common outcome is a thin, O2-dominated atmosphere, unless a long-lived magma ocean or unusually high initial water content is maintained.

The observational evidence for GJ 1132 b therefore favours an evolutionary history in which efficient early atmospheric loss and limited late-stage outgassing suppress the persistence of a detectable present-day atmosphere.

Future detections of even weak CO2- or H2O-dominated envelopes would provide valuable constraints on the planet’s initial volatile inventory and redox state, highlighting the potential of GJ 1132 b as a probe of coupled interior–atmosphere evolution (Nicholls et al. 2025b).

A key question emerging from our results is whether the interior oxidation state can be constrained from atmospheric observations alone.

As shown in Fig 6, volatile inventory exerts a stronger control on total atmospheric mass but not on composition than redox state, while fOsurf
primarily controls atmospheric speciation.

This introduces a degeneracy between volatile content and oxidation state that is difficult to break from bulk atmospheric properties alone.

In this context, accurate atmospheric modelling plays an important role in linking observable upper-atmosphere compositions to near-surface redox chemistry.

Mixing processes and photochemical reactions can modify the vertical distribution of molecular species, potentially obscuring or preserving the redox signature of outgassed volatiles in the observable atmosphere (Pierrehumbert 2010).

Turbulent mixing and photochemical reactions can modify the vertical distribution of molecular species, potentially obscuring or preserving the redox signature of outgassed volatiles in the observable atmosphere (Shorttle et al. 2024; Nicholls et al. 2025a).

While thermochemical equilibrium signatures set in the deep atmosphere may be propagated to observable pressure levels if mixing timescales are short compared to reaction timescales (Tsai et al. 2023; Nicholls et al. 2025a).

It should thus be tested under which conditions disequilibrium atmospheric processes could obscure the outgassed volatile composition and thus redox state.

Together, these considerations suggest that these kind of modelling, would represent a promising avenue for constraining deep-mantle redox conditions from upcoming JWST and ELT observations.

In this study, we assumed volatile exchange only between the melt and atmosphere.

In reality, incorporation of H, C, or O through melt trapping or crystal inclusions (Sim et al. 2024; Krissansen-Totton et al. 2024) could increase the total outgassing efficiency and accelerate mantle oxidation, potentially yielding thinner atmospheres and shorter magma ocean lifetimes (Lebrun et al. 2013; Salvador et al. 2017; Nikolaou et al. 2019; Bower et al. 2019).

In these cases, melt redistribution due to the effects described here would amplify the ability of the mantle to store or release volatiles (Hier-Majumder & Hirschmann 2017; Sim et al. 2024).

The feedbacks between these mechanisms should be studied, but are outside the scope of this work.

Furthermore, atmospheric escape processes are not included.

In particular, close-in rocky planets are expected to experience efficient hydrodynamic and energy-limited escape of light species driven by stellar X-ray and extreme ultraviolet irradiation (e.g.,Watson et al. (1981); Zahnle & Kasting (1986); Schaefer et al. (2016); Owen (2019)).

As a consequence, the large H2 abundances predicted under reducing conditions in our simulations likely represent upper limits on the long-term atmospheric hydrogen content (Schaefer et al. 2016; Nicholls et al. 2024).

However, by varying the initial hydrogen inventory across our may arise from different escape histories, providing a first-order sensitivity analysis of how atmospheric mass and composition respond to hydrogen loss.