An Empirical Approach to Modeling Ion Production Rates in Titan’s Nightside Ionosphere

Wednesday, 17 December 2014
Matthew S Richard1,2, Thomas Cravens2, Calvin Wylie2, Daniel Webb2, Quentin Chediak2, Kathleen Mandt3, Jack H Waite Jr4, Abigail M Rymer5, Cesar Bertucci6 and Anne Wellbrock7, (1)Benedictine College, Physics and Astronomy, Atchison, KS, United States, (2)University of Kansas, Lawrence, KS, United States, (3)Southwest Research Institute San Antonio, San Antonio, TX, United States, (4)Southwest Research Institute San Antonio, Space Sciences and Engineering, San Antonio, TX, United States, (5)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (6)University of Buenos Aires, Buenos Aires, Argentina, (7)University College London, London, United Kingdom
Ionization of neutrals by precipitating electrons and ions is the main source of Titan’s nightside ionosphere. Electron densities generated by theoretical modes are much larger than densities measured by instruments onboard the Cassini Orbiter. This model density overabundance must result either from overproduction or from insufficient loss of ions. This presentation has two goals: (1) characterization of the role of electron impact ionization on the nightside ionosphere for different magnetospheric conditions, and (2) presentation of empirical ion production rates determined using densities measured by the Cassini Ion and Neutral Mass Spectrometer (INMS) on the nightside. The ionosphere between 1000 and 1400 km is emphasized. We adopt electron fluxes measured by the Cassini Plasma Spectrometer - Electron Spectrometer (CAPS-ELS) and the Magnetospheric Imaging Instrument (MIMI) as classified by Rymer et al. [2009]. The current work demonstrates that modeled and empirical ionization rates on the nightside are in agreement with an electron precipitation source above 1100 km. Ion production rate profiles for each of the cases outlined by Rymer et al. are constructed for various magnetic field topologies. Empirical production rate profiles are generated for deep nightside flybys of Titan. The results also suggest that at lower altitudes (below 1100 km) another source, such as ion precipitation, is probably needed.