Kinetic Modeling of the Solar Wind Plasma Interaction with the Moon

Sammanfattning: The main purpose of this research is to understand various aspects of the solar wind plasma interaction with the Earth's Moon by the means of kinetic computer simulations. The Moon is essentially a non-conducting object, that has a tenuous atmosphere and no global magnetic field. Then the solar wind plasma impacts the lunar surface, where it is absorbed or neutralized for the most part. On average about 10% of the solar wind protons reflect in charge form from lunar crustal magnetization and up to 20% reflect from the lunar surface as neutral atoms. First we consider the Moon to be a perfect plasma absorber and we study the global effects of the solar wind plasma interaction with the Moon using a three-dimensional self-consistent hybrid model. We show that due to the plasma absorption in the lunar dayside, a void region forms behind the Moon and a plasma wake forms downstream. Then we study different parameters that control the lunar wake, discuss various mechanisms that fill in the wake, and compare our simulations with observations. We also discuss the effects of lunar surface plasma absorption on the solar wind proton velocity space distribution at close distances to the Moon in the lunar wake. Moreover, we show that three current systems form in the wake that enhance the magnetic fields in the central wake, depress the fields in the surrounding areas, and confine the fields and plasma perturbations within a Mach cone. Finally we study the effects of protons reflected from lunar crustal magnetic fields on the global lunar plasma environment. We show that the reflected protons interact with the solar wind plasma, compress the fields and plasma upstream in the lunar dayside and downstream outside the Mach cone. The conclusion of this thesis work is that the solar wind plasma interaction with the Moon is dynamic and complex. This is, however, due to the kinetic nature of this interaction because of the scales of the interaction regions where the Magnetohydrodynamics (fluid) approach cannot address the detailedphysics. This reveals the importance of kinetic modeling to understand this interaction. The results of this study will feed forward to human space exploration, kinetic theories of plasma interaction with airless bodies, and fundamental plasma physics processes.