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2013 Annual Science Report

NASA Jet Propulsion Laboratory - Titan Reporting  |  SEP 2012 – AUG 2013

Task 2.2.1: Characterization of Aerosol Nucleation & Growth on Titan

Project Summary

The scientific goal of this task is to elucidate the mechanisms and develop a quantitative understanding of particle formation and growth in the Titan atmosphere.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

This work has focused on the vapor nucleation and condensation onto pre-existing particles under conditions in various regions of Titan’s atmosphere. The rate of increase of particle mass is the sum of contributions of different vapors. For particles that are small compared to the mean-free-path of the vapor molecules, λ, the flux is described by the kinetic theory of gases; for particles large compared to λ, the continuum diffusion modeling can be applied. Over the entire range of sizes, the flux is described using the continuum model, with a correction factor that accounts for deviations from free molecular mass transport effects.

Condensation fluxes are also influenced by dipole and Coulombic interactions for particles smaller than about 10 nm radius, as illustrated for C2H6 condensation at 30 km altitude in the Titan atmosphere in Figure 1a, below. For more polar vapor molecules, deviations from simple condensation molecules can extend to much larger particle sizes, as shown for HCN in Figure 1b below.

Figure 1. Influence of dipole and interactions and particle charge on the condensation flux coefficient as a function of particle size under conditions of Titan’s atmosphere. The red dashed lines show the flux coefficients when no charge or dipole effects are present. The solid red line shows the condensation flux to electrically neutral particles. The other lines show the flux coefficients to particles carrying different numbers of elementary charges. The circles denote the point at which the charge on the particle renders it unstable, the so-called Rayleigh limit. (a) Ethane

    Richard Flagan
    Project Investigator

    Objective 3.1
    Sources of prebiotic materials and catalysts