ИСТИНА

It is assumed that the double magnetopause is associated with the current carried by Na+ ions. Two cases are considered when sodium ions prevail outside the Hermean magnetosphere, and when they predominate inside it. We study how much excess Na+ density can be enough to create a wide magnitization magnetopause current and on which side of the magnetopause this current is located. For each case, the influence of northward and southward solar wind magnetic field is analyzed. We found that if there is an excess of Na+ ions in the magnetosheath (magnetoshere), then such a current is on the magnetospheric (magnetosheath) side of the magnetopause. If Na+ ions prevail outside the magnetosphere, this current is directed from dawn to dusk independently of the north-south IMF component. When sodium ions prevail in the magnetosphere, the sodium ions current is directed to the dusk for the southward IMF and to the dawn for the northward IMF. To explain the “double magnetopause” the excess of sodium ions in the magnetosheath should be 1-2 cm**(-3). In the case when sodium ions prevail in the magnetosphere, their excess should be ~4 cm**(-3) for the northward IMF and ~15 cm**(-3) for the southward IMF to create a sodium current out of the magnetopause for the average Bz values in the magnetosheath. Such a predicted structure was not observed, probably because MESSENGER did not intersect the magnetopause along the equatorial plane during a sufficient time on its next trajectories. Another reason could be that the chosen boundary values for Bz were too rough. Perhaps a future BepiColombo mission will be able to answer these questions.