Colloquium: The interplay of surface composition, mineralogy, and physical conditions that affect the surface release processes and particle environment of Mercury

Prof. Dr. Peter Wurz, Director of the Physics Institute of the University of Bern, Switzerland, will talk about Mercury's surface-bound exophere as probed by BepiColombo.

Mercury has a very tenuous atmosphere starting from its surface. There are no collisions between exospheric particles, which is referred to as a surface-bound exosphere. 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, and infrared spectroscopy, X-ray spectroscopy, gamma-ray, and neutron spectroscopy). The external drivers for the particle release from the surface are solar photons, solar wind plasma, and micro-meteoroid 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. The 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.