Sub-Neptune planets that dance in time with the rest of their planetary systems are less dense than those that don't, planetary scientists have found.
Though notably absent from the solar system, the most common planets in the Milky Way are known as "sub-Neptunes," or worlds with sizes between those of Earth and the ice giant Neptune. It is estimated that between 30% and 50% of sun-like stars are orbited by at least one sub-Neptune — but despite these worlds' ubiquity, scientists studying extrasolar planets, or exoplanets, have traditionally had difficulty measuring sub-Neptunes' densities.
