A Response of the Mercury's Magnetopause to the Interplanetary Magnetic Field

The internal dipole field and the magnetic field induced by the metal inner core are the main sources of the Mercurys magnetic fields. The magnetic pressure inside the magnetosphere and the dynamic pressure of the solar wind reach a balance at the magnetopause to form a magnetospheric boundary. Magnetic reconnection caused by southward interplanetary magnetic field (IMF) can erode the magnetopause, resulting in a decrease in the subsolar standoff distance, while this distance remains relatively unchanged for northward IMF. Using observations from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) satellite, we identified 324 magnetopause crossings near the subsolar point and obtained the magnetic field just inside the magnetopause and their corresponding solar wind conditions for each crossing. Unlike the Earth's responses, the subsolar standoff distance of the Mercury's magnetopause is independent of the polarities of the IMF. With an examination in the magnetic field just inside the magnetopause, we find that the power law exponents derived from the relationships between the magnetic field just inside the magnetopause and the subsolar distance for the northward and southward IMFs show only a slight difference. In this presentation, we will discuss possible mechanisms that cause the relatively constant magnetopause locations and the magnetic field just inside the magnetopause in terms of the polarities of IMF from aspects of magnetic reconnection and the high-conducting inner core of the Mercury.