Investigating the noble gas and nitrogen relationship between Ryugu and othercarbonaceous chondrites
M. W. Broadley1, D. J. Byrne1, E. Füri1, L. Zimmerman1, B. Marty1 R. Okazaki2, T. Yada3, F. Kitajima2, S. Tachibana3,4, K.
Yogata3, K. Sakamoto3, H. Yurimoto5, T. Nakamura6, T. Noguchi7, H. Naraoka2, H. Yabuta8, S. Watanabe9, Y. Tsuda3, and theHayabusa2 Initial Analysis Volatile Team
1

Université de Lorraine, CNRS, CRPG, F-54000 Nancy France,, 2Kyushu University, Japan. 3Institute of Space andAstronautical Science, JAXA, Japan, 4University of Tokyo, Japan, 5Hokkaido University, Japan, 6Tohoku University, Japan,7
Kyoto University, Japan, 8Hiroshima University, Japan, 9Nagoya University, Japan.
The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) successfully returned surface material from theC-type asteroid (162173) Ryugu to Earth. This material has now been classified as closely resembling CI-type chondrites,
which are the most chemically pristine meteorites. The analysis of material from the surface of Ryugu therefore provides aunique opportunity to analyze the volatile composition of material that originated from a CI-type asteroid [1] withoutcomplications arising from terrestrial contamination. Given their highly volatile nature, the noble gas and nitrogen inventoriesof chondrites are highly sensitive to different alteration processes on the asteroid parent body, and to terrestrial contamination.
We investigated at CRPG Nancy (France) the nitrogen and noble gas signature of two grains collected from the first andsecond touchdown sites [2] to provide an insight into the formation and alteration history of Ryugu. We find that theconcentration of trapped noble gas in the Ryugu grains is greater than the average composition of previously measured CIchondrites. The trapped noble gases are primarily derived from phase Q, although a significant contribution of presolar
nanodiamonds Xe-HL is noted. The large noble gas concentrations coupled with a significant contribution of presolar
nanodiamonds suggests that the Ryugu grains may represent some of the most primitive unprocessed material from the earlysolar system.
In contrast to the noble gases, the abundance of nitrogen and δ15N composition of the two Ryugu grains are lower than theaverage CI chondrite value. We attribute the lower nitrogen abundances and δ15N measured in this study to the preferential
loss of a 15N-rich phase from our grains during aqueous on a parent planetesimal. The analyses of other grains returned fromRyugu have shown large variations in nitrogen concentrations and δ15Nindicating that alteration fluids heterogeneouslyinteracted with material now present on the surface of Ryugu. Finally, the ratio of trapped noble gases to nitrogen is higher
than CI chondrites, and is closer to refractory phase Q and nanodiamonds. This may indicate that Ryugu experienced aqueousalteration that led to the significant loss of nitrogen likely from soluble organic matter hosted in our two grains without
significant modification of the noble gas budget, which is primarily hosted in insoluble organic matter and presolar diamonds
and is more resistant to aqueous alteration.
References[1] Yokohama et al. 2022 Science DOI: 10.1126/science.abn7850. [2] Okazaki et al. Science, Accepted.