Why inflated exoplanets often dance with a perfect rhythm

Planets beneath Neptune that dance in time with the rest of their planetary systems have lower densities than planets that don't, planetary scientist David Brown has discovered.

Though conspicuously absent from the solar system, the most common planets in the Milky Way are known as "sub-Neptunes," or worlds with sizes between Earth and the ice giant Neptune. It's estimated that between 30% and 50% of Sun-like stars are orbited by at least one sub-Neptune - but despite the ubiquity of these worlds, scientists studying exoplanets, or exoplanets, have traditionally had difficulty measuring the density of sub-Neptunes.

Depending on the techniques ...