Space Weathering of Ice Deposits within Mercury’s Permanently Shadowed Craters

Abstract:

Mercury has an intrinsic magnetic field which generates a magnetosphere around the planet. The solar wind interacts with Mercury’s magnetosphere causing the formation of large-scale structures known as magnetic cusps, which are funnel-shaped areas of focused magnetic field that converge toward the dayside planetary surface at high latitudes. Magnetospheric dynamical processes result in the cusp region being filled with energetic ions and electrons and, because Mercury lacks an atmosphere or ionosphere, plasma particles funneled down the cusp precipitate directly onto the surface of the planet. The latitudinal location of the cusp footprint on the planet varies with solar wind conditions. Since Mercury’s internal magnetic dipole is offset to the north by about 480 km, when the solar wind interplanetary magnetic field is directed northward, the northern cusp moves to very high latitudes > 75^o, mapping directly into the northern polar region. The poles contain permanently shadowed regions (PSR) which allow frozen water ice mixed with organic molecules to exist over long timescales. The energetic precipitating particles can induce chemical radiation processing of the volatile ices into higher-order organics and dark refractory materials overlaying the water ice. Global kinetic magnetospheric simulations in conjunction with MESSENGER spacecraft data are used to characterize the fluxes and energies of the precipitating particles in Mercury's magnetospheric cusp region and the resulting space weathering interactions that take place in the icy materials in the PSRs at high northern latitudes. Existing MESSENGER data and numerical simulation results will be presented along with a discussion of the data gaps expected to be filled by BepiColombo observations.