5171 20210125151805.0 POSTER-2021-0010 Beuthe, Mikael Equivalence between elastic, viscoelastic, and viscous isostasy 2020 2020-09-21 Isostasy explains why observed gravity anomalies are generally much weaker than what is expected from topography alone, and why planetary crusts can sup- port high topography without breaking up. The apparent simplicity of the concept – buoyant support of mountains by iceberg-like roots – is belied by the debate that has been going on for over a century about ‘equal mass’ and ‘equal pressure’ prescriptions. Since these isostatic models only differ at the planetary scale, it has not caused a problem for the application of isostasy to Earth because of its division in tectonic plates (large-scale geoid anomalies due to mantle convection are another reason). By contrast, isostasy on icy moons and dwarf planets is immediately faced with the problem of defining correctly isostasy at the largest scales. For this purpose, new isostatic models based on the minimization of stress, on time-dependent vis- cous evolution, and on stationary viscous flow have recently been published (these models have historical precedents not cited here). The multiplicity of isostatic approaches is too much of a good thing. I will show that these new isostatic approaches are mostly equivalent. PRODEX program managed by ESA and BELSPO/ PRODEX program managed by ESA and BELSPO/ PRODEX program managed by ESA and BELSPO NO 14th Europlanet Science Congress 2020, virtual meeting held online mikael.beuthe@observatoire.be https://meetingorganizer.copernicus.org/EPSC2020/EPSC2020-863.html CPOSTER