;In 1985, sodium was first detected in Mercury’s exosphere (Potter & Morgan, 1985). Afterwards, the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) spacecraft made in-situ measurements about the Mercury’s exosphere and showed two-peak structures of sodium exosphere during the flybys. Both ground-based and in-situ observations had shown us different profiles of Mercury’s sodium exosphere and it is found to be highly variable. This is thought to be resulted from the variability of solar wind conditions and the orientation of interplanetary magnetic field (IMF), given the interaction between solar wind and Mercury’s magnetosphere and sputtering.
We simulate the Mercury’s sodium exosphere with the solar wind proton precipitation data generated from the Amitis simulation code, which is a three-dimensional time-dependent hybrid model of plasma (Fatemi et al., 2017; Fatemi, Poppe & Barabash, 2020). We focus on the datasets generated based on Helios data to trace the realistic solar wind conditions at Mercury and how the Mercury’s magnetosphere and sodium exosphere change with the environment. Our results show the morphology of sodium during a high-speed stream (HSS) event covering pre-HSS, HSS and post-HSS phases. It may explain the north-south asymmetry on Mercury. The relative flux in northern and southern cusps is correlated with Bx. However, the total production rate is still controlled by Bz.
In the future, the numerical algorithm and methodology generated will be applied to a series of solar wind events including interplanetary coronal mass ejections (ICMEs) with a view to participate in the upcoming BepiColombo observations at Mercury beginning in 2025.
