Contributed Talk - Splinter Exoplanets

Thursday, 14 September 2023, 15:30   (H 3007)

Redox state and interior structure control on the long-term habitability of exoplanets

Philipp Baumeister (1,2), Nicola Tosi (1), Caroline Brachmann (1,3), John Lee Grenfell (1), Lena Noack (3)
(1) Institute of Planetary Research, German Aerospace Center (DLR) Berlin; (2) Department of Astronomy and Astrophysics,Technische Universität Berlin; (3) Department of Earth Sciences, Freie Universität Berlin

A major goal in exoplanet science is the search for planets with the right conditions to support liquid water. The habitability of a planet depends strongly on the composition of its atmosphere. Meanwhile, the atmospheres of rocky planets are intricately linked to the interior through feedback processes, and both consequently evolve as a coupled system. In particular, volcanic outgassing of volatile species from the planet’s silicate mantle shapes the atmospheric composition, temperature, and pressure, but the exact composition of outgassed species not only depends on the volatile content and redox state of the mantle, but also on the current state of the atmosphere. This means that the interior dynamics of planets can not be neglected in the discussion of habitability. We explore 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, such as a CO2 weathering cycle, volcanic outgassing, a water cycle between ocean and atmosphere, greenhouse heating, as well as escape processes of H2. Our modeling of more than 280 000 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.