# Phase equilibria of sub-Neptunes and super-Earths

**Authors:** Edward D. Young, Lars Stixrude, James G. Rogers, Hilke E. Schlichting, Sarah P. Marcum  
**arXiv:** [2408.11321](https://arxiv.org/abs/2408.11321)  
**Date:** 2024-08-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2408.11321v1/

## Key points

- Study by Young, Stixrude, Rogers, Schlichting, and Marcum focuses on consequences of non-ideal chemical interactions between silicate and hydrogen-rich envelopes for rocky planets
- Silicate-hydrogen binary solvus crucial in shaping atmospheres and internal layering of rocky planets with H$_2$-rich primary atmospheres
- Temperatures at surfaces of supercritical magma oceans align with silicate-hydrogen solvus, indicating thermal states of planets
- Structure of atmosphere and transit radii of sub-Neptunes influenced by conditions set forth by the solvus
- Neutral buoyancy of metal in silicate melt challenges traditional assumptions about metal core formation in sub-Neptunes and super-Earths

## Summary

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In their study, Edward D. Young, Lars Stixrude, James G. Rogers, Hilke E. Schlichting, and Sarah P. Marcum delve into the consequences of non-ideal chemical interactions between silicate and hydrogen-rich envelopes for rocky planets by applying fundamental principles of phase equilibria. The researchers determine that the silicate-hydrogen binary solvus plays a crucial role in shaping the atmospheres and internal layering of rocky planets with H$_2$-rich primary atmospheres. Their analysis reveals that the temperatures at the surfaces of supercritical magma oceans align with the silicate-hydrogen solvus, indicating key indicators of these planets' thermal states. This insight suggests that the structure of the atmosphere and transit radii of sub-Neptunes are influenced by the conditions set forth by the solvus. Additionally, traditional assumptions regarding metal core formation in sub-Neptunes and super-Earths may be challenged due to neutral buoyancy of metal in silicate melt hindering separation of iron-rich metal to form metal cores at elevated temperatures. Through their comprehensive investigation, Young et al. 's findings shed light on how non-ideal chemical interactions between silicate and hydrogen can impact planetary composition and atmospheric characteristics. This work contributes valuable insights to our understanding of rocky planet formation processes and challenges existing notions about internal layering dynamics in celestial bodies with H$_2$-rich atmospheres.