Study of the April 20, 2007 CME-Comet Interaction Event with an MHD Model

TL;DR

This paper uses MHD modeling to analyze how a coronal mass ejection caused a tail disconnection in comet 2P/Encke, revealing the magnetic field rotations responsible for the event.

Contribution

It presents the first MHD simulation demonstrating CME-induced tail disconnection in a comet, linking magnetic field rotations to the disconnection process.

Findings

CME caused a tail disconnection event on comet 2P/Encke.

The event involved a 180° sudden and 90° gradual IMF rotation.

Simulation matches observed interaction dynamics.

Abstract

This study examines the tail disconnection event on April 20, 2007 on comet 2P/Encke, caused by a coronal mass ejection (CME) at a heliocentric distance of 0.34 AU. During their interaction, both the CME and the comet are visible with high temporal and spatial resolution by the STEREO-A spacecraft. Previously, only current sheets or shocks have been accepted as possible reasons for comet tail disconnections, so it is puzzling that the CME caused this event. The MHD simulation presented in this work reproduces the interaction process and demonstrates how the CME triggered a tail disconnection in the April 20 event. It is found that the CME disturbs the comet with a combination of a $180^\circ$ sudden rotation of the interplanetary magnetic field (IMF), followed by a $90^\circ$ gradual rotation. Such an interpretation applies our understanding of solar wind-comet interactions to determine the \textit{in situ} IMF orientation of the CME encountering Encke.