The Nature and Origin of Charon's Smooth Plains

Charon displays extensive plains that cover the equatorial area and south to the terminator on the sub-Pluto hemisphere observed by New Horizons. We hypothesize that these plains are a result of Charon's global extension and early subsurface ocean yielding a large cryoflow composed of mantle material that completely resurfaced this area leaving the plains and other features we that we observe today. The resurfacing of the plains is not the result of a singular eruptive or effusive center from which cryoflows spread out across the more than 400,000 square kilometers of Vulcan Planitia. We hypothesize that the resurfacing was the result of ammonia-rich cryo-material from the last stages of ocean freezing either buoyantly rising and flowing out on to the pre-Vulcan lowlands, or as a result of more severe disruption that resulted in crustal blocks foundering, and the buoyant, viscous cryo-material under those blocks rising up and spreading out. Under these hypotheses, there would be no singular effusive center, but the sources of the plains material would be in many places across the region, and as the material flowed across the pre-Vulcan lowlands or enveloped the foundering blocks, it would create an extensive plains unit. Geological observations, modeling of possible flow rheology, and an analysis of rille orientations support the conclusion that the extensive plains on Charon are a vast cryoflow emplaced unit, similar to those seen on Ariel and Miranda and possibly other icy worlds in the solar system. Charon fits into the panoply of icy satellites which display evidence for the movement of cryoflows and resurfacing.