The global precipitation of magnetospheric electrons into Titan’s upper atmosphere

Abstract:

We investigate the global precipitation of magnetospheric electrons into Titan’s atmosphere by coupling a two-stream electron transport model to a three-dimensional model of Titan's plasma interaction. First we run several simulations assuming an ‘ideal’ geometry for the magnetospheric interaction, we find that most of the energy from auroral electrons is deposited on the magnetospheric wake-side of Titan's thermosphere and the least amount of energy is deposited on the magnetospheric ram-side. The globally averaged peak energy deposition rates vary between 10 and 13 eV cm^-3 s^-1 near 1200 to 1300 km altitude, depending on the electron distributions in Saturn’s magnetosphere. We find that shorter electron bounce times in Saturn’s magnetosphere and magnetic mirroring above Titan's atmosphere can both strongly reduce the flux of magnetospheric electrons entering Titan’s atmosphere. The total power deposited in Titan's thermosphere by magnetospheric electrons is at least an order of magnitude smaller than the power deposited by solar EUV during the 2007 to 2009 solar minimum. This indicates that magnetospheric electrons are a less significant source of energy for Titan’s upper atmosphere than solar EUV and is comparable to that of magnetospheric ions. Finally, we move beyond idealized simulation geometries and attempt to realistically simulate magnetospheric electron precipitation during a specific flyby. The results of these simulations are directly compared to data from Cassini’s electron spectrometer.