The Interplay of Surface Composition, Mineralogy, and Physical Conditions That Affect the Surface Release Processes and Particle Environment of Mercury

Abstract

Mercury has a very tenuous atmosphere starting at the surface, which is referred to as a surface-bound exosphere, where there are no collisions between exospheric particles. Having a surface-bound exosphere means that the particles in the exosphere have their origin on Mercury’s surface; thus, the composition of the exosphere is connected to the composition of the surface. In situ composition measurements of the exosphere can contribute to the study of the composition of the surface, together with a range of remote sensing techniques (ultraviolet, visible, infrared, X-ray, gamma-ray, and neutron spectroscopy). The external drivers for the particle release from the surface are solar photons, solar wind plasma, and micrometeoroid impacts. These drivers also cause space weathering of the surface, resulting in significant physical and chemical alterations in the regolith, ranging from the very surface to depths up to one meter. Modifications of the surface by space weathering must be considered when interpreting the composition measurements of the exosphere as well as the composition measurements of the surface by the established remote sensing techniques, because their information comes from the space-weathered volume of the surface. Therefore, the particle populations in the exosphere, space weathering, and the composition of the surface are intimately connected and must be studied together. In the following, we will review the connections between the surface and the exosphere of Mercury.