Devolatilisation: A Pathway to Uncover the Chemical Properties of Rocky Exoplanets
As the solar nebula condensed, evaporated and fractionated to form the early Earth, the bulk elemental composition of the Earth was essentially set. To first order, the Earth is a devolatilised piece of the solar nebula. Similarly, rocky exoplanets are also likely devolatilised pieces of the stellar nebulae out of which they and their host stars formed. My PhD research took the planet Earth and the Sun as a Rosetta stone to study the devolatilisation - i.e. depletion of volatiles - in going from the solar nebula to form rocky planets. The devolatilisation is of fundamental importance if we are to understand and quantify what makes a planet suitable for life. By measuring the spectra of host stellar photospheres, the bulk elemental composition of rocky exoplanets can be quantified to first order from the elemental abundances in the star.
My proposed research at ELSI will generalise my investigation of devolatilisation to the whole solar system. This generalisation is critical considering the complexity of planet formation, through processes such as partial condensation, photoevaporation, accretion and collision, as well as giant impacts in conjunction with magmatic solidification. Such a generic devolatilisation relationship, rather than that only for Earth, acts as a thermometer revealing prevailing conditions in the early solar system. The proposed research will result in a practical toolkit for estimating the bulk composition of rocky exoplanets. The exoplanetary bulk compositions are the key to moving the characterisation of exoplanets from the realm of the physical - e.g. planetary orbit, mass and radius - to the chemical, including but not limited to the composition of interior, surface conditions and atmosphere. All of these quantities are of fundamental importance to assess the chemical habitability of rocky exoplanets, beyond the usual classification of planets within or out of the so-called habitable zone.