Magnetopause Boundary Processes Throughout the Solar System

Abstract:

Earth is not the only planet in the Solar System with a natural magnetic shield. Mercury, Jupiter, Saturn, Uranus, and Neptune are similarly protected from the solar wind and cosmic rays. However, like our planet, the magnetic shielding of each of these magnetized planets can break down, driving energy flow through each planetary magnetosphere. Although studies of the magnetopause boundary of Earth’s magnetosphere have shed considerable light on the processes that lead to this breakdown, the extent to which we can apply this understanding to the diverse space plasma environments surrounding other planets remains unclear. Here we review what we have learnt so far about the operation of magnetopause boundary processes at all the magnetized planets in the Solar System, and outline some of the relevant outstanding questions. We start by consolidating present understanding of terrestrial magnetopause processes, which is our reference when considering other boundaries. We focus on selected processes (magnetic reconnection, Kelvin-Helmholtz instability), compare how we expect them to operate at each planetary magnetopause, and assess whether or not this is consistent with in situ spacecraft observations. For each planetary magnetosphere we then discuss the nature of the total interaction with the solar wind, and whether this is expected to be dominant over internal drivers of magnetospheric dynamics. A combination of further spacecraft exploration and dedicated numerical modeling is required in order to address the many outstanding questions concerning this topic. Progress in this direction would have broad implications for other space plasma systems, in our solar system and beyond.