NASA/JPL-Caltech An artistic rendering of a very young star encircled by a disk of gas and dust. The winking star has sand in its eye. Back in 2002, astronomers from Wesleyan University concluded that a star brightening and waning in an unusual 48-day rhythm was dipping in and out of stuff swirling around the star in a so-called protoplanetary disk. At the time one astronomer called the system “a Rosetta stone,” for understanding how planets form. Now, after six more years of observation with an international group of astronomers, led by William Herbst of Wesleyan, researchers say they know what...