Internally Heated Porous Convection: An Idealized Model for Enceladus' Hydrothermal Activity

Thomas Le Reun,Duncan R Hewitt

doi:10.1029/2020je006451

Thomas Le Reun, Duncan R Hewitt

Open Access

https://doi.org/10.1029/2020je006451

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Abstract

AbstractRecent planetary data and geophysical modeling suggest that hydrothermal activity is ongoing under the ice crust of Enceladus, one of Saturn's moons. According to these models, hydrothermal flow in the porous, rocky core of the satellite is driven by tidal deformation that induces dissipation and volumetric internal heating. Despite the effort in the modeling of Enceladus' interior, systematic understanding—and even basic scaling laws—of internally heated porous convection and hydrothermal activity are still lacking. In this article, using an idealized model of an internally heated porous medium, we explore numerically and theoretically the flows that develop close to and far from the onset of convection. In particular, we quantify heat‐transport efficiency by convective flows as well as the typical extent and intensity of heat flux anomalies created at the top of the porous layer. With our idealized model, we derive simple and general laws governing the temperature and hydrothermal velocity that can be driven in the oceans of icy moons. In the future, these laws could help better constraining models of the interior of Enceladus and other icy satellites.

Highlights

Enceladus, a 500 km diameter icy satellite orbiting Saturn, has drawn a lot of attention since the first flybys operated by the Cassini probe in 2005
We show quantitatively that nonlinear heat transport is dominated by advection, which constrains the typical size of hot plumes and thermal anomalies
Throughout this section, we have detailed the properties of heat transport by convection in strongly nonlinear regimes

Summary

Introduction

A 500 km diameter icy satellite orbiting Saturn, has drawn a lot of attention since the first flybys operated by the Cassini probe in 2005. Pictures and in situ astrochemical measurement have revealed the presence of a water vapor and ice plume ejected into outer space. It emerges along fractures in the ice crust at the south pole of Enceladus and is associated with a large heat‐flux anomaly of 12.5 GW (Spencer et al, 2006, 2018). Enceladus' plumes have since been interpreted as evidence for hydrothermal activity occurring below the ice crust of Enceladus This is a surprising implication because, unlike the Earth, Enceladus has radiated away all its initial heat, and its small size makes internal heating by radiogenic elements insufficient to explain the abnormal heat flux (Choblet et al, 2017; Nimmo & Pappalardo, 2016)

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