article published yes Bingqing Cheng author cbe3cda4-d82c-11eb-8dc7-8ff94289fcc90000-0002-3584-9632 Sebastien Hamel author Mandy Bethkenhagen author 201939f4-803f-11ed-ab7e-d8da4bd1517f0000-0002-1838-2129 BiCh department NOMIS Fellowship Program project 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 melting line of diamond, and then reveal the nature of chemical bonding in hydrocarbons at extreme conditions. We finally establish the pressure-temperature phase boundary where it is thermodynamically possible for diamond to form from hydrocarbon mixtures with different atomic fractions of carbon. Notably, here we show 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. https://research-explorer.ista.ac.at/download/12702/12713/2023_NatComm_Cheng.pdf application/pdfno https://creativecommons.org/licenses/by/4.0/ Springer Nature2023 eng 2041-1723 36843123 00093967830000210.1038/s41467-023-36841-1 14 Cheng, B., Hamel, S., &#38; Bethkenhagen, M. (2023). Thermodynamics of diamond formation from hydrocarbon mixtures in planets. <i>Nature Communications</i>. Springer Nature. <a href="https://doi.org/10.1038/s41467-023-36841-1">https://doi.org/10.1038/s41467-023-36841-1</a> Cheng B, Hamel S, Bethkenhagen M. 2023. Thermodynamics of diamond formation from hydrocarbon mixtures in planets. Nature Communications. 14, 1104. Cheng, Bingqing, Sebastien Hamel, and Mandy Bethkenhagen. “Thermodynamics of Diamond Formation from Hydrocarbon Mixtures in Planets.” <i>Nature Communications</i>. Springer Nature, 2023. <a href="https://doi.org/10.1038/s41467-023-36841-1">https://doi.org/10.1038/s41467-023-36841-1</a>. Cheng, Bingqing, et al. “Thermodynamics of Diamond Formation from Hydrocarbon Mixtures in Planets.” <i>Nature Communications</i>, vol. 14, 1104, Springer Nature, 2023, doi:<a href="https://doi.org/10.1038/s41467-023-36841-1">10.1038/s41467-023-36841-1</a>. Cheng B, Hamel S, Bethkenhagen M. Thermodynamics of diamond formation from hydrocarbon mixtures in planets. <i>Nature Communications</i>. 2023;14. doi:<a href="https://doi.org/10.1038/s41467-023-36841-1">10.1038/s41467-023-36841-1</a> B. Cheng, S. Hamel, M. Bethkenhagen, Nature Communications 14 (2023). B. Cheng, S. Hamel, and M. Bethkenhagen, “Thermodynamics of diamond formation from hydrocarbon mixtures in planets,” <i>Nature Communications</i>, vol. 14. Springer Nature, 2023. 127022023-03-05T23:01:04Z2025-04-15T07:39:24Z