Ion Composition in Titan's Exosphere via the Cassini Plasma Spectrometer

Woodson, Adam, Engineering Physics - School of Engineering and Applied Science, University of Virginia
Johnson, Robert, Department of Materials Science and Engineering, University of Virginia

A primary goal of the Cassini mission has been to measure atmospheric loss at Saturn's largest moon, Titan. Multiple processes such as sputtering and electromagnetic pickup of ionized neutrals can erode atmospheres over time. Titan is particularly interesting because unlike satellites of similar size and mass in comparably hostile environments, such as Io, Europa and Ganymede at Jupiter, it has managed to retain a column density nearly 10 times that of Earth and an atmospheric-mass to solid ratio comparable to Venus. However, based on some predicted loss rates Titan should have shed a significant portion of its present atmosphere over the lifetime of the solar system [Johnson, 2009]. Prior to the Cassini mission, therefore, Titan's atmosphere was believed to be the primary source of ambient nitrogen in Saturn's magnetosphere. As it turns out, evidence for that contribution has proven elusive and, instead, Enceladus appears to be the primary source of both water and nitrogen [Smith et al. 2007, 2008]. Here we study the composition of ions in Titan's exosphere in order to understand the loss processes occurring and better explain the atmosphere's resilience in the context of Saturn's erosive magnetospheric plasma.
My research has focused on calibration of Cassini's Ion Mass Spectrometer (IMS) and analysis of data collected by IMS near Titan. This research has culminated in 1) a numerical method for extracting ion compositions from IMS measurements, 2) an analysis of the ion composition sampled by IMS during the T40 Titan encounter and a comparison of that anlaysis with numerical models of Titan's magnetospheric plasma interaction, and 3) the design and partial implementation of an experiment to measure the number statistics of ion-induced electron emission from thin carbon foils as it pertains to time-of-flight mass spectrometers like IMS.

PHD (Doctor of Philosophy)
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