Titan's variable ionosphere during the T118-T119 Cassini flybys

TL;DR

This study compares Titan's ionospheric electron densities during two similar Cassini flybys, revealing significant differences likely due to local plasma production variability and ionization processes.

Contribution

It provides the first detailed comparison of Titan's ionospheric conditions during nearly identical flybys, highlighting unexpected density variations and potential ionization mechanisms.

Findings

Electron density differed by a factor of 5 between T118 and T119.

Two localized electron peaks observed during T118.

Record low electron densities reported during T118.

Abstract

A significant difference in Titan's ionospheric electron density is observed between the T118 and T119 Cassini nightside flybys. These flybys had similar geometry, occurred at the same Saturn local time and while Titan was exposed to similar EUV and ambient magnetic field conditions. Despite these similarities, the RPWS/LP measured density differed a factor of 5 between the passes. This difference was present, and similar, both inbound and outbound. Two distinct electron peaks were present during T118, at 1150 km and 1200 km, suggesting very localised plasma production. During T118, from 1200-1350 km and below 1100 km, the lowest electron density ever observed in Titan's ionosphere are reported. We suggest that an exceptionally low rate of particle impact ionisation in combination with increased dynamics in the ionosphere could be the cause. This is, however, not verified by measurements and the measured ambient high energy particle pressure is in fact higher during T118 than during T119.