Connecting the interior to the atmosphere: should atmospheres of warm rocky planets differ for stagnant-lid and mobile surface regimes?

Abstract

Many factors influence the long-term evolution of the atmosphere of a rocky planet, including star-planet interactions and late accretion of volatiles. However, for planets where gravity is low enough for a primordial atmosphere to escape (i.e. roughly Earth-size and smaller), the main factor driving the atmospheric evolution will be volcanic outgassing from the interior.

While for planets in the habitable zone, where liquid water may exist that could allow for an Earth-like carbon-silicate cycle, planets closer to their host star have been suggested to have Venus-like, thick CO2-dominated atmospheres. Our study focusses on the question, how basic planetary parameters such as size, core mass fraction, and surface regime (either stagnant-lid or mobile, such as plate tectonics) may impact the atmosphere, specifically the range of atmospheric pressures as well as their composition, for warm planets where condensation of water as well as an efficient carbon cycle can be excluded.

We show, that planets with a stagnant lid tend to be hotter in their interior due to the isolating behaviour of the lithosphere, but at the same time tend to have much reduced outgassing efficiencies. At the same time, since volcanic outgassing at the surface of a planet is directly influenced by partial pressures in the atmosphere, compositional variations appear between stagnant-lid or mobile-lid planets, as well as between low-mass and high-mass rocky planets.

Observations with JWST looking at warmer planets (i.e. inside the inner boundary of the habitable zone) might therefore give first-order indications on the outgassing efficiency (coupled with the erosion efficiency of the atmosphere) and surface regime of these rocky planets.