Precipitating Condensation Clouds in Substellar Atmospheres

Abstract

We present a method to calculate vertical proÐles of particle size distributions in condensation clouds of giant planets and brown dwarfs. The method assumes a balance between turbulent di †usion and sedimentation in horizontally uniform cloud decks. Calculations for the Jovian ammonia cloud are compared with results from previous methods. An adjustable parameter describing the efficiency of sedimentation allows the new model to span the range of predictions made by previous models. Calculations for the Jovian ammonia cloud are consistent with observations. Example calculations are provided for water, silicate, and iron clouds on brown dwarfs and on a cool extrasolar giant planet. We Ðnd that precipitating cloud decks naturally account for the characteristic trends seen in the spectra of Land T-type ultracool dwarfs.

Young Jupiters are faint: new models of the early evolution of giant planets

“…This conclusion is also supported by observations of cloudy L-dwarfs, where models that assume the opacity of grains as given by the ISM distribution, without sedimentation, are a very poor match to the data (Chabrier et al, 2000) because they greatly overestimate the dust opacity. However, models that allow for grains to grow and sediment (see Ackerman & Marley, 2001) match spectroscopic data very well Burgasser et al, 2002;Marley et al, 2004). In short, the timescale argument against the core accretion-gas capture scenario is much weaker than had been previously thought, when opacities more appropriate to protoplanetary atmosphere conditions are used.…”

Spectroscopy of planetary atmospheres in our Galaxy

“…Candidate species for condensation at the hot temperatures are silicates, iron (Lunine et al 1989;Ackerman and Marley 2001), or more exotic species present in brown dwarfs, such as TiO, VO, metal hydrides (Lodders 2003;Sharp and Burrows 2007). Other proposed hazes are soots (Zahnle et al 2010;Mousis et al 2011) or sulphur compounds (Zahnle et al 2009).…”

Exoplanet atmospheres: A theoretical outlook

“…Most theory papers focused on irradiated hot Jupiters, emphasizing spectral features and 1D temperature/pressure profiles resulting from the intense heating by the host star (Seager & Sasselov 1998;Marley et al 1999;Sudarsky, Burrows, & Pinto 2000;Barman, Hauschildt & Allard 2001. Cloud modeling (Ackerman & Marley 2001;Cooper et al 2003) and atmospheric 200 S. Seager circulation (Showman & Guillot 2002;Cho et al 2003) were also expected to be important. Calculation of exoplanet illumination phase curves, polarization curves (Seager, Whitney, & Sasselov 2000), and especially transmission spectra Brown 2001;Hubbard et al 2001) set the stage for observed spectroscopy during transit.…”