The Influences of Hydrogen-Silicate-Iron Miscibility on the Demographics of Sub-Neptunes and Super-Earths
TLDR
Hydrogen-silicate-iron miscibility, combined with atmospheric escape, explains the observed demographics and core structures of sub-Neptunes and super-Earths.
Key contributions
- Models reproduce sub-Neptune/super-Earth demographics, radius gap, and radius-period relation.
- Hydrogen-silicate-iron miscibility unifies formation and evolution concepts for these planets.
- Planets with <1% H by mass form discrete metallic cores, like terrestrial planets.
- Higher H concentrations lead to fully miscible interiors with no distinct metal cores.
Why it matters
This paper offers a unifying framework to understand the diverse architectures of sub-Neptunes and super-Earths. It explains observed features like the radius gap and core structures based on hydrogen miscibility, advancing our understanding of planet formation.
Original Abstract
Models based on variable miscibility among hydrogen, molten silicate, and molten iron, coupled with atmospheric escape, can reproduce the observed occurrence density structure of sub-Neptunes and super-Earths in mass-radius space. The models are also consistent with the radius gap and the observed radius-period relationship exhibited by these planets. The degree of overlap between predicted and observed planetary occurrences suggests that hydrogen-silicate-iron miscibility may serve as a unifying concept for the formation and evolution of these planet classes. The well-defined equilibrium conditions at the boundary between supercritical magma oceans and the overlying hydrogen-rich envelopes are important features of the models. Planets formed with less than ~1 % hydrogen by mass develop discrete, terrestrial-like metallic cores, while those accreting greater hydrogen concentrations are predicted to have fully miscible interiors and no discrete metal cores. Hydrogen-silicate-iron miscibility provides an overarching explanation for the full range of sub-Neptune and super-Earth architectures based on the accreted hydrogen mass fraction and the phase equilibria governing silicate, iron metal, and H$_2$ miscibility.
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