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

TL;DR

This study demonstrates that gas flow velocity significantly influences isotope fractionation during evaporation of protoplanetary material, with experiments and theory showing the flow's role as a potential velocimeter in planetary formation environments.

Contribution

It introduces a theoretical framework linking gas flow velocity to isotope fractionation, supported by new experimental Fe and Mg isotope data.

Findings

Gas flow velocity controls isotope fractionation during evaporation.

Isotope fractionation correlates with the ratio of flow velocity to thermal velocity.

Flow dynamics can serve as a velocimeter in planetary environments.

Abstract

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.