High-resolution observations of bright boulders on asteroid Ryugu: 2. Spectral properties

Many small boulders with reflectance values higher than 1.5 times the average have been found on near-Earth asteroid 162173 Ryugu. Based their visible wavelength spectral differences, Tatsumi et al. (2021) defined two bright boulder classes: C-type and S-type. These classifications of different size distributions trends. In this study, we measured spectra 79 investigated detailed properties. Analyses obtained a number important results. First, S-type Ryugu that are similar to those for ordinary chondrites initial experimentally space weathered same way. This suggests there may be populations Ryugu, perhaps originating from impactors hit its parent body. Second, model space-weathering ages meter-size boulders, based change rates derived in previous irradiated chondrites, 0.1-1 Myr, which is consistent crater retention age (<Myr) ~1-m deep surface layer agreement strongly extremely young, implying samples acquired should fresh. Third, lack serpentine absorption clast embedded one large brecciated indicates fragmentation cementation created breccias occurred after termination aqueous alteration. Fourth, exhibit continuous trend heating track low-albedo carbonaceous such as CM CI. Other processes, weathering grain effects, cannot primarily account variation.