Abstract

We investigate the details of Titan's interaction with Saturn's magnetosphere, which includes formation and location of an ionopause, mass loading via ion pickup, and the effects of finite gyroradii. We present new interpretations of the Voyager 1 plasma instrument measurements not addressed by Hartle et al. (1982). Pickup ions H+ and H2+ dominate in the outermost region with respect to Titan's “ionopause,” followed by CH4+ at intermediate distances and N2+ just outside the “ionopause.” Mass loading and slowing down of the ambient plasma is observed to increase as the pickup ion mass increases with decreasing radial distance from Titan's ionosphere. H2 and CH4 are molecules not originally included in the exosphere of Titan by Hartle and coworkers, and the pickup ions of H2+ and CH4+ are a new feature of our model calculations and should be present in Titan's exospheric region. Therefore Titan could be an important source of carbon to Saturn's magnetosphere. Finite gyroradius effects are identified in the plasma interaction with Titan's atmosphere, which results in an asymmetric removal of ambient plasma from Titan's exosphere region. The finite gyroradius effects also show that the observed hot keV ion component of the ambient plasma is a heavy ion such as N+/O+. A minimum “ionopause” altitude of 4800 km is estimated by a new approach using mass loading.