Hayabusa2's optical navigation camera (ONC) found many anomalously bright boulders on the dark surface of C-type asteroid Ryugu. Observations with the ONC and near-infrared spectrometer (NIRS3) indicate that at least six of those bright boulders exhibit reflectance spectra consistent with exogeneous origin; their spectra are similar to those of S-type asteroids. This means that the bright boulders resulted from collisional mixing between Ryugu's parent body and one or more S-type asteroids. On Bennu, the asteroid explored by NASA's OSIRIS-REx, bright boulders with spectra similar to those of V-type asteroids were found. This suggests that Ryugu and Bennu might have different collisional histories. Moreover, the majority of bright boulders on Ryugu have spectra similar to those of C-type asteroids. This type of bright boulders are likely endogenic and they may have been from different parts of Ryugu's parent body, which would have experienced different thermal histories. Because the samples collected from Hayabusua2 may contain those bright materials, we may be able to gain detailed knowledge on Ryugu's collisional and thermal history from the analyses of the Hayabusa2 samples.
Author: Tatsumi et al.
Journal: Nature Astronomy (September 21, 2020 [September 22, JST] )