Seminar – Claire Guimond

Speaker: Claire Guimond, Department of Earth Sciences, Cambridge University

Title: Marble planet propensity: Insights from fundamental geophysics

Abstract: Undetectable differences in how water is distributed on rocky planets will make or break whether they could support dry land, with big consequences for long-term climate stability and the chemical origin of life. Our sample of one marbled world reveals little about the cosmic probability of this planetary form. Indeed, Earth’s land/ocean fraction reflects complex, indeterministic systems tied to its particular tectonic regime. Nevertheless, we can identify more intrinsic processes which promote land or oceans on any rocky planet, and which clue us to their propensity to host both. On one hand, topography increases land area by hollowing out ocean basins, a container for surface water. Geophysical scalings of RMS elevation with planet mass thus tell us the minimum ocean volume that would inundate a planet. On the other hand, silicate mantles will also be a large reservoir for water (i.e., as structurally-bound hydrogen in minerals), with a thermodynamically-limited total capacity predictable from planet mass and bulk composition. All else equal, planets with low capacity for interior water storage could more likely end up covered by deep oceans, if this water cannot be contained elsewhere. Finally, volcanic outgassing links these interior and surface water reservoirs, but as I discuss, determining its actual fluxes is difficult. Overall, the results I show in this talk illustrate how we can leverage geophysical models to understand aspects of rocky worlds not amenable to observation.

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