Possible Formation Mechanism of Lunar Hematite
, Huizi Wang 1,*, Jiang Zhang 1,*, Jian Chen 1, Quanqi Shi 1, Chao Yue 2, Honglei Lin 3, Ruilong Guo 1, Anmin Tian 1, Chao Xiao 1 and Wensai Shang 1
Round 1
Reviewer 1 Report
The paper presents a study based on data treatment using the M3 dataset to discuss on the presence and formation mechanism of lunar hematite. The article has a very simple structure that could be summarized as follows:
-Relative amounts of Hematite and OH/H2O increase with increasing latitude
-This results obviously in a good correlation between the relative amounts of Hematite and OH/H2O and suggest a role of water in the formation of hematite.
-Relative amount of hematite also correlates positively with the optical maturity parameter (OMAT) and this is used to argue that the hematite formation is a slow space-weathering effect.
-Based on literature, it is explained that the required oxygen to form Fe3+ from Fe2+ comes from Earth wind although admittedly there is not direct research showing this.
Taking into account the simplicity of the article contents, I think that the authors should focus more on how the data is processed to produce the parameters they use, which are
-hematite relative concentration.
-OH/H2O ratios.
-OMAT.
However, the authors actually cite previous works for the data treatment to obtain these parameters: hematite relative concentration [25], OH/H2O ratios [31, 24], OMAT [22] and this makes the paper even simpler and most of the discussion and conclusions from the submitted paper are somehow also outlined in the work by S. Li et al., refs. [23] and [25]. I think that the authors should argue better what is the novelty or originality of the submitted paper.
Please find enclosed an annotated version of the paper with some specific comments.
Author Response
Reviewer #1 (Comments for the Author):
Thanks for the reviewer’s comments concerning our manuscript. Those comments are valuable and very helpful. We have read through the comments carefully and have made corrections. We responded to the detailed comments in blue and any necessary changes made in the revised manuscript are marked in red.
The paper presents a study based on data treatment using the M3 dataset to discuss on the presence and formation mechanism of lunar hematite. The article has a very simple structure that could be summarized as follows:
-Relative amounts of Hematite and OH/H2O increase with increasing latitude
-This result obviously in a good correlation between the relative amounts of Hematite and OH/H2O and suggest a role of water in the formation of hematite.
-Relative amount of hematite also correlates positively with the optical maturity parameter (OMAT) and this is used to argue that the hematite formation is a slow space-weathering effect.
-Based on literature, it is explained that the required oxygen to form Fe3+ from Fe2+ comes from Earth wind although admittedly there is not direct research showing this.
Taking into account the simplicity of the article contents, I think that the authors should focus more on how the data is processed to produce the parameters they use, which are
-hematite relative concentration.
-OH/H2O ratios.
-OMAT.
However, the authors actually cite previous works for the data treatment to obtain these parameters: hematite relative concentration [25], OH/H2O ratios [31, 24], OMAT [22] and this makes the paper even simpler and most of the discussion and conclusions from the submitted paper are somehow also outlined in the work by S. Li et al., refs. [23] and [25]. I think that the authors should argue better what is the novelty or originality of the submitted paper.
Please find enclosed an annotated version of the paper with some specific comments.
(We haven’t received this annotated version)
Author’s response: We agree with the reviewer that most of our research was based on the work by S. Li et al., refs. [23] and [25]. But our work actually deepened the understanding of the lunar hematite formation process. This is reflected in the following points.
- The latitude dependence of hematite in our result was clearer, hence we suggested that the latitude dependence of hematite may be derived from the latitude dependence of water. Li et al. (2020) proposed both aqueous and anhydrous mechanisms of hematite formation and pointed out that water can promote the formation of hematite. We further prove water may play an essential role in the formation process of hematite by a significant positive correlation between hematite and water. We also discussed the “ghost feature” of hematite. We didn’t find it, which further proved the important role of water in the formation of hematite.
- Li et al. (2020) pointed out that the hematite formation process has lasted for a long time. And we further prove this point of view by a significant positive correlation between hematite and OMAT.
- We agreed with the point of Li et al. (2020) that the Earth wind provides the oxidizing agent in the hematite formation process. And he thought the O2 is the oxidizer. But current research doesn't provide evidence that O2 can be formed or transported in the lunar orbit. We discussed the current observation of the oxygen particles in lunar orbit or in the magnetosphere. And we inferred that the oxygen particles in the hematite formation process are mainly oxygen ions or molecular oxygen ions during geomagnetically disturbed times.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear Editors and Authors,
This study addresses lunar hematite formation mechanism by new analysis of M3 data. The topic, data and discussion are variable for understanding space weathering, however, some parts must be improved with more explanations.
Main problem
In lines 227-258 of Results and Discussion, the authors discussed about possible sources and energy conditions of oxygen particles which oxidized lunar hematite. However, the discussion is far from the main finding of this work, showing the positive correlation of hematite and water relative contents with an increase of latitude. I recommend deleting the paragraph or clearly showing the relationship between the author’s data and reviewed studies.
Other minor comments:
1) Line 35, Abstract: Understanding the formation process of hematite with different ages may have preserved information on the oxygen evolution of the Earth's atmosphere in the past billions of years.
Lines 52-55, Introduction: Understanding the formation process of hematite …has important scientific value for studying the habitability and evolution of the Earth-Moon system and other celestial bodies in the solar system.
Comment: I checked the abstract of the reference [1], but it looks like the manuscript is not related to the implication of habitability and evolution of the Earth-Moon system. Please check again the reference [1]. The authors may want to associate oxygen particles in the Earth wind with habitability in Earth and Moon, but it was not clear to me if it can be indicator of habitability and evolution of the Earth.
2) Line 52, Introduction: Understanding the formation process of hematite..
Comment: Please insert “on the Moon” after hematite.
3) Line 64, Introduction: Terada et al. (2017)…
Comment: Please insert [10] after Terada et al. (2017).
4) Lines 86-87, Introduction: Li et al. (2020)…
Comment: Please insert [25] after Li et al. (2017). Journal name of reference [25] is missing in the reference list.
5) Line 97, Introduction: Honniball et al. (2022)…
Comment: Please insert [27] after Honniball et al. (2022).
6) Lines 101-102, Introduction: In this study, we intend to analyze the possible formation mechanism of hematite.
Comment: The explanation is not enough. The authors briefly mentioned the hypothesis of lunar hematite formation suggested in the previous studies before this sentence, then authors should explain missing pieces in the previous studies and show new idea to solve the problem here.
7) Lines 103-109, Introduction: The rest of this paper is structured as follows: Section 2 provides a brief description of the Moon Mineralogy Mapper(M3) data and any other data used in this study. In Section 3, we map hematite abundance in the lunar polar regions over a lunar cycle and analyzed its correlation with surface OH/H2O distribution. And we analyze the correlation between hematite and OMAT. Then we discuss the statistical results and how these results refine our understanding of the hematite formation process. We also analyze the possible sources of oxygen forming hematite. Finally, the major conclusions of this paper are provided in Section 4.
Comment: The paragraph should be deleted if the worth of this study is fully explained at lines 101-102.
8) Line 113, Materials and Methods: We analyze them in a lunar cycle due to the IBD…
Comment: Please insert “(Integrated band depth)” after IBD.
9) Lines 127-128, Material and Methods: The integrated band depth (IBD) of hematite represents only the relative content of hematite. The content of hematite mentioned in this article is the relative content of hematite.
Comment: These two sentences can be combined into one.
10) Line 125, 127, Material and Methods: the integrated band depth (IBD)
Comment: Abbreviation should be used for the integrated band depth.
11) Line 141, Material and Methods: Lemelin et al (2022)…
Comment: Please insert [33] after Lemelin et al (2022).
12) Lines 143-144, Material and Methods: the optical maturity parameter (OMAT)…
Comment: Please delete “the optical maturity parameter” and use the abbreviation.
13) Line 153, Results and Discussion: …, which is consistent with the previous study.
Comment: Please add references of the previous study.
14) Lines 161-165, Results and Discussion: At present, studies have shown that biogenic terrestrial oxygen has been transported to the Moon by the Earth wind and implanted into the surface of the lunar regolith[10]. Previous studies have shown that low-energy magnetospheric ions or protons are almost isotropic[33]. So we suggested that the oxygen particles injected into the lunar surface may be independent of the lunar latitude. Therefore, we suggest that the latitude dependence of hematite may be derived from the latitude dependence of water.
Comment: The explanation is too rough. The Authors mentioned water-mediated oxidation to form hematite on the Earth at line 96, Introduction, so I guess they want to interpret the latitude-dependent tendency of hematite IBD by water-mediated oxidation, which is unclear for readers. If so, possible water-mediated chemical reaction for hematite formation should be clearly addressed here, or after line 189.
15) Line 170, Results and Discussion: The probability of 2.8 μm absorption…
Comment: Font of “μ” is not correct.
16) Lines 172-173, Results and Discussion: the orange line oval is caused by highland materials within the Schwarzschild crater.
Comment: Orange line oval is not shown in the figure.
17) Lines 198-199, Results and Discussion: Please delete “the optical maturity parameter” and use the abbreviation.
18) Line 204, Results and Discussion: Allen et al.(1993) inferred…
Comment: Please insert [35] after Allen et al.(1993).
19) Lines 207-208, Results and Discussion: …, the negative correlation between the hematite and OMAT proves that the hematite content is related to the slow and persistent space weathering effect.
Comment: the IBD of hematite and OMAT showed the positive correlation in Figure 3.
20) Line 209, Results and Discussion: Another piece of evidence is that the hematite is pervasive in different polar regions rather than concentrated in a specific area.
Comment: In Figure 1b, I can distinguish the positive anomaly of hematite IBD at longitude 135°. Is the anomaly not a concentration in a specific area?
21) Lines 220-221, Results and Discussion: The main process of oxygen particles with high energy reaching the lunar surface is sputtering, and hematite formation may need the injection of low-energy oxygen particles.
Comment: Could you show the energy condition of oxygen particles that do not cause sputtering?
Comments for author File: 
Comments.pdf
Author Response
Reviewer #2(Comments for the Author):
We are grateful to the reviewer for the thorough review and fruitful comments. That will certainly improve the quality of the manuscript. We responded to the detailed comments in blue and any necessary changes made in the revised manuscript are marked in red.
This study addresses lunar hematite formation mechanism by new analysis of M3 data. The topic, data and discussion are variable for understanding space weathering, however, some parts must be improved with more explanations.
Main problem
In lines 227-258 of Results and Discussion, the authors discussed about possible sources and energy conditions of oxygen particles which oxidized lunar hematite. However, the discussion is far from the main finding of this work, showing the positive correlation of hematite and water relative contents with an increase in latitude. I recommend deleting the paragraph or clearly showing the relationship between the author’s data and reviewed studies.
Author’s response: Thanks for your suggestion. We agreed with you that the positive correlation of hematite and water and OMAT are the two main results of our research.
According to your advice, we deleted the oxidation properties of the oxygen particles and the oxygen particles from the upper atmosphere to the magnetosphere of this part to make it more refined.
The remaining part discussed the possible oxidizers in the lunar hematite formation process. We agreed with the point of Li et.al (2020) that the Earth wind provides the oxidizing agent in the hematite formation process, and he thought that O2 is the oxidizer. We further analyzed current observations of oxygen particles (O+, O2+, O atoms, and O2) in the lunar orbit. And we inferred that the oxygen particles in the hematite formation process are mainly oxygen ions or molecular oxygen ions during geomagnetically disturbed times. We think it’s related to the hematite formation process.
Other minor comments:
1)Line 35, Abstract: Understanding the formation process of hematite with different ages may have preserved information on the oxygen evolution of the Earth's atmosphere in the past billions of years.
Lines 52-55, Introduction: Understanding the formation process of hematite.has important scientific value for studying the habitability and evolution of the Earth-Moon system and other celestial bodies in the solar system.
Comment: I checked the abstract of the reference [1], but it looks like the manuscript is not related to the implication of habitability and evolution of the Earth-Moon system. Please check again the reference [1]. The authors may want to associate oxygen particles in the Earth wind with habitability in Earth and Moon, but it was not clear to me if it can be indicator of habitability and evolution of the Earth.
Author’s response: Thanks for your advice. We updated the reference in this sentence and explained it briefly. We revised this sentence as “Understanding the formation process of hematite might be useful in constraining when the geomagnetic field first appeared and has important scientific value for studying the evolution of the Earth-Moon system(Ozima et al., 2005).”
2) Line 52, Introduction: Understanding the formation process of hematite.
Comment: Please insert “on the Moon” after hematite.
Author’s response: Revision was made as suggested.
3)Line 64, Introduction: Terada et al. (2017)
Comment: Please insert [10] after Terada et al. (2017).
Author’s response: Revision was made as suggested.
4) Lines 86-87, Introduction: Li et al. (2020)
Comment: Please insert [25] after Li et al. (2017). Journal name of reference [25] is missing in the reference list.
Author’s response: Revision was made as suggested.
5) Line 97, Introduction: Honniball et al. (2022)
Comment: Please insert [27] after Honniball et al. (2022).
Author’s response: Revision was made as suggested.
6) Lines 101-102, Introduction: In this study, we intend to analyze the possible formation mechanism of hematite.
Comment: The explanation is not enough. The authors briefly mentioned the hypothesis of lunar hematite formation suggested in the previous studies before this sentence, then authors should explain missing pieces in the previous studies and show new idea to solve the problem here.
7) Lines 103-109, Introduction: The rest of this paper is structured as follows: Section 2 provides a brief description of the Moon Mineralogy Mapper(M3) data and any other data used in this study. In Section 3, we map hematite abundance in the lunar polar regions over a lunar cycle and analyzed its correlation with surface OH/H2O distribution. And we analyze the correlation between hematite and OMAT. Then we discuss the statistical results and how these results refine our understanding of the hematite formation process. We also analyze the possible sources of oxygen forming hematite. Finally, the major conclusions of this paper are provided in Section 4.
Comment: The paragraph should be deleted if the worth of this study is fully explained at lines 101-102.
Author’s response: Thanks for your suggestion. We deleted this paragraph and explained the worth of this study in lines 101-102. “Previous studies have shown that the IBDs (integrated band depth) of hematite have very weak latitudinal dependence(Li et al., 2020). Li et al. (2020) proposed both aqueous and anhydrous mechanisms of hematite formation and pointed out that water can promote the reaction of the oxidation and oxyhydration processes but didn’t give specific evidence about it. In this study, we intend to further analyze the possible formation mechanism of hematite. We modify the method of calculating the IBD of hematite and map hematite abundance in the lunar polar regions over a lunar cycle. Then we analyze its correlation with surface OH/H2O to reveal the role of water in the hematite formation process. We also analyze the correlation between hematite and OMAT to show the relationship between hematite content and space weathering. At last, we discuss the possible oxygen particles participating in the lunar hematite formation process based on the current research near the moon.”.
8) Line 113, Materials and Methods: We analyze them in a lunar cycle due to the IBD.
Comment: Please insert “(Integrated band depth)” after IBD.
Author’s response: Revision was made as suggested.
9) Lines 127-128, Material and Methods: The integrated band depth (IBD) of hematite represents only the relative content of hematite. The content of hematite mentioned in this article is the relative content of hematite.
Comment: These two sentences can be combined into one.
Author’s response: Revision was made as suggested. We combined these two sentences as “The IBD of hematite represents only the relative content of hematite, which is referred to as the content of hematite in this article.”.
10) Line 125, 127, Material and Methods: the integrated band depth (IBD)
Comment: Abbreviation should be used for the integrated band depth.
Author’s response: Revision was made as suggested.
11) Line 141, Material and Methods: Lemelin et al (2022)
Comment: Please insert [33] after Lemelin et al (2022).
Author’s response: Revision was made as suggested.
12) Lines 143-144, Material and Methods: the optical maturity parameter (OMAT).
Comment: Please delete “the optical maturity parameter” and use the abbreviation.
Author’s response: Revision was made as suggested.
13) Line 153, Results and Discussion: …, which is consistent with the previous study.
Comment: Please add references of the previous study.
Author’s response: We add references “(Jones et al., 2018)”. This article performed a simulation of the lunar water.
14) Lines 161-165, Results and Discussion: At present, studies have shown that biogenic terrestrial oxygen has been transported to the Moon by the Earth wind and implanted into the surface of the lunar regolith[10]. Previous studies have shown that low-energy magnetospheric ions or protons are almost isotropic[33]. So we suggested that the oxygen particles injected into the lunar surface may be independent of the lunar latitude. Therefore, we suggest that the latitude dependence of hematite may be derived from the latitude dependence of water.
Comment: The explanation is too rough. The Authors mentioned water-mediated oxidation to form hematite on the Earth at line 96, Introduction, so I guess they want to interpret the latitude-dependent tendency of hematite IBD by water-mediated oxidation, which is unclear for readers. If so, possible water-mediated chemical reaction for hematite formation should be clearly addressed here, or after line 189.
Author’s response: Revision was made as suggested. We add the possible water-mediated chemical reaction after line 189.
“It indicates that water may play an essential role in the formation process of hematite. Current research indicated that water can promote the transformation of iron-oxygen phases ferrihydrite to hematite, and the presence of water can accelerate the crystallization of hematite through increased generation of nucleation sites. It was presumed that the proton transfer between OH groups is facilitated in the presence of water, which is required for the dehydration of ferrihydrite. Higher mobility of the ions accelerates the formation of hematite nuclei so that hematite can grow at a fast rate.(Arinchtein et al., 2020). And possible water-mediated chemical reactions are shown as follows(Li et al., 2020):
Fe/FeO + O particles (Earth wind) + H2O (accumulated from multiple sources) → FeOOH → Fe2O3 (hematite) + H2O”
15) Line 170, Results and Discussion: The probability of 2.8 μm absorption…
Comment: Font of “μ” is not correct.
Author’s response: Revision was made as suggested.
16) Lines 172-173, Results and Discussion: the orange line oval is caused by highland materials within the Schwarzschild crater.
Comment: Orange line oval is not shown in the figure.
Author’s response: Revision was made as suggested. We deleted this sentence.
17) Lines 198-199, Results and Discussion: Please delete “the optical maturity parameter” and use the abbreviation.
Author’s response: Revision was made as suggested.
18) Line 204, Results and Discussion: Allen et al.(1993) inferred…
Comment: Please insert [35] after Allen et al.(1993).
Author’s response: Revision was made as suggested.
19) Lines 207-208, Results and Discussion: …, the negative correlation between the hematite and OMAT proves that the hematite content is related to the slow and persistent space weathering effect.
Comment: the IBD of hematite and OMAT showed the positive correlation in Figure 3.
Author’s response: Revision was made as suggested.
20) Line 209, Results and Discussion: Another piece of evidence is that the hematite is pervasive in different polar regions rather than concentrated in a specific area.
Comment: In Figure 1b, I can distinguish the positive anomaly of hematite IBD at longitude 135°. Is the anomaly not a concentration in a specific area?
Author’s response: That is a great point. We showed Figure 1a and Figure 1b mainly to illustrate the content of hematite increases with increasing latitude in most subregions. Maybe this anomaly can be attributed to the high FeO weight percent in this region.
21) Lines 220-221, Results and Discussion: The main process of oxygen particles with high energy reaching the lunar surface is sputtering, and hematite formation may need the injection of low-energy oxygen particles.
Comment: Could you show the energy condition of oxygen particles that do not cause sputtering?
Author’s response: We used SRIM to simulate oxygen ion bombardment of silica and found that the average sputtering yield of oxygen ions with about 0-300eV is less than 1, which indicated a low sputtering level.
We revised this sentence as “Previous studies put the sputtering yield [amu ion-1] as the basis of the yield of sputtering.(Poppe et al., 2014; Szabo et al., 2018, 2020) . The main process of oxygen particles with high energy reaching the lunar surface is sputtering, and hematite formation may need the injection of low-energy oxygen particles. We used SRIM to simulate oxygen ions bombardment of silica and found that the average sputtering yield of oxygen ions with about 0-300eV is less than 1, which indicated a low sputtering level.”.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
In the first revision the authors were given an annotated version of the manuscript but they have failed to modify the paper, or at least reply, most of the comments made on the annotated version.
Another big concern was the lack of originality/novelty of the paper as compared with the papers by S. Li (refs. [23] and [25]). The authors' reply to argue the novelty of their paper is based on three simple points:
1.-the latitude dependence of hematite may be derived from the latitude dependence of water.
However, this was already stated in the paper by Li et al. (ref. 25) where we can read "a much less reducing and relatively water-richer environment at higher latitudes may fertilize more hematite formation and retention than lower latitudes". Also they argue something about a "ghost feature" that they do not find. This is an addition to the text but they authors should explain better what is this "ghost feature" about or at least provide the convenient references to help the readers to understand what are they talking about.
2.- Li et al. (2020) pointed out that hematite formation has lasted for a long time and the authors argue to have proved this point by showing the existing positive correlation between hematite and OMAT.
However OMAT only reflects the density of craters (not solar/Earth wind) and their values are actually negatively correlated with space weathering degree, therefore the positive correlation only would mean more hematite in craters, not in areas with more prolongued exposure to solar/Earth wind.
3.- Li et al. (2020) suggests that the oxidizing agent is O2, but the authors show that there is no evindence of O2 transported from the Earth, only ionic O and O2.
However, it is rather obvious that solar/Earth winds will only transport ionic species and also it is clear that this species could recombine in the Moon. So I guess Li et al., was also assuming that O2 was not directly transported to the Moon but through ionic forms of O.
Therefore I keep my first opinion that the paper requires really major revision, the authors should reply or modify the paper according to the annotated version that was sent to them in the first revision round.
Comments for author File: Comments.pdf
Author Response
Reviewer #1 (Comments for the Author):
Thanks for the reviewer’s comments concerning our manuscript. Those comments are valuable and very helpful. We have read through the comments carefully and have made corrections. We responded to the detailed comments in blue and any necessary changes made in the revised manuscript are marked in red.
1)Line 35, Abstract: The oxygen involving the oxidization process producing hematite is supposed to originate from the Earth's upper atmosphere, and hematite with different ages may have preserved information on the oxygen evolution of the Earth's atmosphere in the past billions of years.
Comment: Please insert “lunar” before hematite.
Author’s response: Revision was made as suggested.
2) Line 52, The correlation between hematite and optical maturity (OMAT) was analyzed and a significant positive correlation was observed, which suggests that the hematite in the polar regions is the result of gradual and persistent oxidation reactions
Comment: Please insert “parameter” after maturity.
Author’s response: Revision was made as suggested.
3)Line 64, 87, 97, 141, 158, 204, 237, 265
Comment: Use numbers for all the cites, even if you want to use the author's name to begin the sentence. This should also be corrected in other places of the article.
Author’s response: Revision was made as suggested.
4)Line 66, Terada et al. (2017) concluded that biogenic terrestrial oxygen has been
transported to the Moon and implanted into the lunar regolith through analysis of 1-10 keV O+ ion data from the Kaguya mission, which may have lasted for billions of years.
Comment: I would use "thousands of millions" instead of billions to avoid confusion between UK and USA billions
Author’s response: Revision was made as suggested.
5)Line 85, Recent studies have shown that, compared to the solar wind, the scale of oxygen particles is much higher in the Earth wind [3,10], which may promote oxidization/oxyhydration processes.
Comment: Do you mean, the concentration?
Author’s response: Yes, we revised this word to “flux”.
6)Line 88, Li et al. (2020) found the spectral absorption peak of hematite is around 850 nm (4T1 ← 6A1 charge transfer between Fe3+ and O2-), which is less affected by pyroxene or other common minerals.
Comment: What do you mean by less affected? Perhaps do you mean that this transition does not occur in other minerals like pyroxenes?
Author’s response: Yes, in a word, other common minerals like pyroxenes don’t have the absorption peak of 850nm.
7)Line 90, Through the study of the high-latitude M3 datasets, the authors indicated that the absorption peak at 850 nm may represent the existence of hematite, and the integrated band depth between 750 nm and 1200 nm can characterize the relative concentration of hematite.
Comment: Are you still referring to Li et al. (2020)?
Author’s response: Yes, and to avoid ambiguity, we also referred it in this sentence.
8)Line 93, The oxygen from the Earth's upper atmosphere was possibly considered to be the oxidant in the hematite formation process, and the raw materials are ferrous iron or metallic iron on the lunar surface.
Comment: by whom?
Author’s response: Thanks for your suggestion. To avoid ambiguity, we also referred it in this sentence.
9)Line 96, The hematite can be formed by the hydrothermal reaction on the Earth.
Comment: “by the hydrothermal reaction” should be correctted to “by a hydrothermal reaction”
Author’s response: Revision was made as suggested.
10)Line 111, Materials and Methods
Comment: The authors should start describing the M3 dataset and their source
Author’s response: Thanks for your suggestion. We add the sentence of “The M3 imaging spectrometer is a visible and near-infrared spectrometer aboard Chandrayaan-1, covering wavelengths between ~460 nm and 3000 nm. The M3 data were downloaded from the Planetary Data System (http://pds-imaging.jpl.nasa.gov/data/m3/).”
11)Line 114, We analyze them in a lunar cycle due to the IBD data being affected by the observation conditions such as local time.
Comment: “IBD” should be correctted to integrated band depth (IBD)
Author’s response: Revision was made as suggested.
12)Line 122, To reduce the influence of pyroxene on the results, we use the spectra in 750-1000 nm to calculate the IBD parameter as the relative content of hematite.
Comment: This includes the pyroxene band at 950 nm, why not excluding it?
Author’s response: The absorption peak pyroxene is 950 nm, and pyroxene influence the wavelengths from about 800-1100nm. So we can’t completely exclude the influence of pyroxene, we only tried to reduce the influence of pyroxene.
13)Line 146, Results and discussion
Comment: Please clarify whether the results from Fig.1 have been obtained from a data process not previously published or were taken directly from already published data.
Author’s response: For the hematite and OH/H2O data, we calculated their content by processing M3 imaging spectrometer data. For the FeO and nanophase iron data, we used the data which was already published, and we calculated the mean value of each subregion.
To avoid controversy, we added the website of nanophase iron data we downloaded from in the materials and methods section.
14)Line 150, Figure 1 shows the mean content of different materials in the high latitudes of the Moon
Comment: use compounds instead of materials (OH/H2O cannot be considered a material)
Author’s response: Revision was made as suggested.
15)Figure 1
Comment: Would not be better to present maps to get the complete picture?
Author’s response: Figure 1 is mainly to show how different compounds change with latitude. In fact, Li et al. painted distribution map of lunar hematite, but it is hard to identifying the latitude dependence in the distribution map. We also tried to presented maps of hematite, but it’s more difficult to identifying the trend of latitude.
Figure: The IBD of hematite at the northern and southern polar regions from 75° to 90°.
(Li et al., 2020)
Figure: The map of hematite (750nm-10000nm IBD) which was according to our results (northern polar).
Figure: The map of hematite which was according to our results (southern polar).
16)Line 168-182
Comment: The caption text is far too long, most of it should be regular text within the methodology section
Author’s response: Thanks for your suggestion. We put some of the caption text into the methodology section.
17)Figure 2
Comment: This is essentially part of the data shown in fig. 1 but presented in a different way
Author’s response: These two figures definitely used the same data, but expressed different aspects of result. Figure 1 is mainly to show the distribution of different compounds changing with latitude. Figure 2 is mainly to show the correlation between hematite and water. Figure 1 only showed the trend, and it is hard to see the correlation between these compounds in Figure 1.
18)Line 196, Whether the hematite was formed by a rapid process (such as extreme geological events) or accumulated through slow oxidation reactions is another question that needs to be discussed.
Comment: what are you referring to?
Author’s response: I referred to the meteorite impact. And we revised this sentence as “Whether the hematite was formed by a rapid process (such as large meteorite impact events) or accumulated through slow oxidation reactions is another question that needs to be discussed.”
19)Line 218, we investigate the form of Earth wind oxygen particles reaching the Moon and their interaction with the lunar soil.
Comment: I would rather use "discuss" instead of "investigate" as there is not an actual investigation but a discussion based on hypotheses suggested elsewhere.
Author’s response: Revision was made as suggested.
20)Line 220, The main process of oxygen particles with high energy reaching the lunar surface is sputtering.
Comment: Please rephrase
Author’s response: We revised this sentence as “The main process by which energetic oxygen particles reach the lunar surface is sputtering.”.
21)Line 222, According to current laboratory research, exposing the sample to energetic beams of electrons or ions
Comment: which sample are you referring to?
Author’s response: The samples are some active metals such as Ni. In fact, there are fewer experiments on metallic iron. And according to the suggestion of another reviewer, we deleted this part.
22)Line 238, Terada et al. (2017) found 1-10 keV O+ ions with a flux of at least 2.6 × 104 ions cm−2 s−1 from Earth in lunar orbit by the Kaguya data.
Comment: “Kaguya data” should be corrected to “Kaguya satellite data”
Author’s response: Revision was made as suggested.
23)Line 259, Table 1
Comment: This table is never cited in the text.
Author’s response: Thanks for your suggestion. We added the sentence of “As shown in Table 1,” before we discuss this part.
24)Line 285, Data Availability Statement: The M3 data were downloaded from the Planetary Data System (http://pds-imaging.jpl.nasa.gov/data/m3/).
Comment: The M3 database availability should be mentioned within section 2 (materials and methods). Here the authors are supposed to make an statement about the data they have produced not the data they have used to begin the presented investigation.
Author’s response: Thanks for your suggestion. We put the M3 database availability into section 2. We uploaded our data into (https://figshare.com/articles/figure/Possible_formation_mechanism_of_lunar_hematite/21845592) and revised the Data Availability Statement section.
Author Response File: Author Response.docx
Round 3
Reviewer 1 Report
The authors have made an effort to reply all the comments and to modify the manuscript according to them. The paper has greatly improve and it could be published in the present form.
