Particle populations in Mercury's magnetosphere

Observations by Mariner 10 during its first and third flybys showed that Me rcury possesses an intrinsic magnetic field resulting in a small magnetosph ere that can keep the solar wind from directly interacting with the planet' s surface under usual conditions. Since Mercury occupies a large fraction o f its magnetosphere, regions of trapped charged particles in the inner magn etosphere, the plasmasphere and the energetic radiation belts, would all be absent. During the first flyby, energetic particle bursts were detected an d interpreted as hermean substroms analogous to the terrestrial magnetosphe re. Moreover, during this flyby, ULF waves and field-aligned currents were detected in the data. Earth-based observations of Na, K, and Ca populations in the exosphere strongly suggest the existence of dynamic magnetospheric processes at high latitudes interacting with the planet's surface. (C) 2001 Elsevier Science Ltd. All rights reserved.