Pluto and Charon Impact Crater Populations: Reconciling Different Results

The size–frequency distribution (SFD) of objects across the solar system is influenced by their formation and dynamic evolution. Bodies in different areas of the solar system—especially the inner versus outer—have likely experienced different histories, so measuring that SFD across orders of magnitude of solar distance can elucidate those different pasts. Accurate measurement of the SFD is greatly assisted by impact craters, formed from the smaller bodies that strike much larger ones, and it is often easier to measure impact craters’ SFDs than the smaller impactors themselves. One of the main results from New Horizons’ Pluto–Charon encounter was the crater SFD measurement, which illustrated an unexpected SFD with a distinct change in slope near ≈10–15 km diameter features. However, different methods of reporting these impact craters have resulted in some questions in the community about what the SFD actually is of Pluto's and Charon's crater population and therefore what the SFD is of the impactors that formed them. We have performed new crater population studies on both bodies, compared them with previously published work, and demonstrated that there is no ambiguity with respect to whether there is a transition to a shallower SFD population near ≈10–15 km. We find that this shallower slope is approximately −1.7 ± 0.2, while the steeper slope for larger craters is approximately −3.8 ± 0.6, though both of these uncertainties must be considered absolute minima based on fit sensitivity to the exact parameters and craters used. These values are consistent with previously reported results.