Space weathering acts strongly on the uppermost surface of Ryugu

Abstract

Returned samples from Cb-type asteroid (162173) Ryugu exhibit very dark spectra in visible and near-infrared ranges, generally consistent with the Hayabusa2 observations. A critical difference is that a structural water absorption of hydrous silicates is around twice as deep in the returned samples compared with those of Ryugu’s surface, suggesting Ryugu surface is more dehydrated. Here we use laboratory experiments data to indicate the spectral differences between returned samples and asteroid surface are best explained if Ryugu surface has (1) higher porosity, (2) larger particle size, and (3) more space-weathered condition, with the last being the most effective. On Ryugu, space weathering by micrometeoroid bombardments promoting dehydration seem to be more effective than that by solar-wind implantation. Extremely homogeneous spectra of the Ryugu’s global surface is in contrast with the heterogeneous S-type asteroid (25143) Itokawa’s spectra, which suggests space weathering has proceeded more rapidly on Cb-type asteroids than S-type asteroids.

Laboratory Spectral Characterization of Ribbeck Aubrite: Meteorite Sample of Earth-impacting Near-Earth Asteroid 2024 BX1

“…Despite major differences in composition, Ribbeck and carbonaceous chondrites are similar in that they exhibit bluer spectral slopes with increasing grain size (Cloutis et al 2011a;Izawa et al 2016;Kiddell et al 2018;Cantillo et al 2023). In addition to the bluing of slope with increasing grain size, Matsuoka et al (2023) find an increase in the 2.7 μm OH feature band depth with Murchison (CM2) powders. From these results, they suggest that grain size may have a significant role in explaining the discrepancies between returned samples and remote-sensing data from Hayabusa2 observations.…”

Origin of asteroid (101955) Bennu and its connection to the New Polana family

“…Although initial findings from Bennu samples have shown that their 3 µm spectra do not match OVIRS’ spectra and closely resemble those of Ryugu 54 . Matsuoka 55 and Le Pivert 56 identified differences between laboratory spectra, ground-based telescopic, and spacecraft spectra, which may be attributed to factors such as space weathering. We will be able to learn more about the aqueous alteration and thermal histories of Bennu when we analyze its returned samples in detail.…”

Linking Cause and Effect: Nanoscale Vibrational Spectroscopy of Space Weathering from Asteroid Ryugu

“…Remote and laboratory measurements have revealed that Ryuguʼs surface exhibits extremely low reflectance and weak absorption features at 2.7 and 3.4 μm, attributed to a carbon-rich nature and the presence of secondary alteration phases (Kitazato et al 2019(Kitazato et al , 2021Nakamura et al 2023). Pilorget et al (2022) and Matsuoka et al (2023) highlighted important differences between Hayabusa2ʼs remote measurements (Kitazato et al 2019) and Ryugu laboratory spectra. In particular, the band depth of the 2.7 μm absorption, assigned to the hydroxyl group (-OH) in phyllosilicates, happens to be 2 times lower in remote sensing spectra.…”