Investigating the organic compounds in the asteroid Ryugu
Imene Kerraouch1*, Rhonda Stroud1, Larry Nittler2, Cassandra Kraver2, Jens Barosch3,4 and Jianhua Wang3
Buseck Center for Meteorite Studies (BCMS), Arizona State University, USA; 2School of Earth and Space Exploration(SESE), Arizona State University, USA; 3 Earth and Planets Laboratory, Carnegie Institution for Science, USA; 4 Department ofGeoscience, University of Wisconsin-Madison, USA. *ikerraou@asu.edu
1

Organic compounds in meteorites provide insights into the carbon chemistry present in the interstellar medium and solar nebulaand on their alteration on the parent bodies. Further, delivery of these organic compounds could have contributed to Earth’shabitability and life. However, studying these compounds in meteorites is complicated by their exposure to terrestrial organiccontamination after entering the Earth's atmosphere. As such, one of the goals of the Hayabusa2 sample return mission (asteroid(162173) Ryugu) is to understand the nature, origin, and evolution of organic compounds in the early solar system but fromsamples free of terrestrial organic contamination. Here, we examine further samples from asteroid Ryugu that were collectedduring the first touchdown (Chamber A, samples A0079 and A0169; allocated in first Ryugu AO). The goals of our research areto understand diversity, origin, and formation mechanisms of the macromolecular material that dominates Ryugu organics, aswell as the secondary processes involved in their modification, such as heating and aqueous alteration.
Fragments of the two Ryugu samples up to a few 10s of microns in size were pressed
into Au foils for H, C, and N isotope analysis with the Carnegie NanoSIMS 50L ion
microprobe. We used a ~0.4 pA, ~100-nm Cs+ primary beam and acquired data for C
and N isotopes, including 12C2, 12C13C, 12C14N, and 12C15N, as well as 16O, 32S, andsecondary electrons. The prepared samples were then analyzed for 1H, D, and 12C andsecondary electrons with a slightly more intense primary beam. C-rich regions ofinterest (ROIs) were defined in the C-N images and subsequently located and analyzed
in the H-D images.
We have analyzed a total area of ~9,000 m2 across the two samples. Data reduction isin progress. The majority of C-rich ROIs appear rounded in the ion images and range
from ~100 to 900 nm with some to up to a few µm (e.g., Fig.1). Consistent with previous
measurements [2-6], our data shows that the organic material is on average enriched in
D and 15N with most ROIs having compositions consistent within error with averagevalues of D of a few 100 ‰ and 15N~ +50‰. However, one lath-like rectangulargrain was identified in a particle within A0079 (Fig. 1), similar in shape to a grainpreviously reported in Chamber C [5; Fig.3], but larger. This 4.5 × 1 μm grain has anextreme isotopic composition: δD ≈10,000 ‰ and δ15N ≈ +800‰. In order to clarify
the nature and origin of this unusual grain and other select C-rich ROIs, we are currently
extracting focused ion beam (FIB) lift-out sections of D and 15N hotspots. The FIB
sections will be studied with transmission electron microscopy, scanning transmission
electron microscopy, energy dispersive spectroscopy and electron energy loss
spectroscopy at Arizona State University. Results from these investigations will bepresented at the symposium.

Figure 1. (a) Secondary electron (SE)image of a Ryugu particle fromchamber A (A0079) pressed into goldfoil. (b) D and 15N-enriched lath-like(whisker) detected in same particle.

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312, 727–730. [3] Nittler L. R. et al. 2019. Nat. Astron. 3, 659–666. [4] Nittler L. R. et al. 2018). GCA 226, 107–131. [5] Barosch
J. et al. 2022. Abstract#2050. 53rd LPSC; [6] Yabuta, H. et al. 2023. Science 379, eabn9057.