Tectonism and Enhanced Cryovolcanic Potential Around a Loaded Sputnik Planitia Basin, Pluto. Issue 12 (8th December 2021)

• Record Type: Journal Article
• Authors: McGovern, P. J.; White, O. L.; Schenk, P. M.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 12(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-08
• Subjects: Pluto -- Sputnik Planitia -- tectonism -- cryovolcanism -- impact basin -- flexural and membrane support; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2021JE006964
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Sputnik Planitia on Pluto is a vast plain consisting of a nitrogen ice deposit filling a broad topographic depression, likely an impact basin. The basin displays a broad, raised rim and is surrounded by numerous extensional fault systems, each with characteristic orientations with respect to the basin center. The nitrogen ice exerts a large mechanical load on the water ice outer shell crust (here also containing the lithosphere). We calculate models of stress and deformation related to this load, varying dimensional, mechanical, and boundary condition properties of the load and Pluto's lithosphere, in order to constrain the conditions that led to the formation of the observed tectonic and topographic signals. We demonstrate that the tectonic configuration is diagnostic of a particular set of conditions that hold for the Sputnik basin and Pluto, including moderate elastic lithosphere thickness (40–75 km, with higher values favored if initial basin topography is compensated) and a basin that was pan‐shaped and shallow (∼3 km) at the time of nitrogen deposition initiation. These tectonic systems show the contributions of both flexural (bending) and membrane (stretching) responses of the lithosphere, with the latter dominating in proportion to the importance of spherical geometry effects. Rim topography may also show an influence of primordial annular trans‐basin ice shell thickening from the impact process. Analysis of stress‐driven cryomagma transport shows that loading stresses can facilitate ascent of cryomagmas in annular zones around the basin, the locations of which overlap the observed distances from Sputnik of several candidate cryovolcanic sites. Plain Language Summary: The bright Sputnik Planitia region on Pluto is a vast plain consisting of a deposit of frozen nitrogen that fills a broad depressed area. The depression is probably the result of a large object colliding with Pluto; such a depression is called an impact basin. The basin displays a broad, raised rim and is surrounded by numerous cracks that reach outward like spokes on a bicycle wheel. The frozen nitrogen pushes down the outer shell of Pluto, which consists of frozen water (ice). The pushing creates stress in the shell that can fracture it. We use computer models to test for the conditions that would create the configuration of cracks seen around Sputnik Planitia. We show that the models strongly favor a particular range for the shell thickness, 40–75 km. Also, for the most successful models the starting shape of the depression resembled that of a frying pan, and was around 3 km in depth. The stresses created in the ice shell actually assist the rising of liquid water through it, an unusual form of volcanism that may be occurring at several sites in the region surrounding Sputnik Planitia. Key Points: The Sputnik Planitia impact basin on Pluto is filled with nitrogen ice, producing stresses that create outward‐radiating fault systems For likely load distributions, the pattern of faulting is strongly diagnostic of an elastic lithosphere (ice shell) thickness around 50 km The initial basin depth must not have exceeded several km in order to be consistent with the observed topographic level of nitrogen ice