Spectral Study of Five Major Impact Basins and Their Volcanic Infills on Mercury: A Window Into the Mantle's Properties

Abstract NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission has revealed that about 27% of the surface of Mercury is covered by smooth plains, which are mostly volcanic in origin. These plains are mainly located in the northern hemisphere, as well as within and around major impact basins. We used Mercury Atmospheric and Surface Composition Spectrometer data to perform an exhaustive spectral analysis of five major impact basins: Caloris, Rembrandt, Beethoven, Tolstoj, and Rachmaninoff. We highlighted the existence of a new high‐reflectance spectral unit, that had previously only been identified within the Rembrandt basin, as a major unit being more widespread. We named this new unit Young High‐reflectance Red Plains. We found a common sequence of volcanic episodes that infilled the basins and shaped their current surface spectral properties. We have shown that the size of the basin and the age of the volcanic infills are likely important parameters for the layering of different volcanic plains, defining the surface spectral units. Our study gives access to mantle properties, and we suggest that heterogeneity in the mantle is certainly not necessary to explain the spectral properties of effusive volcanism associated with impact basins. Future observations by the ESA‐JAXA‐BepiColombo mission are eagerly awaited to better constrain the planet's spectral, compositional, morphological, and geophysical surface properties.