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Earlier this summer, Mariana Sastre (@marianasastre.bsky.social) posted her first paper as lead author 🌋 "Geophysical and atmospheric implications of fO2-dependent melting on rocky exoplanets" Read the paper: https://arxiv.org/abs/2606.20249 #Exoplanets #PlanetaryScience

You would expect that to rewrite the cooling history. It only does when the planet is volatile-poor. Give it enough water and the outgassed atmosphere holds the mantle above its melting point whatever the curve says.

What the planet breathes out is a different matter. Reduced surfaces give hydrogen and carbon monoxide, oxidised ones water and carbon dioxide. Plot: outgassed composition against mantle oxidation state, for three starting water inventories. 🌍

Test case is the short-period super-Earth GJ 1132 b. The two atmospheres are distinct enough for JWST to tell apart. 🔭 The first image shows the melting curves themselves: reduced in blue melts hotter, oxidised in pink melts cooler.