ATMOSPHERIC DYNAMICS OF THE JOVIAN LIKE PLANETS EPSILON ERIDANI b AND 55 CANCRI d

摘要

Epsilon Eridani b and 55 Cancri d are at present, the two extrasolar planets candidates with the largest orbital period and larger angular separation from its star. Their future detection depends on their albedo, and thus on cloud formation and dynamics. We present in this communication a first attempt to characterize their atmospheric circulatidn on the basis of the best observational available data and on a scale analysis for regular conditions in giant planets. The main basic unknown in this study is the planetary rotational (spin) period. We present different approaches to constraint it that suggests that the expected periods are in the range of those of Jupiter and Saturn. In such a case the usual geostrophic approach for atmospheric motions is expected, with a planetary regime dominated by zonal (East-West) jets. The most interesting case is that of Epsilon Eridani b whose high eccentricity, possible water clouds, and relatively short radiative time constant, could produce large-scale disturbances and profound changes in its dynamical regime along the seasonal cycle. No massive upper clouds are expected for 55 Cnc d, that probably is a very different gaseous planet. We discuss the range of plausible values for the spatial and temporal scales of motions.