Regional Impact Crater Mapping and Analysis on Saturn's Moon Dione and the Relation to Source Impactors

Abstract

AbstractRecent dynamical modeling of the formation and evolution of the Saturnian satellites suggests that the ages of the mid‐sized inner moons (Mimas, Enceladus, Tethys, Dione, and Rhea) could be as young as 100 Myr. This estimate is in contrast to most previous modeling and observational work that suggest an age more contemporaneous with the formation of Saturn 4.5 Ga ago. Given the heritage of using craters to constrain surface ages, we examine the impact craters of Dione using imagery from NASA's Cassini ISS camera and analyze their size‐frequency distributions (SFDs) to understand impactor populations. We survey four areas across different geologic terrains and compare our crater counts to standard outer solar system production functions. In addition to crater counts, we study several crater types such as elliptical and polygonal to further examine the bombardment source for the craters. We find evidence for a Saturn‐specific planetocentric impactor source, as none of the standard production functions fit the data. We compare our Dione data with our work on Tethys and find similarly shaped SFDs between the satellites. However, Dione's surface has been extensively modified to remove smaller craters (D ∼ <5 km) and has been bombarded by larger impactors, creating more D ∼ >20 km on Dione than Tethys. In contrast, Tethys more generally represents an ancient unmodified surface within the Saturn system. More complete observations and assessment of the cratering records on the satellites of Uranus and Neptune's moon Triton would enable better constraints on the bombardment history of the Saturn system.