The contraction/expansion history of Charon with implications for its planetary-scale tectonic belt

Abstract

The New Horizons mission to the Kuiper Belt has recently revealed intriguing features on the surface of Charon, including a network of chasmata, cutting across or around a series of high topography features, conjoining to form a belt. It is proposed that this tectonic belt is a consequence of contraction/expansion episodes in the moon's evolution associated particularly with compaction, differentiation and geochemical reactions of the interior. The proposed scenario involves no need for solidification of a vast subsurface ocean and/or a warm initial state. This scenario is based on a new, detailed thermo-physical evolution model of Charon that includes multiple processes. According to the model, Charon experiences two contraction/expansion episodes in its history that may provide the proper environment for the formation of the tectonic belt. This outcome remains qualitatively the same, for several different initial conditions and parameter variations. The precise orientation of Charon's tectonic belt, and the cryovolcanic features observed south of the tectonic belt may have involved a planetary-scale impact, that occurred only after the belt had already formed.

Charon: A Brief History of Tides

“…Within the images obtained by New Horizons, it appears that craters have not been modified by tectonic features, which suggests that tectonic activity occurred early in Charon's history and was overprinted by craters (Singer et al, 2019). also have possessed a subsurface ocean in its past (Desch, 2015;Desch & Neveu, 2017;Malamud et al, 2017, and references therein). Rhoden et al (2015) determined that an internal ocean would have made Charon much more responsive to the tidal deformation caused by eccentricity, particularly if Charon were evolving from a closer orbit to Pluto.…”

“…An additional mechanism that has been proposed to explain Charon's tectonism is volume expansion due to freezing of an internal ocean (Desch & Neveu, 2017; Malamud et al, 2017; Moore et al, 2016). Stresses associated with freezing are isotropic; that is, they have no preferred orientation.…”

Moonfalls: collisions between the Earth and its past moons

“…Finally, we note that the localization of debris accreted on the the proto-Earth is reminiscent of impacts on Mars and Charon, suggested to produce a hemispheric dichotomy (Wilhelms & Squyres 1984;Andrews-Hanna et al 2008;Marinova et al 2008;Malamud et al 2017). Such low-energy impacts are sufficiently strong as to give rise to a large scale topographic structure on the impacted planets, but not sufficiently strong to give rise to planetary scale mixing.…”

Transneptunian Space and the Post-Pluto Paradigm

“…If the resurfacing of Vulcan Planum is indicative of an epoch of global expansion, then this age is inconsistent with the origin of this expansion being due to the onset of freezing of a global ocean which is likely to occur much later (e.g., Desch & Neveu 2017). Recent models of the thermal evolution of Charon indicate that early epochs of global expansion can be generated by the hydrous alteration of silicates in the rocky core (Malamud et al 2017).…”

“…Subsequent to these discoveries, more detailed interior evolution models were developed for both Pluto and Charon in an effort to explain some of the key observations from flyby -namely, the relatively similar densities of both worlds, Charon's ancient extensional tectonics, and the gravity anomaly inferred from the orientation of Sputnik Planitia. Both Malamud et al (2017) and Bierson & Nimmo (2018) added treatments of porosity removal; Malamud et al (2017) and Desch & Neveu (2017) both tracked two rock phases to account for hydrous alteration of silicate minerals. Desch & Neveu (2017) also included a treatment of suspended rock "fines" which produce a more insulating mantle.…”