New Study Reveals Space Weathering Creates a “Dry” Skin on Water-Rich Asteroid Ryugu
Scientists analyzing samples returned by JAXA’s Hayabusa2 spacecraft have discovered that the surface of the near-Earth asteroid Ryugu appears dehydrated not because the whole body lost water, but due to space weathering processes that modify only the outermost layer. Using detailed laboratory microscopy and spectroscopic analysis, the team found that solar wind and micrometeorite impacts chemically altered surface minerals, reducing iron and driving off hydroxyl groups while the interior remains hydrated. These surface changes explain why remote sensing shows a weak 2.7 µm water absorption feature even though the asteroid’s bulk material contains water-bearing minerals. This work highlights how space weathering can mask the true volatile content of carbonaceous asteroids, potentially impacting interpretations of asteroid spectra and models of water delivery in the early Solar System. Publication of these results underscores the importance of returned sample studies for understanding primitive bodies in our Solar System.

Journal: Nature Astronomy

DOI: 10.1038/s41550-022-01841-6