The nature of the organic matter in interplanetary samples is central to elucidating the formation and early evolution of the Solar System. Although most meteorites derive from asteroids, micrometeorites mainly sample more remote objects. Ultra-carbonaceous Antarctic micrometeorites (UCAMMs), which have the highest carbon content among interplanetary samples, offer a unique window into cometary organics. Here we report a survey of the H, C and N isotopes in four UCAMMs, of which two are 15N-poor (delta 15N similar or equal to -120 parts per thousand), which suggests that their formation involved primordial N2 (delta 15N similar or equal to -380 parts per thousand). Such a composition could be the result of Galactic cosmic ray irradiation of N2 ices at the surface of cold small bodies in the outermost parts of the Solar System, possibly the Oort cloud. The two other UCAMMs exhibit higher delta 15N (75 parts per thousand and 282 parts per thousand), like those reported for carbonaceous chondrites and interplanetary dust particles. They may originate from parent bodies initially on lower heliocentric orbits in the Kuiper belt that have surfaces cold enough to retain N-bearing species, such as cyanides (delta 15N >= 200 parts per thousand), that are richer in 15N than primordial N2. According to their elemental and isotopic composition, UCAMMs constitute a unique probe into the coldest objects of the Solar System, namely those in the Kuiper Belt and the Oort cloud, which are largely out of reach of current space exploration. The hydrogen, carbon and nitrogen isotopic compositions of ultra-carbonaceous Antarctic micrometeorites reveal that they are possibly linked with N-bearing volatile species, including primordial N2, condensed on the coldest objects of the Solar System.

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu's parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu's parent body formed ~2 million years after the beginning of Solar System formation.

TRANSMISSION SPECTRA. Y. Kebukawa*, E. Quirico, E. Dartois, L. Bonal, C. Engrand, J. Duprat, J. Mathurin, A. Dazzi, A. Deniset-Besseau, H. Yabuta, H. Yurimoto, T. Nakamura, T. Noguchi, R. Okazaki, H. Naraoka, K. Sakamoto, S. Tachibana, S. Watanabe, Y. Tsuda, and The Hayabusa2-initial-analysis organic macromolecule team. Yokohama National University, Yokohama, Kanagawa, 240-8501, Japan, IPAG, Université Grenoble Alpes, 38000 Grenoble, France, Institut des Sciences Moléculaires d'Orsay, UMR8214, Université ParisSaclay/CNRS, 91405 Orsay, France, IJCLab, UMR 9012 Université Paris-Saclay/CNRS, 91405 Orsay, France, Muséum National d’Histoire Naturelle, UMR CNRS 7590, SU, IMPMC, Paris, France, Institut Chimie Physique, UMR 8000, Université Paris-Saclay/CNRS, 91405 Orsay, France, Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8526, Japan, Hokkaido University, Sapporo 060-0810, Japan, Tohoku University, Sendai 980-8578, Japan, Kyoto University, Kyoto 606-8502, Japan, Kyushu University, Fukuoka 819-0395, Japan, Japan Aerospace Exploration Agency (JAXA), Sagamihara 252-5210, Japan, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan, Nagoya University, Chikusa-ku, Nagoya, 464-8601, Japan. *Email: kebukawa@ynu.ac.jp

SAMPLES. L. Remusat, M. Verdier-Paoletti, S. Mostefaoui, H. Yabuta, C. Engrand, the Hayabusa2-initialanalysis IOM team, H. Yurimoto, T. Nakamura, T. Noguchi, R. Okazaki, H. Naraoka, K. Sakamoto, S. Watanabe, Y. Tsuda and S. Tachibana IMPMC, Museum National d’Histoire Naturelle, UMR CNRS 7590, Sorbonne Université, Paris, France (laurent.remussat@mnhn.fr), Dept of Earth and Planetary Systems Science, Hiroshima University, Hiroshima, Japan. CSNSM, Université Paris-Saclay; Orsay, France. Hokkaido Univ., Sapporo, Japan, Tohoku Univ., Sendai, Japan, Kyoto Univ., Kyoto, Japan, Kyushu Univ., Fukuoka, Japan, JAXA, Sagamihara, Japan, Nagoya Univ., Nagoya, Japan, Univ. of Tokyo, Tokyo, Japan.

HAYABUSA2 SPATIAL MISSION AND ANTARCTIC MICROMETEORITES (AMMs). L. Bejach1, C. Engrand1, J. Duprat1, E. Dartois,2 J. Mathurin3, A. Dazzi3, A. Deniset-Besseau3, N. Rividi4, C. Sandt5, F. Borondics5, T. Nakamura6, T. Morita6, M. Kikuiri6, K. Amano6, E. Kagawa6, H. Yabuta7, T. Noguchi8, H. Yurimoto9, R. Okazaki10, H. Naraoka10, K. Sakamoto11, S. Tachibana11,12, S. Watanabe13, Y. Tsuda11 and the Hayabusa2-initial-analysis Stone team, 1Univ. Paris-Saclay, CNRS, IJCLab, France (laure.bejach@ijclab.in2p3.fr), 2Univ. Paris-Saclay, CNRS, ISMO, France, 3Univ. Paris-Saclay, CNRS, ICP, France, 4CAMPARIS, Univ. Paris Sorbonne, Jussieu, France, 5Synchrotron SOLEIL, France. 6Tohoku University, Sendai 980-8578, Japan, 7Hiroshima University; Higashi-Hiroshima, Hiroshima, 739-8526, Japan. 8Kyoto University, Kyoto 606-8502, Japan, 9Hokkaido University, Sapporo 060-0810, Japan, 10Kyushu University, Fukuoka 819-0395, Japan, 11Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara 252-5210, Japan, 12The University of Tokyo; Bunkyo-ku, Tokyo,113-0033, Japan, 13Nagoya University; Chikusa-ku, Nagoya, 464-8601, Japan.