Soluble organic matter Molecular atlas of Ryugu reveals cold hydrothermalism on C-type asteroid parent body

Domain: earth_science
Published: 2023-10-16
Editorial outcome: accept

Abstract
The sample from the near-Earth carbonaceous asteroid (162173) Ryugu is analyzed in the context of carbonaceous meteorites soluble organic matter. The analysis of soluble molecules of samples collected by the Hayabusa2 spacecraft shines light on an extremely high molecular diversity on the C-type asteroid. Sequential solvent extracts of increasing polarity of Ryugu samples are analyzed using mass spectrometry with complementary ionization methods and structural information confirmed by nuclear magnetic resonance spectroscopy. Here we show a continuum in the molecular size and polarity, and no organomagnesium molecules are detected, reflecting a low temperature and water-rich environment on the parent body approving earlier mineralogical and chemical data. High abundance of sulfidic and nitrogen rich compounds as well as high abundance of ammonium ions confirm the water processing. Polycyclic aromatic hydrocarbons are also detected in a structural continuum of carbon saturations and oxidations, implying multiple origins of the observed organic complexity, thus involving generic processes such as earlier carbonization and serpentinization with successive low temperature aqueous alteration.

Introduction
The soluble organic matter (SOM) in carbonaceous chondrites is chemically highly diverse and integrates in its chemistry much of the history on temperature events and water-rock interaction on the parent body1–3. Two touch-down samplings by the Hayabusa2 spacecraft in February and July 2019 enabled the collection of surface (samples stored in Chamber A) and possibly sub-surface materials (samples stored in Chamber C) of the near-Earth C-Type asteroid (162173) Ryugu. Samples were returned to Earth on December 6, 2020 and with about 5.4g material that constitutes the fourth returned sample from extraterrestrial bodies following Apollo, Luna and recently Chang’e 5 from the Moon, Stardust from comet 81P/Wild2 and Hayabusa from the near-Earth S-type asteroid Itokawa, respectively. These material from enabled first time the comparison of our knowledge on meteorites to a C-type asteroid4,5. Ryugu is considered as a primitive small Solar-System body and its low-albedo reflectance spectrum in the wavelength range of 1.8 to 3.0 µm6 and spectroscopic similarity7 made it from observation a good candidate in being a parent body of carbonaceous chondrites (CCs), rich in water and organics.

The analysis of the Ryugu material showed the dominance of hydrous silicate minerals including serpentine and saponite associated with dolomite, pyrrhotite and magnetite, reflecting episode of aqueous alteration8 and suggesting similarities with CI chondrites4,8,9. Element analysis confirmed Ryugu with the richest C, N, and H concentrations compared to various types of CCs with signatures comparable to the observed falls Ivuna and Orgueil CI chondrites4,10. The analyzed elements content of C, H, N, S, and pyrolyzable O (not including O of anhydrous silica) was found to be ~21.3 wt% including the carbonates, the sulfides as well as the soluble organic matter (SOM) and the macromolecular insoluble organic matter (IOM)5. Targeted organic analysis of Ryugu A0106 sample revealed ~15 amino acids, including many non-protein amino acids in an approximately racemic mixture indicating a non-biological origin. Their abundances were different to Orgueil CI, reflecting different chemosynthetic or alteration pathway conditions on the asteroid parent bodies4. High abundances of β-alanine, ɣ-amino-n-butyric acid, and δ-aminovaleric acid in the Ryugu samples indicated a higher peak temperature than the CI chondrites as these compounds are typical in CV and CO chondrites processed at elevated temperatures of up to ~300 °C5,11,12. Series of aliphatic amines (i.e., methylamine (CH3NH2), ethylamine (C2H5NH2) and isopropylamine, n-propylamine (C3H7NH2)) and short chained carboxylic acids were analyzed in Ryugu samples as well5. Further targets were polycyclic aromatic hydrocarbons (PAH) as they are ubiquitous in presolar synthesis in interstellar locations13 and the FTIR spectra of Ryugu samples were close to interstellar PAHs spectra, suggesting incorporation of interstellar PAHs to Ryugu during its accretion5. Four-ringed fluoranthene, pyrene, chrysene/triphenylene and methylated fluoranthene and pyrene as well as smaller PAHs as naphthalene, phenanthrene and anthracene were analyzed and their relative abundances were attributed to differential alteration survivals and solubilities in parent body fluids5. Alkylpyridines and alkylimidazoles (aromatic N-heterocycles) and alkylpiperidines (aliphatic N-heterocycles)5,14 were targeted in Ryugu samples and showed a different profile as found earlier in the CM2 Murchison15,16 reflecting a different redox condition on the parent body.

The returned surface sample of Ryugu A0106 enable now a direct analysis of SOM from the surface of the parent body and the comparison with meteoritic SOM. Here, we report the molecular characteristics of Ryugu’s SOM from non-targeted organic analysis. More specifically we compared the ultra high-resolution mass spectroscopy analysis profile of the methanol extracts to 36 CCs that experienced moderate temperatures and partial aqueous alteration to position Ryugu’s organic diversity in the context of possible hydrothermalism.

Results
The Ryugu A0106 sample was extracted sequentially with solvents of increasing polarity, starting with hexane, dichloromethane, methanol and water to generate/isolate chemical fractions of SOM with molecules of increasing polarity. We first optimized injection flow rates to generate maximum scan count and signal-to-noise response to fully use the minimum amount of 5 mg of available extracts for a maximal information output in mass spectrometry and NMR-spectroscopy. We used electrospray ionization in negative (ESI(-)) and positive (ESI(+)) modes as well as atmospheric pressure photoionization in positive mode (APPI(+)) in direct injection Fourier transform-ion cyclotron resonance mass spectrometry (DI-FT-ICR/MS) as previously tested and demonstrated powerful method on many meteorites earlier3,17. We also confirmed that the methanol extract of the sequential extraction procedure and the direct extraction of Murchison CM2 and Aguas Zarcas CM2 fragments converged in the same signal and compositional profiles, making these two methanol extracts directly comparable. One third of the small solution volume available was used for nuclear magnetic resonance (NMR) spectroscopy experiments.

All analyzed FTICR-MS spectra showed very high signal density in the mass range from m/z 120 to 700 very comparable when analyzing CCs, reflecting that rapidly collected CCs are not biased by terrestrial contamination and weathering. The methanol extract in ESI(-) showed regular intense signals of increased intensity that could be assigned to polythiols (disulfate) with a number of sulfur from S3 to S9 (Fig. S1). The less polar hexane and dichloromethane extracts further showed the presence of polythiols as monosulfonates and of polysulfanes with sulfur numbers S3–S8. From all CCs analyzed in this study (Table S1), such intense profiles were observed only in methanol extract of recently fallen Tarda C2-ung material18. Each nominal mass always showed multiple signals with a repeating pattern of mass spacing of 36.3845 mDa following a compositional substitution of CH2 with respect to O reflecting overall structural regularity in chemical homologous series in the mixture1. Moreover, the Gaussian distribution of the mass signals within each nominal mass represents the large number of possible isomers for each exact mass, changing from a higher oxygen degree and carbon unsaturation from lower to higher mass defect as reported19, making any detailed structural annotation nearly impossible. In ESI(+) and APPI(+) the same regularity pattern was observed as well, similarly to patterns earlier described with all meteorite SOMs3,17.

In total, with all ionization modes and extractions we distinguished a molecular richness with more than 200,000 signals at S/N=3. We could reduce them with conservative filter rules to 23,100 elementary compositions in the CHNOS monoisotopic atomic space. These results agree with our previous studies for various classes of CCs from a small molecule mass spectrometry perspective2,3, demonstrating their huge chemical diversity compared to the biological space20,21. Figure 1A–C shows the final counting in elementary compositions assigned from FTICR-MS exact mass data and the overlaps of the compositional space between the different ionization methods and extraction solvents. The overall most abundant chemical families were the N-containing molecules (16,950 formula), followed by CHO/Na (8843 formula), CHOS/Na (5647 formula), CH (1056 formula) and CHS (165 formula). Most abundant molecules were extracted in polar protic methanol, followed by dichloromethane. Highly polar and highly apolar compounds extracted with water and hexane, respectively, showed the most specific compounds in terms of carbon oxidation state, nitrogen or sulfur content (Figs. S2, S4, and S5). In APPI(+) the oxygenation degree of CHO, CHNO and CHOS was similar and independent of the solvent polarity (2-3, O-atoms per molecule). The number of nitrogen, however, increased with increasing polarity indicating the involvement of nitrogen in polar functional groups such as primary or secondary amines increasing molecular basicity and thus promoting APPI(+) ionization (Fig. S3). CH type of molecules detected in APPI(+) showed a continuum in abundance of aliphatic to highly aromatic compounds bearing multiple aromatic rings (Fig. S6). Similarly, in ESI(+), the oxygenation degree is not much affected in the various polarity extracts, but was higher than in APPI (3-4 oxygen atoms per molecule) and particularly characterized by a higher relative abundance of nitrogen-containing ions, especially in the methanol extract. Oxygen being involved in acidic functional groups such as carboxyls, hydroxyls, the profiles are directly impacted by solvent polarity in ESI(-) and show a higher number of oxygen-rich molecules when moving to polar extraction solvents (Figs. S4 and S5). In addition, organosulfurs are more oxygenated toward polar solvent reflecting the extractability of molecules with sulfonations (-SO3) compared to less oxygen bearing compounds bearing sulfidic functional groups (-SH). Only the methanol extract showed composition with multiple heteroatoms.

Data mining of the molecular atlas showed that the most abundant mass differences were found to be equivalent to methylation (CH2), hydration (H2O), hydrogenation (H2), oxygenation (O), sulfurizations (SO4, SO, SO, SO2, S), nitrogenations (HCN, NH, NH2) as presented earlier with Murchison CM2 as well1. The search for removal or addition of these chemical functionalities’ exact masses between all pairs of 23,100 molecular formulas resulted in the reconstruction of a mass difference network (MDiN) covering 154,578 pairs (edges) from among 19,675 molecular formulas (nodes). The remaining molecular formulas could not be connected using these mass transitions. The most abundant mass difference transformations (CH2, H2, O and H2O) amounted to 47% of all detected mass differences, connecting 20,232, 19,349, 17,111, and 16,620 pairs of compositions, respectively. Nitrogen (HCN, NH, NH2) and sulfur-based mass differences (S, SO, SO2, SO3, SO4) accounted for 22.6% and 20.0% of all transformations found, respectively. These structural continuum leads to differential solvent solubility and ionization efficiencies in the various ionization modes in FTICR-MS (Fig. S7).

1H NMR spectra of A0106 methanol extract provided quantitative assessment of key proton and carbon chemical environments, and showed distinct groups of narrow resonances from δH ~0.5-8.5 ppm in which alkyl branching and termination by methyl and carboxylic groups were the defining molecular features, followed by lower abundance of aliphatic OCH units, olefinic (coarsely dH < 6.5 ppm) and aromatic unsaturation (coarsely dH < 7 ppm) (Fig. 2). Olefins were incorporated in alkyl systems whereas aromatic CHar units likely comprised polycyclic aromatic rings with ill-constrained admixture of aromatic carboxylic acids and nitrogen heterocycles. Ammonium (14NH4+) showed a distinct 1:1:1 triplet at δH ~4.5 ppm with 1JNH = 43 Hz and 1.2% relative abundance, exceeding other meteorite extracts. Ratios of methyl (δH < 1 ppm), non-methyl alkyl (δH ~ 1.0-1.65 ppm), and protons proximate to carboxylic acids HOOC-CHα-CHβ- (CHα: δH ~ 2.15 ± 0.15 ppm; CHβ: δH ~ 1.65 ± 0.5 ppm) defined connectivity networks in two dimensional NMR spectra (Fig. S9) and provided reconstruction of average features of aliphatic branching in the methanol extract with minor contributions from aliphatic oxygenation and olefinic unsaturation in A0106 SOM.

The dominance of hydrous silicate minerals (i.e., saponite, serpentine) and the absence of chondrules, already oriented the classification of the return material close to CI-type meteorites like Orgueil6. We compared the methanol extract of the sample A0106 with the methanol extracts of Murchison CM2 and Orgueil CI, two well-studied meteorites representative of their chondritic classes (Fig. 3). All extracts show full mass patterns over a range up to m/z 600. The van Krevelen diagrams of A0106 show the same regular pattern as observed with Murchison that correspond to homolog chemical series but with lower abundance towards higher m/z. Orgueil showed the lowest abundance in mass signals and covers the same range in oxygen-rich region as A0106. Mass difference analysis normalized on CH2-content (Fig. 1E) showed a closest similarity in functionalization of A0106 with Orgueil CI than with Murchison CM2. Both A0106 and Orgueil share the same profile in the abundance of oxygenated hydrocarbon and organosulfur compounds. Murchison and A0106 share the same profile in heteroatom abundance, Orgueil having more molecules with many sulfur atoms.

Comparing the 1H NMR spectra of the methanol extracts of A0106 with Murchison CM2 meteorite19 revealed major distinction. 1H NMR resonances were much narrower in A0106 than those in Murchison, indicating faster transverse (T2) relaxation in Murchison extracts. This reflects the relative proportions of background bulk NMR resonances across the entire shift range δH in Murchison exceeding that of A0106. This indicates a larger chemodiversity of low abundance atomic environments in Murchison. Considerable background 1H NMR resonances of pure aliphatic units (CCCH; δH ~ 0.7-2.5 ppm; Fig. S8B) probably arose from significant contributions of alicyclic rings in Murchison extracts.

To explore the high-dimensional dataset, we computed a principal component analysis (PCA) using SIMCA 13.0.3.0 (Umetrics) based on the intensities of all annotated m/z of the CHNOS compositional space unit-variance (UV) scaled and log transformed (Fig. 4A). We divided the data in a work (25 meteorite samples) and prediction set (11 meteorite samples) as shown in Table S1. The 36 CCs were chosen as to reflect a range of warm to low-temperatures history based on their thermal index from previous studies or known to have experienced strong water alteration and hydro-thermalism22. The work and prediction set were chosen randomly out of the 36 to check for the validity of the model. The variance absorbed by the first two valid components23 is R2X(cum) = 0.51. Additionally, the prevision ability of the model was measured by the Q2 index (Q2(cum) = 0.39). The PCA scores scatter plot (Fig. 4A) differentiates the chemical space in two main regions. In one side, the type-TI CCs having seen low-temperature in various water alterations and in the otherside, the chondrites of CM1, CR1, C1/2-ung, CM1/2, CI types that saw much water in their parent body history (hydro-thermalism). The most relevant masses of these two groups could be extracted based on their highest loading values and a representation in van Krevelen diagrams Fig. 4B.

The sulfurization of nitrogen compounds is mostly abundant at slightly increased temperatures reached in the typical TI-type meteorites24. Lower peak temperatures and higher water alteration corresponding to cold hydro-thermalism show higher abundance of saturated/mono-unsaturated long chained aliphatic carboxylic acid (Fig. 4B).

Methods
Meteorites samples used for analysis and structural comparison
The list of the meteorites analyzed in the study and used for the model in Fig. 4 is given in Table S1.37,38

Sample description
The Ryugu sample extracted was sample A0106, the surface samples stored in Chamber A. It was extracted sequentially with solvents of increasing polarity, starting with hexane, dichloromethane, methanol and water to generate/isolate chemical fractions of SOM with molecules of increasing polarity. This was done at JAXA and samples were distributed to various Labs for analysis as described in ref. 5.

Fourier transform ion cyclotron resonance mass spectrometry
The experimental study was performed on a high-field FT-ICR mass spectrometer from Bruker Daltonics with a 12-T magnet from Magnex. A time domain transient with 4 MWords was obtained and Fourier-transformed into a frequency domain spectrum. The frequency domain was afterward converted to a mass spectrum by the SolariX Control program of Bruker Daltonics. The ion excitations were generated in broadband mode (frequency sweep radial ion excitation) and 3000 scans were accumulated for each mass spectrum in a mass range of 147–1000 amu. Ions were accumulated for 300 ms before ICR ion detection. The pressure in the quadrupole/hexapole and ICR vacuum chamber was 3 × 10−6 and 6 × 10−10 mbar, respectively. For CID-MS/MS, ions were accumulated for 3 s.

The ESI source (Apollo II; Bruker Daltonics) was used in negative ionization mode and the APPI source in positive mode. The methanolic solutions were injected directly into the ionization source by means of a microliter pump at a flow rate of 120 µL h−1 in ESI and at 500 µL h−1 APPI. A source heating temperature of 200 °C was maintained and no nozzle-skimmer fragmentation was performed in the ionization source. The instrument was previously externally calibrated by using arginine negative cluster ions (5 mg L−1 arginine in methanol).

FT-ICR mass spectra with m/z from 95 to 1000 amu were calibrated externally and internally to preclude alignment errors. Subsequently, the mass spectra were exported to peak lists at a signal-to-noise ratio ≥ 3. Elemental formulas were calculated combinatorically within a mass accuracy window of ±0.2 ppm for each peak in batch mode by an in-house software tool and validated via the senior-rule approach/cyclomatic number, assuming valence 2 for S and valence 4 (coordination number) for Mg2.

FT-ICR-MS analysis enables highly resolved (R > 106 at m/z 200) and accurate chemical mass analysis of electrospray generated ions within a 200 ppb error window over a wide mass range from m/z 100–1000. The weight of the ions is measured with a precision lower than the mass of an electron (Δm/z = 0.0003 amu) and the specific signals can be differentiated with the same mass precision due to the ultrahigh resolution. These exact masses of the ions can routinely be converted into unique compositional formula bearing the light elements C-, H-, N-, O-, S-, Mg (or any other element in target), also taking account of their possible Cl and Na adducts and of their natural isotopic abundance.

The solvent extracts generated thousands of individual signals that were converted into elementary compositions (formula); these are all represented in van Krevelen type of diagrams (H/C vs. O/C) or related (H/C vs m/z) in which each formula is represented by a dot (the size of the dot is proportional to its abundance) as a projection of the relative oxygenation degree (O/C) and saturation degree (H/C) for various classes of compound types (CHO, CHNO, CHOS, CHNOS, CH, CHS, CHN, and selected Na+-adducts). Aromaticity equivalents Xc were calculated as reported earlier39 and plotted as in Fig. S6.

Nuclear magnetic resonance spectroscopy
A Bruker Avance III spectrometer and TopSpin 3.5/PL7 software were used to acquire nuclear magnetic resonance (NMR) spectra of aqueous extracts of Hayabusa methanolic extracts of which ~30 µg were exchanged with CD3OD (99.96% 2H, Aldrich) three times on a vacuum line19; after sealing in a 1.7 mm Bruker match tube, the sample was centrifuged without visible solid. Murchison extract A519 was used here for comparison to sample A0106.

A cryogenic inverse geometry 5 mm z-gradient 1H/13C/15N/31P QCI probe (B0 = 18.8 T) was used for 1D 1H NMR and proton-detected 2D NMR spectra. Transmitter pulses were at ~10 µs for 1H and 13C. The one bond coupling constant 1J(CH) used in 2D 1H, 13C DEPT-HSQC spectra (hsqcedetgpsisp2.2) was set to 145 Hz; other conditions: 13C 90 deg decoupling pulse, GARP (70 µs); 50 kHz WURST 180 degree 13C inversion pulse (Wideband, Uniform, Rate, and Smooth Truncation; 1.2 ms); F2 (1H): spectral width of 11160.7 Hz (13.95 ppm); 1.25 s relaxation delay; F1 (13C): SW = 36052 Hz (180 ppm). HSQC-derived NMR spectra were computed to a 8192 × 1024 matrix. Gradient (1 ms length, 450 µs recovery) and sensitivity enhanced sequences were used for all 2D NMR spectra. Absolute value COSY, and phase sensitive echo-antiecho TOCSY spectra (cosygpmfppqf, dipsi2etgpsi) used a spectral width of 9615.4 Hz and were computed to a 16,384 × 2048 matrix; other NMR acquisition conditions are given in Table S2.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The Hayabusa2 mission successfully returned samples from the surface and sub-surface\nof the carbonaceous near-Earth asteroid Ryugu. Analysis of these samples allows us to\ninvestigate the initial conditions in the Solar System and the formation and evolution of\nplanetary bodies. Crucially, the samples are from a known body and have experienced\nminimal terrestrial contamination, providing an opportunity to characterise pristine\norganic matter from the earliest history of the Solar System.\nThis is a generally well-written manuscript that reports on some impressive\nmeasurements and provides a detailed description of organic species in a Ryugu sample.\nThe results will certainly be of interest to researchers in many fields – carbonaceous\nasteroids like Ryugu likely delivered pre-biotic molecules and other volatile species to\nEarth – but the manuscript has several short-comings that should be addressed before it\nis accepted for publication. In particular: -\n- the Introduction doesn’t clearly set out why this research is important or what\nhypothesis is being tested by these measurements.\n- there is no description of the sample. Perhaps this is available in other papers, but as\nRyugu samples vary in mineralogy and degree of aqueous alteration (e.g., Nakamura et\nal. (2022) Science), some information about the analysed particle should be included.\n- The Discussion doesn’t really place these results in the context of what is already\nknown about the formation and evolution of Ryugu. For example, how do these data fit\nwith the recent organic results and interpretation from Yabuta et al. (2023) Science,\nNaraoka et al. (2023), Oba et al. (2023) Nat. Comms., and Parker et al. (2023) GCA, and\nthe aqueous and thermal history of Ryugu inferred from mineralogical studies?\nSummary\nP2 L1-2: second half of this sentence isn’t very clear and should be re-written.\nP2 L5: maybe context rather than light here?\nP2 L7: C-type asteroid hasn’t been defined\nP2 L11: “Results showed…”\nP2 L13: think it needs to be clear that CI chondrites are meteorites. It might not be\nobvious to a non-specialist reader.\nMain Text\nP3 L6: at the time - samples were also returned from the Moon by Chang’e 5 in\nDecember 2020\nP3 L16: either CI or CI1 chondrites. Recommend that you don’t use both because it\nconfuses non-specialists.\nP3 L17-19: this sentence is really unclear. As written, it sounds like C, H, N, O and S\nwere the only elements measured in Ryugu samples, which isn’t the case. Also, those\nelements are mainly present in carbonate and sulphide minerals, and organic matter.\nP3 L19-21: this statement needs a reference!\nP3 L22: don’t need to repeat that Orgueil is a CI chondrite. But you might want to\nmention somewhere that the CI chondrites are all falls.\nP3 L24: suggest, “…aminovaleric acid in the Ryugu samples indicated a higher peak\ntemperature than the CI chondrites as these compounds are typical in CV and CO\nchondrites processed at elevated temperatures of up to ~300°C.”\nP3 L26-28: needs a reference. Also, not clear why these particular species are\nimportant?\nP3 L29: define FTIR.\nAlso, do you mean FTIR spectra of extracted organic matter (i.e., not individual\nparticles)? And the statement needs a reference.\nP3 L36-37: is that surprising? Murchison is a CM chondrite (which isn’t mentioned in the\ntext) from a different parent body. More relevant is how the profile of these species\ncompares to the CI chondrites?\nMolecular Atlas\nP4 L1: what was the sample size/mass? Was any characterisation done before the SOM\nwas extracted? Ryugu samples contain several lithologies with different degrees of\naqueous alteration. Also, was the sample exposed to air prior to extraction? The Ryugu\ngrains are very sensitive to terrestrial contamination and modification on short\ntimescales.\nP4 L7: define NMR\nP4 L17: what is meant by “fresh” CCs? Aguas Zarcas is a recent fall, but Murchison fell\n>50 years ago and I wouldn’t consider it “fresh” because these rocks are so reactive.\nAnd what was the curation history of the analysed samples? For example, Aguas Zarcas\nsamples were collected both before and after rainfall in the area.\nP4 L22: guessing this should be Table S1? It’s not clear from the text if all the samples\nlisted in Table S1 were analysed as part of this study.\nP4 L23: if this is a result of this study, why is an LPSC abstract being cited here?\nP4 L24: mass\nP4 L37: Figure 1 shows…\nP6 L8: which Fig. 6 is this referring to?\nP7 L8: two well-studied meteorites\nP7 L11: …show the same…\nP7 L29: …reflects the relative…\nFig. 3 caption: …are the abundance profiles…\nP8 L3: 25 + 11 = 36 CCs? There are 36 listed in Table S1.\nP8 L9: suggest deleting “nicely” and differentiates\nP8 L10: this is quite confusing to read. To me it looks like Fig. 4a broadly divides the\nmeteorites into less altered type 2’s and the more altered type 1’s, although there is a\nreasonable number of type 2 meteorites on the left side of the plot. Interestingly, the\nCM2’s on the left all appear to be falls (and predicted datasets) – does that suggest a\ndifference between falls and finds?\nP8 L21: what evidence is there for increased temperatures in the type 1 meteorites?\nP9 L24: delete exceptionally\nP9 L30: Flensburg is a C1ung, not a CI chondrite\nP9 L31: “heavy water” is confusing as it could refer to the isotopic composition of the\nwater. I think you mean that these meteorites experienced a high degree of aqueous\nalteration.\nTarda is a type 2 breccia and contains lithologies that were not fully altered. I’m not\naware of any estimates for peak temperatures for Tarda, but if it’s similar to Tagish Lake\nthen it’s likely to contain lithologies that were altered at temperatures >150°C.\nP9 28-36: This paragraph describes the properties of Flensburg (C1ung) and Tarda (C2ung), but then\nconcludes in a single line that Ryugu is most like a CI chondrite. There\nshould be a more detailed comparison of Ryugu to the CI chondrites. Also, based on Fig.\n4a, I’d argue that Ryugu is just as similar to highly CR1 or CM1 chondrites as the CIs.\nThe statement that CI chondrites were highly altered at low temperatures needs a\nreference, and also seems to contradict the earlier claim that Type 1 meteorites were\naltered a slightly elevated temperatures (P8 L21).\nP9 L38: don’t think atlas needs to be capitalised\nP10 L3-6: this statement needs references to support it\nP10 L7: …hydrolysis processes affecting…?\nP10 L11-18: the Ryugu samples contain beautiful, euhedral, and often large, grains of\npyrrhotite that formed during aqueous alteration. The mineralogy of Ryugu is now well-\nconstrained and this should be considered in the discussion of organic synthesis here.\nP10 L21: …processes at lower temperatures. Lower than what?\nP10 L22: …are consistent with A0106 being closely related to…\nI agree that the Ryugu samples are similar to CI1, CM1 (and also CR1) meteorites, but\nthis appears to slightly differ from the claim that they are like CI chondrites (P9 L36).\nP10 L30: mineralogical evidence suggests that Ryugu was altered at temperatures\n<100°C, possibly even <50°C\nSupplementary Materials\nI have several issues with Table S1:-\nFlensburg is a C1ung\nWhere are the weathering grades from? Just because something is a fall, doesn’t make\nit a weathering grade 0. For example, Ivuna and Orgueil contain abundant, terrestrially\nformed sulphates.\nThe two columns describing the degree of alteration / petrologic type need to be\nexplained and are not up-to-date, incomplete, or incorrect. The best starting point for\nthe petrologic classifications is Rubin et al. (2007) GCA 71:2361 (not the Rubin (2007)\nthat is currently cited), while it should also be noted that many of these meteorites are\nbreccias with lithologies altered to different degrees (e.g. Paris is a 2.9 – 2.6). Rubin\ndidn’t look at the CI chondrites and calling them 1 doesn’t make sense in this column.\nAlso, petrographic classifications have been reported for other meteorites e.g., Aguas\nZarcas, Maribo.\nThe Alexander et al. (2013) classification scheme is based on bulk H and C abundances\n(not petrography). Again, some data is missing (e.g., Flensburg) and it should be made\nclear in the caption that a 2.0 in the Rubin scale is not the same degree of alteration as a\n2.0 in the Alexander scale. Not to confuse things further, but a note that bulk\nphyllosilicate abundances have been reported for meteorites such as Moapa Valley and\nMukundpura, where no petrologic classification is given in Table S1.\nThe caption needs to briefly explain what TI means. This is taken from Quirico et al.\n(2018), but is really a combination of XRD/mineral observations of Nakamura (2005)\nand the Raman/IR data of Quirico et al., to estimate peak temperatures for\ncarbonaceous chondrites. The TI meteorites experienced low temperature (<300°C)\naqueous alteration and do not record any post-hydration metamorphism (i.e., TII – IV in\nQuirico et al.). There is published XRD data for many of the samples in Table S1 that is\nconsistent with them being TI (e.g., Howard et al. 2015 GCA 149:206, King et al. 2017\nM&PS 52:1197).\nFig. S1 caption: Orgueil should be CI1 (if using CM2 for Murchison). Also, typo – green.\nFig. S2 caption: The bubble size expresses… …and the colors correspond… …One clearly\nobserves…\nAlso, define n.t. in the figure captions.\nFig. S3 caption: m/z expanded? …One clearly observes…\nFig. S8a: either …an enhanced molecular interaction… or …enhanced molecular\ninteractions…\n…A0106 showed a larger proportion of…", "reviewer_2": "This study highlights the high diversity of Ryugu organic matter using mass\nspectrometry and NMR spectroscopy. The results are interesting (though redundant with\nexisting literature) and worth publishing in Nature Communications. I made comments,\nhereafter provided line by line, that I think will help the reader better understand.\nPage 2, line 3 : Please rephrase “since the parent body”.\n4-7 : Please remove “systematically” and explain why you couldn’t perform ESI(+) on\nhexane extract and APPI(+) on water extract.\n4-32 : What S/N did you use to reduce the 200,000 signals ? What type of information\nhave you possibly lost ?\n4-22 : Table x is Table S1 ?\nFigure 1 (E) : Please invert SO and S columns.\n8-3 : “moderate” in the text corresponds to “warm hydrothermalism” in the figure 4 (A)\n?\nFigure 4 (A) : How exactly did you chose the 2 parameters of the PCA ? The “warm\nhydrothermalism” annotation corresponds to which CCs ? Those in the upper left corner\nof the PCA ?\n9-31 : Do you consider Tarda highly altered only because there is no organomagnesium\ncompounds in it ?\n10-16 : Please rephrase the last sentence of the paragraph.\n11-5 : Please update Naraoka paper.\nTable S2 : Missing figure names ?\nFigure S1 : Please highlights both C17H35O3S and C20H31OS.\nTypos :\nPage 2, line 7 : shines\n3-30 : PAH\n4-24 : mass instead of masse\n9-25 : various\n10-7 : affection\n10-15 sulfide\n10-21 : Please, leave only one “seen”.\n10-26 : reflects\n19-9 : green"}, "author_response": "RESPONSE TO THE REVIEWER´S COMMENTS.\nReviewer 1\nReview of Molecular Atlas of Soluble Organic Matter of Ryugu Reveals Cold Hydrothermalism on\nC-type Asteroid Parent Body (NCOMMS-23-06104-T)\nThe Hayabusa2 mission successfully returned samples from the surface and sub-surface of the\ncarbonaceous near-Earth asteroid Ryugu. Analysis of these samples allows us to investigate the\ninitial conditions in the Solar System and the formation and evolution of planetary bodies. Crucially,\nthe samples are from a known body and have experienced minimal terrestrial contamination,\nproviding an opportunity to characterise pristine organic matter from the earliest history of the\nSolar System.\nThis is a generally well-written manuscript that reports on some impressive measurements and\nprovides a detailed description of organic species in a Ryugu sample. The results will certainly be of\ninterest to researchers in many fields carbonaceous asteroids like Ryugu likely delivered pre-biotic\nmolecules and other volatile species to Earth but the manuscript has several short-comings that\nshould be addressed before it is accepted for publication.\n( We thank the reviewer fort his general impression.\nIn particular: -\n-\ntested by these measurements.\n( We adde the needed information at the End of the introduction\nThe returned surface sample of Ryugu A0106 enable now a direct analysis of SOM from\nthe surface of the parent body and the comparison with meteoritic SOM. Here, we report\nSOM from non-targeted organic analysis. More\nspecifically we compared the ultrahigh-resolution mass spectroscopy analysis profile of the\nmethanol extracts to 36 CCs that experienced moderate temperatures and partial aqueous\nalteration to position Ryugu´s organic diversity in the context of possible\nhydrothermalism.\n- there is no description of the sample. Perhaps this is available in other papers, but as Ryugu\nsamples vary in mineralogy and degree of aqueous alteration (e.g., Nakamura et al. (2022) Science),\nsome information about the analysed particle should be included.\n( The sample description was short in the main text. We added additionally details the references\nneeded in Suplementary materials.\n-\nformation and evolution of Ryugu. For example, how do these data fit with the recent organic results\nand interpretation from Yabuta et al. (2023) Science, Naraoka et al. (2023)[5], Oba et al. (2023) Nat.\nComms.[27], and Parker et al. (2023) GCA, and the aqueous and thermal history of Ryugu inferred from\nmineralogical studies?\n( We added latest references in the discussion to confirme and crosslink the results in the context of\nRyugu´s aqueous and thermal history.\nSummary\nP2 L1- -written.\n( We added the information related to the chemistry reflecting a history n the parent body\nP2 L5: maybe context rather than light here?\n( Yes, we changed accordingly.\nP2 L7: C-\n( the Abstract to focus on the results.\n( Yes, we changed accordingly.\nP2 L13: think it needs to be clear that CI chondrites are meteorites. It might not be obvious to a non-\nspecialist reader.\n( Yes, we changed accordingly.\nMain Text\nP3 L6: at the time -\n( Yes, this was added.\nP3 L16: either CI or CI1 chondrites. -\nspecialists.\n( Typo was changed, thank you.\nP3 L17-19: this sentence is really unclear. As written, it sounds like C, H, N, O and S were the only\nin carbonate and sulphide minerals, and organic matter.\n( We changed the sentens accordingly to give the information on the elements C, H, N, O, S only due\nto their importance in this particular manuscript.\nP3 L19-21: this statement needs a reference!\n( Done\nsomewhere that the CI chondrites are all falls.\n( Added.\nsamples indicated a higher peak temperature than\nthe CI chondrites as these compounds are typical in CV and CO chondrites processed at elevated\n( Exchanged, thank you\nP3 L26-28: needs a reference. Also, not clear why these particular species are important?\n( Done\nP3 L29: define FTIR.\nAlso, do you mean FTIR spectra of extracted organic matter (i.e., not individual particles)? And the\nstatement needs a reference.\n( Theses results are from the ref. (5) added\nP3 L36-\ndifferent parent body. More relevant is how the profile of these species compares to the CI\nchondrites?\n( The data was not compared to CI types in the literature, but showing it is different to CM2 aslo\nconfirms the trend.\nMolecular Atlas\nP4 L1: what was the sample size/mass? Was any characterisation done before the SOM was\nextracted? Ryugu samples contain several lithologies with different degrees of aqueous alteration.\nAlso, was the sample exposed to air prior to extraction? The Ryugu grains are very sensitive to\nterrestrial contamination and modification on short timescales.\n( This information was given in SI also with the main reference (5) describing in detail the procedures\ndone by JAXA.\nP4 L7: define NMR\n( Done\nhistory of the analysed samples? For example, Aguas Zarcas samples were collected both before and\nafter rainfall in the area.\n( Fully agree we adapted the\nwording in the text.\nm the text if all the samples listed in Table\nS1 were analysed as part of this study.\n( Done\nP4 L23: if this is a result of this study, why is an LPSC abstract being cited here?\n( The LPSC abstract only showed preliminary results on the study as the proof of concept.\nP4 L24: mass\n( done, thanks\n( done\nP6 L8: which Fig. 6 is this referring to?\n( It´s Fig. S7\nP7 L8: two well-studied meteorites\n( done\n( done\n( done\n( done\nP8 L3: 25 + 11 = 36 CCs? There are 36 listed in Table S1.\n( ' yes ! thanks, done\n( done\nP8 L10: this is quite confusing to read. To me it looks like Fig. 4a broadly divides the meteorites into\n(\nmore that 100 meteorites confirming even more the differentiation we describe here.\npredicted datasets) does that suggest a difference between falls and finds?\n( Falls are distributed all over (Maribo , Paris, Mukundpura on the right i.e.) and we did not find any\nvalid model to differentiate falls from finds.\nP8 L21: what evidence is there for increased temperatures in the type 1 meteorites?\n( T1-Type meteorites were attributed according to our paper Quirico et al 2018 and are of slightly\nhigher temperature than the C!, CM1 or CM1/2 studied herein.\nP9 L24: delete exceptionally\n( Done\nP9 L30: Flensburg is a C1ung, not a CI chondrite\n( changed\nI think\nyou mean that these meteorites experienced a high degree of aqueous alteration.\nTarda is a type 2 breccia and contains lithologies that were not fully altered.\nlithologies that were altered at temperatures >150°C.\n(\nIn deed with breccia we always will have zones of differential alterations and problems of\nrepresentative samples.\nTarda is in a blue box in the Figure 4 and such as Flensburg, Kolang and NWA 8534 was not used to\nP9 28-36: This paragraph describes the properties of Flensburg (C1ung) and Tarda (C2ung), but then\nconcludes in a single line that Ryugu is most like a CI chondrite. There should be a more detailed\ncomparison of Ryugu to the CI chondrites. A\nsimilar to highly CR1 or CM1 chondrites as the CIs.\nThe statement that CI chondrites were highly altered at low temperatures needs a reference, and\nalso seems to contradict the earlier claim that Type 1 meteorites were altered a slightly elevated\ntemperatures (P8 L21).\n(\nliterature position the Ryugu samples close to CI. I thus rather describe the close profiles of Ryugu\nto the specific types in Figure 4 and adapted the text accordingly to:\n“Consideringtheabundanceprofileofthousandsofoxygenatedmolecularformulaofthemethanol\nextract of 36 meteorites we were able to dress a predictive A0106 being highly water processed at\nlow temperature such as observed in C2-ungTarda,CM1/2,CM1,CR1orCI(Figure4).”\n( I adapted.\nP10 L3-6: this statement needs references to support it\n( done\n( done\nP10 L11-18: the Ryugu samples contain beautiful, euhedral, and often large, grains of pyrrhotite that\nformed during aqueous alteration. The mineralogy of Ryugu is now well-constrained and this should\nbe considered in the discussion of organic synthesis here.\n(\ncesses at lower temperatures. Lower than what?\n(\n( done\nI agree that the Ryugu samples are similar to CI1, CM1 (and also CR1) meteorites, but this appears to\nslightly differ from the claim that they are like CI chondrites (P9 L36).\n( Fully agree ! that´s why I rather precised my close results in the SOM profiles to the whole group of\nmeteorites in P9 L36 -side the high degree of water alteration.\nP10 L30: mineralogical evidence suggests that Ryugu was altered at temperatures <100°C, possibly\neven <50°C\n( Just to be on the good side I jept only 150°C\nSupplementary Materials\nI have several issues with Table S1:-\nFlensburg is a C1ung\n( adapted\nweathering grade 0. For example, Ivuna and Orgueil contain abundant, terrestrially formed\nsulphates.\n( Right CI are rather hydrophilic and see secondary terrestrial transformations. The W -weathering\nvalues were systematically taken from the classification schemes in the MetBull and considered in a\nfirst approach to W0 for falls.\nThe two columns describing the degree of alteration / petrologic type need to be explained and are\nnot up-to-date, incomplete, or incorrect. The best starting point for the petrologic classifications is Rubin\net al. (2007) GCA 71:2361 (not the Rubin (2007) that is currently cited), while it should also be\nnoted that many of these meteorites are breccias with lithologies altered to different degrees (e.g.\nParis is a 2.9\nthis column. Also, petrographic classifications have been reported for other meteorites e.g., Aguas\nZarcas, Maribo.\nThe Alexander et al. (2013) classification scheme is based on bulk H and C abundances (not\npetrography). Again, some data is missing (e.g., Flensburg) and it should be made clear in the caption\nthat a 2.0 in the Rubin scale is not the same degree of alteration as a 2.0 in the Alexander scale. Not\nto confuse things further, but a note that bulk phyllosilicate abundances have been reported for\nmeteorites such as Moapa Valley and Mukundpura, where no petrologic classification is given in\nTable S1.\n( The values in the table are the average ones I was compiling at the time of the modelling study and I\nas reported in the cited literature. The exact values in the literature and\nthe different existing scales themselves followed many debates over the last decade and generally\nbecause these materials are brecciated; these values cover always a wide range as you mentioned\nin your comments. Bischoff nicely showed in his several papers along his career the brecciation of\nthese meterials. For modelling purposes sometimes taken as average/median values of the found\nranges.\nThe trend in model with these calculations is however not affected in little changes in the values.\nThe caption needs to briefly explain what TI means. This is taken from Quirico et al. (2018), but is\nreally a combination of XRD/mineral observations of Nakamura (2005) and the Raman/IR data of\nQuirico et al., to estimate peak temperatures for carbonaceous chondrites. The TI meteorites\nexperienced low temperature (<300°C) aqueous alteration and do not record any post-hydration\nmetamorphism (i.e., TII IV in Quirico et al.). There is published XRD data for many of the samples in\nTable S1 that is consistent with them being TI (e.g., Howard et al. 2015 GCA 149:206, King et al. 2017\nM&PS 52:1197).\n( I added this information in the caption\nFig. S1 caption: Orgueil should be CI1 (if using CM2 for Murchison). Also, typo green.\n( Done\nAlso, define n.t. in the figure captions.\n( Done\n(\n( Done\nReviewer #2 (Remarks to the Author):\nThis study highlights the high diversity of Ryugu organic matter using mass spectrometry and\nNMR spectroscopy. The results are interesting (though redundant with existing literature) and\nworth publishing in Nature Communications. I made comments, hereafter provided line by\nline, that I think will help the reader better understand.\n( We thank the reviewer for his constructive comments.\n( Done\n4-7 :\nhexane extract and APPI(+) on water extract.\n( Explained in the caption of the figure in SI.\n4-32 : What S/N did you use to reduce the 200,000 signals ? What type of information have\nyou possibly lost ?\n( I used S/N higher 3 to extract the data. These contained many signals from the background\nand all isotopologues. 200.000 was counted without checking overlaps, just summing all\nsignals in the various extracts and ionization modes.\nIt was important to considere a conservative way to limit any false positive assignments.\n4-22 : Table x is Table S1 ?\n( Done\nFigure 1 (E) : Please invert SO and S columns.\n( Done\n8-3 :\nthe PCA ?\n(\nThe warm hydrothermalism correspond to all green dots in the figure.\n9-31 : Do you consider Tarda highly altered only because there is no organomagnesium\ncompounds in it ?\n( Tarda was predicted as well by our model model as highly altered confirming also our\nearlier published finding\n10-16 : Please rephrase the last sentence of the paragraph.\n( done\n11-5 : Please update Naraoka paper.\n( Done\nTable S2 : Missing figure names ?\n( Done\nFigure S1 : Please highlights both C17H35O3S and C20H31OS.\n( Done in the caption\nTypos :\nPage 2, line 7 : shines\n3-30 : PAH\n4-24 : mass instead of masse\n9-25 : various\n10-7 : affection\n10-15 sulfide\n10-\n10-26 : reflects\n19-9 : green\n( Done thank you"}]

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