Diamond formation from hydrocarbon mixtures in planets

Abstract

Hydrocarbon mixtures are extremely abundant in the Universe, and diamond formation from them can play a crucial role in shaping the interior structure and evolution of planets. With first-principles accuracy, we first estimate the diamond nucleation rate in pure liquid carbon, and then reveal the nature of chemical bonding in hydrocarbons at extreme conditions. We finally establish the pressure-temperature phase boundary where diamond can form from hydrocarbon mixtures with different atomic fractions of carbon. Notably, we find a depletion zone at pressures above 200~GPa and temperatures below 3000~K-3500~K where diamond formation is thermodynamically favorable regardless of the carbon atomic fraction, due to a phase separation mechanism. The cooler condition of the interior of Neptune compared to Uranus means that the former is much more likely to contain the depletion zone. Our findings can help explain the dichotomy of the two ice giants manifested by the low luminosity of Uranus, and lead to a better understanding of (exo-)planetary formation and evolution.

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• An Accurate and Transferable Machine Learning Potential for Carbon
• Quantum-mechanical exploration of the phase diagram of water
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• Diamond formation from hydrocarbon mixtures in planets
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• Electronic Density Response of Warm Dense Matter
• Diamond formation from hydrocarbon mixtures in planets
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• Full-scale ab initio simulations of laser-driven atomistic dynamics
• Stochastic and Mixed Density Functional Theory within the projector augmented wave formalism for the simulation of warm dense matter
• The Possibility of Hydrogen-Water Demixing in Uranus, Neptune, K2-18b and TOI-270d
• Optical and Transport Properties of Plasma Mixtures from Ab Initio Molecular Dynamics
• Crystal nucleation rates in one-component Yukawa systems
• Machine-Learned Bond-Order Potential for Exploring the Configuration Space of Carbon
• The Evolution and Internal Structure of Neptunes and Sub-Neptunes: The importance of thermal conductivity in non-convective regions
• Cyclic random graph models predicting giant molecules in hydrocarbon pyrolysis