is significant as it is the first system discovered with more than 3 orbiting planets. The orbits of Kepler 11b to f would fit within that of Mercury in our Solar System, whilst Kepler 11g orbits at 0.462 AU, comparable to a distance roughly half-way between Mercury and Venus. The smaller planets (b to f) have orbital periods between 10 and 47 days, whilst Kepler 11g completes its orbit in 119 days. Despite this close orbital configuration, dynamical simulations suggest that the system would be stable, with only weak chaotic perturbations detected. Kepler 11d, e and f are thought to have atmospheres possibly consisting of hydrogen, although the volume of this envelope would be less than in the past due to atmospheric escape and stripping of H+ by high energy solar particles that make up the solar wind, especially if the planet has a weak or absent magnetic field. Planets b and c are thought to be either rich in volatile ices (primarily of water, methane or ammonia) or a hydrogen/helium mixture, or a combination of both. The surface temperatures on all of Kepler 11’s companion planets would be too great to support life, especially if any of the planets have a substantial atmosphere of any kind as the greenhouse conditions would only increase temperatures, possibly culminating in the runaway greenhouse effect experienced on Venus.
If you’re as interested in worlds beyond our Solar System as I am, then the findings of the Kepler Space Telescope are likely to provide you with much cause for excitement in the coming months as more data and discoveries are published.
The information above is derived from the paper by Lissauer et al. 2010 outlining the discovery of Kepler 11’s planetary system (draft copy). The nature paper (requires subscription) is here. More information can be found at the Ames Research Centre page here.