Space weather at Mercury Original Research Article

The trajectories of a large number of ions have been traced in Mercury’s fields in order to evaluate the effect of photoions on atmospheric neutrals. We present the structure of the Hermean magnetosphere obtained using the [J. Geophys. Res. 98 (1993) 1339-1344] model of an open magnetosphere supplemented with the [Phys. Space Plasmas 14 (1996)] potential solver to represent the convection electric field. We ran our magnetosphere code under boundary conditions appropriate at Mercury to determine the trajectories of 3500 Na photoions in the Hermean magnetosphere. We have counted the number of ions returning at various points on the disk versus the number of ions created at these points. We conclude that photoions can influence the distribution of atmospheric neutrals. We forecast that the column density of neutrals is influenced by photoion production and subsequent photoion loss, and that ions initiate a short-term shift in neutral morphology. Our results reflect the assumption of a predominant dawn to dusk electric field, which will produce a dawnside enhancement in the number of ions reimpacting the surface. The resulting pattern will change as the exact nature of the electric field becomes known. The solar wind ion sputtering effect will further amplify atmospheric patchiness. We have not yet considered the possible effects of neutralization of ions on the nightside.