Revised constraints on absolute age limits for Mercury's Kuiperian and Mansurian stratigraphic systems

摘要

Following an approach similar to that used for the Moon, Mercury's surface units were subdivided into five time-stratigraphic systems based on geologic mapping using Mariner 10 images. The absolute time scale originally suggested for the time periods associated with these systems was based on the assumption that the lunar impact flux history applied to Mercury. However, we find that the duration and onset of corresponding periods in the stratigraphic sequences on Mercury and the Moon are not the same. Using high-resolution and multiband image data obtained by the MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) spacecraft, we identify and catalog fresh impact craters interpreted to have formed during Mercury's two most recent periods, the Mansurian and Kuiperian. We use the densities of the inferred Kuiperian- and Mansurian-aged crater populations to estimate new limits for the age boundaries of these time intervals. Results suggest that both the Mansurian and Kuiperian periods began more recently and extended for significantly shorter durations of time than previously suggested. The Kuiperian is estimated to have initiated as recently as ~280 ± 60 Ma and the Mansurian as recently as ~1.7 ± 0.2 Ga.