Transport and distribution of sodium ions in Mercury’s magnetosphere:
results from multi-fluid MHD simulations
Abstract
In the absence of a substantial ionosphere, solar wind protons dominate
the plasma content within Mercury’s magnetosphere. However, Mercury is
surrounded by a tenuous neutral exosphere composed primarily of sodium
atoms, which can be continuously ionized. The production of sodium ions
is concentrated on the dayside, and these ions can subsequently be
transported to the magnetotail and flanks. MESSENGER spacecraft
observations revealed dawn-dusk asymmetric distributions of sodium ions
$Na^+$. In this study, we present a two-fluid MHD model that is
coupled with an empirical sodium exosphere profile to investigate the
circulation, distribution, and influence of $Na^+$ on global
magnetospheric convection. Our findings indicate that the observed
dawn-dusk asymmetries in $Na^+$ distributions are driven by the
separation of $H^+$ and $Na^+$ flows, with the Hall-driven
global convection preferentially transporting $Na^+$ ions to the
morning sector.