Science: Planetary systems are born around young stars and grow from vast clouds of dust and gas called protoplanetary disks. Models predict that as our own solar system's protoplanetary disk evolved, the dust and gas pushed each other around while constantly being stirred and jolted by magnetic fields and gravitational torques. The resulting mixing and motion set the chemical compositions of the planetesimals that formed and from which planets eventually grew. Although evidence for mixing is found in objects in our solar system, such as primitive meteorites, questions remain about the details of the processes responsible and whether this mixing was common in other protoplanetary disks. A new paper in Science on observations of the disk around the star AA Tau that suggest that we will soon be able to address these questions.