Presentation #303.02 in the session Pluto through the Ages.
New Horizons showed that Pluto has a diverse array of surface terrains. Volatile ices appear to play a large role in the type of surfaces we observe. Pluto’s youngest and most active terrains (e.g., Sputnik Planitia) are covered in large deposits of volatile ices (mantles), and some of Pluto’s oldest terrains show evidence of degraded mantles as well. Past work has used crater dating to constrain the resurfacing ages of Pluto’s terrains to as young as 50 M.y. old to nearly the age of the solar system. In this work, we study the processes that have degraded these terrains by studying the morphology of Pluto’s impact craters. Impact craters provide constraints on the extent of surface degradation by comparing the current crater morphology to the predicted pristine morphology. However, this type of analysis is difficult when there is significant variation in the bedrock materials (e.g., the large mantles of volatile ice in some terrains). We begin by hypothesizing the initial morphology of craters that form into volatile ice using terrestrial and Martian analogues of impacts into ice and marine environments. We then use the current morphology of Pluto’s crater population to constrain how its terrains have changed over time and discuss the implications of these measurements for the history of surface processes on Pluto. Specifically, we consider which of the two primary modes of crater degradation on Pluto are most common: erosion (sublimation) or viscous relaxation. We find a range of crater morphologies on Pluto from entirely degraded to anomalously deep, and there does not appear to be a correlation between the geologic surface age and the level of degradation. There is, however, a longitudinal relationship with the level of degradation. This may hint that Pluto underwent a significant change in conditions in its past (e.g., polar wander). We find the most significant crater modification exists within the Venera group, but degradation cannot be explained by relaxation or erosion alone, suggesting it may be a combination of both. In Cthulhu Macula, moderate crater degradation seems only explainable via relaxation, but the conditions that allowed for the relaxation of water ice under Pluto conditions remain unclear.