Puffy baby planets reveal a missing stage of planet formation

Astronomers have discovered four extremely young planets in the V1298 Tau system that reveal how super-Earths and sub-Neptunes—the most common planet types in our galaxy—actually form. Using a decade of observations, researchers found these 20-million-year-old planets are remarkably "puffy," with densities like cosmic cotton candy despite being five to ten times Earth's size. These bloated worlds are rapidly losing their thick atmospheres and will eventually shrink into the compact super-Earths and sub-Neptunes found throughout the Milky Way, solving a long-standing mystery about planetary evolution.