Modeling the Enceladus plume--plasma interaction

TL;DR

This study models the interaction between Saturn's plasma and Enceladus' plumes, revealing charge exchange as dominant and highlighting the influence of hot electrons and neutral source rates on plasma chemistry.

Contribution

It introduces a physical chemistry model tailored for water-group reactions to simulate plasma-plume interactions around Enceladus.

Findings

Charge exchange dominates local chemistry.

H3O+ is the main water-group ion downstream.

Pickup ion amount depends on neutral source and hot electrons.

Abstract

We investigate the chemical interaction between Saturn's corotating plasma and Enceladus' volcanic plumes. We evolve plasma as it passes through a prescribed H2O plume using a physical chemistry model adapted for water-group reactions. The flow field is assumed to be that of a plasma around an electrically-conducting obstacle centered on Enceladus and aligned with Saturn's magnetic field, consistent with Cassini magnetometer data. We explore the effects on the physical chemistry due to: (1) a small population of hot electrons; (2) a plasma flow decelerated in response to the pickup of fresh ions; (3) the source rate of neutral H2O. The model confirms that charge exchange dominates the local chemistry and that H3O+ dominates the water-group composition downstream of the Enceladus plumes. We also find that the amount of fresh pickup ions depends heavily on both the neutral source strength and on the presence of a persistent population of hot electrons.