Core-envelope miscibility in sub-Neptunes and super-Earths.

Area of Science:

• Planetary Science
• Exoplanetology
• Astrochemistry

Background:

• Sub-Neptunes and super-Earths are common exoplanets with radii between Earth and Neptune.
• Their internal structure and origin remain poorly understood.
• Sub-Neptunes are hypothesized to have rocky cores with hydrogen-rich envelopes.

Purpose of the Study:

• Investigate the miscibility of silicate (core) and hydrogen (envelope) at exoplanet core-envelope interface conditions.
• Determine the nature and extent of chemical reactions between core and envelope materials.
• Understand the implications for sub- નેptune and super-Earth evolution.

Main Methods:

• First-principles molecular dynamics simulations.
• Density functional theory (DFT) calculations.
• Modeling of pressure-temperature conditions exceeding several gigapascals and several thousand kelvin.

Main Results:

• Silicate and hydrogen are completely miscible across a wide range of plausible core-envelope conditions.
• Extensive chemical reactions occur, forming silane, SiO, and water species.
• Core-envelope miscibility significantly affects planetary evolution by dissolving hydrogen in the core.

Conclusions:

• Miscibility profoundly impacts the evolution of sub-Neptunes and super-Earths.
• Dissolving hydrogen in the core and driving core-envelope exchange alters planetary structure.
• Formation of silane, SiO, and water may be detectable by current or future observational missions.