Hall Effect in the coma of 67P/Churyumov-Gerasimenko

TL;DR

This paper uses Hall magnetohydrodynamics simulations to show that the Hall effect significantly influences the magnetic field topology and reconnection processes in the inner coma of comet 67P, explaining recent Rosetta observations.

Contribution

It demonstrates the importance of the Hall effect in modeling cometary plasma environments, revealing complex magnetic structures and reconnection phenomena.

Findings

Hall effect causes complex magnetic topology in the inner coma.

Magnetic reconnection occurs on the dayside due to Hall physics.

Weak magnetic field regions outside the diamagnetic cavity are explained.

Abstract

Magnetohydrodynamics simulations have been carried out in studying the solar wind and cometary plasma interactions for decades. Various plasma boundaries have been simulated and compared well with observations for comet 1P/Halley. The Rosetta mission, which studies comet 67P/Churyumov-Gerasimenko, challenges our understanding of the solar wind and comet interactions. The Rosetta Plasma Consortium observed regions of very weak magnetic field outside the predicted diamagnetic cavity. In this paper, we simulate the inner coma with the Hall magnetohydrodynamics equations and show that the Hall effect is important in the inner coma environment. The magnetic field topology becomes complex and magnetic reconnection occurs on the dayside when the Hall effect is taken into account. The magnetic reconnection on the dayside can generate weak magnetic filed regions outside the global diamagnetic cavity, which may explain the Rosetta Plasma Consortium observations. We conclude that the substantial change in the inner coma environment is due to the fact that the ion inertial length (or gyro radius) is not much smaller than the size of the diamagnetic cavity.