The influence of primordial atmospheric composition on the long-term habitability of stagnant-lid planets

Understanding the role of a planet’s interior in establishing habitable conditions is a critical, yet often overlooked, aspect of planetary evolution. The atmosphere and interior of a rocky planet do not form separate systems, but are coupled by a complex network of feedback processes which link the evolution of the atmosphere to the evolution of the interior. For example, 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 oxidation state of the mantle, but also on the current state - i.e., pressure, composition, and temperature - of the atmosphere. As such, the composition of the earliest atmosphere can drastically change the evolutionary path of the planet. In addition, the early surface conditions set the stage for which stabilizing feedback cycles initiate. For example, the carbonate-silicate cycle on Earth, which regulates the amount of CO2 in the atmosphere to ensure a temperate climate, heavily relies on liquid water for surface weathering, and on plate tectonics to transport carbonates back into the mantle.

However, many terrestrial exoplanets are expected to be stagnant-lid planets, i.e. those without active plate tectonics, such as Mars. Although the interior-atmosphere coupling in these planets is weaker, feedback cycles still play an important role in their evolution, and some form of carbonate-silicate cycling may still work even in the absence of plate tectonics. Stagnant-lid planets therefore offer an ideal test bed to explore the baseline conditions required for habitability.

In an earlier work, we showed that long-term habitability on stagnant-lid planets depends on a narrow range of mantle volatile contents and redox states. In this study, we explore in particular how the primary atmosphere, outgassed during the magma ocean stage of formation, predisposes a stagnant-lid planet to different long-term atmospheric states. For this, we use our 1D planet evolution code TEMPURA to simulate the long term coupled evolution of planet interior and atmosphere, including a comprehensive array of feedback processes between atmosphere and interior, such as a CO2 weathering cycle, volcanic outgassing, a water cycle between ocean and atmosphere, greenhouse heating, as well as atmospheric escape processes.

We aim to identify the critical processes and conditions that produce long-term habitable conditions (even in the absence of active tectonic recycling) across a wide range of terrestrial planets.