Dissecting the complex Ne-Ar-N signature of asteroid Ryugu by step-heating analysis
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Keywords: noble gases, nitrogen, Ryugu, Hayabusa2, mass spectrometry
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Abstract
Figures
 Figure 1 (a) 20Ne, (b) 36Ar, and (c) N2 abundances (filled bars) and isotope ratios (filled circles) of particle C0015 for 85 extraction steps. Abundances are weighted by the extraction duration (i.e. 4 min for the first 26 steps and 12 min for the following 59 steps). Isotope ratios are shown for heating steps with <30 % blank contributions. The different colours represent the laser power used for the extraction (i.e. 1 to 45 % of the total power of 32 W). The dashed lines indicate the calculated “bulk” 20Ne/22Ne, 38Ar/36Ar, and δ15N values. Isotope ratios of the solar wind (SW), phase Q, and Ne-HL are shown for comparison (see Ott, 2014 and references therein). Uncertainties are 1σ and error bars are, in most cases, smaller than symbol sizes. |  Figure 2 (a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022; Broadley et al., 2023; Meshik et al., 2023; Okazaki et al., 2023 and references therein). Different Ne end members are represented by grey crosses (Ott, 2014). Ne-E is mainly carried by presolar graphite and silicon carbide. (b) Close-up (corresponding to the dashed rectangle in panel (a) of the Ne isotopic variations observed for the 85 extraction steps of particle C0015. The different colours represent the laser power used for each extraction. Uncertainties are 1σ. |  Figure 3 Nitrogen isotopic composition (δ15N) as a function of the inverse of the N concentration of Ryugu samples compared to CI chondrites and Y-980115, a CI chondrite recovered in Antarctica that has recently been recommended to be re-classified as a Yamato-type (CY) carbonaceous chondrite (King et al., 2019). Adapted from Okazaki et al. (2023) and Hashizume et al. (2024), including data reported in Table S-2. A simple two-component mixture, between a N-rich phase with δ15N up to +70 ‰ and a N-depleted phase with δ15N near 0 ‰, fails to explain the N signature of Ryugu particle C0015. |  Figure 4 Evolution of the residual N isotopic composition (δ15Nresidual) of particle C0015 as a function of the fraction of N extracted by progressive heating. |
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Introduction
The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) collected 5.4 g of regolith on the Cb-type asteroid (162173) Ryugu during two touchdowns in 2019 and returned the samples to Earth on December 6th, 2020 (Tsuda et al., 2020
Tsuda, Y., Saiki, T., Terui, F., Nakazawa, S., Yoshikawa, M., Watanabe, S. (2020) Hayabusa2 mission status: Landing, roving and cratering on asteroid Ryugu. Acta Astronautica 171, 42–54. https://doi.org/10.1016/j.actaastro.2020.02.035
). The mineralogy and the chemical and isotopic compositions of the samples revealed a close relationship between Ryugu and Ivuna-type (CI) carbonaceous chondrites (Nakamura et al., 2022Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Yokoyama et al., 2023Yokoyama, T., Nagashima, K., Nakai, I., Young, E.D., Abe, Y. et al. (2023) Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites. Science 379, eabn7850. https://doi.org/10.1126/science.abn7850
). However, unlike CI chondrites collected on Earth, material from Ryugu has not been affected by heating processes during atmospheric entry or by terrestrial weathering. Since carbonaceous chondrites may have played an important role in supplying volatile elements to Earth (e.g., Alexander et al., 2012Alexander, C.M.O’D., Bowden, R., Fogel, M.L., Howard, K.T., Herd, C.D.K., Nittler, L.R. (2012) The provenances of asteroids, and their contributions to the volatile inventories of the terrestrial planets. Science 337, 721–723. https://doi.org/10.1126/science.1223474
; Marty, 2012Marty, B. (2012) The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters 313–314, 56–66. https://doi.org/10.1016/j.epsl.2011.10.040
; Alexander, 2022Alexander, C.M.O’D. (2022) An exploration of whether Earth can be built from chondritic components, not bulk chondrites. Geochimica et Cosmochimica Acta 318, 428–451. https://doi.org/10.1016/j.gca.2021.12.012
), Ryugu samples are key for better understanding the origin of terrestrial volatiles. The Hayabusa2-initial-analysis volatile team and the Phase-2 curation team carried out the first noble gas and N analyses, thus providing insights into the volatile composition, formation, and alteration history of Ryugu (Nakamura et al., 2022Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
). The noble gases were found to be mainly primordial (i.e. carried by the so called phase Q and a variety of presolar components), with variable contributions from solar wind (SW) and cosmogenic isotopes. Okazaki et al. (2023)Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
concluded that the heterogeneous N contents and isotopic compositions of Ryugu samples, including four small pelletised samples and three splits of a large aggregate sample (Naraoka et al., 2023Naraoka, H., Takano, Y., Dworkin, J.P., Oba, Y., Hamase, K. et al. (2023) Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu. Science 379, eabn9033. https://doi.org/10.1126/science.abn9033
), indicate the presence of at least two carrier phases: a N-rich phase with δ15N up to +70 ‰ and a N-depleted phase with δ15N near 0 ‰. These results were subsequently discussed in more detail by Broadley et al. (2023)Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
and Hashizume et al. (2024)Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
. Here, we aim to better understand the nature and behaviour of Ne-Ar-N carriers in Ryugu material by performing a large number (n = 85) of extraction steps at incrementally increasing temperature. This is the first time, to our knowledge, that a single asteroidal particle has been heated in so many steps for coupled noble gas and N analyses, thereby providing unprecedented insight into the complex Ne-Ar-N makeup of primitive extraterrestrial matter.top
Material and Methods
Particle C0015 (1.8 ± 0.2 mg), collected during the second touchdown on Ryugu within a crater created by the spacecraft’s small carry-on impactor, was targeted for step-heating Ne-Ar-N analysis at the Centre de Recherches Pétrographiques et Géochimiques (CRPG) noble gas facility. The particle was never in contact with Earth’s atmosphere and was constantly kept within a dry N2 atmosphere or under vacuum during sample preparation, storage, and analysis. The particle was heated under static vacuum using a CO2 laser at increasing laser power, and the fraction of noble gases (Ne, Ar) and N (in the form of N2) extracted at each step was analysed using a Noblesse–HR noble gas mass spectrometer in multi-collection. A total of 85 heating steps were performed to study the progressive release of different noble gas and N components. Details on the analytical procedure and data treatment are provided in the Supplementary Information.
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Ne-Ar-N Release Patterns of Particle C0015
Figure 1 shows the release patterns of Ne, Ar, and N (analysed in the form of N2) and the corresponding isotope ratios measured at each heating step. Most of the Ne was released at very low laser power (≤3 %) at which the camera view showed no visible heating (indicated by an orange glow) of the particle. The 20Ne/22Ne ratio was nearly constant (12.92 ± 0.47) during the first 38 extraction steps (Fig. 1a), only slightly below the Ne isotope ratio of SW (13.74 ± 0.02 to 14.00 ± 0.04; Ott, 2014
Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
) and close to that of the protosolar nebula (∼13.36; Heber et al., 2012Heber, V.S., Baur, H., Bochsler, P., McKeegan, K.D., Neugebauer, M., Reisenfeld, D.B., Wieler, R., Wiens, R.C. (2012) Isotopic mass fractionation of solar wind: evidence from fast and slow solar wind collected by the Genesis mission. The Astrophysical Journal 759, 121. https://doi.org/10.1088/0004-637X/759/2/121
). This plateau likely results from the extraction of a pure Ne component. While trapping of nebular gas in CI-type material cannot be ruled out, the 3He/4He ratio of solar-gas-rich Ryugu samples analysed previously is consistent with implanted SW-derived gas (Meshik et al., 2023Meshik, A., Pravdivtseva, O., Okazaki, R., Yogata, K., Yada, T. et al. (2023) Noble gas mass-spectrometry for extraterrestrial micro-samples: analyses of asteroid matter returned by Hayabusa2 JAXA mission. Journal of Analytical Atomic Spectrometry 38, 1785–1797. https://doi.org/10.1039/D3JA00125C
; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
). Neon released at low temperatures must, therefore, be predominantly derived from the SW, fractionated to an isotopically lighter value upon implantation and grain surface sputtering (Grimberg et al., 2006Grimberg, A., Bauer, H., Bochsler, P., Bühler, F., Burnett, D.S., Hays, C.C., Heber, V.S., Jurewicz, A.J.G., Wieler, R. (2006) Solar wind neon from Genesis: implications for the lunar noble gas record. Science 17, 1133–1135. https://doi.org/10.1126/science.1133568
). At higher temperatures, the 20Ne/22Ne ratio first decreased significantly to 9.39 ± 0.12, before increasing to 12.03 ± 0.18. Since the 21Ne/22Ne ratio varied only between ∼0.026 and 0.049 (Fig. 2), which implies a small proportion of cosmogenic Ne (i.e. <0.1 % 21Necosm) in particle C0015, the 20Ne/22Ne variations are inferred to predominantly reflect the release of the primordial components Ne-Q and Ne-HL. The Ne amounts released during the last 15 steps were too low for reliable isotope ratio measurements. The results indicate the presence of at least three Ne components in Ryugu particle C0015: SW-derived Ne implanted at the grain surface, Ne-HL carried by presolar nanodiamonds, and Ne-Q (or P1) carried by phase Q (Fig. 2b). Overall, the Ne composition of particle C0015 is dominated by the SW component (Fig. 2a), similar to two pellets studied by the Hayabusa2-initial-analysis volatile team (Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
) and several particles analysed by the Phase-2 curation team (Nakamura et al., 2022Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
).Figure 1 (a) 20Ne, (b) 36Ar, and (c) N2 abundances (filled bars) and isotope ratios (filled circles) of particle C0015 for 85 extraction steps. Abundances are weighted by the extraction duration (i.e. 4 min for the first 26 steps and 12 min for the following 59 steps). Isotope ratios are shown for heating steps with <30 % blank contributions. The different colours represent the laser power used for the extraction (i.e. 1 to 45 % of the total power of 32 W). The dashed lines indicate the calculated “bulk” 20Ne/22Ne, 38Ar/36Ar, and δ15N values. Isotope ratios of the solar wind (SW), phase Q, and Ne-HL are shown for comparison (see Ott, 2014
Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
and references therein). Uncertainties are 1σ and error bars are, in most cases, smaller than symbol sizes.Figure 2 (a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022
Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Broadley et al., 2023Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
; Meshik et al., 2023Meshik, A., Pravdivtseva, O., Okazaki, R., Yogata, K., Yada, T. et al. (2023) Noble gas mass-spectrometry for extraterrestrial micro-samples: analyses of asteroid matter returned by Hayabusa2 JAXA mission. Journal of Analytical Atomic Spectrometry 38, 1785–1797. https://doi.org/10.1039/D3JA00125C
; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
and references therein). Different Ne end members are represented by grey crosses (Ott, 2014Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
). Ne-E is mainly carried by presolar graphite and silicon carbide. (b) Close-up (corresponding to the dashed rectangle in panel (a) of the Ne isotopic variations observed for the 85 extraction steps of particle C0015. The different colours represent the laser power used for each extraction. Uncertainties are 1σ.The 40Ar signal was small for steps #2 and #5, and comparable to the blank value throughout the rest of the heating procedure, demonstrating the absence of any adsorbed atmospheric Ar. The 38Ar/36Ar ratio of the Ar fraction released at low laser power first oscillated between the Ar-SW (0.1818 ± 0.0005 to 0.1828 ± 0.0010; Ott, 2014
Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
) and Ar-Q values (0.1872 ± 0.0007; Wieler et al., 1992Wieler, R., Anders, E., Baur, H., Lewis, R.S., Signer, P. (1992) Characterisation of Q-gases and other noble gas components in the Murchison meteorite. Geochimica et Cosmochimica Acta 56, 2907–2921. https://doi.org/10.1016/0016-7037(92)90367-R
), then plateaued around Ar-Q (Fig. 1b). Ar-HL (0.227 ± 0.003; Ott, 2014Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
), expected to be released from presolar diamonds at relatively low temperatures (Supplementary Information), likely also contributed to the observed variations. Unlike Ne, a large amount of Ar was released at higher temperatures, implying that a significant proportion of Ar in particle C0015 was carried by refractory phases. The elevated 38Ar/36Ar ratios observed during sample melting (i.e. after step #80, at ≥24 % laser power) can be explained by a very small contribution of cosmogenic 38Ar ((38Ar/36Ar)cosm ∼1.54; Wieler, 2002Wieler, R. (2002) Cosmic-ray-produced noble gases in meteorites. In: Porcelli, D., Ballentine C., Wieler, R. (Eds.) Reviews in Mineralogy and Geochemistry, vol. 47. Mineralogical Society of America, Washington, D.C., 125–170. https://doi.org/10.2138/rmg.2002.47.5
). The calculated bulk 38Ar/36Ar ratio (0.1865 ± 0.0001; Table S-1) is comparable to that of Ar-Q and similar to the values previously reported for Ryugu (0.186 ± 0.001 to 0.194 ± 0.007; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
).The amount of N released and the corresponding δ15N varied significantly for the different extraction steps, reflecting the presence of several, isotopically distinct N components in Ryugu material. The blank contribution exceeded 30 % of the measured N2 signal at step #1, and a δ15N of +18.4 ± 1.0 ‰ was measured at step #2. This indicates that the contribution of any dry N2 adsorbed onto the sample surface during sample storage and handling must be negligible, provided that this component is characterised by an atmospheric isotope signature. Whereas the δ15N ranged from +18.1 ± 1.0 up to +44.5 ± 1.1 ‰ during the first 52 steps (i.e. at a low laser power, ≤4 %), δ15N increased to +65.8 ± 1.1 ‰ at step #69 and then suddenly dropped to +1.0 ± 1.0 ‰ at step #70. No clear SW contribution (δ15NSW = –407 ± 7 ‰; Marty et al., 2011
Marty, B., Chaussidon, M., Wiens, R.C., Jurewicz, A.J.G., Burnett, D.S. (2011) A 15 N-poor isotopic composition for the solar system as shown by Genesis solar wind samples. Science 332, 1533–1536. https://doi.org/10.1126/science.1204656
) could be identified, even for low temperature extraction steps. Thus, the N release pattern is clearly decoupled from that of Ne. Assuming an unfractionated SW 20Ne/14N elemental abundance ratio of 1.14 (Marty et al., 2010Marty, B., Zimmermann, L., Burnard, P.G., Wieler, R., Heber, V.S., Burnett, D.S., Wiens, R.C., Bochsler, P. (2010) Nitrogen isotopes in the recent solar wind from the analysis of Genesis targets: Evidence for large scale isotope heterogeneity in the early solar system. Geochimica et Cosmochimica Acta 74, 340–355. https://doi.org/10.1016/j.gca.2009.09.007
), any SW-derived N is indeed expected to be undetectable in the 20Ne-rich particle C0015.The production of cosmogenic 15N during exposure to cosmic rays can potentially modify the N isotope ratio of extraterrestrial samples. Combined analyses of noble gases and N make it possible to quantify the amount of 15Ncosm and to identify the isotopic composition of primordial N. Previous Ne analyses revealed that Ryugu samples record short cosmic ray exposure (CRE) ages of ∼100 kyr to 8 Myr (Nakamura et al., 2022
Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
). The Ne isotopic composition of particle C0015 studied here closely resembles that of pellets A0105-15 and A0105-06, which are dominated by Ne-SW and contain a negligible amount of cosmogenic Ne. By using the same 21Necosm production rate as Okazaki et al. (2023)Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
(i.e. P21 = 1.34 × 10–13 mol g–1 Myr–1), together with a simplified one-stage irradiation model, the CRE age of particle C0015 is estimated at ∼30,000 years. This exposure duration could result in the production of ∼4 × 10–17 mol 15N (when using the maximum (15N/21Ne)cosm = 5.5 from Mathew and Murty, 1993Mathew, K.J., Murty, S.V.S. (1993) Cosmic ray produced nitrogen in extra terrestrial matter. Journal of Earth System Science 102, 415–437. https://doi.org/10.1007/BF02841731
, estimated for H/L chondrites), which is negligible compared to the bulk N content of the sample. Since particle C0015 has neither been measurably affected by the production of cosmogenic 15N nor atmospheric contamination and N-SW implantation, it preserves key information on N components and carrier phases in Ryugu and CI-type material. However, distinguishing between different labile and more refractory N components in particle C0015 is challenging because, in contrast to the noble gases, the nature and N isotope compositions of potential chondritic N carrier phases are highly complex, as detailed in the Supplementary Information. While the different N carrier phases cannot be deciphered, the observed N release pattern (Fig. 1c) and the summed bulk N signature (Fig. 3) require the presence of more than just two N components, in contrast to previous findings of Okazaki et al. (2023)Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
and Hashizume et al. (2024)Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
.Figure 3 Nitrogen isotopic composition (δ15N) as a function of the inverse of the N concentration of Ryugu samples compared to CI chondrites and Y-980115, a CI chondrite recovered in Antarctica that has recently been recommended to be re-classified as a Yamato-type (CY) carbonaceous chondrite (King et al., 2019
King, A.J., Bates, H.C., Krietsch, D., Busemann, H., Clay, P.L., Schofield, P.F., Russell, S.S. (2019) The Yamato-type (CY) carbonaceous chondrite group: Analogues for the surface of asteroid Ryugu? Geochemistry 79, 125531. https://doi.org/10.1016/j.chemer.2019.08.003
). Adapted from Okazaki et al. (2023)Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
and Hashizume et al. (2024)Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
, including data reported in Table S-2 . A simple two-component mixture, between a N-rich phase with δ15N up to +70 ‰ and a N-depleted phase with δ15N near 0 ‰, fails to explain the N signature of Ryugu particle C0015.top
Discussion
The mineralogical, chemical, and isotopic characteristics of Ryugu revealed a close relationship with CI-chondrites (Nakamura et al., 2022
Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Yokoyama et al., 2023Yokoyama, T., Nagashima, K., Nakai, I., Young, E.D., Abe, Y. et al. (2023) Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites. Science 379, eabn7850. https://doi.org/10.1126/science.abn7850
). The CI group nominally comprises the five falls Orgueil, Alais, Ivuna Tonk, and Revelstoke, whose bulk N isotopic compositions vary between +31 and +61 ‰ (based on analyses of Alais, Ivuna, and Orgueil; Table S-2 and references therein) (Fig. 3). It is noteworthy that the Meteoritical Bulletin lists an additional four CIs that were recovered in the Yamato Mountains in Antarctica (Y-86029, Y-86737, Y-980115, and Y-980134), two of which (Y-86029 and Y-980115) have been recommended to be re-classified as Yamato-type (CY) chondrites (King et al., 2019King, A.J., Bates, H.C., Krietsch, D., Busemann, H., Clay, P.L., Schofield, P.F., Russell, S.S. (2019) The Yamato-type (CY) carbonaceous chondrite group: Analogues for the surface of asteroid Ryugu? Geochemistry 79, 125531. https://doi.org/10.1016/j.chemer.2019.08.003
). The bulk δ15N of Y-980115 was reported to vary from –2.8 ‰ to +4.0 (Chan et al., 2016Chan, Q.H.S., Chikaraishi, Y., Takano, Y., Ogawa, N.O., Ohkouchi, N. (2016) Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios. Earth, Planets and Space 68, 7. https://doi.org/10.1186/s40623-016-0382-8
; Hashizume et al., 2024Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
) (Fig. 3), distinct from the CI signature.The N abundances and isotopic compositions of several particles collected at Ryugu’s surface (Ryugu-A samples) or within an artificial crater (Ryugu-C samples) fall within the CI range; however, some samples show lower N contents and/or δ15N values (Fig. 3; Nakamura et al., 2022
Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Broadley et al., 2023Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
; Naraoka et al., 2023Naraoka, H., Takano, Y., Dworkin, J.P., Oba, Y., Hamase, K. et al. (2023) Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu. Science 379, eabn9033. https://doi.org/10.1126/science.abn9033
; Oba et al., 2023Oba, Y., Koga, T., Takano, Y., Ogawa, N.O., Ohkouchi, N. et al. (2023) Uracil in the carbonaceous asteroid (162173) Ryugu. Nature Communications 14, 1292. https://doi.org/10.1038/s41467-023-36904-3
; Hashizume et al., 2024Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
). The four pelletised samples analysed by the Hayabusa2-initial-analysis volatile team have particularly low N contents (Table S-2). The bulk δ15N of +24.43 ± 0.17 ‰ of particle C0015 (Table S-1) is comparable to the values previously obtained for the pellets A0105-05 and C0106-06 by noble gas mass spectrometry at CRPG (+18.14 ± 0.94 ‰ and +19.47 ± 0.89 ‰; Broadley et al., 2023Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
), whereas its summed bulk N abundance (1760 ± 195 ppm; Table S-1) is consistent with the range observed in most CI chondrites (1400 to 2400 ppm; Table S-2 and references therein). Notably, particle C0015 contains more Ne and Ar than CI chondrites (36Ar = 4.33 ± 2.78 × 10–11 mol/g and 20Ne = 1.53 ± 0.03 × 10–11 mol/g, on average, in CIs; Broadley et al., 2023Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
and references therein), but the large noble gas abundance predominantly results from SW irradiation.Broadley et al. (2023)
Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
suggested that preferential loss of 15N-rich soluble organic matter during aqueous alteration on Ryugu’s parent body may have resulted in a lower δ15N and lower N concentrations in Ryugu samples than in CIs, without significantly affecting the noble gas budget. According to this scenario, the N heterogeneities between the various small, (sub-)milligram-sized Ryugu samples could be due to variable degrees of aqueous alteration on the initial parent body, prior to the catastrophic break-up that turned Ryugu into a rubble-pile asteroid and led to mixing between more and less altered clasts (Broadley et al., 2023Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
). However, this process alone can neither explain the association of “intermediate” δ15N values with high N abundances in particles C0015 (this study) and A0033 (Nakamura et al., 2022Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
), nor the very low δ15N value and high N content of particle C0082 (Nakamura et al., 2022Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
) (Fig. 3). Significant heterogeneities of the N distribution must, therefore, exist at the scale of (sub-)milligram-sized Ryugu regolith particles, as also demonstrated by in situ secondary ion mass spectrometry analyses of N (Nakamura et al., 2022Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
).CI-type material is inferred to have played an important role in supplying volatile elements (e.g., H, C, N) to Earth’s surface (Piani et al., 2020
Piani, L., Marrocchi, Y., Rigaudier, T., Vacher, L.G., Thomassin, D., Marty, B. (2020) Earth’s water may have been inherited from material similar to enstatite chondrite meteorites. Science 369, 1110–1113. https://doi.org/10.1126/science.aba1948
). However, since thermal metamorphism and accretionary heating could have resulted in extensive devolatilisation and loss of 15N-rich components (Alexander et al., 1998Alexander, C.M.O’D., Russell, S.S., Arden, J.W., Ash, R.D., Grady, M.M., Pillinger, C.T. (1998) The origin of chondritic macromolecular organic matter: A carbon and nitrogen isotope study. Meteoritics & Planetary Science 33, 603–622. https://doi.org/10.1111/j.1945-5100.1998.tb01667.x
, Alexander et al., 2007Alexander, C.M.O’D., Fogel, M., Yabuta, H., Cody, G.D. (2007) The origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter. Geochimica et Cosmochimica Acta 71, 4380–4403. https://doi.org/10.1016/j.gca.2007.06.052
; Pearson et al., 2006Pearson, V.K., Sephton, M.A., Franchi, I.A., Gibson, J.M., Gilmour, I. (2006) Carbon and nitrogen in carbonaceous chondrites: Elemental abundances and stable isotopic compositions. Meteoritics & Planetary Science 41, 1899–1918. https://doi.org/10.1111/j.1945-5100.2006.tb00459.x
; Grewal, 2022Grewal, D.S. (2022) Origin of nitrogen isotopic variations in the rocky bodies of the solar system. The Astrophysical Journal 937, 123. https://doi.org/10.3847/1538-4357/ac8eb4
), assessing the evolution of the N content and isotopic composition during progressive heating is key for understanding the contribution of CIs to Earth’s volatile budget. The numerous heating steps performed on Ryugu particle C0015 provide key information on N abundance and isotopic variations induced by thermal processing, especially since Ryugu never experienced temperatures >150 °C (based on analyses of soluble organic matter in Ryugu; Naraoka et al., 2023Naraoka, H., Takano, Y., Dworkin, J.P., Oba, Y., Hamase, K. et al. (2023) Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu. Science 379, eabn9033. https://doi.org/10.1126/science.abn9033
). Figure 4 illustrates that the “bulk” δ15N value of particle C0015 was not significantly modified during the first 60 heating steps (i.e. δ15N = 22.05 ± 0.22 ‰ to 24.47 ± 0.17 ‰ for 1 to 7 % of the maximum laser power), although up to ∼73 % of the total initial N content was lost. As heating proceeded and particle C0015 started to melt at step #80, the δ15N decreased to 4.47 ± 0.47 ‰ (with concomitant loss of ∼99 % N). This observation confirms that Ryugu samples contain a refractory N component with an isotopic composition similar to Earth’s atmosphere (Hashizume et al., 2024Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
) whose proportion of the total amount of N, however, is very small.Figure 4 Evolution of the residual N isotopic composition (δ15Nresidual) of particle C0015 as a function of the fraction of N extracted by progressive heating.
Overall, N-rich material collected at Ryugu’s surface is predominantly characterised by an isotopic signature that is comparable to, or only slightly lighter than, that of CI chondrites (δ15N ≥ +18 ‰; Fig. 3; Table S-2). Furthermore, our new data demonstrate that low temperatures can result in extensive N loss from CI-type material, without significantly affecting the bulk N isotope composition. Only high temperatures result in loss of a 15N-rich component and a notable decrease of the bulk δ15N value by ∼20 ‰. Consequently, and despite potential losses of thermally labile N-bearing phases, N isotopes remain a reliable and powerful tool for tracing contributions from inner and outer Solar System sources, and they imply that CI- or Ryugu-type material can be ruled out as the major source of N in Earth’s mantle.
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Acknowledgements
The Hayabusa2 mission was developed under the leadership of the Japan Aerospace Exploration Agency (JAXA), with contributions from the German Aerospace Center (DLR) and the Centre National d’Études Spatiales (CNES), and in collaboration with NASA, and other universities and institutes. This work was primarily funded by the European Union (ERC, IRONIS, 101087562). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. Support from the Centre National d’Études Spatiales (CNES) is also acknowledged. We thank Michael W. Broadley for his help with handling the Hayabusa2 samples as well as Bouchaib Tibari and Allan Bauer for their assistance with the noble gas mass spectrometry analyses at CRPG. We are also grateful to R. Wieler, C.M.O’D. Alexander, and an anonymous reviewer for their constructive comments, and to A. Shahar for editorial handling. This is CRPG contribution 2858.
Editor: Anat Shahar
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References
Alexander, C.M.O’D. (2022) An exploration of whether Earth can be built from chondritic components, not bulk chondrites. Geochimica et Cosmochimica Acta 318, 428–451. https://doi.org/10.1016/j.gca.2021.12.012
Show in context Since carbonaceous chondrites may have played an important role in supplying volatile elements to Earth (e.g., Alexander et al., 2012; Marty, 2012; Alexander, 2022), Ryugu samples are key for better understanding the origin of terrestrial volatiles.
View in article
Alexander, C.M.O’D., Russell, S.S., Arden, J.W., Ash, R.D., Grady, M.M., Pillinger, C.T. (1998) The origin of chondritic macromolecular organic matter: A carbon and nitrogen isotope study. Meteoritics & Planetary Science 33, 603–622. https://doi.org/10.1111/j.1945-5100.1998.tb01667.x
Show in context However, since thermal metamorphism and accretionary heating could have resulted in extensive devolatilisation and loss of 15N-rich components (Alexander et al., 1998, Alexander et al., 2007; Pearson et al., 2006; Grewal, 2022), assessing the evolution of the N content and isotopic composition during progressive heating is key for understanding the contribution of CIs to Earth’s volatile budget.
View in article
Alexander, C.M.O’D., Fogel, M., Yabuta, H., Cody, G.D. (2007) The origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter. Geochimica et Cosmochimica Acta 71, 4380–4403. https://doi.org/10.1016/j.gca.2007.06.052
Show in context However, since thermal metamorphism and accretionary heating could have resulted in extensive devolatilisation and loss of 15N-rich components (Alexander et al., 1998, Alexander et al., 2007; Pearson et al., 2006; Grewal, 2022), assessing the evolution of the N content and isotopic composition during progressive heating is key for understanding the contribution of CIs to Earth’s volatile budget.
View in article
Alexander, C.M.O’D., Bowden, R., Fogel, M.L., Howard, K.T., Herd, C.D.K., Nittler, L.R. (2012) The provenances of asteroids, and their contributions to the volatile inventories of the terrestrial planets. Science 337, 721–723. https://doi.org/10.1126/science.1223474
Show in context Since carbonaceous chondrites may have played an important role in supplying volatile elements to Earth (e.g., Alexander et al., 2012; Marty, 2012; Alexander, 2022), Ryugu samples are key for better understanding the origin of terrestrial volatiles.
View in article
Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
Show in context These results were subsequently discussed in more detail by Broadley et al. (2023) and Hashizume et al. (2024).
View in article
(a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022; Broadley et al., 2023; Meshik et al., 2023; Okazaki et al., 2023 and references therein).
View in article
The N abundances and isotopic compositions of several particles collected at Ryugu’s surface (Ryugu-A samples) or within an artificial crater (Ryugu-C samples) fall within the CI range; however, some samples show lower N contents and/or δ15N values (Fig. 3; Nakamura et al., 2022; Broadley et al., 2023; Naraoka et al., 2023; Oba et al., 2023; Hashizume et al., 2024).
View in article
The bulk δ15N of +24.43 ± 0.17 ‰ of particle C0015 (Table S-1) is comparable to the values previously obtained for the pellets A0105-05 and C0106-06 by noble gas mass spectrometry at CRPG (+18.14 ± 0.94 ‰ and +19.47 ± 0.89 ‰; Broadley et al., 2023; Okazaki et al., 2023), whereas its summed bulk N abundance (1760 ± 195 ppm; Table S-1) is consistent with the range observed in most CI chondrites (1400 to 2400 ppm; Table S-2 and references therein).
View in article
Notably, particle C0015 contains more Ne and Ar than CI chondrites (36Ar = 4.33 ± 2.78 × 10–11 mol/g and 20Ne = 1.53 ± 0.03 × 10–11 mol/g, on average, in CIs; Broadley et al., 2023 and references therein), but the large noble gas abundance predominantly results from SW irradiation.
View in article
Broadley et al. (2023) suggested that preferential loss of 15N-rich soluble organic matter during aqueous alteration on Ryugu’s parent body may have resulted in a lower δ15N and lower N concentrations in Ryugu samples than in CIs, without significantly affecting the noble gas budget.
View in article
According to this scenario, the N heterogeneities between the various small, (sub-)milligram-sized Ryugu samples could be due to variable degrees of aqueous alteration on the initial parent body, prior to the catastrophic break-up that turned Ryugu into a rubble-pile asteroid and led to mixing between more and less altered clasts (Broadley et al., 2023).
View in article
Chan, Q.H.S., Chikaraishi, Y., Takano, Y., Ogawa, N.O., Ohkouchi, N. (2016) Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios. Earth, Planets and Space 68, 7. https://doi.org/10.1186/s40623-016-0382-8
Show in context The bulk δ15N of Y-980115 was reported to vary from –2.8 ‰ to +4.0 (Chan et al., 2016; Hashizume et al., 2024) (Fig. 3), distinct from the CI signature.
View in article
Grewal, D.S. (2022) Origin of nitrogen isotopic variations in the rocky bodies of the solar system. The Astrophysical Journal 937, 123. https://doi.org/10.3847/1538-4357/ac8eb4
Show in context However, since thermal metamorphism and accretionary heating could have resulted in extensive devolatilisation and loss of 15N-rich components (Alexander et al., 1998, Alexander et al., 2007; Pearson et al., 2006; Grewal, 2022), assessing the evolution of the N content and isotopic composition during progressive heating is key for understanding the contribution of CIs to Earth’s volatile budget.
View in article
Grimberg, A., Bauer, H., Bochsler, P., Bühler, F., Burnett, D.S., Hays, C.C., Heber, V.S., Jurewicz, A.J.G., Wieler, R. (2006) Solar wind neon from Genesis: implications for the lunar noble gas record. Science 17, 1133–1135. https://doi.org/10.1126/science.1133568
Show in context Neon released at low temperatures must, therefore, be predominantly derived from the SW, fractionated to an isotopically lighter value upon implantation and grain surface sputtering (Grimberg et al., 2006).
View in article
Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
Show in context These results were subsequently discussed in more detail by Broadley et al. (2023) and Hashizume et al. (2024).
View in article
While the different N carrier phases cannot be deciphered, the observed N release pattern (Fig. 1c) and the summed bulk N signature (Fig. 3) require the presence of more than just two N components, in contrast to previous findings of Okazaki et al. (2023) and Hashizume et al. (2024).
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Adapted from Okazaki et al. (2023) and Hashizume et al. (2024), including data reported in Table S-2
View in article
The bulk δ15N of Y-980115 was reported to vary from –2.8 ‰ to +4.0 (Chan et al., 2016; Hashizume et al., 2024) (Fig. 3), distinct from the CI signature.
View in article
The N abundances and isotopic compositions of several particles collected at Ryugu’s surface (Ryugu-A samples) or within an artificial crater (Ryugu-C samples) fall within the CI range; however, some samples show lower N contents and/or δ15N values (Fig. 3; Nakamura et al., 2022; Broadley et al., 2023; Naraoka et al., 2023; Oba et al., 2023; Hashizume et al., 2024).
View in article
This observation confirms that Ryugu samples contain a refractory N component with an isotopic composition similar to Earth’s atmosphere (Hashizume et al., 2024) whose proportion of the total amount of N, however, is very small.
View in article
Heber, V.S., Baur, H., Bochsler, P., McKeegan, K.D., Neugebauer, M., Reisenfeld, D.B., Wieler, R., Wiens, R.C. (2012) Isotopic mass fractionation of solar wind: evidence from fast and slow solar wind collected by the Genesis mission. The Astrophysical Journal 759, 121. https://doi.org/10.1088/0004-637X/759/2/121
Show in context The 20Ne/22Ne ratio was nearly constant (12.92 ± 0.47) during the first 38 extraction steps (Fig. 1a), only slightly below the Ne isotope ratio of SW (13.74 ± 0.02 to 14.00 ± 0.04; Ott, 2014) and close to that of the protosolar nebula (∼13.36; Heber et al., 2012).
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King, A.J., Bates, H.C., Krietsch, D., Busemann, H., Clay, P.L., Schofield, P.F., Russell, S.S. (2019) The Yamato-type (CY) carbonaceous chondrite group: Analogues for the surface of asteroid Ryugu? Geochemistry 79, 125531. https://doi.org/10.1016/j.chemer.2019.08.003
Show in context Nitrogen isotopic composition (δ15N) as a function of the inverse of the N concentration of Ryugu samples compared to CI chondrites and Y-980115, a CI chondrite recovered in Antarctica that has recently been recommended to be re-classified as a Yamato-type (CY) carbonaceous chondrite (King et al., 2019).
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It is noteworthy that the Meteoritical Bulletin lists an additional four CIs that were recovered in the Yamato Mountains in Antarctica (Y-86029, Y-86737, Y-980115, and Y-980134), two of which (Y-86029 and Y-980115) have been recommended to be re-classified as Yamato-type (CY) chondrites (King et al., 2019).
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Marty, B. (2012) The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters 313–314, 56–66. https://doi.org/10.1016/j.epsl.2011.10.040
Show in context Since carbonaceous chondrites may have played an important role in supplying volatile elements to Earth (e.g., Alexander et al., 2012; Marty, 2012; Alexander, 2022), Ryugu samples are key for better understanding the origin of terrestrial volatiles.
View in article
Marty, B., Zimmermann, L., Burnard, P.G., Wieler, R., Heber, V.S., Burnett, D.S., Wiens, R.C., Bochsler, P. (2010) Nitrogen isotopes in the recent solar wind from the analysis of Genesis targets: Evidence for large scale isotope heterogeneity in the early solar system. Geochimica et Cosmochimica Acta 74, 340–355. https://doi.org/10.1016/j.gca.2009.09.007
Show in context Thus, the N release pattern is clearly decoupled from that of Ne. Assuming an unfractionated SW 20Ne/14N elemental abundance ratio of 1.14 (Marty et al., 2010), any SW-derived N is indeed expected to be undetectable in the 20Ne-rich particle C0015.
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Marty, B., Chaussidon, M., Wiens, R.C., Jurewicz, A.J.G., Burnett, D.S. (2011) A 15 N-poor isotopic composition for the solar system as shown by Genesis solar wind samples. Science 332, 1533–1536. https://doi.org/10.1126/science.1204656
Show in context Whereas the δ15N ranged from +18.1 ± 1.0 up to +44.5 ± 1.1 ‰ during the first 52 steps (i.e. at a low laser power, ≤4 %), δ15N increased to +65.8 ± 1.1 ‰ at step #69 and then suddenly dropped to +1.0 ± 1.0 ‰ at step #70. No clear SW contribution (δ15NSW = –407 ± 7 ‰; Marty et al., 2011) could be identified, even for low temperature extraction steps.
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Mathew, K.J., Murty, S.V.S. (1993) Cosmic ray produced nitrogen in extra terrestrial matter. Journal of Earth System Science 102, 415–437. https://doi.org/10.1007/BF02841731
Show in context This exposure duration could result in the production of ∼4 × 10–17 mol 15N (when using the maximum (15N/21Ne)cosm = 5.5 from Mathew and Murty, 1993, estimated for H/L chondrites), which is negligible compared to the bulk N content of the sample.
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Meshik, A., Pravdivtseva, O., Okazaki, R., Yogata, K., Yada, T. et al. (2023) Noble gas mass-spectrometry for extraterrestrial micro-samples: analyses of asteroid matter returned by Hayabusa2 JAXA mission. Journal of Analytical Atomic Spectrometry 38, 1785–1797. https://doi.org/10.1039/D3JA00125C
Show in context While trapping of nebular gas in CI-type material cannot be ruled out, the 3He/4He ratio of solar-gas-rich Ryugu samples analysed previously is consistent with implanted SW-derived gas (Meshik et al., 2023; Okazaki et al., 2023).
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(a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022; Broadley et al., 2023; Meshik et al., 2023; Okazaki et al., 2023 and references therein).
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Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
Show in context The mineralogy and the chemical and isotopic compositions of the samples revealed a close relationship between Ryugu and Ivuna-type (CI) carbonaceous chondrites (Nakamura et al., 2022; Yokoyama et al., 2023).
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The Hayabusa2-initial-analysis volatile team and the Phase-2 curation team carried out the first noble gas and N analyses, thus providing insights into the volatile composition, formation, and alteration history of Ryugu (Nakamura et al., 2022; Okazaki et al., 2023).
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Overall, the Ne composition of particle C0015 is dominated by the SW component (Fig. 2a), similar to two pellets studied by the Hayabusa2-initial-analysis volatile team (Okazaki et al., 2023) and several particles analysed by the Phase-2 curation team (Nakamura et al., 2022).
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(a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022; Broadley et al., 2023; Meshik et al., 2023; Okazaki et al., 2023 and references therein).
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Combined analyses of noble gases and N make it possible to quantify the amount of 15Ncosm and to identify the isotopic composition of primordial N. Previous Ne analyses revealed that Ryugu samples record short cosmic ray exposure (CRE) ages of ∼100 kyr to 8 Myr (Nakamura et al., 2022; Okazaki et al., 2023).
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The mineralogical, chemical, and isotopic characteristics of Ryugu revealed a close relationship with CI-chondrites (Nakamura et al., 2022; Yokoyama et al., 2023).
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The N abundances and isotopic compositions of several particles collected at Ryugu’s surface (Ryugu-A samples) or within an artificial crater (Ryugu-C samples) fall within the CI range; however, some samples show lower N contents and/or δ15N values (Fig. 3; Nakamura et al., 2022; Broadley et al., 2023; Naraoka et al., 2023; Oba et al., 2023; Hashizume et al., 2024).
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However, this process alone can neither explain the association of “intermediate” δ15N values with high N abundances in particles C0015 (this study) and A0033 (Nakamura et al., 2022), nor the very low δ15N value and high N content of particle C0082 (Nakamura et al., 2022) (Fig. 3).
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Significant heterogeneities of the N distribution must, therefore, exist at the scale of (sub-)milligram-sized Ryugu regolith particles, as also demonstrated by in situ secondary ion mass spectrometry analyses of N (Nakamura et al., 2022).
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Naraoka, H., Takano, Y., Dworkin, J.P., Oba, Y., Hamase, K. et al. (2023) Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu. Science 379, eabn9033. https://doi.org/10.1126/science.abn9033
Show in context Okazaki et al. (2023) concluded that the heterogeneous N contents and isotopic compositions of Ryugu samples, including four small pelletised samples and three splits of a large aggregate sample (Naraoka et al., 2023), indicate the presence of at least two carrier phases: a N-rich phase with δ15N up to +70 ‰ and a N-depleted phase with δ15N near 0 ‰.
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The N abundances and isotopic compositions of several particles collected at Ryugu’s surface (Ryugu-A samples) or within an artificial crater (Ryugu-C samples) fall within the CI range; however, some samples show lower N contents and/or δ15N values (Fig. 3; Nakamura et al., 2022; Broadley et al., 2023; Naraoka et al., 2023; Oba et al., 2023; Hashizume et al., 2024).
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The numerous heating steps performed on Ryugu particle C0015 provide key information on N abundance and isotopic variations induced by thermal processing, especially since Ryugu never experienced temperatures >150 °C (based on analyses of soluble organic matter in Ryugu; Naraoka et al., 2023).
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Oba, Y., Koga, T., Takano, Y., Ogawa, N.O., Ohkouchi, N. et al. (2023) Uracil in the carbonaceous asteroid (162173) Ryugu. Nature Communications 14, 1292. https://doi.org/10.1038/s41467-023-36904-3
Show in context The N abundances and isotopic compositions of several particles collected at Ryugu’s surface (Ryugu-A samples) or within an artificial crater (Ryugu-C samples) fall within the CI range; however, some samples show lower N contents and/or δ15N values (Fig. 3; Nakamura et al., 2022; Broadley et al., 2023; Naraoka et al., 2023; Oba et al., 2023; Hashizume et al., 2024).
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Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
Show in context The Hayabusa2-initial-analysis volatile team and the Phase-2 curation team carried out the first noble gas and N analyses, thus providing insights into the volatile composition, formation, and alteration history of Ryugu (Nakamura et al., 2022; Okazaki et al., 2023).
View in article
Okazaki et al. (2023) concluded that the heterogeneous N contents and isotopic compositions of Ryugu samples, including four small pelletised samples and three splits of a large aggregate sample (Naraoka et al., 2023), indicate the presence of at least two carrier phases: a N-rich phase with δ15N up to +70 ‰ and a N-depleted phase with δ15N near 0 ‰.
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While trapping of nebular gas in CI-type material cannot be ruled out, the 3He/4He ratio of solar-gas-rich Ryugu samples analysed previously is consistent with implanted SW-derived gas (Meshik et al., 2023; Okazaki et al., 2023).
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Overall, the Ne composition of particle C0015 is dominated by the SW component (Fig. 2a), similar to two pellets studied by the Hayabusa2-initial-analysis volatile team (Okazaki et al., 2023) and several particles analysed by the Phase-2 curation team (Nakamura et al., 2022).
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(a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022; Broadley et al., 2023; Meshik et al., 2023; Okazaki et al., 2023 and references therein).
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The calculated bulk 38Ar/36Ar ratio (0.1865 ± 0.0001; Table S-1) is comparable to that of Ar-Q and similar to the values previously reported for Ryugu (0.186 ± 0.001 to 0.194 ± 0.007; Okazaki et al., 2023).
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Combined analyses of noble gases and N make it possible to quantify the amount of 15Ncosm and to identify the isotopic composition of primordial N. Previous Ne analyses revealed that Ryugu samples record short cosmic ray exposure (CRE) ages of ∼100 kyr to 8 Myr (Nakamura et al., 2022; Okazaki et al., 2023).
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By using the same 21Necosm production rate as Okazaki et al. (2023) (i.e. P21 = 1.34 × 10–13 mol g–1 Myr–1), together with a simplified one-stage irradiation model, the CRE age of particle C0015 is estimated at ∼30,000 years.
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While the different N carrier phases cannot be deciphered, the observed N release pattern (Fig. 1c) and the summed bulk N signature (Fig. 3) require the presence of more than just two N components, in contrast to previous findings of Okazaki et al. (2023) and Hashizume et al. (2024).
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Adapted from Okazaki et al. (2023) and Hashizume et al. (2024), including data reported in Table S-2
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The bulk δ15N of +24.43 ± 0.17 ‰ of particle C0015 (Table S-1) is comparable to the values previously obtained for the pellets A0105-05 and C0106-06 by noble gas mass spectrometry at CRPG (+18.14 ± 0.94 ‰ and +19.47 ± 0.89 ‰; Broadley et al., 2023; Okazaki et al., 2023), whereas its summed bulk N abundance (1760 ± 195 ppm; Table S-1) is consistent with the range observed in most CI chondrites (1400 to 2400 ppm; Table S-2 and references therein).
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Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
Show in context The 20Ne/22Ne ratio was nearly constant (12.92 ± 0.47) during the first 38 extraction steps (Fig. 1a), only slightly below the Ne isotope ratio of SW (13.74 ± 0.02 to 14.00 ± 0.04; Ott, 2014) and close to that of the protosolar nebula (∼13.36; Heber et al., 2012).
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Different Ne end members are represented by grey crosses (Ott, 2014).
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The 38Ar/36Ar ratio of the Ar fraction released at low laser power first oscillated between the Ar-SW (0.1818 ± 0.0005 to 0.1828 ± 0.0010; Ott, 2014) and Ar-Q values (0.1872 ± 0.0007; Wieler et al., 1992), then plateaued around Ar-Q (Fig. 1b).
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Ar-HL (0.227 ± 0.003; Ott, 2014), expected to be released from presolar diamonds at relatively low temperatures (Supplementary Information), likely also contributed to the observed variations. Unlike Ne, a large amount of Ar was released at higher temperatures, implying that a significant proportion of Ar in particle C0015 was carried by refractory phases.
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Pearson, V.K., Sephton, M.A., Franchi, I.A., Gibson, J.M., Gilmour, I. (2006) Carbon and nitrogen in carbonaceous chondrites: Elemental abundances and stable isotopic compositions. Meteoritics & Planetary Science 41, 1899–1918. https://doi.org/10.1111/j.1945-5100.2006.tb00459.x
Show in context However, since thermal metamorphism and accretionary heating could have resulted in extensive devolatilisation and loss of 15N-rich components (Alexander et al., 1998, Alexander et al., 2007; Pearson et al., 2006; Grewal, 2022), assessing the evolution of the N content and isotopic composition during progressive heating is key for understanding the contribution of CIs to Earth’s volatile budget.
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Piani, L., Marrocchi, Y., Rigaudier, T., Vacher, L.G., Thomassin, D., Marty, B. (2020) Earth’s water may have been inherited from material similar to enstatite chondrite meteorites. Science 369, 1110–1113. https://doi.org/10.1126/science.aba1948
Show in context CI-type material is inferred to have played an important role in supplying volatile elements (e.g., H, C, N) to Earth’s surface (Piani et al., 2020).
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Tsuda, Y., Saiki, T., Terui, F., Nakazawa, S., Yoshikawa, M., Watanabe, S. (2020) Hayabusa2 mission status: Landing, roving and cratering on asteroid Ryugu. Acta Astronautica 171, 42–54. https://doi.org/10.1016/j.actaastro.2020.02.035
Show in context The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) collected 5.4 g of regolith on the Cb-type asteroid (162173) Ryugu during two touchdowns in 2019 and returned the samples to Earth on December 6th, 2020 (Tsuda et al., 2020).
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Wieler, R. (2002) Cosmic-ray-produced noble gases in meteorites. In: Porcelli, D., Ballentine C., Wieler, R. (Eds.) Reviews in Mineralogy and Geochemistry, vol. 47. Mineralogical Society of America, Washington, D.C., 125–170. https://doi.org/10.2138/rmg.2002.47.5
Show in context The elevated 38Ar/36Ar ratios observed during sample melting (i.e. after step #80, at ≥24 % laser power) can be explained by a very small contribution of cosmogenic 38Ar ((38Ar/36Ar)cosm ∼1.54; Wieler, 2002).
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Wieler, R., Anders, E., Baur, H., Lewis, R.S., Signer, P. (1992) Characterisation of Q-gases and other noble gas components in the Murchison meteorite. Geochimica et Cosmochimica Acta 56, 2907–2921. https://doi.org/10.1016/0016-7037(92)90367-R
Show in context The 38Ar/36Ar ratio of the Ar fraction released at low laser power first oscillated between the Ar-SW (0.1818 ± 0.0005 to 0.1828 ± 0.0010; Ott, 2014) and Ar-Q values (0.1872 ± 0.0007; Wieler et al., 1992), then plateaued around Ar-Q (Fig. 1b).
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Yokoyama, T., Nagashima, K., Nakai, I., Young, E.D., Abe, Y. et al. (2023) Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites. Science 379, eabn7850. https://doi.org/10.1126/science.abn7850
Show in context The mineralogy and the chemical and isotopic compositions of the samples revealed a close relationship between Ryugu and Ivuna-type (CI) carbonaceous chondrites (Nakamura et al., 2022; Yokoyama et al., 2023).
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The mineralogical, chemical, and isotopic characteristics of Ryugu revealed a close relationship with CI-chondrites (Nakamura et al., 2022; Yokoyama et al., 2023).
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Supplementary Information
The Supplementary Information includes:
- Detailed Methodology
- Figures S-1 and S-2
- Tables S-1 and S-2
- Supplementary Information References
Download the Supplementary Information (PDF)
Figures
Figure 1 (a) 20Ne, (b) 36Ar, and (c) N2 abundances (filled bars) and isotope ratios (filled circles) of particle C0015 for 85 extraction steps. Abundances are weighted by the extraction duration (i.e. 4 min for the first 26 steps and 12 min for the following 59 steps). Isotope ratios are shown for heating steps with <30 % blank contributions. The different colours represent the laser power used for the extraction (i.e. 1 to 45 % of the total power of 32 W). The dashed lines indicate the calculated “bulk” 20Ne/22Ne, 38Ar/36Ar, and δ15N values. Isotope ratios of the solar wind (SW), phase Q, and Ne-HL are shown for comparison (see Ott, 2014
Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
and references therein). Uncertainties are 1σ and error bars are, in most cases, smaller than symbol sizes.
Figure 2 (a) Neon isotopic composition of Ryugu particle C0015 (bulk represented by the yellow star; individual extraction steps represented by the small circles) compared to pelletised and fragment Ryugu samples analysed by the Hayabusa2-initial-analysis volatile team and particles analysed by the Phase-2 curation team (Institute for Planetary Materials, Okayama University) (pink diamonds), as well as CI chondrites (grey squares) (Nakamura et al., 2022
Nakamura, E., Kobayashi, K., Tanaka, R., Kunihiro, T., Kitagawa, H. et al. (2022) On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective. Proceedings of the Japan Academy, Series B 98, 227–282. https://doi.org/10.2183/pjab.98.015
; Broadley et al., 2023Broadley, M.W., Byrne, D.J., Füri, E., Zimmermann, L., Marty, B. et al. (2023) The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites. Geochimica et Cosmochimica Acta 345, 62–74. https://doi.org/10.1016/j.gca.2023.01.020
; Meshik et al., 2023Meshik, A., Pravdivtseva, O., Okazaki, R., Yogata, K., Yada, T. et al. (2023) Noble gas mass-spectrometry for extraterrestrial micro-samples: analyses of asteroid matter returned by Hayabusa2 JAXA mission. Journal of Analytical Atomic Spectrometry 38, 1785–1797. https://doi.org/10.1039/D3JA00125C
; Okazaki et al., 2023Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
and references therein). Different Ne end members are represented by grey crosses (Ott, 2014Ott, U. (2014) Planetary and pre-solar noble gases in meteorites. Geochemistry 74, 519–544. https://doi.org/10.1016/j.chemer.2014.01.003
). Ne-E is mainly carried by presolar graphite and silicon carbide. (b) Close-up (corresponding to the dashed rectangle in panel (a) of the Ne isotopic variations observed for the 85 extraction steps of particle C0015. The different colours represent the laser power used for each extraction. Uncertainties are 1σ.
Figure 3 Nitrogen isotopic composition (δ15N) as a function of the inverse of the N concentration of Ryugu samples compared to CI chondrites and Y-980115, a CI chondrite recovered in Antarctica that has recently been recommended to be re-classified as a Yamato-type (CY) carbonaceous chondrite (King et al., 2019
King, A.J., Bates, H.C., Krietsch, D., Busemann, H., Clay, P.L., Schofield, P.F., Russell, S.S. (2019) The Yamato-type (CY) carbonaceous chondrite group: Analogues for the surface of asteroid Ryugu? Geochemistry 79, 125531. https://doi.org/10.1016/j.chemer.2019.08.003
). Adapted from Okazaki et al. (2023)Okazaki, R., Marty, B., Busemann, H., Hashizume, K., Gilmour, J.D. et al. (2023) Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution. Science 379, eabo0431. https://doi.org/10.1126/science.abo0431
and Hashizume et al. (2024)Hashizume, K., Ishida, A., Chiba, A., Okazaki, R., Yogata, K., Yada, T., Kitajima, F., Yurimoto, H., Nakamura, T., Noguchi, T., Yabuta, H., Naraoka, H., Takano, Y., Sakamoto, K., Tachibana, S., Nishimura, M., Nakato, A., Miyazaki, A., Abe, M., Okada, T., Usui, T., Yoshikawa, M., Saiki, T., Terui, F., Tanaka, S., Nakazawa, S., Watanabe, S.-i., Tsuda, Y., Broadley, M.W., Busemann, H., Hayabusa2 Initial Analysis Volatile Team (2024) The Earth atmosphere-like bulk nitrogen isotope composition obtained by stepwise combustion analyses of Ryugu return samples. Meteoritics & Planetary Science. https://doi.org/10.1111/maps.14175
, including data reported in Table S-2 . A simple two-component mixture, between a N-rich phase with δ15N up to +70 ‰ and a N-depleted phase with δ15N near 0 ‰, fails to explain the N signature of Ryugu particle C0015.
Figure 4 Evolution of the residual N isotopic composition (δ15Nresidual) of particle C0015 as a function of the fraction of N extracted by progressive heating.