2012 Annual Science Report
NASA Jet Propulsion Laboratory - Titan Reporting | SEP 2011 – AUG 2012
Task 2.2.1 Characterization of Aerosol Nucleation and Growth
One goal has been to elucidate the mechanisms and develop a quantitative understanding of particle formation and growth in the Titan atmosphere. Work has focused on elucidating the role of molecular interactions in growth of Titan aerosol particles using numerical simulations.
Co-Investigator Richard Flagan and graduate student Xerxes Lopez-Yglesias have continued to study aerosol growth and formation in the Titan atmosphere. Models that have been developed to date consider the physical processes involved, with limited attention to the molecular interactions that have been found to be crucial to understanding aerosols in the atmosphere of Earth. To address this issue, a rigorous model has been developed and used to calculate the flux for particle radii from 0.2 nm to 10 μm using several different vapors: HCN, C6H2, CH4, H2O and C6N2 and particle compositions: HCN, C6H2, CH4, and a “bare” tholin-like aerosol. It is found that at the smallest sizes under consideration, 0.3 nm radius, the model yields an enhancement of an order of magnitude or more to a neutral cluster or particle. For polar species the enhancement can cover the entire size range under consideration. Moreover, the addition of charge on the particle increases uptake by another order of magnitude at the smallest particle sizes. Progressively higher charge states further increase the flux, but they may be unimportant on physical grounds. Their frequency will depend not only upon the atmospheric charge distribution, but also on the state of the particle itself. In this case, a liquid particle’s size and surface tension is used to estimate the maximum number of charges it can support. Polar species and C6N2 are able to support higher charge states at smaller sizes due to their high surface tension. The results of these calculations suggest that initial growth of clusters in the Titan atmosphere may be substantially faster than predicted using models that assume non-interacting molecules.