Cassini observations of Saturn's southern polar cusp

TL;DR

This paper reports on Cassini's observations of Saturn's southern polar cusp, revealing plasma entry via reconnection, variable conditions, and oscillating cusp morphology linked to Saturn's magnetospheric periodicities.

Contribution

It provides the first detailed analysis of Saturn's polar cusp using Cassini data, highlighting plasma entry mechanisms and dynamic cusp behavior.

Findings

Evidence of magnetosheath plasma entry via reconnection

Cusp entry occurs under various solar wind conditions

Double cusp morphology linked to magnetospheric oscillations

Abstract

The magnetospheric cusps are important sites of the coupling of a magnetosphere with the solar wind. The combination of both ground- and space-based observations at Earth have enabled considerable progress to be made in understanding the terrestrial cusp and its role in the coupling of the magnetosphere to the solar wind via the polar magnetosphere. Voyager 2 fully explored Neptune's cusp in 1989 but highly inclined orbits of the Cassini spacecraft at Saturn present the most recent opportunity to repeatedly studying the polar magnetosphere of a rapidly rotating planet. In this paper we discuss observations made by Cassini during two passes through Saturn's southern polar magnetosphere. Our main findings are that i) Cassini directly encounters the southern polar cusp with evidence for the entry of magnetosheath plasma into the cusp via magnetopause reconnection, ii) magnetopause reconnection and entry of plasma into the cusp can occur over a range of solar wind conditions, and iii) double cusp morphologies are consistent with the position of the cusp oscillating in phase with Saturn's global magnetospheric periodicities.