This week’s crop
The year 2007 is off to a reasonably good start. Three more planets were announced by the Geneva Planet Search team at a conference in Chile, bringing the total planet crop for ’07 up to seven.
The rate of planet discovery, however, has definitely leveled off. For the past four years, the detection rate has remained fixed at 26 new planets per year. The low-hanging fruit — the 51 Pegs, the 47 Ursae Majorii, the Upsilon Andromedaes — have all been harvested from the bright nearby stars, and increasingly extractive methods are being brought to bear. Transits are starting to contribute significantly to the overall detection rate. Radial velocity is pushing to planets with progressively lower masses. Surveys such as N2K are rapidly screening metal-rich stars that have high a-priori probabilities for harboring readily detectable planets. The neccessity of finding more planets is driving up the average metallicity of the known planet-bearing stars:
The three new planets, HD 100777b, HD 190647b, and HD 221287b are quite ordinary as far as extrasolar planets go. They all have masses somewhat greater than Jupiter, and they all take more than a year to orbit their parent stars. Their discovery seems not to have registered with the news media:
HD 100777 b, however, is actually deserving of some attention. Its orbital period of 383.7 days places it squarely in the habitable zone of its parent star. The eccentricity, e=0.36, is fairly high, and likely leads to interesting seasonal effects in the atmosphere of the planet.
HD 100777 b lies a regime where we expect to see white water clouds forming in the visible atmosphere. The planet is probably very reflective in the optical region of the spectrum (quite unlike the hot Jupiters, which are likely cloud-free, and which are known to absorb almost all of the starlight that strikes them). Convection of interior heat to the surface of HD 100777b is almost certainly driving collossal thunderstorms, and the atmospheric disturbances created by the thunderstorms likely feed giant vortical storms similar to Jupiter’s great red spot.
It’s also possible that the atmosphere is much clearer in regions where air wrung dry by rainfall is downwelling. This phenomenon occurs on Jupiter, where highly transparent patches occur over several percent of the Jovian surface:
The Galileo entry probe went right into one of these regions, and sampled very dry air. On HD 100777, the regions of high atmospheric transparency will probably preferentially absorb red and green light (as a result of Rayleigh scattering of incoming photons). The surface, then, in the vicinity of a downwelling region may look something like this: