Under the moonlit sky, on quiet, tropical beaches, baby sea turtles hatch from their eggs and scramble toward the surf. Drawn by the shimmer of starlight on the water, they rush over the sand and vanish into the waves. For scientists, this is one of the great mysteries—an animal born in one location, who leaves right away for another. From that moment, the young turtles disappear into the open ocean for years—sometimes a decade or more—before anyone sees them again.