“…The exosphere of Mercury has also been examined in detail and contains ions and neutrals that originate from the solar wind interacting with the space environment and the planet’s surface. Evidence for excited alkali (Na), alkaline earth (Ca and Mg) atoms, H + , He + , He 2+ , Na + , and Ca + ions, and O, Al, K, and Fe atoms, was presented by Killen et al, , Vervack et al, Bida et al, Leblanc et al, and Raines et al Specifically, observations by the Mercury atmospheric and surface composition spectrometer (MACS) revealed the presence of neutral Mg in the antisunward region as well as differing spatial distributions of Mg, Ca, and Na atoms in both the tail and night side near the planet exosphere. Recent observations from the fast imaging plasma spectrometer (FIPS), taken <400 km from the surface, have shown a plasma cusp with energetic heavy ions (i.e., Na + and O + groups).…”