Abstract
The earliest atmospheres of rocky planets originate from extensive volatile release during magma ocean epochs that occur during assembly of the planet. These establish the initial distribution of the major volatile elements between different chemical reservoirs that subsequently evolve via geological cycles. Current theoretical techniques are limited in exploring the anticipated range of compositional and thermal scenarios of early planetary evolution, even though these are of prime importance to aid astronomical inferences on the environmental context and geological history of extrasolar planets. Here, we present a coupled numerical framework that links an evolutionary, vertically resolved model of the planetary silicate mantle with a radiative‐convective model of the atmosphere. Using this method, we investigate the early evolution of idealized Earth‐sized rocky planets with end‐member, clear‐sky atmospheres dominated by either H2, H2O, CO2, CH4, CO, O2, or N2. We find central metrics of early planetary evolution, such as energy gradient, sequence of mantle solidification, surface pressure, or vertical stratification of the atmosphere, to be intimately controlled by the dominant volatile and outgassing history of the planet. Thermal sequences fall into three general classes with increasing cooling timescale: CO, N2, and O2 with minimal effect, H2O, CO2, and CH4 with intermediate influence, and H2 with several orders of magnitude increase in solidification time and atmosphere vertical stratification. Our numerical experiments exemplify the capabilities of the presented modeling framework and link the interior and atmospheric evolution of rocky exoplanets with multiwavelength astronomical observations.
Highlights
The debate surrounding the formation and long-term evolution of rocky planets has been dominated by the wealth of data obtained from the terrestrial planets and planetary materials in the Solar System
The earliest atmospheres of rocky planets originate from extensive volatile release during magma ocean epochs that occur during assembly of the planet
We explore the energetic feedback between a solidifying magma ocean and its outgassed atmosphere
Summary
Having so far only glimpsed the richness and diversity of the exoplanet census, statistical evaluation of basic physical properties—such as mass, radius, and atmospheric features—teach us that individual rocky planets differ substantially from one another and from the terrestrial planets of the Solar System (Jontof-Hutter, 2019; Owen, 2019; Pierrehumbert & Hammond, 2019). Further out, being born from volatile-rich building blocks, solid-dominated planets may resemble scaled-up versions of the icy moons of the outer Solar System (Kuchner, 2003; Léger et al, 2004), where high-pressure ice phases at the mantle-atmosphere interface inhibit Earth-like geochemical cycling of nutrients (Journaux et al, 2020; Kite & Ford, 2018; Noack et al, 2017). For the more massive super-Earths, the crushing pressures at depth generate a supercritical fluid of equilibrated vapor and rock (Kite et al, 2019; Madhusudhan et al, 2020), rendering a surface absent in the traditional sense
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