Doublet craters on Charon and implications for km-sized binaries in the outer solar system

Doublet craters throughout the solar system are hypothesized to be formed by near-simultaneous impacts of binaries. While the trans-Neptunian region hosts a large number and a variety of binaries at sizes viewable by Earth-based telescopes, the binarity among km-sized trans-Neptunian objects remains unknown due to the large distance from the Earth and lack of dedicated spacecraft missions. In this study, we examined doublet craters in Vulcan Planitia on Pluto's moon Charon to infer the fraction of km-sized binaries with sufficient separations to form doublet craters ( f bin ). We observed 39 crater pairs to be possible doublets and 16 of which are likely based upon morphological analyses. Assuming a plausible range of 10–20% of binaries to form doublets, our result suggests that f bin ≤ 40–81%. If only “likely” pairs are considered, then f bin ≤ 17–33%. We performed Monte Carlo simulations to independently constrain f bin using nearest neighbor distances of synthetic crater distributions in Vulcan Planitia. Our results suggest that f bin ≤ 10–40% and a large value of f bin ( ≥ 50%) fails to replicate the observed crater distribution. • We obtained 39 doublet crater candidates. • Doublet crater analysis suggests the binary fraction ≤ 40–81%. • Simulations show binary fraction to be ≤ 10–40%, favoring a smaller fraction.