RIDGES ON ENCELADUS: INITIAL MODELS OF FORMATION AND FLEXURE

Enceladus’s proposed polar dichotomy – a warm, actively jetting south pole versus an older, colder north pole – is one of the most challenging and fundamental puzzles of the outer solar system. The differences between the active south and ancient north may be related to differences in ice shell thickness, depth to liquid water, and/or energy flux and how these characteristics have changed through time. The formation, morphological characteristics, and subsequent modification of geologic structures observed in both hemispheres provide an opportunity to constrain the geologic history of the ice shell.

In this work, we focus on the formation of Enceladus’s ridges that are morphologically similar to features observed on other icy satellites, in particular those on Europa. First, we characterize the structure and morphology of different types of ridges on Enceladus and map their locations using Cassini data. For ridges showing similar morphological characteristics for both Enceladus and Europa, we investigate formation mechanisms proposed for Europa, within the context of measured Enceladus ridge morphologies and expected range of ice shell thickness. We model proposed formation mechanisms including a crystalizing shallow water body (e.g. Johnston and Montési, 2014) and a shallow water sill intrusion invoking flexure and flanking fractures at the surface (e.g. Dombard et al., 2013). Models consider fracturing processes, heat transfer, induced thermal regimes and fluid flow in order to provide insight into ridge building, lithostatic flexure and the required physical parameters of the ice shell including thickness and induced stresses. These models can therefore provide a greater understanding of ridge formation and ice shell characteristics at Enceladus. Additionally, as processes may be similar on other icy bodies with shallow liquid water, including Europa, the models can also give insight into ridge building processes and ice shell characteristics on icy bodies in general.

References: Johnston and Montési (2014), Icarus, 237, 190–201; Dombard et al. (2013), Icarus, 223, 74–81.