Near-Earth asteroid Ryugu was previously covered in flowing water, say researchers examining samples returned by the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 mission, with implications for scientists’ understanding of space impacts like those that formed Earth. While researchers have long believed that asteroids composed of ice and dust, like Ryugu, brought the liquid to Earth, many details of the events are uncertain. Such a finding indicated that carbonaceous asteroids like Ryugu may have contained much more water than previously suspected by two to threefold. Additionally, they seek to compare the findings with other asteroid samples, such as those NASA’s OSIRIS-REx collected from Bennu, to determine how unique Ryugu’s conditions may be. The paper, “Late Fluid Flow in a Primitive Asteroid Revealed by Lu-Hf Isotopes in Ryugu,” appeared in Nature on September 11, 2025.