Abstract
Understanding the composition of Mercury's crust is key to comprehending the formation of the planet. The regolith, derived from the crustal bedrock, has been altered via a set of space weathering processes. These processes are the same set of mechanisms that work to form Mercury's exosphere, and are moderated by the local space environment and the presence of an intrinsic planetary magnetic field. The alterations need to be understood in order to determine the initial crustal compositions. The complex interrelationships between Mercury's exospheric processes, the space environment, and surface composition are examined and reviewed. The processes are examined in the context of our understanding of these same processes on the lunar and asteroid regoliths. Keywords: Mercury (planet) Space weathering Surface processes Exosphere Surface composition Space environment 3
Highlights
Space weathering is a term used for the set of processes that alter over time the observable physical, chemical, and mineralogical properties of the surfaces of atmosphere-free bodies
This paper examines the system from a reverse perspective in order to understand the material that is left on the surface and how it is altered by exosphere-generating processes
Many observational and laboratory studies of particle irradiation pertain to the generation of exospheres, we examine corresponding surface effects in our surface-centric approach resulting from the processes of ion implantation, physical sputtering, chemical sputtering, desorption induced by electronic transitions (DIET), and thermal desorption
Summary
Space weathering is a term used for the set of processes that alter over time the observable physical, chemical, and mineralogical properties of the surfaces of atmosphere-free bodies. Studies of lunar samples at ultraviolet (UV) wavelengths show that space weathering alters spectral signatures in this wavelength region by (1) brightening (increasing spectral albedo), (2) degrading the near- and mid-UV absorption edge, and (3) bluing (decreasing the slope of the continuum reflectance with increasing wavelength) (Hendrix and Vilas 2006; Hendrix et al 2012) These effects must be factored into the interpretation of spectral measurements in terms of the specific mineral compositions of surface material. Asteroids span a considerable range of heliocentric distance (from rocky objects in the outer solar system and main-belt asteroids to Sun-grazing asteroids in the nearEarth population), so their surfaces have been collectively subjected to a wide range of fluxes and energies of micrometeoroids and solar-wind electrons and ions These objects have long been known from spectral studies to experience space weathering processes (e.g., Chapman 2004). Mercury’s surface composition is compared and contrasted with that of lunar surface materials and examined in light of inferred space weathering effects
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