Overview

• Lu–Hf dating of minute Ryugu grains produced impossible ages near 4.8 billion years, indicating the isotopic system was reset by late fluid flow.
• From the extent of lutetium loss, researchers estimate Ryugu’s parent body contained roughly 20–30% water by volume, far above prior assumptions.
• The team infers a collision about a billion years after formation melted buried ice and circulated liquid water at depths beyond solar heating reach.
• Pristine 5.4 grams of material collected by JAXA’s Hayabusa2 and returned in 2020 enabled high-precision measurements unaffected by terrestrial alteration.
• The findings strengthen the case for asteroids as major water couriers to early Earth, with researchers suggesting delivery could be two to three times higher than earlier models, and follow-up work will probe phosphate veins and comparisons with Bennu.