A team of researchers, including those at the University of Tokyo, discovered that liquid water once flowed on the asteroid that spawned near-Earth asteroid Ryugu more than a billion years after it first formed. The finding, based on tiny rock fragments returned by the Hayabusa2 spacecraft of the Japan Aerospace Exploration Agency (JAXA), overturns long-held assumptions that water activity on asteroids only occurred in the earliest moments of solar system history. This could impact current models, including those describing the formation of Earth.