The trans-Neptunian region is observed to host a large proportion and a wide variety of binary systems (components with > a few tens of km in size), offering unique opportunities for studying planetesimal formation from the protoplanetary disk and subsequent evolution. Since trans-Neptunian objects (TNOs) reside far from the Earth, observing TNOs smaller than km-scale remains challenging and consequently, the binarity in this size range is unknown.
Doublet craters are generally defined as a pair of adjacent, similarly-sized craters, and are hypothesized to form through simultaneous impacts of widely-separated binaries. The derivable impactor population for Pluto and Charon consists of TNOs smaller than km-scale based upon standard crater scaling laws. Hence, cratering records on these bodies likely contain valuable information about < km-sized widely-separated binaries.
We will present results from our study of doublet craters on Vulcan Planum, Charon, which is the most suitable region owing to its relative low density of craters. We define a potential doublet as a pair of craters with a separation smaller than 1.2 the diameter of the larger crater, and with a ratio of the two diameters greater than 0.25. Through visual inspection, potential doublets are categorized as “unlikely” based on geomorphology such as superposition and/or different degree of degradation, and the rest as “possible”. We obtained 28 possible doublets which yields 5.7% (28 out of 488 craters). Assuming that all possible doublets are true doublets and adopting 15% as the likely fraction of binary impacts resulting in doublets, approximately 38% of < km-scale TNOs may be widely-separated binaries. Moreover, we will discuss implications of spatial analyses and the inferred binary population among km-scale TNOs.