
upright=1.5|thumb|Size comparison of Earth and Neptune with the mega-Earth TOI-1853 b (center), a very dense Neptune-sized [[exoplanet believed to be nearly entirely made of solid rock, metal, and water.]]
upright=1.5|thumb|Size comparison of Earth and Neptune with the mega-Earth TOI-1853 b (center), a very dense Neptune-sized [[exoplanet believed to be nearly entirely made of solid rock, metal, and water.]]
A mega-Earth or massive solid planet is type of terrestrial exoplanet that is very massive and dense—more massive than super-Earths and about as massive as Neptune. The term "mega-Earth" was coined in 2014, though it remained an informal category until a quantitative definition was proposed for it in 2026. Based on the measured radii and densities of known exoplanets , mega-Earths appear to be a distinct category of exoplanets that are between 2.1 and 5.0 Earth radii () and have densities higher than Earth's ().
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).