Centrifugal acceleration of ions near Mercury

We investigate the parallel acceleration of ions inside Mercury’s magnetosphere. We focus on centrifugal effects associated with the large scale plasma convection. We demonstrate that, because curvature radii of the E´B drift paths are much smaller at Mercury than at Earth, centrifugal effects are enhanced and lead to prominent parallel energization during transport from high to low latitudes. For moderate convection rates, model trajectory calculations reveal that these E´B related centrifugal effects yield energization of heavy ions sputtered from Mercury’s surface(e.g., Na + ) of several tens or a few hundreds of eV within minutes. This suggests that, at Mercury,material of planetary origin is rapidly raised up to plasma sheet energies. Such a situation contrasts with that prevailing at Earth where these centrifugal effects are relatively weak, yielding energization of ionosphere originating ions of at most a few tens of eV on the time scale of hours.