Isotope velocimetry: Experimental and theoretical demonstration of the potential importance of gas flow for isotope fractionation during evaporation of protoplanetary material

We use new experiments and a theoretical analysis of the results to show that the isotopic fractionation associated with laser-heating aerodynamic levitation experiments is consistent with the velocity of flowing gas as the primary control on the fractionation. The new Fe and Mg isotope data are well explained where the gas is treated as a low-viscosity fluid that flows around the molten spheres with high Reynolds numbers and minimal drag. A relationship between the ratio of headwind velocity to thermal velocity and saturation is obtained on the basis of this analysis. The recognition that it is the ratio of flow velocity to thermal velocity that controls fractionation allows for extrapolation to other environments in which molten rock encounters gas with appreciable headwinds. In this way, in some circumstances, the degree of isotope fractionation attending evaporation is as much a velocimeter as it is a barometer. (C) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

This study utilizes new experiments and a theoretical analysis to demonstrate that the isotopic fractionation associated with laser-heating aerodynamic levitation experiments is primarily controlled by the velocity of flowing gas. The research successfully explains the new Fe and Mg isotope data by treating the gas as a low-viscosity fluid and considering high Reynolds numbers and minimal drag. Furthermore, a relationship between the ratio of headwind velocity to thermal velocity and saturation is established. The findings suggest that in environments where molten rock encounters gas with appreciable headwinds, the degree of isotope fractionation during evaporation serves as both a velocimeter and a barometer.