Large-scale solar wind flow around Saturn's nonaxisymmetric magnetosphere

TL;DR

This study uses 3D MHD simulations and Cassini data to analyze how Saturn's nonaxisymmetric magnetosphere influences large-scale solar wind flow and magnetosheath dynamics, revealing polar flow enhancement and force-driven plasma acceleration.

Contribution

It provides the first detailed analysis of Saturn's nonaxisymmetric magnetosheath flow and the dominant forces involved, improving understanding of solar wind-magnetosphere interactions.

Findings

Saturn's polar-flattened magnetosphere channels ~20% more flow over the poles.

Plasma pressure gradient is the main driver of magnetosheath plasma acceleration.

Nonaxisymmetry significantly affects downstream magnetopause conditions.

Abstract

The interaction between the solar wind and a magnetosphere is fundamental to the dynamics of a planetary system. Here, we address fundamental questions on the large-scale magnetosheath flow around Saturn using a 3D magnetohydrodynamic (MHD) simulation. We find Saturn's polar-flattened magnetosphere to channel ~20% more flow over the poles than around the flanks at the terminator. Further, we decompose the MHD forces responsible for accelerating the magnetosheath plasma to find the plasma pressure gradient as the dominant driver. This is by virtue of a high-beta magnetosheath, and in turn, the high-MA bow shock. Together with long-term magnetosheath data by the Cassini spacecraft, we present evidence of how nonaxisymmetry substantially alters the conditions further downstream at the magnetopause, crucial for understanding solar wind-magnetosphere interactions such as reconnection and shear flow-driven instabilities. We anticipate our results to provide a more accurate insight into the global conditions upstream of Saturn and the outer planets.