Fossil magnetic fields due to Titan's plasma interaction revisited:The role of the electric conductivities in the ionosphere and in Titan's interior

NEUBAUER, F. M.; HOERDT, A.; WENNMACHER, A.; SIMON, S.; BERTUCCI, C.; DOUGHERTY, M. K.

Congreso; AGU Fall Meeting 2010; 2010

The concept of fossil magnetic fields has been introduced into the physics of Titan's plasma interaction a few years ago ( Neubauer et al.,J.geophys.Res.,2006) and has first been applied to Titan magnetic field data by Bertucci et al.(Science, 2008) .The concept is based on the idea that because of very low plasma velocities near Titan, magnetic flux tubes entering Titan's near plasma environment through an upstream fiducial plane at approximately XTIIS= - 3 RTitan (say) can spend up to a few hours in Titan's environment as intact structures until they reach their lowest altitude. Eventually they are flushed out of the system. We discuss an extension of this idea by allowing the flux tubes to enter the lower ionosphere, where the frozen-in -fields concept starts to break down and diffusion of magnetic fields becomes dominant due to the increasing resistivity. However, the age of a field line can still be defined by considering a discontinuity (e.g. magnetopause related) to enter Titan's environment through the fiducial plane referred to above. The age is shown to reach a relative maximum of several hours inside the ionosphere. Even larger ages of ~ ten days can be reached if a conducting ocean exists below Titan's subsurface and yet larger ones if a conducting core exists. We show that observations at low altitudes and/or in a corridor in the wake of Titan are needed for observations of these fields, which are within the reach of the Cassini flyby trajectories. However, the required special inflow conditions occur relatively rarely.