Electron-Scale Dynamics of the Diffusion Region during Symmetric Magnetic Reconnection in Space

TL;DR

This study presents in-situ measurements of electron-scale dynamics during symmetric magnetic reconnection in Earth's magnetotail, revealing super-Alfvenic electron jets, electron meandering, and a laminar reconnection process despite turbulence.

Contribution

First in-situ observation of electron-scale processes in symmetric magnetic reconnection, providing detailed measurements of electron jets, meandering, and diffusion region dimensions.

Findings

Electron jets reach 20,000 km/s, super-Alfvenic speeds.

Electron meandering and acceleration produce crescent structures.

Reconnection rate estimated at 0.1-0.2, with largely laminar electron dynamics.

Abstract

Magnetic reconnection is an energy conversion process important in many astrophysical contexts including the Earth's magnetosphere, where the process can be investigated in-situ. Here we present the first encounter of a reconnection site by NASA's Magnetospheric Multiscale (MMS) spacecraft in the magnetotail, where reconnection involves symmetric inflow conditions. The unprecedented electron-scale plasma measurements revealed (1) super-Alfvenic electron jets reaching 20,000 km/s, (2) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures, (3) spatial dimensions of the electron diffusion region implying a reconnection rate of 0.1-0.2. The well-structured multiple layers of electron populations indicate that, despite the presence of turbulence near the reconnection site, the key electron dynamics appears to be largely laminar.