Charon: A Brief History of Tides. Issue 7 (6th July 2020)

• Record Type: Journal Article
• Authors: Rhoden, Alyssa Rose; Skjetne, Helle L.; Henning, Wade G.; Hurford, Terry A.; Walsh, Kevin J.; Stern, S. A.; Olkin, C. B.; Spencer, J. R.; Weaver, H. A.; Young, L. A.; Ennico, K.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-06
• Subjects: Charon -- satellite tides -- orbital evolution -- tectonics -- tides -- interiors and fractures on Charon; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2020JE006449
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: In 2015, the New Horizons spacecraft flew past Pluto and its moon Charon, providing the first clear look at Charon's surface. New Horizons images revealed an ancient surface, a large, intricate canyon system, and many fractures, among other geologic features. Here, we assess whether tidal stresses played a significant role in the formation of Charon's tensile fractures. Although presently in a circular orbit, most scenarios for Charon's orbital evolution include an eccentric orbit for some period of time and possibly an internal ocean. Past work has shown that these conditions could have generated stresses comparable in magnitude to other tidally fractured moons, such as Europa and Enceladus. However, we find no correlation between observed fracture orientations and those predicted to form due to eccentricity driven tidal stress. It, thus, seems more likely that Charon's orbit circularized before its ocean froze and that either tidal stresses alone were insufficient to fracture the surface or subsequent resurfacing removed these ancient fractures. Plain language summary: Charon's surface displays many fractures that appear to have formed when the surface was pulled apart. The source of stress that created these fractures is currently debated. We test the hypothesis that, in the past, Charon had a slightly elliptical orbit, which would have stressed the surface, potentially creating the observed fractures. We find that this model provides a poor match to the observed fractures over a wide range of parameter values. These findings suggest that Charon's orbit was circular for most of its history and that its ocean froze out after the orbit became circular. The observed fractures were likely formed as part of the freezing process, which has been suggested for other icy moons with canyons and fracture systems similar to those seen on Charon, although the details of this process are not well understood. Key Points: Charon's tectonic features are inconsistent with eccentricity tidal stresses If Charon had an internal ocean, it froze out after orbit circularization Charon's fractures lack the equatorial symmetry of most tidal stress patterns