Aims. The secondary atmospheres of terrestrial planets form and evolve as a consequence of interaction with the interior over geological time. We aim to quantify the influence of planetary bulk composition on the interior–atmosphere evolution for Earth-sized terrestrial planets to aid in the interpretation of future observations of terrestrial exoplanet atmospheres. Methods. We used a geochemical model to determine the major-element composition of planetary interiors (MgO, FeO, and SiO2) following the crystallization of a magma ocean after planet formation, predicting a compositional profile of the interior as an initial condition for our long-term thermal evolution model. Our 1D evolution model predicts the pressure–temperature structure of the interior, which we used to evaluate near-surface melt production and subsequent volatile outgassing. Volatiles are exchanged between the interior and atmosphere according to mass conservation. Results. Based on stellar compositions reported in the Hypatia catalog, we predict that about half of rocky exoplanets have a mantle that convects as a single layer (whole-mantle convection), and the other half exhibit double-layered convection due to the presence of a mid-mantle compositional boundary. Double-layered convection is more likely for planets with high bulk planetary Fe-content and low Mg/Si-ratio. We find that planets with low Mg/Si-ratio tend to cool slowly because their mantle viscosity is high. Accordingly, low-Mg/Si planets also tend to lose volatiles swiftly through extensive melting. Moreover, the dynamic regime of the lithosphere (plate tectonics vs. stagnant lid) has a first-order influence on the thermal evolution and volatile cycling. These results suggest that the composition of terrestrial exoplanetary atmospheres can provide information on the dynamic regime of the lithosphere and the thermo-chemical evolution of the interior.

Context. Stars in the solar neighbourhood have refractory element ratios slightly different from that of the Sun. It is unclear how much the condensation of solids and thus the composition of planets forming around these stars is affected. Aims. We aim to understand the impact of changing the ratios of the refractory elements Mg, Si, and Fe within the range observed in solar-type stars within 150 pc of the Sun on the composition of planets forming around them. Methods. We use the GGchem code to simulate the condensation of solids in protoplanetary disks with a minimum mass solar nebula around main sequence G-type stars in the solar neighbourhood. We extract the stellar elemental composition from the Hypatia Database. Results. We find that a lower Mg/Si ratio shifts the condensation sequence from forsterite (Mg2SiO4) and SiO to enstatite (MgSiO3) and quartz (SiO2); a lower Fe/S ratio leads to the formation of FeS and FeS2 and few or no Fe-bearing silicates. Ratios of refractory elements translate directly from the gas phase to the condensed phase for T < 1000 K. However, ratios with respect to volatile elements (e.g. oxygen and sulphur) in the condensates – the building blocks of planets – differ from the original stellar composition. Conclusions. Our study shows that the composition of planets crucially depends on the abundances of the stellar system under investigation. Our results can have important implications for planet interiors, which depend strongly on the degree of oxidation and the sulphur abundance.

Carbon-enriched rocky exoplanets have been proposed around dwarf stars as well as around binary stars, white dwarfs and pulsars. However, the mineralogical make up of such planets is poorly constrained. We performed high-pressure high-temperature laboratory experiments (P = 1´2 GPa, T = 1523´1823 K) on chemical mixtures representative of C-enriched rocky exoplanets based on calculations of protoplanetary disk compositions. These P´T conditions correspond to the deep interiors of Pluto-to Mars-size planets and the upper mantles of larger planets.Our results show that these exoplanets, when fully-differentiated, comprise a metallic core, a silicate mantle and a graphite layer on top of the silicate mantle. Graphite is the dominant carbon-bearing phase at the conditions of our experiments with no traces of silicon carbide or carbonates. The silicate mineralogy comprises olivine, orthopyroxene, clinopyroxene and spinel, similar to the mineralogy of the mantles of carbon-poor planets such as the Earth, and largely unaffected by the amount of carbon. Metals are either two immiscible iron-rich alloys (S-rich and S-poor) or a single iron-rich alloy in the Fe-C-S system with immiscibility depending on the S/Fe ratio and core pressure.We show that for our C-enriched compositions the minimum carbon abundance needed for C-saturation is 0.05´0.7 wt% (molar C/O " 0.002´0.03). Fully differentiated rocky exoplanets with C/O ratios more than needed for C-saturation would contain graphite as an additional layer on top of the silicate mantle. For a thick enough graphite layer, diamonds would form at the bottom of this layer due to high pressures.We model the interior structure of Kepler-37b and show that a mere 10 wt% graphite layer would decrease its derived mass by 7%, suggesting future space missions that determine both radius and mass of rocky exoplanets with insignificant gaseous envelopes could provide quantitative limits on their carbon content. Future observations of rocky exoplanets with graphite-rich surfaces would show low albedos due to the low reflectance of graphite. The absence of life-bearing elements other than carbon on the surface likely makes them uninhabitable.

Rocky planet compositions regulate planetary evolution by affecting core sizes, mantle properties, and melting behaviors. Yet, quantitative treatments of this aspect of exoplanet studies remain generally underexplored. We attempt to constrain the range of potential bulk terrestrial exoplanet compositions in the solar neighborhood (<200 pc). We circumscribe probable rocky exoplanet compositions based on a population analysis of stellar chemical abundances from the Hypatia and GALAH catalogs. We apply a devolatilization model to simulate compositions of hypothetical, terrestrial-type exoplanets in the habitable zones around Sun-like stars, considering elements O, S, Na, Si, Mg, Fe, Ni, Ca, and Al. We further apply core–mantle differentiation by assuming constant oxygen fugacity, and model the consequent mantle mineralogy with a Gibbs energy minimization algorithm. We report statistics on several compositional parameters and propose a reference set of (21) representative planet compositions for use as end-member compositions in imminent modeling and experimental studies. We find a strong correlation between stellar Fe/Mg and metallic-core sizes, which can vary from 18 to 35 wt%. Furthermore, stellar Mg/Si gives a first-order indication of mantle mineralogy, with high-Mg/Si stars leading to weaker, ferropericlase-rich mantles, and low-Mg/Si stars leading to mechanically stronger mantles. The element Na, which modulates crustal buoyancy and mantle clinopyroxene fraction, is affected by devolatilization the most. While we find that planetary mantles mostly consist of Fe/Mg silicates, the core sizes and relative abundances of common minerals can nevertheless vary significantly among exoplanets. These differences likely lead to different evolutionary pathways among rocky exoplanets in the solar neighborhood.

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