# Crater Density Predictions for New Horizons flyby target 2014 MU69

## TL;DR

This paper predicts the crater density on Kuiper Belt object 2014 MU69 using crater data from Pluto and Charon, suggesting it will be lightly cratered and revealing insights into early planetesimal formation.

## Contribution

It introduces a method to estimate crater density on MU69 based on observed crater fields and Kuiper Belt projectile distributions, linking surface features to formation history.

## Key findings

- MU69 should have a lightly cratered surface below 1 km.
- Most bombardment may come from slow-moving exogenic projectiles.
- The crater size distribution reflects primordial planetesimal formation processes.

## Abstract

In preparation for the Jan 1/2019 encounter between the New Horizons spacecraft and the Kuiper Belt object 2014 MU69, we provide estimates of the expected impact crater surface density on the Kuiper Belt object. Using the observed crater fields on Charon and Pluto down to the resolution limit of the 2015 New Horizons flyby of those bodies and estimates of the orbital distribution of the crater-forming projectiles, we calculate the number of craters per unit area formed as a function of the time a surface on 2014 MU69 has been exposed to bombardment. We find that if the shallow crater-size distribution from 1-15 km exhibited on Pluto and Charon is indeed due to the sizes of Kuiper Belt projectiles, 2014 MU69 should exhibit a surface that is only lightly cratered below 1 km scale, despite being bombarded for $\sim4$~billion years. Its surface should therefore be more clearly indicative of its accretionary environment. In addition, this object may the first observed for which the majority of the bombardment is from exogenic projectiles moving less than or near the speed of sound in the target materials, implying morphologies more akin to secondary craters elsewhere in the Solar System. Lastly, if the shallow Kuiper Belt size distribution implied from the Pluto and Charon imaging is confirmed at MU69, then we conclude that this size distribution is a preserved relic of its state $\simeq$4.5~Gyr ago and provides a direct constraint on the planetesimal formation process itself.