Puffy baby planets reveal a missing stage of planet formation

Astronomers were surprised to learn in recent years that most Sun-like stars host at least one planet that falls between Earth and Neptune in size and orbits closer than Mercury does in our own solar system -- sizes and orbits absent from our solar system. These worlds, known as super-Earths and sub-Neptunes, turn out to be the most abundant type of planet in the Milky Way. Yet for all their prevalence, how they form has remained unclear. An international research team has now iden...