Halekas, Jasper - The Latest From ARTEMIS

Abstract: 
The two ARTEMIS probes continue their successful extended mission around the Moon, studying the interaction of terrestrial and solar plasma with the lunar environment, and serving as a solar wind beacon. ARTEMIS provides continuous monitoring of the incoming plasma, including protons and doubly ionized helium (alpha particles) in the solar wind, and magnetospheric plasma during the Moon's passage through the geomagnetic tail. These ARTEMIS observations are critical to developing a complete understanding of the dynamics of the complex neutral exosphere recently revealed by LADEE. The highly variable plasma influx directly supplies a portion of the lunar exosphere, most notably helium. The flowing plasma also liberates other exospheric species from the surface through charged particle sputtering, and acts as the final sink for a large proportion of the exosphere, by picking up ionized constituents and sweeping them away from the Moon. Incoming plasma also contributes to weathering of the surface, with the plasma contribution to space weathering (as well as solar wind sputtering) reduced in regions with strong intrinsic magnetic fields, where a significant fraction of the incoming plasma reflects before reaching the surface. ARTEMIS observations cast new light on the physics of the plasma-magnetic field interaction, with implications for both the surface and the exosphere.  In concert with LADEE and LRO, the ARTEMIS probes help provide a complete picture of the coupled plasma-surface-exosphere system.