Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth

International audienceThe Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid

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

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

Compositional Characterization of the Hayabusa 2 Returned Samples with MicrOmega, Within the Curation Facility

International audienceThe composition of the Hayabusa2 returned samples will be characterized, within the curation facility, by hyperspectral near infrared microscopy, using the MicrOmega instrument

Constraints on Solar System early evolution by MicrOmega analysis of Ryugu carbonates

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Space weathering record and pristine state of Ryugu samples from MicrOmega spectral analysis

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Interaction between clay minerals and organics in asteroid Ryugu

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First compositional analysis of Ryugu samples by the MicrOmega hyperspectral microscope

International audienceThe characterization of objects that have best preserved the mineralogical and molecular phases formed in the earliest stages of the Solar System evolution is key to understanding the processes that led to the formation of the planets in their diversity. The Hayabusa2 mission of the Japan Aerospace Exploration Agency has returned for the first time samples collected at the surface of a C-type asteroid, Ryugu1,2. They are now preserved at the Extraterrestrial Samples Curation Center of the Japan Aerospace Exploration Agency at the Institute of Space and Astronautical Science in Sagamihara, Japan, where they are submitted to a first round of purely non-destructive analyses. The MicrOmega hyperspectral microscope developed at the Institut d'Astrophysique Spatiale (Orsay, France), which operates in the near-infrared range (0.99-3.65 µm), is performing their mineralogical and molecular characterization down to the scale of a few tens of micrometres. Strong features at 2.7 µm (indicating their OH-rich content) and at 3.4 µm (diagnostic of the presence of organics) dominate at a global scale, but key distinctive signatures have been identified at a submillimetre scale. In particular, carbonates (a fraction of them enriched in iron) as well as NH-rich compounds have been detected. The occurrence of volatile-rich species, likely originating from the outer Solar System, would support Ryugu having preserved both pristine material and altered phases, which are now available for refined laboratory analyses with the potential to draw new insights into the formation and evolution paths of planetary bodies in our Solar System

Ryugu’s Anhydrous Ingredients and Their Spectral Link to Primitive Dust from the Outer Solar System

International audienceAbstract Ryugu is a second-generation C-type asteroid formed by the reassembly of fragments of a previous larger body in the main asteroid belt. While the majority of Ryugu samples returned by Hayabusa2 are composed of a lithology dominated by aqueously altered minerals, clasts of pristine olivine and pyroxene remain in the least-altered lithologies. These clasts are objects of great interest for revealing the composition of the dust from which the original building blocks of Ryugu's parent asteroid formed. Here we show that some grains rich in olivine, pyroxene, and amorphous silicates discovered in one millimeter-sized stone of Ryugu have infrared spectra similar to the D-type asteroid Hektor (a Jupiter Trojan), to comet Hale–Bopp, and to some anhydrous interplanetary dust particles of probable cometary origin. This result indicates that Ryugu's primary parent body incorporated anhydrous ingredients similar to the building blocks of asteroids (and possibly some comets) formed in the outer solar system, and that Ryugu retained valuable information on the formation and evolution of planetesimals at different epochs of our solar system's history