Local Magnetic Field Control of Energetic Electron Fluxes in the Mercury Magnetosphere

Abstract:

Energetic electrons are known to be a result of substorm processes that form quasi-permanent structures in Mercury’s magnetosphere. These energized electrons can become trapped on magnetic field lines and have been observed by MESSENGER instruments to drift on closed field lines in the Hermean magnetosphere. We have used the high time resolution electron measurements from the Gamma-Ray Spectrometers (GRS) previously onboard MESSENGER to study the confinement (or lack thereof) of energetic electrons in the outer parts of the dayside magnetosphere of Mercury. We used 20Hz magnetometer data to identify magnetopause boundary locations as the MESSENGER spacecraft traversed the dayside region. We saw many cases of strong particle confinement where intense electron fluxes were observed just inside the magnetopause boundary, that then significantly decreased upon reaching the local magnetosheath. Conversely, we documented cases showing lack of confinement where magnetospheric electrons appeared to be leaking across the dayside magnetopause. We are seeking to understand, in a statistical sense, how frequently the magnetopause represents a strong barrier to particle escape and also when leakage from the magnetosphere can occur.