NEWS & EVENTS

Both Earth and Mercury possess internal magnetic fields with similar structures. However, Earth’s magnetic moment is much larger than Mercury’s, and Mercury has a thin atmosphere and lacks a stable ionosphere. The characteristics of their external solar wind also differ; Mercury’s dynamic pressure and interplanetary magnetic field (IMF) strength are much stronger than Earth’s, resulting in higher magnetosphere compression, a smaller magnetosphere volume and a shorter subsolar magnetopause distance. Furthermore, compared to Earth, Mercury’s highly conductive core occupies a larger volume within its magnetosphere. This dayside compression induces currents on the core surface, altering the magnetic field strength just inside the magnetopause. When the balance between magnetospheric magnetic pressure and solar wind dynamic pressure is disrupted, the magnetopause distance changes. The degree of compression can be defined as the ratio of the magnetic field strength just inside the magnetopause to the strength of a pure dipolar magnetic field at the same location. The results show that this ratio on Earth and Mercury exhibits completely opposite trends with the magnetopause distance. In addition, the north-south orientation of the IMF also affects the magnetopause distance. On Earth, when the IMF points southward, the magnetopause distance decreases due to magnetic reconnection at the magnetopause; when the IMF points northward, the change is minimal. However, on Mercury, only when the IMF strength is very high, a significant difference in the magnetopause distance corresponding to southward and northward IMF.