A new study published in the Astrophysical Journal suggests that the most common type of planet in the galaxy, known as sub-Neptunes, may not have a layered internal structure like Earth. Traditionally, rocky planets were thought to have a dense metallic core, a silicate mantle, and a thin atmosphere. However, research indicates that at high temperatures and pressures, hydrogen, silicate, and iron can mix into a single fluid. If a sub-Neptune accumulates more than 1% of its mass in hydrogen, it lacks a distinct core and mantle, leading to a homogeneous interior. This finding helps explain the radius gap observed in exoplanets and suggests that young sub-Neptunes may release hydrogen from their interiors, causing them to appear larger than expected. The study's authors emphasize that while their model is based on theoretical extrapolations, it provides a bold new perspective on planetary formation and structure, indicating that Earth may be an exception rather than the norm in the universe.