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Re-Calculation of Impact and Cratering Rates onto Pluto, Charon, and Arrokoth and Their Younger Surface Ages

Presentation #308.08 in the session Pluto System (Oral Presentation)

Published onOct 23, 2023
Re-Calculation of Impact and Cratering Rates onto Pluto, Charon, and Arrokoth and Their Younger Surface Ages

We have re-computed the impact and cratering rates onto New Horizons targets Pluto, Charon, and Arrokoth using recent observational updates on their impactor populations. We use the most recent size distribution from the Outer Solar System Origins Survey (OSSOS), that exhibits an exponential taper at large sizes with a rollover to an asymptotic slope of alpha=0.4 for both the cold and hot transneptunian object (TNO) populations (Kavelaars et al 2021 and Petit et al 2023) and a break to a shallower alpha=0.14 slope for projectile diameters d<2 km that correspond to crater diameters D≲13 km craters on Charon (Singer et al 2019 and Robbins & Singer 2021). In addition, we use OSSOS orbital models, population estimates, and albedos for the hot, cold, and resonant populations relevant to the cratering of these three bodies. The methods and crater scaling laws of Greenstreet et al (2015, for Pluto and Charon) and Greenstreet et al (2019, for Arrokoth) were used, with a comparison of the new compaction crater scaling law explored for Arrokoth in McKinnon et al (2022). We find that the dynamically hot TNO populations dominate the crater formation rates on Pluto, Charon, and Arrokoth. While this was already true for our 2015 study of Pluto and Charon, it reverses our 2019 Arrokoth finding that the cold classicals dominate Arrokoth’s impact flux. This reversal is due to the newer OSSOS population estimate of twice as many hot classical objects than cold classicals (Petit et al 2023). In our new analysis, we find that the largest expected craters on Pluto, Charon, and Arrokoth are consistent with those observed by New Horizons to within a factor of 2. With the higher number of impactors expected from today’s Kuiper belt and accounting for the erosion of the current populations over the past 4 Gyr, we compute younger surface ages than our previous calculations estimated for all three target bodies. We find that Arrokoth’s crater record is consistent with 4 Gyr of bombardment, but Charon’s observed crater densities and those on Pluto’s oldest terrains show a surface age of only 1-2 Gyr, indicating resurfacing events not only on Pluto but also on Charon on these timescales.

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