Rates of protoplanetary accretion and differentiation set nitrogen budget of rocky planets

Abstract

The effect of protoplanetary differentiation on the fate of life essential volatiles like nitrogen and carbon and its subsequent effect on the dynamics of planetary growth is unknown. Because the dissolution of nitrogen in magma oceans depends on its partial pressure and oxygen fugacity, it is an ideal proxy to track volatile redistribution in protoplanets as a function of their sizes and growth zones. Using high pressure and high temperature experiments in graphite undersaturated conditions, here we show that the iron loving character of nitrogen is an order of magnitude higher than previous estimates across a wide range of oxygen fugacity. The experimental data combined with metal, silicate and atmosphere fractionation models suggest that asteroid sized protoplanets, and planetary embryos that grew from them, were nitrogen depleted. However, protoplanets that grew to planetary embryo size before undergoing differentiation had nitrogen rich cores and nitrogen poor silicate reservoirs. Bulk silicate reservoirs of large Earth like planets attained nitrogen from the cores of latter type of planetary embryos. Therefore, to satisfy the volatile budgets of Earth like planets during the main stage of their growth, the timescales of planetary embryo accretion had to be shorter than their differentiation timescales, that is, Moon to Mars sized planetary embryos grew rapidly within 1 to 2 million years of the Solar System formation.

44 pages, 6 figures, 9 extended data figures. Nat. Geosci. (2021)

References in corpus (4)

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• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• Escape and fractionation of volatiles and noble gases from Mars-sized planetary embryos and growing protoplanets
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Cited by in corpus (11)

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• Super-Earths and Earth-like Exoplanets
• The distribution of volatile elements during rocky planet formation
• Numerous chondritic impactors and oxidized magma ocean set Earth's volatile depletion
• Internal or external magma oceans in the earliest protoplanets -- perspectives from nitrogen and carbon fractionation
• Impact Induced Atmosphere-Mantle Exchange Sets the Volatile Elemental Ratios on Primitive Earths
• Volatile atmospheres of lava worlds
• Redox evolution of the crystallizing terrestrial magma ocean and its influence on atmosphere outgassing
• The origin of Earth's mantle nitrogen: primordial or early biogeochemical cycling?
• Multiverse Predictions for Habitability: Stellar and Atmospheric Habitability
• Coupling dynamical accretion and chemical differentiation: A unified framework for the diversity of Earth and Mars