Enceladus: An estimate of heat flux and lithospheric thickness from flexurally supported topography

Abstract

We have identified flexural uplift along a rift zone of the Harran Sulci, Enceladus, using Cassini images and stereo-derived topography. On the assumption that the upraised topography is related to a flexed elastic plate, shape modeling yields an effective lithospheric thickness of 0.3 km and, combined with the strength envelope, a mechanical lithospheric thickness of 2.5 km with heat fluxes of 200-270 mW/m2 at the time of formation. The heat fluxes are comparable to average heat flux values measured in Enceladus’ active south polar region, and they are consistent with estimates derived via models of unstable extension of the lithosphere at this location. Surface porosity can reduce the obtained heat fluxes to an estimated minimum of 45-60 mW/m2. Crater-size frequency counts fix the time of formation (from present-day) of the rift zone at either 3.5 Ga (assuming an asteroid-type impact chronology) or 0.45 Ga (assuming a comet-type impact chronology).