The Geology and Geophysics of Cold Classical Kuiper Belt Object (486958) 2014 MU69
Abstract
On January 1st 2019, at 43.2 AU from the sun, the New Horizons spacecraft flew past the 32-km long Kuiper Belt object 2014 MU69 at a range of 3,500 km. MU69 is a member of the "Cold Classical" Kuiper Belt, the most dynamically and physically primitive known population of objects in the solar system, and is the first such object to be observed at close range. MU69 is a contact binary, composed of two distinct components which make contact at a bright, narrow, "neck". The largest component is nicknamed "Ultima", and the smaller one "Thule". Both are flattened, with their smallest axes and equators aligned. This configuration strongly suggests that the two components formed independently, and orbited each other in a tidally-locked configuration before coming gently together. On both components, the surface is generally smooth at the resolution of the best images (33 m/pixel), though pits which are possibly impact craters are seen near the terminator, and bright spots away from the terminator may also be bright-floored pits. These pits have a shallow size/frequency distribution similar to that of small craters in the Pluto system. Though relatively sparse, the pits, if they are impact craters, indicate a surface age of at least 4 Ga, given the expected low cratering rates in the Kuiper Belt. The sparseness of modification by impact cratering, the lack of plausible long-lived sources of significant internal heat, and the undisturbed nature of MU69's orbit, make it likely that the visible surface, at the scale of New Horizons' images, is the oldest yet seen in the solar system, dating back to the final stages of accretion. The two lobes have distinctly different appearances. Thule is marked by complex albedo patterns with sinuous margins, while Ultima has more subtle albedo patterns, consisting of scattered dark hills and ridges on a lighter background. Ultima is divided into several sub-units with differing surface textures, separated by shallow linear depressions. The sub-units may provide evidence for assembly of Ultima from smaller bodies, though the continuity of some surface texture units across some of the bounding linear features argues for some of the unit boundaries being relatively young. MU69 has no detectable rings, and no satellites larger than 180 meters diameter within a radius of 8000 km.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23541904S