¹L. G. Vacher,¹V. T. H. Phan,¹L. Bonal,²M. Iskakova,¹O. Poch,¹P. Beck,¹E. Quirico,²R. C. Ogliore
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70019]
¹CNRS IPAG, Univ. Grenoble Alpes, Grenoble, France
²Department of Physics, Washington University in St. Louis, St. Louis, Missouri, USA
Published by arrangement with John Wiley & Sons

C-type asteroids, such as asteroid (162173) Ryugu, may have played a key role in delivering light elements to early Earth. Nitrogen (N)-bearing molecules have been chemically identified in some Ryugu grains, and based on the faint 3.06 μm absorption band observed by the hyperspectral microscope MicrOmega, NH-bearing compounds seem to be spread at the global scale in the collection. However, the chemical forms of these NH-bearing compounds—whether organic molecules, ammonium (NH4+) salts, NH4+- or NH-organics-bearing phyllosilicates, or other forms—remain to be better understood. In this study, we report the characterization of two Ryugu particles (C0050 and C0052) using infrared spectroscopy at millimeter, micrometer, and nanometer scales, along with NanoSIMS techniques to constrain the nature and origin of NH-bearing components in the Ryugu asteroid. Our findings show that Ryugu’s C0052 particle contains rare (~1 vol%), micrometer-sized NH-rich organic compounds with peaks at 1660 cm−1 (mainly due to C=O stretching of the amide I band) and 1550 cm−1 (mainly due to N-H bending vibration mode of the amide II band), indicative of amide-related compounds. In contrast, these compounds are absent in C0050. Notably, N isotopic analysis reveals that these amides in C0052 are depleted in 15N (δ15N ≃ −200‰), confirming their indigenous origin, while carbon (C) and hydrogen (H) isotopic compositions are indistinguishable from terrestrial values within errors. The amides detected in C0052 could have formed through hydrothermal alteration from carboxylic acids and amines precursors on Ryugu’s parent planetesimal. Alternatively, they could have originated from the irradiation of 15N-depleted N-bearing ice by ultraviolet light or galactic cosmic rays, either at the surface of the asteroid in the outer Solar System or on the mantle of interstellar dust grains in the interstellar medium. Amides delivered to early Earth by primitive small bodies such as asteroid Ryugu may have contributed to the prebiotic chemistry.

¹Konstantin M. Ryazantsev,¹Marina A. Ivanova,²Alexander N. Krot,³Chi Ma,¹Cyril A. Lorenz,⁴Vasily D. Shcherbakov
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70020]
¹Vernadsky Institute of Geochemistry of the Russian Academy of Sciences, Moscow, Russia
²Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁴Department of Geology, Lomonosov Moscow State University, Moscow, Russia
Published by arrangement with John Wiley & Sons

Ultrarefractory Ca,Al-rich inclusions (UR CAIs) in the Sayh al Uhaymir (SaU) 290 CH3 carbonaceous chondrite consist of ultrarefractory Zr,Sc-rich minerals (allendeite, kangite, tazheranite, warkite, and Y-perovskite), grossite, grossmanite, hibonite, melilite, and spinel. Several of them have a core–mantle structure with ultrarefractory minerals concentrated in the core. The unfragmented inclusions are surrounded by layers of spinel, melilite, Sc-diopside, and diopside (not all layers are present around individual inclusions). The UR CAIs have uniform ¹⁶O-rich compositions: Most inclusions have Δ¹⁷O of ~ −23 ± 2‰; a grossite-rich CAI is slightly ¹⁶O-depleted (Δ¹⁷O ~ −17‰). The CAIs are highly enriched in Zr, Hf, Sc, Y, and Ti compared to typical and previously studied UR CAIs from CM2, CO3, and CV3 carbonaceous chondrites. Similar to UR CAIs from other chondrites, the ultrarefractory minerals in SaU 290 CAIs are enriched in heavy rare earth elements (HREEs) relative to more volatile light rare earth elements (LREEs). We conclude that (1) UR CAIs from SaU 290 formed by gas–solid condensation from a gaseous reservoir having variable but mostly solar-like O-isotope composition, most likely near the proto-Sun, and were subsequently transported outward to the accretion region of CH chondrites. (2) The UR oxides and silicates are important carriers of UR REE patterns recorded their possible early fractionation.