The chemical consequences of vapour loss during planetary accretion

Planets have long been thought to be made from building blocks of primitive (chondritic) meteorites.

Yet it has become increasingly clear that such models fail to reproduce the composition of the best constrained planet, Earth.

Problematically, no combination of chondritic meteorites can simultaneously explain Earth’s major element composition and isotopic characteristics. This striking dilemma points to the need for a radical reassessment of the current paradigm of planet formation. A tacit assumption of most previous models has been growth with a chemically closed system.

Recent work has pointed to the likelihood of significant vapour loss during energetic, collisional accretion. Substantial modifications of the composition of a planet could occur as a result of vapour loss during this accretion.

However, there is a critical lack of data to establish whether this drastically different model of planet formation accounts for the apparently conflicting perspectives on planetary origins from isotopic and elemental data. In this proposal I will therefore quantify the consequences of such major vapour loss during violent planetary growth.

In a multi-faceted approach, I will undertake i) pioneering, high-temperature experiments mimicking partial vaporisation of molten planetary bodies, combined with ii) analysis of critical elemental and isotopic distributions between the liquid and co-existing vapour from the experiments as well as in key meteorites and terrestrial samples, and iii) numerical modelling to trace the chemical evolution of a planetary body as vapour loss proceeds in various astrophysical scenarios.

In combination, this work will allow me to assess rigorously the value of promising models of vapour loss in accounting for the long problematic volatile contents of planetary bodies as well as the unique abundances of Earth’s main constituents.