This sketch illustrates a family tree of exoplanets. Planets are born out of swirling disks of gas and dust called protoplanetary disks. The disks give rise to giant planets like Jupiter as well as smaller planets mostly between the sizes of Earth and Neptune. Researchers using data from the W. M. Keck Observatory and NASA's Kepler mission discovered that the smaller planets can be cleanly divided into two size groups: the rocky Earth-like planets and super-Earths, and the gaseous mini-Neptunes. | NASA/Kepler/Caltech (T. Pyle)

The Family Tree of Exoplanets Has Just Divided Into Two Branches

An analysis of nearly 3,500 known exoplanets shows that planets in our galaxy overwhelmingly fall into two groups.