Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu

Abstract

C-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2–7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.

First compositional analysis of Ryugu samples by the MicrOmega hyperspectral microscope

“…The wavelength calibration of the illumination beam has been characterized at the Institut d'Astrophysique Spatiale using two reference targets: a Wavelength Calibration Standard from Labsphere and a calcite pellet. To eventually redo calibration within the Curation Facility, reference targets made of Spectralon 99% and Infragold from Labsphere were set in the Curation chamber after an in-depth ultracleaning procedure 4 . The potential contribution of the sapphire window to the signal has been removed using acquisitions performed without any sample in the field of view.…”

“…It is worth noting that characterization by a NIR hyperspectral microscope has never been performed in the preliminary analyses of returned extraterrestrial samples. The primary goal is to achieve a global description of the entire collection, through the analyses of the bulk samples and of a few hundreds of grains extracted from them 4 . The latter stage will support the detailed analyses of a selection of grains by the already-nominated international teams for initial analyses, who started their activity in July 2021, and will contribute to building a catalogue for the distribution of samples to the international community, through Announcements of Opportunity, starting in mid-2022.…”

Connecting Asteroids and Meteorites with visible and near-infrared spectroscopy

“…They note that matches based on featureless spectra in the 0.45-2.5-m region are notional and may be superseded by data from other wavelength regions. Preliminary results from Hayabusa2 find that while Ryugu has a composition similar to CI chondrites, it has a lower albedo, higher porosity and is more fragile (Yada et al 2021).…”

Hayabusa2 returned samples: A unique and pristine record of outer Solar System materials from asteroid Ryugu

“…The Ryugu asteroid particles were recovered from the Hayabusa2 reentry capsule and transported to the JAXA Curation Facility at Sagamihara Japan without terrestrial atmospheric contamination (Yada et al, 2021). After initial and non-destructive characterizations at the JAXA Curation Facility, an airtight sample transport vessel (FFTC) and a sample capsule pack (made of sapphire glass and stainless steel with 10 mmϕ or 15 mmϕ depending on sample size) were used to avoid chemical reactions with the surrounding environment and/or terrestrial contaminants (e.g., water vapor, hydrocarbon, atmospheric gases, and small particles) and cross-contamination between samples during sample preparation and transportation among institutes and universities (Ito et al, 2020).…”

“…Carbonaceous chondrites are fragments from C-type asteroids and provide evidence that these generally organic-rich (Garvie and Buseck, 2007) bodies experienced extensive aqueous alteration early in Solar System history (Alexander et al, 2014). On 6th December 2020, ~5.4g of material was delivered to Earth from the C-type asteroid 162173 Ryugu by the Hayabusa2 spacecraft (Yada et al, 2021). Here we present the results of an integrated bulk and micro-analytical study of Ryugu particles, which provides a unique insight into the interrelationship between aliphatic-rich organics and surrounding hydrous minerals at a sub-micrometer scale.…”