Studying the Microphysics of Particles in Outer Solar System Atmospheres with PlanetCARMA

ERIKA BARTH, Southwest Research Institute

     Abstract Number: 425
     Working Group: Planetary Aerosols: From Earth to Exoplanets

Abstract
The Community Aerosol and Radiation Model for Atmospheres (CARMA) tracks the vertical transport, coagulation, and nucleation/growth/evaporation of particles in a column of atmosphere and solves for their radiative effects. PlanetCARMA applies the core CARMA physics to a number of planetary atmospheres, including Titan, Pluto, Jupiter, Saturn, Uranus, and Neptune. This allows for a comparison/contrasting of aerosol types and the important processes controlling aerosol properties in these planetary atmospheres. Titan’s haze layer includes photochemically created carbon-hydrogen-nitrogen particles coated with various hydrocarbon and nitrile ices. At the poles, the larger vapor abundances and seasonal cooling allow for the formation of optically thick clouds of HCN (hydrogen cyanide), C6H6 (benzene), and C2H6 (ethane). Methane (CH4) is abundant enough to form clouds in the troposphere. Raindrops from these clouds may provide a mechanism of transporting the stratospheric ices to Titan’s surface. Pluto’s atmosphere includes some of the hydrocarbon and nitrile volatiles as Titan’s, but at lower pressures and colder temperatures. Still, modeling has shown that nucleation of these species can occur onto the haze particles seen from the New Horizons flyby. However, the cold temperatures may inhibit further growth by condensation, particularly for HCN. In the giant planet stratospheres, impact delivered water vapor may homogeneously nucleate to form water ice particles that can then serve as condensation nuclei for hydrocarbons deeper in their atmospheres.