23/out/20 – Geophysical evolution during rocky planet formation (Dr. Tim Lichtenberg, University of Oxford)

In the last few decades astronomical observations have revealed that planetary objects are plentiful in the galactic neighbourhood and truly diverse in nature. However, exoplanet measurements are so far limited to assessing only the most basic parameters, such as radius, mass, and bulk density of a planet, from which detailed characterisation of smaller, Earth-sized planets remain challenging. In order to gain a more comprehensive understanding of the exoplanet census, contextual information on the delivery of major volatile elements and constraints on physical mechanisms that shape such planets are needed. In this talk, I will discuss how the inhomogeneous enrichment of forming planetary systems with short-lived radionuclides like Al-26 in typical star-forming environments may control the interior evolution and volatile loss of planetesimals that accrete to form terrestrial planets. Their resulting internal geophysical evolution sub-divides rocky exoplanetary systems into distinct populations: enriched systems with Solar-like or higher levels tend to form water-depleted planets, while not- or barely-enriched systems dominantly form ocean worlds, with water levels comparable to the icy moons of the outer Solar System. The dependence on the abundance of internal radioactive heat sources that are formed in massive stars suggests a direct link between the star-forming birth environment of planetary systems and the compositional make-up and long-term evolution of rocky planets that form in them. Systematic deviations in the composition of young star-forming regions qualitatively distinguish planetary systems’ formation and evolution, and may control the distribution and prevalence of terrestrial planets with Earth-like bulk compositions.