Energetic neutral atom imaging of Mercury's magnetosphere 2. Distribution of energetic charged particles in a compact magnetosphere

In order to investigate the feasibility of energetic neutral atom (ENA) ima ging of Mercury's magnetosphere interacting with the tenuous exosphere, we developed a simple model simulating dynamics of hot proton plasma near Merc ury. We did not consider specific acceleration mechanisms but parameterised the proton source by its location, size and the distribution function of t he injected protons. The characteristics of the source are free parameters of the model and can be easily varied. To model the magnetic field in the m agnetosphere we used the Tsyganenko's model scaled for Mercury's conditions . The dynamics of energetic protons 1 keV < E < 50 keV are calculated in th e drift approximation taking into account the convective electric field pro duced by the solar wind interaction with the magnetosphere. This enabled to establish the particle steady-state distribution. As for more energetic pr otons, E > 50 keV, the large Larmour radius results in their almost immedia te loss via intercepting the Hermean magnetopause. The model was tested for 10, 30, and 50 keV protons injected from a source of the size 1R(m) x 1R(m ) located at 3R(m), 2.5R(m), 2R(m), and 1.5R(m) in the tail (R-m is the Her mean radius). This simple model turned out to be rather useful and flexible , and can be used to study proton dynamics in Mercury's magnetosphere. (C) 2001 Elsevier Science Ltd. All rights reserved.