AOPP Seminar - Devolatilization during rocky planet formation: Observations, theories, and implications

Devolatilization — depletion of volatile elements (e.g., C, O, S, Na and K) in rocky planets relative to their host stars — is a common feature that has been observed in both the Solar System and exoplanet systems. Various mechanisms have been proposed to explain this common feature, ranging from incomplete condensation of dust materials from an ultra-hot nebula with a host stellar composition, partial evaporation of planetesimals by collisional kinetic energy and/or short-lived radiogenic heating, and vaporization of rock-forming volatiles by giant impacts. While summarizing historical data and understandings of this potentially universal phenomenon of devolatilization in rocky planet formation, I will also present in this talk a novel model based on state-of-the-art pebble accretion theory, constrained by volatile depletion of Earth and Mars, that lend support to a hybrid formation scenario where the inner solar system rocky planets grow by a combination of rapid pebble accretion and a prolonged period of planetesimal accretion and giant impacts.

Extending this model to exoplanet systems, aided by disc observations with JWST and ALMA and high-precision bulk-density observations with current and near-future facilities (e.g., CARMENES, SPECULOOS, HARPS3, and PLATO), will help make quantitative predictions of volatile budget and bulk composition of rocky exoplanets. The outcome will provide an important testbed for evaluating rocky exoplanetary habitability, together with unprecedented atmospheric observations with JWST and upcoming ELT. It will further provide guidance on target selections for next-generation space missions dedicated to searching for habitable worlds and exo-life signals (e.g., HWO and LIFE).