One‐hundred‐km‐scale basins on Enceladus: Evidence for an active ice shell

Abstract

Stereo‐derived topographic mapping of ∼50% of Enceladus reveals at least 6 large‐scale, ovoid depressions (basins) 90–175 km across and 800‐to‐1500 m deep and uncorrelated with geologic boundaries. In contrast, the south polar depression is larger and apparently shallower and correlates with active resurfacing. The shape and scale of the basins is inconsistent with impact, geoid surface deflections, or with dynamically supported topography. Isostatic thinning of Enceladus' ice shell associated with upwellings (and tidally‐driven ice melting) can plausibly account for these basins. Thinning implies upwarping of the base of the shell of ∼10–20 km beneath the depressions, depending on total shell thickness; loss of near‐surface porosity due to enhanced heat flow may also contribute to basin lows. Alternatively, the basins may overly cold, inactive, and hence denser ice, but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice.

Surface, Subsurface and Atmosphere Exchanges on the Satellites of the Outer Solar System

“…This is much less than observed on Tethys and Iapetus (see below), and much more than observed on Europa (R m = 1562 km) and Ganymede (R m = 2632 km) if divided by the bodies' mean radii. Different from Europa and Ganymede, Enceladus exhibits large-scale (comparable to R m ) depressions that are likely to be supported isostatically (Schenk and McKinnon 2009). Elastically-supported topography has been identified at a rift zone showing an elevated flanking ridge (Fig.…”

Gravitational spreading, bookshelf faulting, and tectonic evolution of the South Polar Terrain of Saturn’s moon Enceladus

“…Each of these three terrains includes a circumferential belt that encloses one or more other structurally deformed units. The ''semi-squared" SPT (Gioia et al, 2007) is a topographical depression 500-1500 m below its surrounding regions (Porco et al, 2006;Schenk and McKinnon, 2009). The region may be underlain by a local or global ocean (Collins and Goodman, 2007;Patthoff and Kattenhorn, 2011;Spencer and Nimmo, 2013;Iess et al, 2014;McKinnon, 2015;Thomas et al, submitted for publication).…”

“…These images are available publically from NASA's Planetary Data System (PDS). We also use digital topographic data derived from stereo images and photoclinometry by Schenk and McKinnon (2009) to aid our structural interpretations. The spatial resolutions of the satellite images used in this study vary from $9 m to 110 m per pixel (http://photojournal.…”

A unified nomenclature for tectonic structures on the surface of Enceladus

“…The corrugated ridge belts that occur just within the SPT boundary have been interpreted to have formed as thrust belts (Spencer et al, 2009) and the increase in overall elevation of the corrugated ridge belts is cited as evidence of contractional deformation (e.g., Schenk and McKinnon, 2009). However, our analysis of the morphology and topography of corrugated ridge belts does not support this hypothesized formation mechanism.…”