Ice Film Growth Thickness on Simulated Lunar Rock Surfaces as a Function of Controlled Water Vapor Concentration

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript is devoted to the very actual problem of the existence of water ice on the Moon.

The main problem of this study is that the aimed goal (study of water ice behavior on the Moon) is not achieved in these experiments. Why? The studied ranges of pressures (0.01 – 100 Pa) and temperatures (203 – 303 К) do not correspond to the real conditions of the presence of water ice at the poles of the Moon where temperatures are very low (less than 100 K) and there is no pressure because the Moon has no atmosphere. Ices at such high temperatures and pressures can survive on the Moon for a short time only after impacts of big comets. However, such impacts occur very rarely (one impact per 10⁷-10⁸ years) and it is very unlikely that there is a possibility to observe such impacts in the nearest future. Studied ranges of temperatures and pressures correspond better to conditions on the present-day Mars but discussed experiments were performed with lunar simulants. For this reason, I would like to propose to rewrite Introduction to the paper and suggest to authors to describe in Introduction the real processes for which the developed model and performed experiments can be applied.    

My minor remarks are following:

Lines 96-98. T1 is defined at line 96 and later at line 98. Please define this value only once.

Figure 1. Provide logarithmic scale for sublimation speed.

Author Response

Thank you for your comments.

Comments 1.1: [ The main problem of this study is that the aimed goal (study of water ice behavior on the Moon) is not achieved in these experiments. Why?]

Response 1.1: [ In this study, basalt blocks with large and small pores, glass (SiO₂), and aluminum alloy surfaces were tested to evaluate their water ice adsorption capacity under identical temperature and pressure conditions.

Basalt is a common type of rock on the Moon, as evidenced by lunar samples collected by China, the United States, and the former Soviet Union. The reason for choosing glass is that its main component is SiO₂, and glass beads have been observed in the returned lunar soil samples. Aluminum alloy was selected because many materials used in human exploration equipment are made of aluminum alloy. Therefore, this study investigates the behavior of water ice forming ice films on different material surfaces under conditions approximating the lunar environment (low pressure and low temperature).]

Comments 1.2: [ The studied ranges of pressures (0.01 – 100 Pa) and temperatures (203 – 303 К) do not correspond to the real conditions of the presence of water ice at the poles of the Moon where temperatures are very low (less than 100 K) and there is no pressure because the Moon has no atmosphere. Ices at such high temperatures and pressures can survive on the Moon for a short time only after impacts of big comets. However, such impacts occur very rarely (one impact per 10⁷-10⁸ years) and it is very unlikely that there is a possibility to observe such impacts in the nearest future. Studied ranges of temperatures and pressures correspond better to conditions on the present-day Mars but discussed experiments were performed with lunar simulants.]

Response 1.2: [ I sorry for that I don’t write clearly. The temperatures (203 – 303 К) is the generation of water molecules. I control the temperature of water molecules generator. Then, I use the TDLAS to was employed to provide real-time feedback on water vapor concentration within the experimental apparatus. The simulation environment temperature is 80K which caused by LN2 system. I have revised the content ‘the liquid nitrogen inlet and export keep the temperature of cold platform near 80K range.’ from the third paragraph of Section 4.1.

My research focuses on the adsorption and deposition characteristics of water ice on different materials. In the lunar environment, the primary factors influencing the adsorption and deposition of water molecules on material surfaces are ambient temperature and pressure. However, the extremely low temperature (<80 K) and high vacuum (10⁻¹⁰ Pa) of the lunar environment are difficult to reproduce in a laboratory setting. According to the phase diagram of water, once ice is formed from the gaseous phase under constant temperature conditions, vaporization will not occur. Therefore, in this study, I generated a water molecule flow field by sublimating ice, enabling the molecules to adsorb and form ice at temperatures close to 80 K. Even though the experimental pressure is higher than the lunar vacuum, it would only alter the crystalline structure of the ice. While the probability of big comets impacting the Moon is very low, with direct observations made only in recent years, the widespread distribution of impact craters indicates that, long before humanity possessed observational capabilities, the cumulative effect of impacts from small celestial bodies carrying ice was significant.]

Comments 2: [ Lines 96-98. T1 is defined at line 96 and later at line 98. Please define this value only once.]

Response 2: [ Thank you for pointing this out. We agree with this comment. To avoid confusion in the definitions of terms, we have reversed the order of T₁ and P_v(T₁). First, we define T₁ as the absolute temperature at sublimation, followed by P_v(T₁), which is the equilibrium vapor pressure of ice at temperature T₁. You can see in the revised manuscript what we have highlighted.

Where J is the sublimation rate, T₁ is the absolute temperature at sublimation, P_v(T₁) is the equilibrium vapor pressure of ice at temperature T₁, M is the molar mass of water (0.018 kg/mol), R is the ideal gas constant (8.314 J/(mol·K)), P_s1 is the sublimate the actual air pressure on the surface.]

Comments 3: [ Figure 1. Provide logarithmic scale for sublimation speed.]

Response 3: [ Thank you for pointing this out. We agree with this comment.

We have modified Figure 1. The sublimation speed is displayed on logarithmic scale.]

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper is clearly of interest to support lunar ISRU activities. However, the fact that temperature under consideration in this paper is relatively warm (-30C), does not make it very applicable to the Moon (which is cryogenic). I would recommend extending temperature limit to sub -100C. 

There has been a lot of work done on the water vapor deposition for understanding comets. I recommend, for example, reviewing work by Bastian Gundlach. 

In addition, pls review other papers such as Andreas et al. New estimates for the sublimation rate for ice on the Moon, Icarus 186 (2007) 24–30

 

Author Response

Thank you for your comments.

Comments 1: [ However, the fact that temperature under consideration in this paper is relatively warm (-30C), does not make it very applicable to the Moon (which is cryogenic). I would recommend extending temperature limit to sub -100C.]

Response 1: [ I sorry for that I don’t write clearly. The temperatures -30℃ is the generation of water molecules. I control the temperature of water molecules generator. Then, I use the TDLAS to was employed to provide real-time feedback on water vapor concentration within the experimental apparatus. The simulation environment temperature is 80K which caused by LN2 system. I have revised the content ‘the liquid nitrogen inlet and export keep the temperature of cold platform near 80K range.’ from the third paragraph of Section 4.1.]

Comments 2: [ There has been a lot of work done on the water vapor deposition for understanding comets. I recommend, for example, reviewing work by Bastian Gundlach. In addition, pls review other papers such as Andreas et al. New estimates for the sublimation rate for ice on the Moon, Icarus 186 (2007) 24–30.]

Response 2: [ We greatly appreciate your provision of highly helpful literature references for our research work and content. We agree with this comment. We have reviewed the relevant literature and added the appropriate citations in the last paragraph of the Introduction.

This study employs a vapor deposition technique[20] to form water-ice films on rock sample surfaces. We analyzed the factors influencing the sublimation rate of wa-ter molecules[21] and their adsorption velocity during this process.

20 Gundlach, B.; Skorov, Y.; Blum, J. Outgassing of Icy Bodies in the Solar System - I. The Sublimation of Hexagonal Water Ice through Dust Layers. Icarus 2011, 213, 710–719, doi:10.1016/j.icarus.2011.03.022.

21 Andreas, E.L. New Estimates for the Sublimation Rate for Ice on the Moon. Icarus 2007, 186, 24–30, doi:10.1016/j.icarus.2006.08.024.]

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Scientifically very sound article with excellent illustrations which are convincing about the level of research (e.g. 9/10 and 16/17).

The article gives a good overview of related mission results and makes at the beginning a good link with ISRU. Unfortunately this level is not maintined by the conclusion sufficiently.

The conclusion is related to the experiment only. A reader would expect though some extrapolation of the results towards ISRU as this expectation is raised at the start of the article...

This is the biggest weakness of the article and needs some additional work... how do the results of the research correspond with real life implementation? How does this work relate to ISRU? Which part of this reasearch can be implemented in ISRU (like production capaciry etc.).

I strongly suggest to rework the conclusion as the reader is now left with question marks, rather with suggestions for ISRU.

Similarly, suggestions for next phase research would be useful to make the ISRU link further evident...

 

Detailed remarks:

line 199 : it is not clear how fig. 2 shows the risks as suggested

line 200 : in the following ARTICLE (...) : unclear (next paper?)

line 201 : suggest to link the minus fixed to the degrees (-30) confusing now with line breaks

 

318 : check wether (...) : looks more a checklist sntence than a real sentence...

376 : verify (...) : same, is no sentence

List of abbreviations : very useful, but would be more useful if alphabetical...

References : suggest some review needed..., 

• Journals in italics would avoid confusion
• reference 16 is not complete
• reference 17 is not complete
• doctoral thesis: publicly published? in this case better reference needed (DOI or others).

Author Response

Thank you for your comments.

Comments 1: [ This is the biggest weakness of the article and needs some additional work... how do the results of the research correspond with real life implementation? How does this work relate to ISRU? Which part of this reasearch can be implemented in ISRU (like production capaciry etc.) I strongly suggest to rework the conclusion as the reader is now left with question marks, rather with suggestions for ISRU.]

Response 1: [ We greatly appreciate the suggestions you provided. We have incorporated some additional content at the beginning of the Conclusion to explain the relationship between the content of our research and the development of lunar water-ice resources, as well as their application prospects.

This reveals the mechanism of water molecule adsorption and deposition on rock surfaces within the permanently shadowed regions (PSRs) of the lunar poles. The findings of this study can provide a fundamental reference for understanding the occurrence state of water ice on rock surfaces, the abundance of water ice resources, and the distribution characteristics of water ice on the surfaces within PSRs. Moreover, it offers preliminary insights for future exploration, development, and utilization of lunar water ice resources.]

Comments 2: [ line 199 : it is not clear how fig. 2 shows the risks as suggested.]

Response 2: [ Thank you for pointing this out. We agree with this comment. In response to your inquiry, we provide the following explanation. The red dashed line in Figure 2(a) corresponds to the triple point vapor pressure of 611.73 Pa (corresponding to a water molecule concentration of 6435.4 mg/m³ within the system). Exceeding this threshold may cause liquefaction, thereby interfering with the vapor deposition process. Additionally, based on your feedback, we have revised Figure 2(a) to enhance the clarity of the risk threshold line.]

Comments 3: [ line 200: in the following ARTICLE (...) : unclear (next paper?).]

Response 3: [ Thank you for pointing this out. We agree with this comment. The unclear phrase has been removed without compromising the sentence's continuity.

Therefore, only the occurrence and control of water molecule processes will be studied in the range from -30℃to 30℃.]

Comments 4: [ line 201 : suggest to link the minus fixed to the degrees (-30) confusing now with line breaks.]

Response 4: [ Thank you for pointing this out. We greatly appreciate your suggestions. Accordingly, we have conducted a full review of the entire manuscript and addressed this issue.]

Comments 5: [ 318 : check wether (...) : looks more a checklist sntence than a real sentence...]

Response 5: [ Thank you for pointing this out. We agree with this comment. We have revised the corresponding sentences. 3.2.1

it will be necessary to check the airtightness of the device.]

Comments 6: [ 376 : verify (...) : same, is no sentence.]

Response 6: [ Thank you for pointing this out. We agree with this comment. We have revised the corresponding sentences.

The fluctuation range between the water vapor concentration inside the closed‑loop controlled apparatus and the target concentration was verified.]

Comments 7: [ List of abbreviations : very useful, but would be more useful if alphabetical...]

Response 7: [ Thank you for pointing this out. We agree with this comment. We have reorganized the list of abbreviations in alphabetical order.]

Comments 8: [ References: suggest some review needed..., Journals in italics would avoid confusion; reference 16 is not complete; reference 17 is not complete; doctoral thesis: publicly published? in this case better reference needed (DOI or others).]

Response 8: [ Thank you for pointing this out. We agree with these comments and have made the corresponding revisions.

1 We have changed the journal names in the references to italic format.

2 We have incorporated relevant information from the paper Detection of Water on the Moon by the Chang’E-5 Lander in the revised manuscript.

3 We have replaced the original 13th and 17th references to ensure their accessibility.

13 Schultz, P.H.; Hermalyn, B.; Colaprete, A.; Ennico, K.; Shirley, M.; Marshall, W.S. The LCROSS Cratering Experiment. Science 2010, 330, 468–472, doi:10.1126/science.1187454.

17 Liu, J.; Liu, B.; Ren, X.; Li, C.; Shu, R.; Guo, L.; Yu, S.; Zhou, Q.; Liu, D.; Zeng, X.; et al. Evidence of Water on the Lunar Surface from Chang’E-5 in-Situ Spectra and Returned Samples. Nat. Commun. 2022, 13, 3119, doi:10.1038/s41467-022-30807-5.]

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors added an important phrase about cooling of the platform to about 80 K. This temperature is comparable to temperature of the surface of the Moon during the night. Thank you for this suggestion. I incorrectly understood that discussed temperature corresponds to temperature of the simulant.

The authors incorporated suggestion of the reviewer to the manuscript. However, the main point is still unresolved. Namely, the authors did not discuss real situations on the Moon which could be modeled taking into account the results of these experiments.

In your answer on my question, you wrote “I sorry for that I don’t write clearly. The temperatures (203 – 303 К) is the generation of water molecules. I control the temperature of water molecules generator. Then, I use the TDLAS to was employed to provide real-time feedback on water vapor concentration within the experimental apparatus. The simulation environment temperature is 80K which caused by LN2 system. I have revised the content ‘the liquid nitrogen inlet and export keep the temperature of cold platform near 80K range.’ from the third paragraph of Section 4.1.

My research focuses on the adsorption and deposition characteristics of water ice on different materials. In the lunar environment, the primary factors influencing the adsorption and deposition of water molecules on material surfaces are ambient temperature and pressure. However, the extremely low temperature (<80 K) and high vacuum (10⁻¹⁰ Pa) of the lunar environment are difficult to reproduce in a laboratory setting. According to the phase diagram of water, once ice is formed from the gaseous phase under constant temperature conditions, vaporization will not occur. Therefore, in this study, I generated a water molecule flow field by sublimating ice, enabling the molecules to adsorb and form ice at temperatures close to 80 K. Even though the experimental pressure is higher than the lunar vacuum, it would only alter the crystalline structure of the ice. While the probability of big comets impacting the Moon is very low, with direct observations made only in recent years, the widespread distribution of impact craters indicates that, long before humanity possessed observational capabilities, the cumulative effect of impacts from small celestial bodies carrying ice was significant”

Please add to the manuscript (to Introduction and Conclusions) what real situations on the Moon can be modeled using the results of your experiments. Such vapor flows can be formed only during impact processes on the Moon.

 

My other remarks about updates of the manuscript are following:

Line 68 You added the reference to Andreas (2007). However, other important references such as Vasavada, Paige, and Wood (1999) and Paige et al. (2010) are still missing.

Lines 98-99 Modify “Ps1 is the sublimate the actual air pressure on the surface”. In the current form it has no sense at all. I suggest that you mean “Ps1 is the actual air pressure on the surface of the sublimate”

Line 450 Figure 20 is missing

Lines 514-520 You wrote “This reveals the mechanism of water molecule adsorption and deposition on rock surfaces within the permanently shadowed regions (PSRs) of the lunar poles. The findings of this study can provide a fundamental reference for understanding the occurrence state of water ice on rock surfaces, the abundance of water ice resources, and the distribution characteristics of water ice on the surfaces within PSRs. Moreover, it offers preliminary insights for future exploration, development, and utilization of lunar water ice resources.”

Again, you provided only general phrases about practical application of your studies without giving examples. Deposition of water molecules occurs also at the night side of the Moon. So your results can be used for analysis of behavior of water not only at the poles of the Moon but also at the night equatorial lunar regions.

Author Response

Answer and revised:

We sincerely appreciate your detailed guidance on our manuscript.

Comments 1: [ Please add to the manuscript (to Introduction and Conclusions) what real situations on the Moon can be modeled using the results of your experiments. Such vapor flows can be formed only during impact processes on the Moon.]

Response 1: [In response to your specific guidance, we have revised the final paragraph of the “Introduction”to clarify that the simulation scenario of this study is set within the lunar polar permanently shadowed regions. The modifications (Line 83-85) have been incorporated into the manuscript, as indicated below.

“This study simulates the adsorption and deposition of water molecules on rock surfaces in the lunar polar permanently shadowed regions (PSRs), and their subsequent formation of a thin ice film.”]

 

Comments 2: [ Line 68 You added the reference to Andreas (2007). However, other important references such as Vasavada, Paige, and Wood (1999) and Paige et al. (2010) are still missing.]

Response 2: [We are grateful for your suggestion. Based on the newly added references, we have incorporated a paragraph to enhance the readability (Line65-76and“References”). The modifications have been incorporated into the manuscript, as indicated below.

“Gundlach et al. experimentally confirmed that dust layer thickness is negatively corre-lated with gas permeability, affecting sublimated gas transport efficiency [20]. Andreas, using a new low-temperature vapor pressure formula, determined that the ice subli-mation rate is extremely low in the lunar polar environment of 40-70K, providing a reference for experimental temperature control [21]. Vasavada et al. revealed through thermal modeling that temperature distribution in polar craters regulates ice sublima-tion stability [22]. Paige et al. verified with Diviner radiometer data that surface tem-peratures in permanent shadow regions like the lunar south pole's Cabeus crater are as low as 29K, with an annual average temperature at 2cm depth of about 38K, and that ice molecule diffusion and migration are negligible in this environment, further clari-fying key parameters for simulating polar cold traps in experiments [23].”

“Vasavada, A. Near-Surface Temperatures on Mercury and the Moon and the Stability of Polar Ice Deposits. Icarus 1999, 141, 179–193, doi:10.1006/icar.1999.6175.

Paige, D.A.; Siegler, M.A.; Zhang, J.A.; Hayne, P.O.; Foote, E.J.; Bennett, K.A.; Vasavada, A.R.; Greenhagen, B.T.; Schofield, J.T.; McCleese, D.J.; et al. Diviner Lunar Radiometer Observations of Cold Traps in the Moon’s South Polar Region. Science 2010, 330, 479–482, doi:10.1126/science.1187726.”]

 

Comments 3: [ Lines 98-99 Modify “Ps1 is the sublimate the actual air pressure on the surface”. In the current form it has no sense at all. I suggest that you mean “Ps1 is the actual air pressure on the surface of the sublimate”]

Response 3: [Thank you for your guidance. We have corrected the grammatical errors. The modifications (Line 111-112) have been incorporated into the manuscript, as indicated below.

“Ps1 is the actual air pressure on the surface of the sublimate.”]

 

Comments 4: [ Line 450 Figure 20 is missing]

Response 4: [We have checked the document and verified that Figure 20（JPEG） is included. You can review the relevant figures at Line 462.]

 

Comments 5: [ Again, you provided only general phrases about practical application of your studies without giving examples. Deposition of water molecules occurs also at the night side of the Moon. So your results can be used for analysis of behavior of water not only at the poles of the Moon but also at the night equatorial lunar regions.]

Response 5: [We sincerely appreciate your detailed feedback on our paper. We have added the relevant content to the “Conclusion”. The modifications (Line 526-529) have been incorporated into the manuscript, as indicated below.

“Trhe esults can be utilized not only to elucidate the adsorption and deposition behavior of water molecules on rock surfaces within the lunar polar permanently shadowed regions (PSRs), but also to analyze the deposition of water molecules at the night lunar equatorial regions.”]

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for addressing my comments. 

Author Response

We sincerely appreciate your guidance and support on our paper.

Reviewer 3 Report

Comments and Suggestions for Authors

I appreciate the attention spent on reflecting on the comments, and the article is now more solid.

Although not mandatory for this scientific article, a touch of real-life results could be improved answering more globally the question 'how does this research correlates with ISRU objectives' in terms of forecasted results of the implementation (expected amount of water per square meter surface e.g. yearly)

Again, would be nice add-on and ensure that the research catches attention...

Author Response

Answer and revised:

We sincerely appreciate your detailed guidance on our manuscript.

Comments 1: [ Although not mandatory for this scientific article, a touch of real-life results could be improved answering more globally the question 'how does this research correlates with ISRU objectives' in terms of forecasted results of the implementation (expected amount of water per square meter surface e.g. yearly)

Again, would be nice add-on and ensure that the research catches attention...]

Response 1: [Thank you for your suggestion. Please allow me to clarify our explanation.

While such estimates would indeed be valuable for guiding subsequent engineering solutions, it is challenging to provide specific parameters. This is because impact events involving water-ice-bearing asteroids are highly stochastic, and the water content they carry is inherently uncertain. We believe that reliable estimation would only be feasible through the tracking, monitoring, and eventual on-site verification of specific impact events. For these reasons, specific applications have not been elaborated in our conclusion.]

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

I have no futher comments regarding your manuscript.

I suggest to publish the manuscript in the present form.