Nitrogen, neon, and argon analysis of a single Ryugu grain by step-heating
J. Gamblin1, E. Füri1, B. Marty1, L. Zimmermann1, D.V. Bekaert1, and M.W. Broadley1
1
Université de Lorraine, CNRS, CRPG, Nancy, France
Introduction: Carbonaceous chondrites are primitive, volatile-rich meteorites, considered to originate from C-type asteroids,
which may have contributed to Earth’s volatile budget. Studying these objects is key to understand the origin of Earth’svolatiles, but terrestrial weathering makes it difficult to distinguish between primary and secondary features. In December
2020, JAXA’s Hayabusa2 mission returned to Earth 5.4 g of regolith collected on the C-type asteroid (162173) Ryugu,permitting the analysis of material not altered by terrestrial weathering [1]. The first analyses of noble gases and nitrogen wereperformed by the ‘initial analysis volatile team’ [2-3], providing key information about Ryugu, especially its formation,composition, and alteration history. Noble gases were found to be mainly of primordial and presolar origin, with variable
contributions from solar wind and cosmogenic components. Nitrogen was present in lower abundances (700 to 900 ppm [2-3])
than in typical CI chondrites, with ẟ15N values ranging from 0.0±0.4 ‰ [2] up to +43±4 ‰ [4], indicating sample
heterogeneity and the presence of at least two carrier phases: a N-rich phase with ẟ15N up to +70 ‰ and a N-depleted phasewith ẟ15N near 0 ‰.
Sample and experimental method: For this study, we targeted grain A-0164 (2.6 mg), which was sampled during the first
touchdown on the asteroid and corresponds to surface material. The grain was analyzed at the Centre de Recherches
Pétrographiques et Géochimiques (CRPG, Nancy, France) by step-heating with a CO2 laser. By performing a large number ofextraction steps, various components of nitrogen and noble gases, carried by different phases, can be distinguished. A total of
85 heating steps were performed at increasing laser power to successively analyze the different phases carrying nitrogen andnoble gases. Nitrogen, neon, and argon abundances and isotope ratios were analyzed at each step using a Nu Instruments
Noblesse HR mass spectrometer, a state-of-the-art instrument for multi-collection, high-precision, static-vacuum analysis.
Preliminary results:
Noble gases. Neon was mainly released at low temperature steps, whereas Ar was extracted over a wide temperature range.
The sample presents a mainly solar wind-like isotopic composition for noble gases, as shown for neon in Figure 1. Step
heating allowed us to identify other components, including primordial and presolar components (possibly phase Q and/or HL),as well as a minor cosmogenic contribution.
Nitrogen. Nitrogen is present in higher abundance (1219±113 ppm) than in previous studies, with a bulk ẟ15N value of+24.4±0.1 ‰, with significant variations during successive extractions (+1.0±1.0 ‰ to +65.8±1.1 ‰), pointing to the presenceof at least four N-carrier phases.

Figure 1.

Ne (20Ne/22Ne) isotope ratio (colored circles) and 20Ne abundance (gray histogram) measured for each of the 85 extraction steps

at increasing laser power. The Ne isotopic compositions of the solar wind, Phase Q, and Ne-HL are shown for comparison.

References[1] Tsuda Y. et al. 2020. Acta Astronautica 171 42:54. [2] Okazaki R. et al. 2023. Science 379 6634. [3] Broadley M.W. et al.
2023. Geochemica et Cosmochimica Acta 345 62:74. [4] Yabuta H. et al. 2023. Science 379 6634.