Cloud Formation in Extra-solar Giant Planets
J.I. Lunine, W.B. Hubbard (LPL, The University of Arizona), A. Burrows, C. Sharp, D. Sudarsky (Steward Observatory, The University of Arizona), M. Marley (Dept. of Astronomy, New Mexico State University), T. Guillot (Dept. of Meteorology, University of Reading, U.K.), D. Saumon (Dept. of Physics and Astronomy, Vanderbilt University), R. Freedman (Sterling Software, NASA Ames Research Center)
Our group has constructed a new and comprehensive suite of non-grey models of
extra-solar giant planets and brown dwarfs, with effective temperatures from
Jupiter's up to 1300 K, to aid observers in both the search and
characterization of such objects. This paper describes the conditions under
which grain (cloud) formation occurs in the atmospheres of such objects, as
well as the composition and physical properties of the condensate, as a
function of effective temperature and surface gravity. The onset of
condensation is determined by the saturation pressure of the condensable
and the temperature pressure-profiles we construct for the atmospheres. We
use simple grain growth timescales following on the earlier work of Lunine
et al. (Ap.J. 338, 314, 1989) to predict mean particle or droplet
size. Water cloud formation occurs in the radiatively-relevant region of the
atmosphere from effective temperatures of 200 K up through 400 K. Magnesium
silicate and iron clouds occur in the discernible atmosphere above effective
temperatures of about 1600 K for Jovian-class surface gravities. Other, minor,
cloud-forming species may affect the radiative balance to a lesser extent at
intermediate effective temperatures. The most difficult issue to quantify is
the areal uniformity, or lack thereof, of such clouds, with the Galileo probe
results on Jupiter an important lesson in this regard. In the abstract by
Marley et al. the effects of clouds on the spectra, and the potential for
diagnosing cloud properties, are studied.