Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu samples

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized

Four‐dimensional‐STEM analysis of the phyllosilicate‐rich matrix of Ryugu samples

Ryugu asteroid grains brought back to the Earth by the Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate the mineralogy of their phyllosilicate-rich matrix with four-dimensional scanning transmission electron microscopy (4D-STEM). We have identified and mapped the mineral phases at the nanometer scale (serpentine, smectite, pyrrhotite), observed the presence of Ni-bearing pyrrhotite, and identified the serpentine polymorph as lizardite, in agreement with the reported aqueous alteration history of Ryugu. Furthermore, we have mapped the d-spacings of smectite and observed a broad distribution of values, ranging from 1 to 2 nm, with an average d-spacing of 1.24 nm, indicating significant heterogeneity within the sample. Such d-spacing variability could be the result of either the presence of organic matter trapped in the interlayers or the influence of various geochemical conditions at the submicrometer scale, suggestive of a range of organic compounds and/or changes in smectite crystal chemistry

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

Ryugu spectral surface regions via unsupervised machine learning classification of NIRS3 data

The Japanese Hayabusa2 space mission approached the Near-Earth asteroid 162173 Ryugu in June 2018. Since then, it is taking data and mapping in detail the asteroid surface, finding a very dark and boulder rich asteroid with very homogenous spectral reflectance properties in the near IR. Statistical and machine learning tools are applied on NIRS 3 spectrometer data to explore them and search for structure emndedded in the data and study their characteristics and correlation with geomorphological structures

Distribution of the spectral slope in the NIR range of the Ryugu surface

The Near-Earth asteroid 162173 Ryugu is the target of the JAXA sample return Hayabusa2 mission, which arrived at the asteroid in June 2018 and will analyse the surface until December 2019. Reflectance spectra of the Ryugu surface, acquired by the NIRS3 spectrometer (Near-Infrared Spectrometer), revealed a dark object with a positive slope, ranging from 0.10 to 0.29. A detailed analysis about areas with different spectral slopes has been performed, with the aim to detect physical/chemical variations and better constrain the history of Ryugu

Characteristics of dark and bright areas on the asteroid Ryugu

The Japanese Hayabusa2 space mission approached the Near-Earth asteroid 162173 Ryugu in June 2018. Since then, it is taking data and mapping in detail the asteroid surface, finding a very dark and boulder rich asteroid with very homogenous spectral reflectance properties in the near IR. By using the data obtained by the NIRS 3 spectrometer, the intent of this work is to detect dark and bright patches and to study their characteristics, with the support of statistical and machine learning tools