Parametric study of the solar wind interaction with the Hermean magnetosphere for a weak interplanetary magnetic field

TL;DR

This study uses simulations to analyze how the solar wind interacts with Mercury's magnetosphere under weak interplanetary magnetic field conditions, revealing that the magnetosphere remains relatively stable and larger than Mercury itself across various solar wind parameters.

Contribution

It provides a comprehensive parametric simulation of Mercury's magnetosphere under weak interplanetary magnetic field conditions, incorporating realistic solar wind ranges and detailed magnetic field modeling.

Findings

Magnetopause remains outside Mercury's surface across all conditions.

Weak interplanetary magnetic field results in a stable, larger magnetosphere.

Higher dynamic pressure compresses the magnetosphere and alters magnetic topology.

Abstract

The aim of this study is to simulate the interaction of the solar wind with the Hermean magnetosphere when the interplanetary magnetic field is weak, performing a parametric study for all the range of hydrodynamic values of the solar wind predicted on Mercury for the ENLIL + GONG WSA + Cone SWRC model: density from $12$ to $180$ cm$^{-3}$, velocity from $200$ to $500$ km/s and temperatures from $2 \cdot 10^4$ to $18 \cdot 10^4$ K, and compare the results with a real MESSENGER orbit as reference case. We use the code PLUTO in spherical coordinates and an asymmetric multipolar expansion for the Hermean magnetic field. The study shows for all simulations a stand off distance larger than the Mercury radius and the presence of close magnetic field lines on the day side of the planet, so the dynamic pressure of the solar wind is not high enough to push the magnetopause on the planet surface if the interplanetary magnetic field is weak. The simulations with large dynamic pressure lead to a large compression of the Hermean magnetic field modifying its topology in the inner magnetosphere as well as the plasma flows from the magnetosheath towards the planet surface.