Statistical Study of the Energetic Proton Environment at Titan's Orbit From the Cassini Spacecraft

L H Regoli,J G Luhmann,E Roussos,X Jia,N Sergis,K Dialynas,G H Jones,I J Rae,A J Coates,A Azari,N Krupp,D Román

doi:10.1029/2018ja025442

Abstract

AbstractA statistical study of the energetic proton environment at Titan's orbit as captured by the MIMI/LEMMS and MIMI/CHEMS instruments is performed. The data analyzed cover all the dedicated flybys of Titan by Cassini as well as the orbit crossings that happen far from the moon. The energetic environment is found to be highly variable on timescales comparable to that of the duration of a flyby. Analysis of H+ ion fluxes reveals a weak asymmetry in Saturn local time with the highest fluxes occurring in the premidnight sector of the magnetosphere. A correlation between the energetic ion fluxes and the location of Cassini in the magnetosphere with respect to the center of the current sheet can be observed. Finally, an empirical model of proton spectra for energies above 20 keV is derived based on fits to Kappa distribution functions. This model can be used to better understand the interaction of Titan with the magnetosphere and the energy deposition by energetic particles below the main ionospheric peak.

Highlights

The interaction of Titan with its surrounding environment is arguably one of the most complex interactions of its kind in the Solar System
As visible from both spectra shown, the Kappa distribution function provides a good description of the plasma population with energies above 20 keV, whereas below that threshold, the distribution seems to be closer to an inverse power law, which is most likely representative of a second Kappa distribution that peaks at lower energies [Dialynas et al, 2009]
In order to simplify the environment description, we have looked for correlation between the three spectrum coefficients, so that we can reduce the free parameters of the spectrum from three to one.In terms of interdependence of the parameters, the plots from

Summary

Key Points:

Derivation of empirical model of ion spectra based on Kappa distribution function. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

Introduction

Findings

Discussion and Conclusions