Lunar Plasma Environment in Cases with Extreme Solar Wind Conditions. First Results from 3-D Hybrid Kinetic Modeling and Comparison with ARTEMIS Observations

The study of lunar plasma environment's response to the extreme solar wind condition is the main subject of our investigation in this report. Photoionization and charge exchange of protons with the lunar exosphere are the ionization processes included in our model. The computational model includes the self-consistent dynamics of the light ({H^+} or {H_2^+} and {He^+}), and heavy ({Na^+}) pickup ions. The electrons are considered as a fluid. The lunar interior is considered as a weakly conducting body. In this report we consider for the first time the effects of the extreme solar wind density and bulk velocity on a formation of lunar plasma structures and wakes. The input parameters are taken from the ARTEMIS observations. The modeling demonstrates a formation of the various plasma structures near the Moon: (a) bow shock wave with split shock transition in case of extreme solar wind density and standard bulk velocity; (b) hyper-sonic/Alfvenic Mach cone in case of extreme solar wind bulk velocity and moderate solar wind density. The modeling shows a strong asymmetry in the solar wind ion velocity distribution function which connected with a plasma compression and ion reflection at the shock wave/Mach cone front. This research was supported by NASA SSW2018 Grant 80NSSC20K0146.