A mega-Earth or massive solid planet is a type of terrestrial exoplanet that is very massive and dense — more massive than super-Earths. 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 as of March 2026, mega-Earths appear to be a distinct category of exoplanets that are between 2.1 and 5.0 Earth radii (R🜨) and have densities higher than Earth's.