Titan's Magnetic Field

Self-consistent modeling of induced magnetic field in Titan’s atmosphere accounting for the generation of Schumann resonance

Author:

Béghin

Abstract:

This model is worked out in the frame of physical mechanisms proposed in previous studies accounting for the generation and the observation of an atypical Schumann Resonance (SR) during the descent of the Huygens Probe in the Titan’s atmosphere on 14 January 2005. While Titan is staying inside the subsonic co-rotating magnetosphere of Saturn, a secondary magnetic field carrying an Extremely Low Frequency (ELF) modulation is shown to be generated through ion-acoustic instabilities of the Pedersen current sheets induced at the interface region between the impacting magnetospheric plasma and Titan’s ionosphere. The stronger induced magnetic field components are focused within field-aligned arcs-like structures hanging down the current sheets, with minimum amplitude of about 0.3 nT throughout the ramside hemisphere from the ionopause down to the Moon surface, including the icy crust and its interface with a conductive water ocean. The deep penetration of the modulated magnetic field in the atmosphere is thought to be allowed thanks to the force balance between the average temporal variations of thermal and magnetic pressures within the field-aligned arcs. However, there is a first cause of diffusion of the ELF magnetic components, probably due to feeding one, or eventually several SR eigenmodes. A second leakage source is ascribed to a system of eddy-Foucault currents assumed to be induced through the buried water ocean. The amplitude spectrum distribution of the induced ELF magnetic field components inside the SR cavity is found fully consistent with the measurements of the Huygens wave-field strength. Waiting for expected future in-situ exploration of Titan’s lower atmosphere and the surface, the Huygens data are the only experimental means available to date for constraining the proposed model.