The heat flow of Europa

The heat flow from Europa has profound implications for ice shell thickness and structure, as well as for the existence of an internal ocean, which is strongly suggested by magnetic data. The brittle-ductile transition depth and the effective elastic thickness of the lithosphere are here used to perform heat flow estimations for Europa. Results give preferred heat flow values (for a typical geological strain rate of 10−15s−1) of 70-110 mW m−2 for a brittle-ductile transition 2 km deep (the usually accepted upper limit for the brittle-ductile transition depth in the ice shell of Europa), 24-35 mW m−2 for an effective elastic thickness of 2.9 km supporting a plateau near the Cilix impact crater, and >130 mW m−2 for effective elastic thicknesses of ⩽0.4 km proposed for the lithosphere loaded by ridges and domes. These values are clearly higher than those produced by radiogenic heating, thus implying an important role for tidal heating. The ⩾19-25 km thick ice shell proposed from the analysis of size and depth of impact structures suggests a heat flow of ⩽30-45 mW m−2 reaching the ice shell base, which in turn would imply an important contribution to the heat flow from tidal heating within the ice shell. Tidally heated convection in the ice shell could be capable to supply ∼100 mW m−2 for superplastic flow, and, at the Cilix crater region, ∼35-50 mW m−2 for dislocation creep, which suggests local variations in the dominant flow mechanism for convection. The very high heat flows maybe related to ridges and domes could be originated by preferential heating at special settings.