Cassini in situ observations of long-duration magnetic reconnection in Saturn's magnetotail

TL;DR

This paper reports the first in situ observation of a prolonged magnetic reconnection event in Saturn's magnetotail by Cassini, highlighting its role in plasma loss and its implications for rapidly rotating magnetospheres.

Contribution

It provides the first direct evidence of a long-duration diffusion region in Saturn's magnetotail, demonstrating sustained reconnection activity.

Findings

Reconnection observed over 19 hours in Saturn's magnetotail.

Reconnection acts as a significant plasma loss mechanism.

Prolonged reconnection challenges the view of it being purely transient.

Abstract

Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn's magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn. This counters the view of reconnection as a transient method of internal plasma loss at Saturn. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies.