A super-Earth is a planet more massive than Earth but well below the mass of Neptune, typically between about one and ten Earth masses. Nothing like it exists in our solar system, yet it appears to be among the most common types of planet in the galaxy. Whether a given super-Earth is a scaled-up rocky world or a smaller version of an ice giant often depends on its density, which requires measuring both radius and mass. Their frequency around red dwarf stars makes them prime targets in the search for habitable conditions.