Theoretical evidence of H-He demixing under Jupiter and Saturn conditions

XJ Chang and B Chen and QY Zeng and H Wang and KG Chen and QC Tong and XX Yu and DD Kang and S Zhang and FY Guo and Y Hou and ZX Zhao and YS Yao and YM Ma and JY Dai, NATURE COMMUNICATIONS, 15, 8543 (2024).

DOI: 10.1038/s41467-024-52868-4

The immiscibility of hydrogen-helium mixture under the temperature and pressure conditions of planetary interiors is crucial for understanding the structures of gas giant planets (e.g., Jupiter and Saturn). While the experimental probe at such extreme conditions is challenging, theoretical simulation is heavily relied in an effort to unravel the mixing behavior of hydrogen and helium. Here we develop a method via a machine learning accelerated molecular dynamics simulation to quantify the physical separation of hydrogen and helium under the conditions of planetary interiors. The immiscibility line achieved with the developed method yields substantially higher demixing temperatures at pressure above 1.5 Mbar than earlier theoretical data, but matches better to the experimental estimate. Our results suggest a possibility that H-He demixing takes place in a large fraction of the interior radii of Jupiter and Saturn, i.e., 27.5% in Jupiter and 48.3% in Saturn. This indication of an H-He immiscible layer hints at the formation of helium rain and offers a potential explanation for the decrease of helium in the atmospheres of Jupiter and Saturn. The immiscibility of H-He mixtures in gas giants remains poorly understood. Here the authors use large scale machine learning accelerated molecular dynamics simulations to suggest that H-He demixing may occur within large interior radii of Jupiter and Saturn.

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