Chemical evolution of primordial salts and organic sulfur molecules in the asteroid 162173 Ryugu

Samples from the carbonaceous asteroid (162173) Ryugu provide information on the chemical evolution of organic molecules in the early solar system. Here we show the element partitioning of the major component ions by sequential extractions of salts, carbonates, and phyllosilicate-bearing fractions to reveal primordial brine composition of the primitive asteroid. Sodium is the dominant electrolyte of the salt fraction extract. Anions and NH4+ are more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the order SO42− > Cl− > S2O32− > NO3− > NH4+. The salt fraction extracts contain anionic soluble sulfur-bearing species such as Sn-polythionic acids (n < 6), Cn-alkylsulfonates, alkylthiosulfonates, hydroxyalkylsulfonates, and hydroxyalkylthiosulfonates (n < 7). The sulfur-bearing soluble compounds may have driven the molecular evolution of prebiotic organic material transforming simple organic molecules into hydrophilic, amphiphilic, and refractory S allotropes.

L133-137: The "missing sulfur problem" concerns sulfur in molecular clouds and dense cores.The abundance of sulfur in small molecules in the gas phase does not reach the cosmic value, which means that a sulfur reservoir is hidden somewhere.There is no consensus on this issue, but it seems that sulfur could be present at the surface of grains as organic sulfur molecules (e.g.Laas et al., 2019) or elemental sulfur produced by GCR radiolysis (Shingledecker et al., 2020).However, there is no missing sulfur in chondrites, and sulfur abundance (normalized to Si) is similar to that of the Sun.L154-155: Four extractions were run: hot ultra-pure water, Me-OH, and HCl.Regarding phyllosilicates, do you mean that ions were trapped in the interlayer space of saponite, and then expelled by Cl-exchange?Another point is that some sulfides are soluble in HCl and release sulfur (this is clearly observed during the HCl sequence of Insoluble Organic Matter extraction, the supernatant turns to yellow/green).Can you warrant this sulfur does not interfere with your other analyzes?L214-215: I think this issue was fixed already by Gounelle and Zolensky (2001).In Orgueil, a fraction of sulfates is terrestrial, but not all sulfates.L251: I don't understand how this equation is introduced.Spatolisano+2021 is not relevant to asteroidal conditions, it is an Engineering publication.At L254, this equation is even modified, by replacing H2S with (Fe, Ni)S.Why remove H2O and keep SO2?What is the justification of this equation?It seems it comes out of the blue.L256 Zolotov ( 2012) is cited several times.I think it would be helpful to the reader to add a text section that summarizes how the results of this very comprehensive thermodynamical modelling are consistent with the manuscript's new findings.L310-311: As pointed out before, the "missing sulfur problem" concerns molecular clouds and dense cores, and cannot be solved by analyzing Ryugu grains.L316: Surface irradiation by what?There is no reference here, and in any case, the electronic and nuclear doses should be estimated.Experimental studies are also necessary to conclude about the conditions that lead to the formation of S allotropes.L327-328: A CI chondrite is very different from comet 67P/CG, which has never experienced intense aqueous alteration.One salt has been detected (NH4+; HS-) by both ROSINA and VIRTIS instruments.In that case, it is likely a solid-state thermally activated reaction between H2S and NH3.To say this is quite disconnected from Ryugu samples.
Reviewer #3 (Remarks to the Author): The authors report the results of anion and cation analysis of Ryugu samples and demonstrate the abundance of soluble sulfur-bearing compounds.Based on the results, the authors propose transformation mechanisms that could explain the formation of various sulfur-bearing species in Ryugu.The results and proposed mechanism are important for understanding sulfur evolution in the early solar system which is still poorly constrained.
The authors performed sequential extractions; however, the methodology is poorly explained which does not allow the methods to be reproduced and to evaluate the data and efficiency of the carbonate/phyllosilicate extraction steps.In my opinion, some of the data interpretation and the proposed transformation mechanisms of sulfur-bearing compounds need to be addressed prior to being considered for publication.My comments are summarized below.

Main comments:
1. Extraction procedure Sequential extraction procedure steps are poorly described which makes it hard to evaluate the data and efficiency of carbonate/phyllosilicate extraction steps.I recommend the following information be added and questions be addressed The references must be provided to support that #9 HCOOH and #10 HCl extractions are selective extractions for carbonates and phyllosilicates.Are carbonates and phyllosilicates completely dissolved?Are other phases extracted by HCOOH and HCl?The presence of both Fe and Ni in the extracted solutions (Supplementary Table 1) is indicative that sulfides were also dissolved.The authors discuss that soluble inorganic salts, including chlorides and sulfates, were not detected (or were present in trace amounts) in Ryugu samples (starting line 197), and then propose that organosulfur-bearing anions are counterions to Na.However, the manuscript lacks a clear discussion of where sulfate/thiosulfate/chloride were released from during the hot water extraction.In the case of sulfate/thiosulfate, where they present as adsorbed species, originated from organic sulfur-bearing species or from oxidizing sulfides?

Transformation mechanism of sulfur-containing species
The alteration model of Nakamura et al., 2022 shows that aqueous alteration of Ryugu resulted in alkaline conditions, however, the authors indicate that acidic conditions are necessary to stabilize polythionates.How did acidic conditions develop?Can the authors speculate about the timing of the process?Did it happen before or after the aqueous alteration?What water-to-rock ratio is necessary for reactions 2-4 to occur?  2 and Naraoka+2023)" Should it be Extended Data Fig. 1b? 3. l. 177-178 "The pH of the salt fraction at 24.6 °C (#7-1 in Supplementary Fig. 1) was weakly acidic…" why is there ref to this figure as no pH data is shown there? 4. Fig. 2 Please references where Ca, Mg, Na, and K were taken from for Orgueit, Tarda, Aguas Zarcas, and Jbilet Winselwan.If these samples were analyzed in this work, please add the data to Supplementary Table 1 "cosmic abundance (stars) also plotted for reference" Please add references 5. Fig. 3 Dissolved carbonate is shown in (a) but it is unclear how it was detected.Was it measured with IC or was it a part of a different study?If the second, please add a reference 6. Suppl Table 2 " Note that dissolved inorganic carbon and silica were not measured" HCO3-is reported in the Fig. 3a, please clarify

Replies to Reviewer's comments on the manuscript #NCOMMS-23-08319-T
We appreciate the constructive comments on our manuscript (#NCOMMS-23-08319-T) entitled "Chemical evolution of primordial salts and organic sulfur molecules in the asteroid (162173) Ryugu" (by Yoshimura et al.).We carefully read all of the comments in the reviews and modified the manuscript based on your helpful feedback.The changes that we made based on the comments are shown in red text in the revised manuscript/supporting information.We have chosen the option of "Transparent peer review", to make public the discussion during the review process.We believe our point-by-point responses to each comment will clarify the entire context of the paper.
Reviewer #1 (Remarks to the Author): The only comment I have is that the result section is rather short and the discussion section rather long.The discussion section is a mix between results and actual discussion about the meaning of the results.The paper would be better readable if the part of the discussion section, which contains results, is moved to results.
# We thank the reviewer for their advice.We have reorganized the Results and Discussion sections.Please see the revised manuscript.

Reviewer #2 (Remarks to the Author):
L69-71: NH4 + is not listed in the abstract, but it is mentioned on pages 30 and 31.
# We revised the abstract as suggested: "Anions and NH4 + were more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the following order: SO4 &9 > Cl 9 > S2O3 &9 > NO3 9 > NH4 + ".As the reviewer pointed out, we also detected ammonia, but we included most of the information on NH4 + in the supplementary information, since the matter was not directly related to the discussion of sulfur compounds.
Reviewer #1 also commented that we should include additional description of the results, so we have added a description of the NH4 + to the Results section.
L133-137: The "missing sulfur problem" concerns sulfur in molecular clouds and dense cores.
The abundance of sulfur in small molecules in the gas phase does not reach the cosmic value, which means that a sulfur reservoir is hidden somewhere.There is no consensus on this issue, but it seems that sulfur could be present at the surface of grains as organic sulfur molecules (e.g.Laas et al., 2019) or elemental sulfur produced by GCR radiolysis (Shingledecker et al., 2020).
However, there is no missing sulfur in chondrites, and sulfur abundance (normalized to Si) is similar to that of the Sun.
# We agree.Since there is still some uncertainty about this matter, we revised the text to tone down this point.
L310-311: As pointed out before, the "missing sulfur problem" concerns molecular clouds and dense cores, and cannot be solved by analyzing Ryugu grains.
# These two lines (L136 and 340 of marked manuscript) were removed from the main text.

L316: Surface irradiation by what?
There is no reference here, and in any case, the electronic and nuclear doses should be estimated.Experimental studies are also necessary to conclude about the conditions that lead to the formation of S allotropes.
# According to Okazaki (2023, Science), the galactic cosmic ray (GCR) irradiation period of the Ryugu samples is 5 million years based on the result of GCR-produced noble gases.Although we now have new data on the reaction pathways of sulfur species, we agree that there is a difference in the environment of formation, as the reviewer pointed out, and that additional verification is needed to suggest the existence of similar processes from the present data.We have revised lines 134 and 138 of the manuscript according to this comment, and added that future experimental verification is required.
[Reference] # In the reaction with HCl, a color change of the supernatant was observed (see the photograph below).We reported various S-bearing compounds from the #7-1 hot H 2 O fraction.In contrast, very small amounts of S-bearing compounds were obtained from the #9 HCOOH and #10 HCl fractions, as confirmed by our Orbitrap-MS analysis.The Fe concentrations of A0106 and C0107 are 0.16 and 0.37 mmol/g, respectively.If we assume that the S measured in the #7-1 fraction was all derived from FeS, and ignore magnetite and phyllosilicates, the amount of S released was about 1/600 of the total amount of SO 4 &9 and 1/400 of the total amount of S 2 O 3 &9 in the #7-1 fractions of A0106 and C0107.Thus, the effect of sulfide dissolution on the composition of dissolved species in the solution was small.Sulfide dissolution mainly occurred in the #10 HCl and #9 HCOOH fractions: ~1000 to 8000 times more Fe was detected in the HCOOH and HCl fractions than in the #7-1 hot H 2 O fraction.
In addition, the calculated Mg# (Mg/Mg+Fe) for the #7-1 fractions of Ryugu is ~82, which # As pointed out by the reviewer, there is no doubt that a water-mediated reaction occurred, so we have deleted Equation 2. Because there are few good references that specify this reaction step, we cited this ion chromatography analysis paper.The lack of reference papers is probably due to analytical complications, because many sulfur species are intermediate products in the oxidative environment on Earth.
It was difficult to determine whether liquid-phase or solid-phase reactions were predominant, so we proposed both.The coexistence of dissolved sulfur species and dissolved organic matter in the fluid inclusions of pyrrhotite has been reported by Nakamura et al. (2023, Science).
L256 Zolotov ( 2012) is cited several times.I think it would be helpful to the reader to add a text section that summarizes how the results of this very comprehensive thermodynamical modelling are consistent with the manuscript's new findings.
# We added the following summary of the chemical modeling results."Chemical equilibrium modeling of aqueous alteration of the Ryugu parent body, with mixing of rocks, water containing CO 2 and HCl, and organic matter, yields low Water/Rock ratios (W/R, ranging from 0.06-0.1 for least-altered to 0.2-0.9 for extensively altered The solutes with high solubility extracted by our hot H 2 O method also yield a Na-rich composition, consistent with the chemical modeling." L327-328: A CI chondrite is very different from comet 67P/CG, which has never experienced intense aqueous alteration.One salt has been detected (NH 4 + ; HS -) by both ROSINA and VIRTIS instruments.In that case, it is likely a solid-state thermally activated reaction between H2S and NH3.To say this is quite disconnected from Ryugu samples.
# We agree with this comment and have revised the text.

Reviewer #3 (Remarks to the Author):
1 Details of the following experiment have been added to the Methods section.As pointed out by the reviewer, hydrolysis with HCl acid was also performed (fraction #7-2).This hydrolysis was done by dividing the sample in two after #7-1, then hydrolyzing one part at 100°C for 20 h.However, this fraction was not used in this study because it was preferentially used for other SOM analyses.There is also the possibility of confusion with the #10 HCl fraction, so we would like to omit explanation of fraction #7-2 from this study.Note that the amounts of major cations and anions in each fraction are divided by the initial weights of the starting solid materials used for sequential leaching (in qmol/g, Figs. 1, 3, 5).
The percentages of clay mineral and carbonate standards dissolved in the HCOOH and HCl are shown in Supplementary Table 5.Samples from Tarda (15.76 mg), Aguas Zarcas (15.51 mg), and Jbilet Winselwan (14.90 mg) were also subjected to the same extraction experiments for comparison, but only the HCOOH and HCl fractions could be used in this study because they were preferentially used for the analysis of other soluble organic matter.
The results for these meteorites are also shown in Supplementary Table 6.This method was previously applied to carbonaceous chondrites such as Murchison as a rehearsal analysis for the Hayabusa2 project, and the concentrations of dissolved constituents in the HCOOH and HCl fractions have been reported (Yoshimura+2020).
The other chemical extraction step using organic solvents and ultrapure water is shown in Extended Fig. 1B.Sample weights used for #2 to #5 were 17.15 mg of A0106, 17.36 mg of C0107, and 17.56 mg of Orgueil.These samples were subjected to sequential extraction with organic solvents in the order hexane (#2), dichloromethane (#3), and methanol (#4).At each step, the extract was sonicated for 15 min, after which the supernatant was recovered.At the end of the organic solvent extraction, the fractions were extracted with ultrapure water (#5) at room temperature, but only the Orgueil results could be used for this study." The references must be provided to support that #9 HCOOH and #10 HCl extractions are selective extractions for carbonates and phyllosilicates.Are carbonates and phyllosilicates completely dissolved?Are other phases extracted by HCOOH and HCl?The presence of both Fe and Ni in the extracted solutions (Supplementary Table 1) is indicative that sulfides were also dissolved.
# In sequential leaching, mineral phases other than the main target minerals are also partly dissolved according to their solubility.For this study, we verified that sufficient extraction was possible using standard samples of the main target minerals for dissolution, and have added this information to the Methods and Supplementary Information.
First, dolomite is the main carbonate mineral of Ryugu as well as other CI chondrites.We conducted an experiment in which the dolomite standard published by the National Institute of Advanced Industrial Science and Technology (AIST) was reacted with the formic acid used in this study under the same conditions.The dissolution rate was calculated from the Ca concentration in the HCOOH after the reaction.The dolomite yield was 103.3% ± 5.0% (2SD), indicating that it was completely decomposed.
The solubility of clay minerals in HCOOH and HCl was verified by using JCSS reference materials.According to our experiment, almost all of the saponite became dissolved in 20% HCl (please see the table below).Other phyllosilicates, montmorillonite, dickite, kaolinite, and pyrophyllite were also tested in the same way.Dissolution of clay minerals was evaluated by measurement of the aluminum or magnesium concentration.The dissolution rate of saponite was 103.3% ± 2.2% (2 SD).Although the concentrations varied slightly behavior of saponite varied with the acidity of the monocarboxylic acid according to the test using 6.0% (1M) CH 3 COOH (see the table below).These results have also been added to the Supplementary Information to improve the reproducibility of the experiment protocol.
In addition, the amount of S released was about 1/600 and 1/400 of the total amount of SO 4 &9 and S2O3 &9 , respectively, in the #7-1 hot H2O fractions of A0106 and C0107.Sulfide dissolution mainly occurred in the #10 HCl and #9 HCOOH fractions.Approximately 1,000 to 8,000 times more Fe was detected in the HCOOH and HCl fractions than in the #7-1 hot H2O fraction.In the BCR method, which is a commonly used stepwise extraction method for terrestrial soils, dissolution of sulfide requires a strong oxidation reaction with H2O2.HCl is a strongly acidic solution, although it basically does not have oxidizing power, and the largest dissolution of sulfide was observed in the #10 HCl fraction.We have added a description of these dissolution behaviors to the Results section.# The dissolution of sulfides is as described above and is small in the #7-1 fraction.Please also see our replies to Reviewer #2 and your comment 4 below.
3. Origin of sulfate/thiosulfate/chloride detected in the hot water extraction The authors discuss that soluble inorganic salts, including chlorides and sulfates, were not detected (or were present in trace amounts) in Ryugu samples (starting line 197), and then propose that organosulfur-bearing anions are counterions to Na.However, the manuscript lacks a clear discussion of where sulfate/thiosulfate/chloride were released from during the hot water extraction.In the case of sulfate/thiosulfate, where they present as adsorbed species, originated from organic sulfur-bearing species or from oxidizing sulfides?
# In this report, we discussed the SOM of the hot H2O fraction, from which most of the dissolved sulfur species were also eluted.The absence of inorganic sulfate salts has been mineralogically confirmed by Nakamura et al. (2023, Science), and the contribution from sulfides is only a few hundredths of that from dissolved S species, as discussed previously.
As for adsorption on clay minerals, as the reviewer pointed out, saponite generally generates a negative charge by isomorphous substitution of Si 4+ for Al 3+ in the surface tetrahedral layer;  the redox process of organic matter.The presence of elemental sulfur S8, which Aponte et al.
(2023, Earth Planets and Space) successfully detected, may be evidence of molecular evolution with progressive oxidation reactions in organic molecules after aqueous alteration.
For example, monocarboxylic acid has been successfully detected in the Ryugu SOM (Naraoka et al., 2023, Science); monocarboxylic acid is weakly acidic, and we consider that the pH of the dissolved fractions also reflects these SOM characteristics.
Regarding the specific age of the reaction, the molecular functional groups present in the insoluble organic matter of the Ryugu sample indicate that the organic matter was affected by aqueous alteration in the Ryugu parent body, and no subsequent history of hightemperature impact heating has been reported (Yabuta et al., 2023, Science).That study concluded that the insoluble organic matter, which was mainly affected by aqueous alteration reactions, has not suffered significant alteration at Ryugu's surface (Yabuta et al., 2023, Science).Episodes of aqueous alteration and carbonate precipitation occurred between 2.5 and 5 Myr after CAI formation (Yokoyama+2023, Science).Soluble organic matter likely experienced a similar history, although subsequent molecular evolution is generally more likely to affect soluble organic matter than insoluble organic matter.
The water/rock ratio for aqueous denudation should be considered as the initial conditions, as indicated by Nakamura et al. ( 2023) (0.06-0.1 for least-altered and up to 0.9 for extensively altered lithologies); however, the question of whether the reaction conditions for organosulfur species can be considered as an extension of the fully reductive secondary mineral precipitation model is difficult to answer.The molecular evolution of the SOM may have been influenced by radical reactions, methylation and hydration, hydration, hydroxylation, and sulfurization, as well as general cosmic ray irradiation and solar heating (Naraoka et al., 2023, Science).We recognize that constraining the reaction conditions is a task to be accomplished as part of future work.
Other comments: 1. Online methods/ Ion chromatography: what is exchangeable carbonate?
# This term was incorrect.The correct term is "exchangeable ions, carbonates," Should it be Extended Data Fig. 1b?

#7- 1
Please add water volume, temperature, and extraction duration.Was O2-free water used for this extraction to avoid oxidation of sulfides?Was extraction performed in an inert atmosphere (ex., N2, Ar)? #7-2 Please add HCl volume, concentration, and extraction duration #8 Please add DCM/MeOH ratio, extraction duration, volume #9 Please add HCOOH concentration, volume, duration #10 Please add HCl concentration, volume, duration

2.
Acidic pH of the hot water extraction (l.177-180) Why pH was acidic at the end of hot water extraction?The presence of strong base cations (Na, Ca, Mg), strong acid anions (SO4, Cl, NO3), and weak acid anions (S2O3) could lead to neutral or alkaline pH.Is it possible that sulfide oxidative dissolution occurred during this extraction step resulting in a pH decrease and release of SO42-and S2O32-? 3. Origin of sulfate/thiosulfate/chloride detected in the hot water extraction Nishiizumi et al. (2022, LPSC, Reference below) also give irradiation ages determined by cosmogenic nuclides on the order of millions of years.For formation of S allotropes, we considered cosmic-ray radiation as proposed by Shingledecker et al. (2020, Astrophys.J.).
lithologies) and high Na concentrations in both fluids and the secondary mineral saponite (Nakamura+2023).Previous comprehensive thermodynamical modeling has demonstrated that, under low W/R conditions, neutralization of the initial HCl-containing acidic solution results in a Na-rich alkaline fluid in which Na-containing secondary minerals such as saponite can stably exist(Zolotov, 2012).The Ryugu results suggest the existence of Mg-Na-Cl-rich solutions in the early stages of aqueous alteration, which evolved into more reductive, Na-Cl alkaline brines that coexisted with H 2 -rich gas phases (Nakamura+2023).

# 8
Please add DCM/MeOH ratio, extraction duration, volume #9 Please add HCOOH concentration, volume, duration #10 Please add HCl concentration, volume, duration # We have included additional description of this sequential solvent extraction method, which follows Naraoka +Science (2023)."Sample weights used for chemical extraction treatments #7-1 to #10 in Extended Fig. 1B were 17.15 mg of A0106, 17.36 mg of C0107, and 17.91 mg of Orgueil meteorite (CI type, from National Museum of Denmark).A sequential extraction was performed on these samples using 600 qL of each of the solvents in the order hot H2O (#7-1), dichloromethane and methanol (#8), HCOOH (#9), and HCl (#10).The samples sealed in a vacuum were first extracted with #7-1 hot H2O, weighed immediately after vial opening, and reacted with N2 gas-purged ultrapure water (Tamapure AA100, Tama Chemical) for 20 h at 105°C in a flame-sealed ampoule with the headspace also purged with N2 gas.The reaction tube was centrifuged at 14,000 rpm for 8 min, opened, and the supernatant was recovered.Dichloromethane (DCM, PCB analysis grade, FUJIFILM Wako Pure Chemical Corporation) and methanol (MeOH, QTofMS analysis grade, Fujifilm Wako pure chemical corporation) were then mixed at a volume ratio of 1:1.The DCM/MeOH extraction (#8) was carried out in an ultrasonic bath (Branson, CPX1800-J) at room temperature for 15 min, and the supernatant was recovered after centrifugation at 12,000 rpm for 5 min.Next, >99% HCOOH (#9, Fujifilm Wako pure chemical corporation) was reacted overnight at room temperature.Finally, a 15-min sonication with 20% HCl (#10, Tamapure AA100, Tama Chemical) at room temperature was performed to complete the extraction of soluble substances.The #9 and #10 fractions were centrifuged under the same conditions as ultrapure water.
around 100%, the JCSS elemental reference values themselves differed by 8.0% (2SD) among three different laboratories (Miyawaki et al., 2010, Clay Science, in Japanese), so basically a 100% yield was achieved.The >99% HCOOH, which was the extraction fraction before #10 HCl, also dissolved about 10% of the saponite.The SOM extraction method of Naraoka et al. (2023, Science) used very concentrated formic acid, but the dissolution ., et al., 2010.Some Reference Data for the JCSS Clay Specimens.Journal of the Clay Science Society ofJapan, 48, (in Japanese with English abstract) Supplementary Table5.The percentages of clay mineral and carbonate standards dissolved in the sequential extraction acids of Naraoka+2023a.The percentage of dissolution was calculated by measuring Al or Mg for clay minerals and Ca for carbonates.The ratio of solid to liquid phase of clay minerals is the same as the solid/liquid ratio of Naraoka+2023a, with 600 qL of reagent added for 15 mg of solids.As the abundance of carbonates in Ryugu is a few percent, the sample weight of dolomite experiment was reduced to 1.5 mg of sample.2. Acidic pH of the hot water extraction (l.177-180) Why pH was acidic at the end of hot water extraction?The presence of strong base cations (Na, Ca, Mg), strong acid anions (SO 4 , Cl, NO 3 ), and weak acid anions (S 2 O 3 ) could lead to neutral or alkaline pH.Is it possible that sulfide oxidative dissolution occurred during this extraction step resulting in a pH decrease and release of SO4 2-and S2O3 2-?
thus, cation adsorption is basically predominant.Laboratory experiments on the pH dependence of anion exchange capacity (AEC) and cation exchange capacity (CEC) of smectite have shown that CEC increases from approximately 25 to 32 as pH rises from about 5 to 8, whereas AEC is very small and shows no change(Wada et al., 1981, see the figure below).The total ratio of cations and anions eluted by the hot H 2 O extraction is approximately 3:1, but such a large amount of anions probably cannot be produced by desorption from saponite because of the ion balance.Therefore, it is likely that the anions are stored as functional groups of soluble organic matter or their salts.Information on these possibilities has been added to the revised manuscript.Although it is difficult to specify the exact timing of molecular evolution, we assume that the main chemical composition of the soluble organic matter was determined during the latest or ongoing aqueous alteration processes.However, since we have not yet obtained any proof of this, we have avoided stating this (as also inNaraoka et al., 2023, Science).In recent years, there have been reports on the heterogeneity of the localization of Ryugu indigenous organic matter and the identification of chemical formulae in mineral grains(Hashiguchi et   al. 2023, Earth Planets and Space; Schmitt-Kopplin et al. 2021, Hayabusa symposium).The latter paper is on Ryugu, but as the formation ages of carbonates, for example, are often constrained by Mn-Cr ages, the localization of sulfur-containing organic matter in specific minerals may allow us to determine the timing of molecular evolution in detail.[Reference]Schmitt-Kopplin, P. et al.Highest molecular diversity and structural complexity revealed with ultrahigh resolution mass spectrometry and nuclear magnetic resonance spectroscopy of Ryugu's samples.# Abstract S3-9, Hayabusa symposium (2021).

Figure
Figure of the pH dependence of CEC and AEC of montmorillonites based on data of Wada 1981 (Shirozu, 2010, "Introduction to clay mineralogy : fundamentals for clay science" Asakura Publishing Co.Ltd.).

2.
Fig 1b caption: Please define Exchangeable ions.What minerals are they associated with?"We measured evaporitic salts (via #7-1 hot water extraction, see IDs in Extended Data Fig. 2 and Naraoka+2023a)" Another point is that some sulfides are soluble in HCl and release sulfur (this is clearly observed during the HCl sequence of Insoluble Organic Matter extraction, the supernatant turns to yellow/green).Can you warrant this sulfur does not interfere with your other analyzes?
Nishiizumi, K. et al.Exposure conditions of samples collected on Ryugu's two touchdown sites determined by cosmogenic nuclides 10 Be and 26 Al.Lunar and Planetary Science Conference (LPSC), #1777 (2022).L154-155: Four extractions were run: hot ultra-pure water, Me-OH, and HCl.Regarding phyllosilicates, do you mean that ions were trapped in the interlayer space of saponite, and then expelled by Cl-exchange?