<div>The Mercury plasma environment is enriched in heavy ions (mass-per-charge ratio m/q > 4) from photo-ionization of the tenuous exosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) time-of-flight spectrometer Fast Imaging Plasma Spectrometer (FIPS) has detected many planetary ion species of which He<sup>+</sup>, the Na<sup>+</sup>-group (including Na<sup>+</sup>, Mg<sup>+</sup> and Si<sup>+</sup>) and the O<sup>+</sup>-group (including O<sup>+</sup> and several water group ions) are the most abundant. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) UltraViolet and Visible Spectrometer (UVVS) has also detected Ca<sup>+</sup> ions in the nightside plasma sheet. Models of the planetary ion distribution inside Mercury's magnetosphere have mostly concentrated on the abundant Na<sup>+</sup> and H<sup>+</sup> ion populations. Comparison with FIPS data has been limited to the first two MESSENGER flybys and no comparison has been made with MASCS/UVVS observations.</div><div>&#160;</div><div>We have developed a Monte Carlo test-particle model which describes the ion density distribution produced from photo-ionization of several neutral species in Mercury's exosphere. The global ion density and energy distribution of Ca<sup>+</sup>, Mg<sup>+</sup>, Na<sup>+</sup>, O<sup>+</sup> and He<sup>+</sup> will be presented here. We will review the influence of the interplanetary magnetic field (IMF) B<sub>x</sub> and B<sub>y</sub>&#160;components on the global structure of the ion density distribution, the composition of the nightside plasma sheet and the evolution of the Na<sup>+</sup> ion density along the Mercury year.</div>
K.P. Sagarik and R. Ahlrichs, Molecular dynamics simulations of liquid CHClF2 with a test-particle model potential
