Séminaire Henri Samuel

Abstract

Terrestrial planets likely experienced at least one early global silicate magma ocean stage. Upon cooling, vigorous convective motions are commonly thought to efficiently outgas dissolved volatiles, progressively forming a secondary atmosphere. Atmospheric blanketing, fed by exsolved volatiles can significantly affect the solidification of magma oceans, thereby altering the final thermo-chemical state of planetary mantles, their long-term evolution, and in fine their habitability. In this context, efficient volatile outgassing is a common hypothesis made in coupled magma ocean-atmosphere studies. However, despite extremely vigorous convective motions, volatile outgassing may be limited by the fact that fluid parcels containing dissolved volatiles need to reach shallow exsolution depths to form bubbles that are subsequently outgassed into the atmosphere. To test these hypotheses, I will present computational and analog fluid dynamics experiments conducted at various convective vigour and turbulent states, designed to reproduce planetary magma ocean dynamics. These experiments allowed to derive for the first time the flux of exsolved volatiles out of a magma ocean of evolving thickness. These fluxes indicate that the common assumption of efficient (equilibrium) outgassing is far from being systematically true. I will then discuss the consequences of such inefficient (i.e., out-of-equilibrium) volatile outgassing in terrestrial magma oceans.