Non-Thermal Processing of Titan's Atmosphere and Analysis of Tholin Analogs
Carl Sagan coined the term "tholins" to describe the condensed products he recovered by irradiating nitrogen rich atmospheres that are analogs to that Saturn's moon Titan. These dark red-brown materials are nitrogen rich polymers and polyaromatics. These substances are believed to be the major source of haze in Titan's atmosphere.
Experiments with organic mixtures and water ices can also be carried out on thin films of hydrocarbons which will be used to simulate nonpolar ices and aerosol surfaces such as those present within Titan's atmosphere. This atmosphere is rich with organic molecules including ethane, benzene, methane and various nitriles. The rapid polymerization of organic molecules due to irradiation is well known and indeed forms the basis of many polymer processing strategies. Although Titans haze is optically thick, modeling studies are beginning to show that thermal gas phase chemistry alone is not enough to account for the observed atmospheric composition and solar EUV, cosmic ray, and magnetospheric particle radiations are important[Wilson and Atreya]. Simulations of tholins made from plasma discharges strongly resemble the spectra observed at Titan[Sagan et al., 1992a; Sagan et al., 1992b; Thompson et al., 1994]. While some of these laboratory analogs were produces in the gas or liquid phase, there is evidence that solid state, water ice[Khare et al., 1993], or aerosol droplet surface reactions[Wilson and Atreya] are important.
The tholin formation process. Credit: Southwest Research Institute.
Members on Project
Gregory Grieves
Funding
NASA