A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu

Abstract

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

Understanding the Dust Environment at Mercury: From Surface to Exosphere

“…More recent studies have identified additional opaque components in lunar samples including Fe silicides (e.g., Hapkeite and associated phases; Anand et al 2004) and phases that likely form through oxidation processes by reaction with surrounding glass and/or H 2 O, including FeO and Fe 3 O 4 (e.g., Thompson et al 2016;Burgess & Stroud 2018). In returned samples from S-type and C-type asteroids, we observe nanoparticles enriched in S, including FeS, MgS (Noguchi et al 2011(Noguchi et al , 2014(Noguchi et al , 2023, and FeNiS. When we consider the composition of opaque phases beyond the Moon, the microstructural characteristics produced via space weathering are predicted to be heavily dependent on the starting composition of the surface.…”

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

“…It is similar to that of Ivuna-like carbonaceous chondrites (Ito et al 2022;Nakamura et al 2023;Yada et al 2022;Yokoyama et al 2023;Leroux et al 2023), which are the most primitive chondrites and have a composition almost identical to that of the bulk solar system (Lodders 2003). Noguchi et al (2022Noguchi et al ( , 2023 and Matsumoto et al (2024) have observed unique features not previously observed in meteorites, including particular surface textures attributed to space weathering. They consist in a submicrometer sized assemblage of glassy silicates containing vesicles and nanosulfides that are draping the surface of typical phyllosilicaterich Ryugu grains.…”

“…The section mounted on the TEM grid was thinned to a thickness of ∼150 nm using 16 or 30 kV Ga + ion beams. The damaged layers were removed using a 2 kV Ga + ion beam (Noguchi et al 2022).…”

A history of mild shocks experienced by the regolith particles on hydrated asteroid Ryugu

“…Recent high-resolution TEM analysis reported that some surfaces of Ryugu particles have space weathering features caused by solar wind irradiation and/or (micro-)meteorite bombardment 49 . Amongst them, the outermost frothy layer is interpreted as the melting products of the phyllosilicates-rich matrix by the latter process on Ryugu's surface.…”