  Recent planetary data and geophysical modelling 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 modelling 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 idealised model of an internally-heated
porous medium, we explore numerically and theoretically the flows that develop
close 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 idealised 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.
