Magnetospheric O+ Precipitation and Sputtering at Titan

Titan's dense and extended atmosphere is not protected by an internally generated magnetic field, exposing it to charged particle precipitation in Saturn's outer magnetosphere or, on occasion, the solar wind. Quantifying magnetospheric particle precipitation is important because the influx of ions affects the chemistry and structure of the atmosphere and the resulting sputtering contributes to atmospheric loss. We investigate magnetospheric O⁺ precipitation using a three-dimensional Monte Carlo model of ion precipitation coupled to a multifluid model of Titan's interaction with Saturn's magnetosphere. We determine that the sputtering rate of nitrogen is on the order of 10²⁴ atoms s^-1, similar to the findings of pre-Cassini studies that assumed that primary ion in Saturn's magnetosphere near Titan was N₂⁺_. We will investigate how the sputtering rate varies with fluctuations in Titan's upstream plasma environment, and atmospheric and exospheric density. We will also determine the uncertainty associated with assumptions in the model. Previous models trying to explain the density of oxygen-bearing molecules in Titan's atmosphere assumed the number of O⁺ entering the atmosphere is on the order of 10⁶ cm^-2 s^-1 referred to the surface. Our results suggested theses fluxes are about an order of magnitude too large, depending on Titan's plasma environment. Again, we will investigate how the influx varies for a range of upstream parameters.