Earth-like cores may be the oddity in the galaxy's most common planets
A new study argues that the galaxy's most common planets—sub-Neptunes—may not have Earth-like layered interiors with a distinct metallic core and silicate mantle. If these planets accrete more than about 1% hydrogen by mass, hydrogen, iron, and silicate can mix into a single, homogeneous interior, changing how they cool, hold onto atmospheres, and evolve their radii. This could explain features like the radius gap and how radii relate to orbital period, and it offers testable predictions for JWST observations, though the model rests on extrapolations of material behavior under extreme pressures. In short, Earth-like cores might be the exception rather than the rule in the galaxy.
