Excess of Sodium Ions Density Required to Create a Wide Current at the Hermean Magnetopause

Abstract

In this paper we consider an unusual structure, twice observed at the magnetopause of Mercury, and called the “Double Magnetopause”. Presumably, it is associated with a current sheet created by Na+ ions. Two alternative scenarios are considered. The first one: Sodium ions prevail outside the Hermean magnetosphere. The second: Sodium ions predominate inside the magnetosphere of Mercury. These ions have been observed inside and outside the magnetosphere. We analyze what Na+ density excess can be sufficient for creation of a wide diamagnetic magnetopause current and on which side of the magnetopause this current is located. For each scenario, two directions of the north-south (Z) component of the solar wind magnetic field are considered.