Ultima Thule (486958; 2014 MU69): Necklace, Composition, Rotation, Formation. (arXiv:1902.00997v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Katz_J/0/1/0/all/0/1">J. I. Katz</a>
Flyby images of Ultima Thule (486958; 2014 MU69) show a comparatively bright
“necklace” between its two lobes, in contrast to its generally low albedo.
The necklace is found in the most shaded, and therefore coolest, part of its
surface. It may be clean, high albedo, “hoarfrost” condensed from vapor
evaporated from the low albedo dirty ice elsewhere. Ammonia, the likely major
constituent of Ultima Thule, has the necessary vapor pressure. The rotation
period of $15 pm 1,$h is at least twice its breakup period, indicating either
that its formation was not limited by angular momentum or that half its angular
momentum was lost after formation, perhaps to surrounding gas in the
proto-Solar System. The lobes of Ultima Thule must have spherized under
conditions different than those encountered by its present, post-contact,
configuration.
Flyby images of Ultima Thule (486958; 2014 MU69) show a comparatively bright
“necklace” between its two lobes, in contrast to its generally low albedo.
The necklace is found in the most shaded, and therefore coolest, part of its
surface. It may be clean, high albedo, “hoarfrost” condensed from vapor
evaporated from the low albedo dirty ice elsewhere. Ammonia, the likely major
constituent of Ultima Thule, has the necessary vapor pressure. The rotation
period of $15 pm 1,$h is at least twice its breakup period, indicating either
that its formation was not limited by angular momentum or that half its angular
momentum was lost after formation, perhaps to surrounding gas in the
proto-Solar System. The lobes of Ultima Thule must have spherized under
conditions different than those encountered by its present, post-contact,
configuration.
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