Electrical properties of ions in the atmosphere of Titan

Abstract

The Permittivity, Wave and Altimetry (PWA) package on the Huygens probe measured atmospheric electrical activity during its 14 January 2005 descent into Titan's atmosphere. Electrical mobilities of positive ions have been estimated using a combination of predictions of mass from the available chemical models, and the atmospheric properties measured by Huygens. Disc-shaped relaxation probes were used on the PWA to measure air conductivity. In this paper we present the extension of an inversion technique, originally developed to extract ion mobility information from cylindrical relaxation probe data, to the disc geometry. The maximum distance from which typical positive ion species are influenced by the electric field of the relaxation probe in Titan's troposphere and stratosphere is calculated, and found to be ∼10μm. However, loss of positive ion data from the Huygens probe prevents the application of the new technique. Based on the Huygens data, evidence for, and possible characteristics of, a global electric circuit on Titan are also discussed.