Rocky planets larger than Earth are expected to undergo internal geochemical reactions that promote secondary atmospheres rich in water and carbon dioxide. But the highly turbulent fluid flow of internal magma oceans may change this simplified picture. Here, I argue that the magma circulation regime in the interiors of sub-Neptunes may preserve some of the mantle composition inherited from planetary formation, which affects what types of atmospheres we can expect to find with exoplanet surveys.

The earliest history of the Solar System is inscribed in meteorites and the present-day structure of the inner terrestrial and outer gaseous and ice-rich planet population. We developed a new theory that explains our own home planetary system as the result of formation in two distinct episodes. This sets the inner and outer planets on divergent evolutionary paths already during the accretion of the proto-Sun and reinterprets the origins of the Earth’s earliest atmosphere and oceans.

The form and availability of carbon compounds on the surface sensitively govern long-term climate and the chemistry of life, but curiously carbon is strongly depleted on the terrestrial planets of the Solar System. To better understand what separates potentially habitable from non-habitable worlds, we modelled disk and planetary processes that drive carbon sequestration and loss during planet formation. We found these to be a strong function of time: disk evolution and outgassing from planetesimals can lead to several orders of magnitude decrease in the carbon abundance on planetary system-wide scales, which limits the delivery of carbon and introduces a crucial parameter that influences the volatile inheritance of terrestrial worlds: timing.

Carbon in and on the terrestrial planets

Carbon is perhaps the most essential of the elements of life. About 19% of your body is made of carbon and all bio-essential chemistry is driven by carbon-based molecules…

Our own world started out as a literal hell — at the onset of the ‘Hadean’ eon the Moon-forming impact melted and vaporized large parts of the adolescent Earth. The resulting ‘magma ocean’ cooled down over a few million years, eventually allowing the water vapor in the atmosphere to rain out and form the earliest oceans not too long after the last giant collision — or so the story goes, according to the combined picture from geochemical, astronomical, and planetary science studies. But does this story hold equally well for other planets, such as Venus, Mars, or even rocky planets in other, extrasolar planetary systems?

The inner life of rocky planets’ seeds

The terrestrial worlds of the solar system were born out of growing swarms of so-called planetesimals. These…

Tim Lichtenberg

Postdoctoral Fellow @ Atmospheric, Oceanic and Planetary Physics, University of Oxford.

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