Whistler-mode waves in the tail of Mercury’s magnetosphere: A numerical study^⋆

¹ LPP, CNRS/Sorbonne Université/Université Paris-Saclay/Observatoire de Paris/Ecole Polytechnique Institut Polytechnique de Paris, Palaiseau, France
e-mail: giulio.ballerini@lpp.polytechnique.fr
² Dipartimento di Fisica “E. Fermi”, Università di Pisa, Pisa, Italy
³ Laboratoire Lagrange, Observatoire de la Côte d’Azur, Université Côte d’Azur, CNRS, Nice, France
⁴ LPC2E, CNRS, Université d’Orléans, CNES, Orléans, France

Received: 23 December 2023
Accepted: 24 April 2024

Abstract

Context. Mercury presents a highly dynamic, small magnetosphere in which magnetic reconnection plays a fundamental role.

Aim. We aim to model the global characteristics of magnetic reconnection in the Hermean environment. In particular, we focus on waves observed during the third BepiColombo flyby.

Method. In this work, we used two fully kinetic three-dimensional (3D) simulations carried out with the iPIC3D code, which models the interaction of the solar wind with the Hermean magnetosphere. For the simulations, we used southward solar wind conditions that allow for a maximum magnetic coupling between the solar wind and the planet.

Results. Our simulations show that a significant wave activity, triggered by magnetic reconnection, develops near the diffusion region in the magnetotail and propagates at large scales in the night-side magnetosphere. We see an increase in electron temperature close to the diffusion region and we specifically observe narrowband whistler waves developing near the reconnection region. These waves propagate nearly parallel to the magnetic field at frequency f ∼ 0.5f_ce. In addition to the electromagnetic component, these waves also exhibit an electrostatic one. Furthermore, we observe a strong electron temperature anisotropy, suggesting it plays a role as the source of these waves.