Distant planets might not have a solid metal core at all according to a new model.
Scientists have always assumed that rocky planets are organized like Earth, with a heavy metal core at the center and a rocky mantle on top. This new research shows that hydrogen, silicate, and iron can actually mix together into a single messy soup under certain pressures. This means many Super-Earths might be giant balls of blended material instead of having distinct layers. The demographics of these planets depend heavily on how these elements mix as the planet cools. This changes how we look for life, as a planet without a solid core would have a very different magnetic field and atmosphere.
The Influences of Hydrogen-Silicate-Iron Miscibility on the Demographics of Sub-Neptunes and Super-Earths
arXiv · 2604.28135
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 unifyin