Insights into Early Solar System Isotopic Reservoirs Inferred from Ryugu
Quinn R. Shollenberger1, Jan Render1, and Gregory A. Brennecka1
1
Lawrence Livermore National Laboratory
Introduction: Returned primitive Solar System material presents a unique opportunity to address multiple important
planetary science questions. Recent work has demonstrated that material returned from the Japan Aerospace Exploration
Agency’s (JAXA) Hayabusa2 mission from Cb-type asteroid (162173) Ryugu is most closely related to Ivuna-type (CI)
carbonaceous chondrites [e.g., 1-2], which have a chemical composition similar to that of the Sun’s photosphere. The pristinenature and CI-like chemical composition of Ryugu samples allows researchers to use bulk-rock nucleosynthetic isotope
anomalies to establish genetic relationships to planetary bodies and to refine our knowledge of the isotopic evolution of theSolar System, as well as the accretion history of the terrestrial planets [e.g., 1-6].
The initial isotopic study of four Ryugu particles found it has an indistinguishable Fe isotope composition from CI
chondrites—which is itself different from all other carbonaceous chondrites [2]. This led to the conclusion that a third isotopic
reservoir may have existed in the early Solar System for CI and CI-like bodies to form separate from the carbonaceous andnon-carbonaceous reservoirs. However, the existence of a third isotopic reservoir has recently been challenged through two
different models [7-8], and those studies have shown that the isotopic dichotomy between carbonaceous and non-carbonaceous
meteorites extends to Fe isotopes. These authors suggest that the appearance of an apparent third isotopic reservoir in themeteorite record reflects a lack of Fe isotope data from carbonaceous achondrites [8]. Here we report Fe and Ti isotopic
analyses with the addition of Ni isotope compositions on a bulk sample from Ryugu to shed new light on the isotopic
reservoirs present in the early Solar System.
Methods: Ryugu particle A0208, provided by JAXA, was analyzed in this study. This particle was part of a surface sample
that was collected in Chamber A during the first touchdown of the Hayabusa2 spacecraft. Approximately 8 mg of Ryugu
particle A0208 was weighed and dissolved in a pre-cleaned PFA vial using a combination of concentrated HF:HNO3, followedby aqua regia. Two procedural blanks as well as the geostandards BCR-2 and BHVO-2 were processed alongside our Ryugu
sample for all procedures. Following dissolution, we obtained major and trace element concentrations using a Thermo
Scientific Element XR ICP-MS at Lawrence Livermore National Laboratory (LLNL) following previously published methods[9].
All samples were processed through multiple chemical separations to purify the elements of interest using previously
established procedures. The first separation was to isolate Fe from the sample matrix [10] followed by purification of Ti [e.g.,11] and Ni [e.g., 12]. Yields of our procedures were >80% and the blanks were negligible considering the total amount ofmaterial processed for Fe, Ti, and Ni. Iron and Ni isotopic analyses were performed on a Thermo Scientific Neptune Plus MCICPMS at LLNL while Ti isotopes were measured on a Thermo Scientific Neoma MC-ICPMS at LLNL [e.g., 2, 11-12].
Results and Discussion: Whereas the previously analyzed Ryugu particles were all around 25 mg or less [1-2], our particle
A0208 weighed only 8 mg. Despite this difference and the limited masses in general, we observe that our Ryugu particle
exhibits elemental concentrations comparable to what has been reported in previous work (Fig. 1). Shown in figure 1 are major
and trace element concentrations obtained for particle A0208 against the average concentration data from the initial Ryugu
study [1], demonstrating overall excellent agreement. A few
small differences exist between the two works (the mostnotable being Be), which are readily explained byheterogeneities at these small sample scales (< 25 mg).
Figure 1. Major and trace element abundances of Ryugu A0208
particle of this work plotted against the average concentrations
determined for Ryugu particles A0106, A0107, and C0108 from[1]. With a few exceptions, most elements are in good agreement
between the two studies. Uncertainties for ICP-MS data from thisstudy are estimated to be ±5%, whereas error bars shown for datafrom [1] are two standard deviations of the two ICP-MS
measurements reported in that work.

Shown in Figure 2 are select Ti, Fe, and Ni isotope data commonly used for genetic comparison of meteoritic materials.
Our measured Fe and Ti isotopic compositions are indistinguishable from other Ryugu particles as well as from CI chondrites[1-2]. The overlapping Fe and Ti isotopic compositions of our Ryugu particle with previous measurements indicate that sample
heterogeneity is not a big concern for major elements analyzed here. Although specific values and uncertainties were notprovided in [13], our Ni isotope data from Ryugu particle A0208 appear to be consistent with these previous Ni isotope
measurements as well as CI chondrites (Fig. 2). This result offers further support to the interpretation that Ryugu is mostclosely related to CI chondrites [1-2, 13].
The new Ti, Fe, and Ni isotopic data obtained in this study demonstrate that Ryugu and CI chondrites may plot on acontinuation of a trend defined by the carbonaceous chondrites. Previous studies have suggested that CI chondrites and Ryugu
may have formed at greater heliocentric distances compared to other carbonaceous chondrites [e.g., 2, 13-14] and our data aresupportive of this interpretation given that Ryugu and CI chondrites are an endmember in the carbonaceous reservoir. While
our data do not clearly provide evidence for the existence of a third isotopic reservoir in the early Solar System as previously
suggested [2], this is not ruled out, either. Additional isotopic measurements are underway at LLNL for Cr and any finalized
data and further interpretations will be reported at the meeting.

Figure 2. Plots of µ54Fe vs. µ50Ti, µ62Ni vs. µ50Ti, and µ54Fe vs. µ62Ni, where µ designates parts per million deviation from a terrestrial
standard. Ryugu particle A0208 from this study is the large light blue diamond, previous Ryugu measurements are shown as a light blue
triangle, average CI chondrite as a light blue circle, carbonaceous chondrites (CC) as dark blue circles, non-carbonaceous meteorites (NC) in
red circles, and Earth as a green square. Iron and Ti isotopic data from [2]. Ni isotopic data compiled from [15-19].

Acknowledgements: The authors thank JAXA for providing Ryugu particle A0208 that was used in this study. This work
was performed under the auspices of the U.S. DOE by LLNL with contract DE-AC52-07NA27344 with release number
LLNL-ABS-848622. This work was funded by the Laboratory Directed Research and Development program of Lawrence
Livermore National Laboratory (23-LW-015).
References[1] Yokoyama T. et al. (2022) Science 10.1126/science.abn7850. [2] Hopp T. et al. (2022) Science Advances 8, eadd8141. [3]Fischer-Gödde M. & Kleine T. (2017) Nature 541, 525-527. [4] Burkhardt C. (2021) Science advances 7, eabj7601. [5]Schiller M. et al. (2020) Science Advances 6, eaay7604. [6] Burkhardt C. et al. (2019) Geochimica et Cosmochimica Acta 261,145-170. [7] Marrocchi Y. et al. (2023) The Astrophysical Journal Letters 954, L27. [8] Yap T. & Tissot F.L.H. (2023) Icarus
405, 115680. [9] Wimpenny J. et al. (2022) Earth & Planetary Science Letters 578, 117318. [10] Rolison J. M. et al. (2019)
Applied Geochemistry 103, 97-105. [11] Shollenberger Q. R. et al. (2022) Geochimica et Cosmochimica Acta 324, 44-65. [12]Render J. et al. (2018) The Astrophysical Journal 862, 26. [13] Spitzer F. et al. (2023) LPSC #2488. [14] Desch S.J. (2018)
The Astrophysical Journal 238, 11. [15] Steele R.C.J. et al. (2012) The Astrophysical Journal 758,59. [16] Tang H. & Dauphas
N. (2012) Earth & Planetary Science Letters 359-360, 248-263. [17] Tang H. & Dauphas N. (2014) Earth & Planetary Science
Letters 390, 264-274. [18] Regelous M. et al. (2008) Earth & Planetary Science Letters 272, 330-338. [19] Burkhardt C. et al.
(2017) Meteoritics & Planetary Science 52, 807-826.