Abstract
At a low activity comet the plasma is distributed in an asymmetric way.
The hybrid simulation code Amitis is used to look at the spatial
evolution of ion velocity distribution functions (VDFs), from the
upstream solar wind to within the comet magnetosphere where the solar
wind is heavily mass-loaded by the cometary plasma. We find that the
spatial structures of the ions and fields form a highly asymmetric,
half-open induced magnetosphere. The VDFs of solar wind and cometary
ions vary drastically for different locations in the comet
magnetosphere. The shape of the VDFs differ for different species. The
solar wind protons show high anisotropies that occasionally resemble
partial rings, in particular at small cometocentric distances. A second,
decoupled, proton population is also found. Solar wind alpha particles
show similar anisotropies, although less pronounced and at different
spatial scales. The VDFs of cometary ions are mostly determined by the
structure of the electric field. We perform supplementary dynamic
particle backtracing to understand the flow patterns of solar wind ions
that lead to these anisotropic distributions. This tracing is needed to
understand the origin of cometary ions in a given part of the comet
magnetosphere. The particle tracing also aids in interpreting observed
VDFs and relating them to spatial features in the electric and magnetic
fields of the comet environment.