Interior structure, mantle-atmosphere co-evolution, and habitability of low-mass exoplanets

Abstract

A solid understanding of the interior composition and processes of exoplanets is a necessary foundation for addressing some of the fundamental questions in planetary science, encompassing the types of planets that may exist, the mechanisms governing planet formation and evolution, the uniqueness of our Solar System, and the potential existence of extraterrestrial life. Three first-author publications form the basis of this dissertation, which explores two avenues for studying planetary interiors. Baumeister et al. (2020) and Baumeister and Tosi (2023) present a novel machine learning-based model, which can provide first estimates of potential planet interiors from a given mass and radius in fractions of a second. The fast computation times of this model allows, for the first time, a rapid large-scale interior characterization of exoplanets. Furthermore, both publications show that measuring the fluid Love number k2, which may be inferred from a planet's shape or the precession of its orbit, would help to significantly constrain the interior of the planet. Moreover, a planet is not a static entity. The interior and atmosphere of rocky planets co-evolve as a coupled system through a variety of interactions and feedback processes. Baumeister et al. (2023) explores the long-term habitability of stagnant-lid exoplanets - those without plate tectonics - as a function of key planetary parameters, such as planet mass, the size of the iron core, and the oxidation state and water content of the mantle. The model includes a comprehensive array of feedback processes and interactions between interior and atmosphere. The modeling of more than 280000 coupled atmosphere-interior evolutions shows that a wide diversity of atmospheric compositions develops in response to interior properties. Only a narrow range of mantle oxidation states allows long-term habitable conditions, and many planets end up with Venus-like hot, dense atmospheres instead. On planets with large iron cores, these conditions are less likely to develop due to generally lower volcanic activity. Altogether, this work underscores the value of a holistic approach in studying exoplanets, ranging from the characterization of interiors to the assessment of habitability.