Space Physics Seminar winter-2014

The Earth's Moon, often thought of as a passive absorber of plasma, is in fact a surprisingly prolific source of non-thermal ions. As we have learned in recent years, a significant fraction of the incident solar wind proton population reflects above magnetized regions of the lunar crust. In addition, sputtering from the surface and ionization of the tenuous exosphere produce heavy lunar ions. Both populations react to the convection electric field, with lunar ions following cycloidal trajectories, and reflected protons following prolate or curtate cycloids, depending upon their initial velocity after reflection. Reflected protons interact with the incoming solar wind, driving foreshock-like turbulence and large scale perturbations of the plasma environment around the Moon. Lunar ions, on the other hand, have little apparent effect on the ambient plasma, but carry information about the lunar atmosphere and its sources, composition, and dynamics. These two ion populations, both readily observed by ARTEMIS, allow us to understand the Moon's interaction with the ambient plasma, by utilizing remote ion observations to unfold the details of processes occurring at or near the surface.