Differing Enceladean Ocean Circulation And Ice Shell Geometries Driven By Tidal Heating In The Ice Versus The Core


Thermodynamic and dynamic fields from the “heat-from-below” scenario. Panels (a-d) show the zonally-averaged temperature T, zonal flow speed U, salinity S and meridional streamfunction Ψ (blue color denotes clock-wise circulation). The orientation of the tangent cylinder is marked by dashed curves. The vertical axis spans the whole 39.2 km ocean, and the origin is set at the interface between ice and ocean. The zero speed contours are plotted in panel (b) using gray solid lines to mark the transition between easterlies to westerlies. Isothermal and isosaline contours are plotted in panels (a,c) to highlight the meridional gradients. Panels (e,f) shows the zonally-averaged freezing rate and the vertically and zonally integrated meridional heat transport as a function of latitude. The dynamics of the “equatorial rolls” is presented in panels (g,h). Panel (g) shows the equatorial vertical section of temperature T (shading), zonal speed U and vertical speed W (arrows). Panel (h) shows a horizontal plot of W at the level marked by a solid black line in panel (g).

Beneath the icy shell encasing Enceladus, a small icy moon of Saturn, a global ocean of liquid water ejects geyser-like plumes into space through fissures in the ice, making it an attractive place to investigate habitability and to search for extraterrestrial life.

The existence of an ocean on Enceladus has been attributed to the heat generated in dissipative processes associated with deformation by tidal forcing. However, it remains unclear whether that heat is mostly generated in its ice shell or silicate core. Answering this question is crucial if we are to unravel patterns of ocean circulation and tracer transport that will impact both the habitability of Enceladus and our ability to interpret putative evidence of any habitability and/or life.

Using a nonhydrostatic ocean circulation model, we describe and contrast the differing circulation patterns and implied ice shell geometries to be expected as a result of heating in the ice shell above and heating in the core below Enceladus' ocean layer. If heat is generated primarily in the silicate core we would predict enhanced melting rates at the equator. In contrast, if heat is primarily generated in the ice shell we would infer a poleward-thinning ice geometry consistent with Cassini Mission observations.

Wanying Kang, Suyash Bire, Jean-Michel Campin, Christophe Sotin, Christopher German, Andreas Thurnherr, John Marshall

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2008.03764 [astro-ph.EP] (or arXiv:2008.03764v1 [astro-ph.EP] for this version)
Submission history
From: Wanying Kang
[v1] Sun, 9 Aug 2020 17:02:46 UTC (3,721 KB)
https://arxiv.org/abs/2008.03764
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