Photodetachment and Test-Particle Simulation Constraints on Negative Ions in Solar System Plasmas

TL;DR

This paper investigates negative ions in solar system plasmas, focusing on photodetachment processes, to better understand their abundance, behavior, and potential for future space missions, especially in outer solar system environments.

Contribution

It combines experimental and theoretical methods to calculate photodetachment rates and models negative ion trajectories, providing new insights into their prevalence and stability in diverse solar system regions.

Findings

Negative ions can form stable populations at greater heliocentric distances.

Photodetachment rates vary with ion type and solar photon spectrum.

Predictions suggest increased negative ion presence in outer solar system environments.

Abstract

Negative ions have been detected in abundance in recent years by spacecraft across the solar system. These detections were, however, made by instruments not designed for this purpose and, as such, significant uncertainties remain regarding the prevalence of these unexpected plasma components. In this article, the phenomenon of photodetachment is examined and experimentally and theoretically derived cross-sections are used to calculate photodetachment rates for a range of atomic and molecular negative ions subjected to the solar photon spectrum. These rates are applied to negative ions outflowing from Europa, Enceladus, Titan, Dione and Rhea and their trajectories are traced to constrain source production rates and the extent to which negative ions are able to pervade the surrounding space environments. Predictions are also made for further negative ion populations in the outer solar system with Triton used as an illustrative example. This study demonstrates how, at increased heliocentric distances, negative ions can form stable ambient plasma populations and can be exploited by future missions to the outer solar system.