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

Recent 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 ∼ 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. Plain Language Summary NASA's Cassini mission left a major unresolved question: How old are the mid‐sized inner moons (Mimas, Enceladus, Tethys, Dione, Rhea) of Saturn? Models that form the moons and change their orbits around Saturn over time have suggested that these moons may be as young as 100 million years old. In contrast, previous work inferred these moons formed at the same time as Saturn (age ∼4.5 Ga), or later in Saturn's history but still long ago (ages between 4.5 and 1 Ga). Because impact cratering is a common process throughout solar system history, crater distributions can provide additional insight as to the formation of these moon. However, we are missing a piece of information that is critical to interpreting craters: the source and frequency of objects that hit the moons over time. Here, we mapped 4002 impact craters on Saturn's moon Dione over fo