On Mautner-Type Probability of Capture of Intergalactic Meteor Particles by Habitable Exoplanets

Round 1

Reviewer 1 Report

To the editor,

I have read this paper carefully, before submitting this comment.

First, I observe that the expression “Mautner-Type” is not common in English and should not be used in the title.

Second, I shall note than gravitation focusing is irrelevant at intergalactic speed. While, this is stated in the third paragraph of the section 2.3.2, this also means that the whole section should be rewritten accordingly.

Third, the whole statistical analysis is based on the false premise that the know population of exoplanets in the habitable zone is representative of the reality, which is not at all. Indeed, the list used by the authors to build their probability distribution comes mostly from the Kepler space mission. The planetary size and especially the distance distribution observed are a consequence of the observational technique used by this mission and not the true spatial distribution of exoplanets. For example, the increase of the planetary radius with distance is a direct consequence of the observational method and has no astrophysical basis. Hence, the whole paper is fundamentally flawed by using this distribution.

The probability values have no unit. Is it per particle encounter or per year? In the second case, the reported observation of a collision of an IMP with Earth is very unlikely to be true.

The whole discussion should be brought in the introduction section, since it does very little to discuss the results of the paper itself. The whole section “Some Parallels with Biological Immigration Models” is irrelevant to the paper topic.

I shall also point out that the distance to the Earth is not the same thing as the distance to the centre of the Galaxy. The Earth being at about 8,000 pc from the galactic centre. Hence distance to Earth has no physical relevance and the conclusion that “The clustering is increasing toward the inner region of Galaxy.” is fundamentally false.

While the statistical methodology might be appropriate, the fundamental assumptions are flawed. The whole paper would have to be reworked to make it physically correct. Hence, I would recommend rejecting this paper.

 

Author Response

RC:I have read this paper carefully, before submitting this comment. A:We thank the Reviewer very much for reading our work. We deeply appreciate the Reviewer’s comments and suggestions and answered them point by point. All changes in the manuscript are given in bold face. RC:First, I observe that the expression “Mautner-Type” is not common in English and should not be used in the title. A:We thank the Reviewer for the comment and acknowledge Reviewer's concern about our choice of expression 'Mautner-type'. We would like to let us mention some notable examples of papers with expressions '-type': - Dynamical astronomy Petr Pokorn and David Vokrouhlický, 'Opik-type collision probability for high-inclination orbits: Targets on eccentric orbits', Icarus Volume 226, Issue 1, September–October 2013, Pages 682-693 - Mathematics Kamenev-type function in Z. Han, T. Li, S. Sun & W. Chen 'Oscillation Criteria for Second-Order Nonlinear Neutral Delay Differential Equations', Advances in Difference Equationsvolume 2010, Article number: 763278 (2010) However if there is a possibility that audience will be broader than experts only then the title can omit expression '-type' from its formulation. RC: Second, I shall note than gravitation focusing is irrelevant at intergalactic speed. While, this is stated in the third paragraph of the section 2.3.2, this also means that the whole section should be rewritten accordingly. A: We thank the Reviewer for the comment. Gravitational focusing was not implemented in any calculations due to the reason Reviewer mentioned. We did not intend to indicate gravitational focusing and we have therefore altered the text to specify that as follows: $b=R(1+\frac{2GM}{Rv^{2}_{\infty}})^{0.5}$ (where $G$ is gravitational constant) {\bf converges} to planet's radius $ R$, while the planet mass $M$ does not play any role as it can be seen {\bf (i.e. the right parameter in the brackets is vanishing i.e. gravitational focusing is irrelevant)}. RC:Third, the whole statistical analysis is based on the false premise that the know population of exoplanets in the habitable zone is representative of the reality, which is not at all. A:A: We thank the Reviewer for the comment. We did not mention explicitly that observed planets are not representative of reality, actually at one point in the text we mention that there are estimates about number of exoplanets of order 10^10 in our Galaxy. Thus, we revised the text to be more specific with following sentence: We note that the known population of exoplanets are not representative of the reality, since expected number of them is aabout 10^10. RC:Indeed, the list used by the authors to build their probability distribution comes mostly from the Kepler space mission. The planetary size and especially the distance distribution observed are a consequence of the observational technique used by this mission and not the true spatial distribution of exoplanets. For example, the increase of the planetary radius with distance is a direct consequence of the observational method and has no astrophysical basis. Hence, the whole paper is fundamentally flawed by using this distribution. A: We thank the Reviewer for these comments. We agree that it is a scientific fact that each method of measuring something has an inherent sampling bias. It is one of the constraints in any scientific study. Because of that we need a new surveys and more data, to recalculate and adjust our theories. Since Kepler examined over 200,000 stars to detect dips in starlight caused by transiting exoplanets, much of the analysis of the Kepler data had to be done by computers. Standard search algorithms attempt to identify sudden drops in brightness, and the team of astronomers are constantly developing a smarter algorithm that takes into account more parameters in order to 'extract' exoplanets from the light curves. R. Heller, M. Hippke and K. Rodenbeck published in Astronomy and Astrophysics (2019) 'Discovery and validation of 17 new sub- to super-Earth-sized planets in multi-planet systems from K2'. We assume that any analysis of the data could help designers of missions to adjust and improve the instruments and algorithm pipelines. We agree that this explanation is speculative at this level of observational and computational technology of extracitng exoplanets data, and we have edited the text to state that our conclusion is only suggested by our results: Because our results reflect the underlying exoplanets observational bias, we caution readers to keep this in mind when assessing the results. For example, the planetary size and especially the distance distribution observed are a consequence of the observational techniques and not the true spatial distribution of exoplanets. The increase of the planetary radius with distance is a direct consequence of the observational method and has no astrophysical basis. Also we added follwoing lines in Conclusion: In our study we employed available data from previous decades of exoplanets observations which were dedicated to the constraining the exoplanet population in the Milky Way on zeroth level (orbital parameters, radii and densities). However, the next generation of telescopes (e.g., James Webb Telescope, the European Extremely Large Telescope; Ariel) will provide data on the atmospheric properties of exoplanets, and improve those already obtained. It is hoped that the calculations outlined in this article will be useful to make atlases (i.e. collection of maps) of interstellar and intergalactic transfer of material within our Galaxy, indicating possible hot spots of panspermia activity, because it builds on our empirical knowledge. The future observational evidence will improve the prediction both of the HZEP probabilites and IMPs influx probabilites, and thus our understanding of the habitability of the Universe. RC:The probability values have no unit. Is it per particle encounter or per year? In the second case, the reported observation of a collision of an IMP with Earth is very unlikely to be true. A: We thank the Reviewer for this comment. We explained more thorughly how hit probabilities are calculated in the section Methods and Materials: {\bf A simple analogy with military operations theory \citep{Bin78}, can aid in understanding the overall process. The calculation of the probability that a bullet impacts a target is reduced to estimating the hit probability into some region of a certain geometric shape. The basic interaction between weapon and target is given by damage function (or lethal area) D(r), which is the probability that the target is hit by a bullet if the relative distance between them (the miss distance) is r. The simple assumption that target is a planar figure with the density distribution of the position relative to the weapon PD(x,y). Then the probability of hit is determined by the double integral over the whole combat plane $\iint D(r)PD(x,y) \mathrm{d}\,x \mathrm{d}\,y$. If the target was uniformly distributed within some large $\Delta y$ area then distribution of relative target positions reduces to $PD(x,y)=1/\Delta y$ and double integral becomes $\frac{1}{\Delta y} \iint\limits_{\Delta y} D(\sqrt{x^2+y^2}) \mathrm{d}\,x \mathrm{d}\, y$. However, in our case damage function would reduce to the area of exoplanet cross section ($A_t$) and $\Delta y= \pi (\delta y)^2$ where $\delta y$ is a resolution of target's uncertainity position. Thus, the double integral would reduce to the ratio $\frac{A_t}{\Delta y}$. This is an essence of estimate of impact probabilities by adopting \cite{MM79} method. Note, that such defined probability is dimensionless.} RC:The whole discussion should be brought in the introduction section, since it does very little to discuss the results of the paper itself. A A: We thank the Reviewer for the comment. We improved the results and discussion section. Also it is possible to unite them into one section Results/Results and Discussion. RC:The whole section “Some Parallels with Biological Immigration Models” is irrelevant to the paper topic. A: We thank the Reviewer for the comment. We wrote following paragraph to connect this subsection with the main topic in the paper, i.e. IMP: {\bf Some recent studies on interplanetary transfer of photosynthesis organism \citep{Co08} and simple life forms or bio material \citep{LL17} employed analogies with Earth ecological models of 'immigration' to qualitatively explore the possibility of interplanetary material immigration. Namely, in these analogies planets are seen as islands and even continents, and ‘immigration’ would essentially amount to transfer of lifeforms (or genetic material) via vehicles such as meteoroids. This enables us to make some qualitative description of IMPs immigration, if we assume that galaxies are 'continents' and the material exchange could probably occur only within our Local Group of galaxies. For example, the large-scale distribution of the galaxies observed by VIPERS \citep[see Fig. 15 in][]{Sco17} shows quite clearly the abundance of structures, and the segregation of the overall galaxy population as a function of the local galaxy density.} RC: I shall also point out that the distance to the Earth is not the same thing as the distance to the centre of the Galaxy. The Earth being at about 8,000 pc from the galactic centre. Hence distance to Earth has no physical relevance and the conclusion that “The clustering is increasing toward the inner region of Galaxy.” is fundamentally false. A: We thank the Reviewer for this comment! We corrected the sentence as follows: The clustering is increasing toward the Solar system. RC:While the statistical methodology might be appropriate, the fundamental assumptions are flawed. The whole paper would have to be reworked to make it physically correct. Hence, I would recommend rejecting this paper. AC: We thank the Reviewer for this comment. We corrected typos and grammatical errors, improved sentences, added paragraphs to better explain the methods, we added a new Figure 1 to better explain the geometric and kinematic concept of the problem, we rewrite the whole Conclusion section.

Reviewer 2 Report

The topic and paper is very interesting, relevant, and overall it was an exciting read.

Except for few grammatical errors, the manuscript is well written, and easy to read by someone with general math training.

The only major concerns I have are: (i) some of the more complex mathematical formulas have to be better explained in text, to help readers from different fields better follow the logic; (ii) the last sections (Parallel with...) needs better connection with the process addressed in the rest of the paper (parallel should not be taken in its mathematical sense); and (iii) conclusions also have to be rewritten. They are currently written more of a summary list rather than conclusive remarks.

I provide line-by-line comments throughout the PDF, that hopefully will help clarify aspects mentioned above.
Other than that, I greatly appreciate the author's imagination and effort to share it.

Comments for author File: Comments.pdf

Author Response

RC:Except for few grammatical errors.. Response to the Reviewer 1: We sincerely thank the Reviewer for carefully reviewing our manuscript and providing insightful feedback throughout the review process. Their comments have vastly improved the quality of this study. Accordingly, the revised manuscript has been systematically improved with new information and additional interpretations. Our responses (A) to the Reviewer’s comments (RC) are given below. Changes in the manuscript are given in bold face. A: We thank the Reviewer for all grammatical corrections. The sentences are corrected, references are added as well as the whole text is revised to improve the flow as per the Reviewer’s suggestions. RC: The only major concerns I have are: (i) some of the more complex mathematical formulas have to be better explained in text, to help readers from different fields better follow the logic; A: (I) We agree with the Reviewer's comment. The mathematical formulas were better explained following detailed Reviewer's comments given in the PDF of version 1. The conceptualization of the geometry, kinematics and parameters used in the impact probabiliies formulas is schematized in newly-added Figure 1. We also added following lines in the section Materials and Methods to help reader to follow overall calculation process: {\bf The statistical impact probability of IMPs with HZEP, can be equivalently stated as calculating probability of cooccurrence of a planet being in the habitable zone and hit by an IMP. As the geophysical properties of potentially habitable exoplanets are currently unknown, it is not possible to determine exact HZEP probabilities. Instead, we calculated HZEP probabilities as a probability density function with respect to observationally constrained planet properties (distances and radii), assuming a very optimistic geometrical HZ boundaries. The probablity density function was estimated by machine learning implementation of 2D kernel density estimate (KDE) in Python. } and {\bf Calculated HZEP probabilities are small due to small sample of HZEP confined in very large parametric space. Also, hit probabilities are small as a ratio of exoplanet cross section area and IMP's letal area. The cooccurence of such rare events can not be calculated classically by their coupling, instead the information theory metrics must be employed. For this purpose we used Entropy index.} (ii) the last sections (Parallel with...) needs better connection with the process addressed in the rest of the paper (parallel should not be taken in its mathematical sense); A:(ii) We thank the Reviewer for this comment. The last subsection (Parallel with...) is connected with the rest of the paper by following lines and new references: {\bf Some recent studies on interplanetary transfer of photosynthesis organism \citep{Co08} and simple life forms or bio material \citep{LL17} employed analogies with Earth ecological models of 'immigration' to qualitatively explore the possibility of interplanetary material immigration. Namely, in these analogies planets are seen as islands and even continents, and ‘immigration’ would essentially amount to transfer of lifeforms (or genetic material) via vehicles such as meteoroids. This enables us to make some qualitative description of IMPs immigration, if we assume that galaxies are 'continents' and the material exchange could probably occur only within our Local Group of galaxies. For example, the large-scale distribution of the galaxies observed by VIPERS \citep[see Fig. 15 in][]{Sco17} shows quite clearly the abundance of structures, and the segregation of the overall galaxy population as a function of the local galaxy density.} iii) conclusions also have to be rewritten. They are currently written more of a summary list rather than conclusive remarks. A: (III) We absolutely agree with the Reviewer's comments. We rewrite the whole Conclusion, emphasizing methods and explaining obtained results. RC: Does the group have a name? (page 2) A: The Local Group is the galaxy group that includes the Milky Way. Local Group is the name, do not invite an astronomer to be a godfather.. RC: you mean diversity? It's not entirely clear (page 2) A: We added following lines to clarify meaning: {\bf On the chemical space we assume the property space spanned by all possible molecules and chemical compounds under a given set of construction principles and boundary conditions}. RC: A bit more clarity is needed here. is HIP 13044 a star? Is it bout to the galaxy? and what type of object is the companion. All these are unclear A: We agree with Reviewer comment. We added following lines: {\bf HIP 13044, a very metal-poor star on the red Horizontal Branch and a member of the Helmi stream, was probably bounded to the Milky Way several Gyr ago from a satellite galaxy}. {\bf Because of the long galactic relaxation timescale, it is most likely that its planet (HIP 13044 b with mass of 1.25 mass of Jupiter) was not captured by any Milky Way star.} RC: Betatron mechanism a short explanation in brackets would be much appreciated A: We added following line: {\bf (i. e. acceleration happens when the particle drift motion is in resonance with changes in the induction electric field caused by the variable magnetic field)} RC: What do you mean? How small, and from where (solar, galactic, extragalactic)? (small projectiles ) A: We clarfy the sentence as follows: projectiles ({\bf of negligible dimensions, moving on Keplerian orbits around Sun}) RC:Reference needed. Also, what is the estimate unit, e.g. year? A: We provided the unit and reference as follows: are $\lesssim10^{-8}$ {\bf per orbital revolution} Rickman et al. 2014 RC:Also, my logic line breaks a bit here: how does a particle enter our galaxy from the position of our solar system? Does it enter the disk tangential from outside towards the solar system? It has to be better worded here. A: We added Figure 1 to clarify geometry of the problem and also we added following lines; For simplicity, we will assume that an IMP follows a straight line {\bf when} entering into our Galaxy from position of our solar system. {\bf Trajectory of an IMP is within ecliptic plane and perhaps further studies should make use of 3D probes}. RC: Isn't it similar with predicting the probability of being hit by raindrops while walking? If so, maybe some parallel could be drawn to help simplify the visualization of the process. (page 3) A: Thank you it is really nice comment! We added following analogy: {\bf A simple analogy with military operations theory \citep{Bin78}, can aid in understanding the overall process. The calculation of the probability that a bullet impacts a target is reduced to estimating the hit probability into some region of a certain geometric shape. The basic interaction between weapon and target is given by damage function (or lethal area) D(r), which is the probability that the target is hit by a bullet if the relative distance between them (the miss distance) is r. The simple assumption that target is a planar figure with the density distribution of the position relative to the weapon PD(x,y). Then the probability of hit is determined by the double integral over the whole combat plane $\iint D(r)PD(x,y) \mathrm{d}\,x \mathrm{d}\,y$. If the target was uniformly distributed within some large $\Delta y$ area then distribution of relative target positions reduces to $PD(x,y)=1/\Delta y$ and double integral becomes $\frac{1}{\Delta y} \iint\limits_{\Delta y} D(\sqrt{x^2+y^2}) \mathrm{d}\,x \mathrm{d}\, y$. However, in our case damage function would reduce to the area of exoplanet cross section ($A_t$) and $\Delta y= \pi (\delta y)^2$ where $\delta y$ is a resolution of target's uncertainity position. Thus, the double integral would reduce to the ratio $\frac{A_t}{\Delta y}$. This is an essence of estimate of impact probabilities by adopting \cite{MM79} method. Note, that such defined probability is dimensionless.} RC: Is this the first and only time used in the paper. It gives the feeling that the computation may be done in ML context. One has to be specific if that is not the case. Also, since you mention that you borrow a tool/concept from ML you could provide a reference. Cross-validation is not specific to ML anyways, e.g. it is widely used in time series/climate change statistics A: We clarifed the term with following lines: {\bf We used KDE implemented in machine learning package of Pyhton scikit-learn. KDE can be considered as a form of machine learning \citep{WS19}, where we want to estimate density but not to predict a new data given certain set of known data}. {\bf KDE discretize user-defined evaluation space (or grid), computing the density in equally separated grid points. So, the evaluation space can be represented as a multi-dimensional matrix. We defined the separation between grid points, so that we have 800 points in each dimension of 2D parameter space defined by exoplanet distances and radii. The output is KDE of the same dimensions as defined grid \citep{IV14,LN15}}. RC: what is the impact parameter b? I have not seen it before. A: We provided following definition: the impact parameter {\bf (defined as the perpendicular distance between the velocity direction of a projectile and the center of an object that the projectile is approaching)} RC: unclear to me what mean of information means. Is it a statistical mean? Maybe different wording (or some bracket explanation) to could help. A: We clarifed the sentence as follows: Entropy {\bf can be viewed as the expectation of $\log(f (X))$ where $f$ is the probability density function (PDF) of a random variable X}, RC: per what unit of time? and, does count represent some sort of total number of events? (PAGE 5) A: We explained it as follows: {\bf It is not given per any unit of time since the probabilities of a planet being hit by an IMP are dimensionless and $V_{j}$ are probabilities}. RC: what is a cell? I would give a bit more clarification either here or methods of how cells, equations and plots relate. A: We explained it in the section Methods as follwos: {\bf KDE discretize user-defined evaluation space (or grid), computing the density in equally separated grid points. So, the evaluation space can be represented as a multi-dimensional matrix. We defined the separation between grid points, so that we have 800 points in each dimension of 2D parameter space defined by exoplanet distances and radii. The output is KDE of the same dimensions as defined grid \citep{IV14,LN15}}. RC: you just mentioned project (176001) bellow. A: We thank the Reviewer for careful reading all lines in our manuscript. Our Ministry requiers to be mentioned in Acknowldg. only.

Round 2

Reviewer 1 Report

To the editor

I have read the second version of “On Mautner-Type Probability of Capture of

Intergalactic Meteor Particles by Habitable Exoplanets” by Andjelka B. Kovačević.

The paper is interesting but the methodology does not bring a meaningful answer to the question posed. Indeed, the key question raised by this article is : What is the typical distance of an Earth-like planet hits by an intergalactic particle.

If you assume a homogeneous Earth-like planet population on relevant distance scale (kpc), the problem resolved simply to the calculation of the average distance on the nearest Earth-like planet. This is a tricky problem due to the strong bias of the present exoplanet survey. To this problem, the presented paper provides no solution accepting the fact the survey it used is strongly biased. This also means that the resulting calculation is not very meaningful.

Moreover, such calculation has been carried out recently on the Kepler dataset for FGK type star. The result is an average of 0.27 planet per star of this type. Assuming 1 planet of this type per 60 pc³ (Recons dataset), one habitable exoplanet per 222 pc³ exists, and its average distance is 4,25 pc. The large value derived in the paper comes from the fact that the Kepler survey only a small fraction of the sky. I note that if Earth-like planets do exist around M stars, they will be even closer to Earth as their population amount for 70 % of the nearby star and since the number and the fraction of planet per star is even higher (https://arxiv.org/pdf/1905.05900.pdf ).

In consequence, the present paper conclusion is highly erroneous, even if the introduction and discussion are interesting.

This is why I would not recommend accepting this publication unless the methodology used is completely revised.

Reference:

Danley C. Hsu, Eric B. Ford, Darin Ragozzine, Keir Ashby. Occurrence Rates of Planets Orbiting FGK Stars: Combining Kepler DR25, Gaia DR2, and Bayesian Inference. The Astronomical Journal, 2019; 158 (3)

Author Response

The paper is interesting but the methodology does not bring a meaningful answer to the question posed. Indeed, the key question raised by this article is: What is the typical distance of an Earth-like planet hits by an intergalactic particle. We thank the Reviewer for the comment. We did not intend to indicate what is the typical distance of an Earth-like planet hits by an intergalactic particle, and we have therefore added the sentence to specify that we are considering exoplanets (not only earth-like planets) within HZ and probability they are being hit. We make this point on lines at the bottom of Introduction : In this study we consider the exoplanets in habitable zones (HZEP) as targets and IMPs as a projectile on a trajectory crossing their orbits. We focus on the random probability that an IMP, during its cruise through our Galaxy, will collide with some of HZEP. If you assume a homogeneous Earth-like planet population on relevant distance scale (kpc), the problem resolved simply to the calculation of the average distance on the nearest Earth-like planet. We thank the Reviewer for the comment. We did not consider Earth-like population planets. We explained it in the previous answer. This is a tricky problem due to the strong bias of the present exoplanet survey.To this problem, the presented paper provides no solution accepting the fact the survey it used is strongly biased. This also means that the resulting calculation is not very meaningful. We thank the Reviewer for the comment. We calculate variable whether any exoplanet belong to the Habitable Zone. This variable is not outcome of any survey since no one survey was designed to hunt planets within Habitable zones. Consequently, since variable whether any exoplanet belong to the HZ is not record of the surveys it mitigates bias from the surveys. This is a practice in Statistics (e.g. Hosmer et al. 2013). We added following sentence in the section Results: Note that variable whether any exoplanet belong to the Habitable Zone is not outcome of any survey since no one survey was designed to hunt planets within Habitable zones. Consequently, this variable mitigates bias from the surveys (see e.g. Hosmer et al. 2013).

Reviewer 2 Report

The author has brought significant improvement over the previous manuscript version, particularly in terms of clarifying confusing aspects, and using a new, intuitive analogy for calculating probabilities of impact of extrasolar bodies. The author has also completely reshaped the Conclusions section, albeit there is still some room for improvement. For last part of results section, a new paragraph explaining the meaning of these results is needed to close the results. I also recommend that the author double check if all references are cited, and the format is consistent throughout.

I have added my line-by-line suggestions on the PDF file, which hope will help the author further improve the manuscript.

All in all the paper was an exciting read throughout.

(These are the same comments I submitted to the Editor)

Comments for author File: Comments.pdf

Author Response

R1: You mentioned in a response to Reviewer 1 that gravity was considered negligible... We thank the Refereefor giving us the possibility to further correct our manuscript. We have highlighted the changes within the manuscript. Referee comments are marked as *R* and our response as *A*. A1:We thank the Reviewer for the comment. What we said to the Reviewer 1 is that the Gravitational focusing was not implemented--which means we do not apply enhanced gravitational capture. R2:Is there a real map presented in this MS? A2:We do not use word the map in the cartogrphy sense, instead it is used as mathematical synonym for functions and its plot. R3:the currently ? A3: The sample of exoplanets is updating almost daily so we would like to adopt "an available sample". R4: Rewrite for clearer understanding. What do you mean by simplest case, and high value of transient distribution ? For abstract try to use an intuitive language accessible for a really broad audience. You would want to capture not only IP, but also as many T readers as possible.I would close with an overarching conclusive remark and notes/projection for the future (e.g. relevance). A4: We thank the Reviewer for this point. We added following lines at the end of the abstract as suggested by the Reviewer: We further adopted a model from immigration theory, to show that the {\bf time dependent distribution of single molecule immigration of material indicates high survivability of the immigrated material taking into account birth and death processes on our planet. At present immigration of material can not be observationally constrained but it seems reasonable to think that it is feasible/it will be possible in the near future, and to u R5: I would use a more intuitive number, e.g. km^-3, or even 1g X^-3 A5: We thank the Reviewer for suggestion. However, g/cm-3 is used by Afanasiev et al in their work and also this unit is very likely in density measures of astronomical objects. R6: how is this related to intergalactic busing, likely resulting from supernovae A6:We thank the Reviewer for this point. The sentence "material exchange between rocky planets" is a part of a wider paragraph which explains what we know about exchange of material. The paragraph ends up with observational facts about extragalacitic planet captured by our Galaxy. R7:the logic is a bit convoluted. I suggest state it more straightforward (remove negations) how the planet ended up around a captured star. A7: We added following lines to clarify the statement: {\bf However, study of {2014A&A...562A.129J} did not confirm existence of this planet, thus in catlogues it is designed as controversial}. HIP 13044, a very metal-poor star on the red Horizontal Branch and a member of the Helmi stream, was probably bounded to the Milky Way several Gyr ago from a satellite galaxy. {\bf Because of the long galactic relaxation timescale, it is most likely that both star HIP 13044 and its planet (HIP 13044 b with mass of 1.25 mass of Jupiter) was captured by Milky Way}. R8: organic ? A8: We thank for the point. We think about molecules in general. R9: Would you make the code available as potentially useful tool for other researchers? A9: We thank for the point. KDE is available in any modern realese of Python. R10: 3D probes.. To do what? What do you mean? A10: We mean that in the future will be possible to calculate IMP orbits in 3D. However, to avoid confusion we omitted it from the rest of sentence. R11: Calculated HZEP probabilities...Current literature calculations, or calculated in this paper? A11: To clarify sentence we added following: Our calculated R12: lethal area? 12: We apologize for not referring where it is defined, we correct it as follows: ({\bf defined in the subsection Probabilities estimates}) R13:Entropy index ... defined below? A13: We added following line to clarify: {\bf (EI) defined in subsection Information theory metrics} R14: proper motion of star..clarify this part A14: We added following lines in the caption of Figure 1: As a star has real motion in 3D space, that motion projected on the line of sight of observer will be seen as proper motion. Naturally, planet will follow mother star and thus will have uncertainity in position. } R15:bearing life and being in a habitable zone are not the same. I would be careful here, since we don't know of "life as we don't know it". A15: We agree with the Reviewer, however we still do not have a nice defintion of HZ. R16: I notice you have not presented EI in full words before. Please check and address this. A16: We apologize for this typo. We corrected it at the end of Introduction adding following line: For this purpose we used Entropy index (EI) defined in subsection Information theory metrics. R17:this number seems close to 1g/g. If resource is just rock, what would remaining 26.7 mg represent? Is the total 1g assumed to represent resource+biomass? 17: We thank for this point. c_res is an average concentration of mentioned essential elements in chondrites which can support biomass of 180g/kg. In essential elements are not included all possible essential elements which are found in asteroids such as Al Si Ti Cr Mn Fe Co Ni Cu Zn Cl, which can constitute the remainig mass. R18:are they microorganisms? if so, they are simple life forms too. Unless by simple life forms you mean other microorganisms. 18:We agree with the Reviewer they are simple too, however we would like to emphasize possibility they can sustain photosynthesis. 19:A paragraph on the meaning of these results is needed with some context. Is it stands it reads unfinished. A19: We thank the Reviewer for this point. We added following lines at the end of subsection some paralles with biological immigration models: {\bf Time dependent distribution of single molecule immigration of material indicates high survivability of the immigrated material taking into account birth and death processes on our planet. At present immigration of material can not be observationally constrained but it seems reasonable to think that it will be possible in the near future, and to use it along other proposed parameters for life sustainability on some planet.}} R20: Checking references A20: We thank for this point. Some references where shuffled inappropirately. We corrected the order of the references through the text and in the list of references.

Round 3

Reviewer 1 Report

To the editor,

First, I would like to apologize for the long delay in the review process. For some technical reason, I was under the impression that I could no longer complete my review as requested.

Second, I must not that me previous concern were not addressed by the last paper modification. For example, the answer #1 of the author are inconsistent with the data provide in the paper iself. Indeed, while he claim:

“… We did not intend to indicate what is the typical distance of an Earth-like planet hits by an intergalactic particle, and we have therefore added the sentence to specify that we are considering exoplanets (not only earth-like planets) within HZ and probability they are being hit...”

But the database used in the paper (http://phl.upr.edu/projects/habitable-exoplanets-catalog) is clearly described as the “Habitable Exoplanets database”. Those are clearly Earth-like exoplanets. Therefore, my previous concern as not been addressed and as I pointed out, the conclusion of the paper is clearly wrong compared to results already published in the literature.

I note also that this database now contains 55 planets and it is not clear the use the same criteria as the one claimed by the author. The be consistent with himself, the author should apply his own criteria to a more complete exoplanets database like “The Extrasolar
Planets Encyclopaedia” (http://exoplanet.eu/). Alternatively, I suggest using the Kepler database and apply a simple geometrical correction to take account of the narrow field of view of this instrument to get the appropriate result.

Comment #2 refers to comment #1 and, hence, is irrelevant. As for comment number #3, the claim “This variable is not outcome of any survey since no one survey was designed to hunt planets within Habitable zones.” is wrong as this was the goal of the Kepler mission,

As I noted in my previous comment, the relation between planetary radius and distance is unphysical and is produced by the detection technique and as no astrophysical meaning. Hence, the statistical approach used in based on incorrect assumption, neither the statistical approach will unbiased the result.

In conclusion, none on the clarifications added to the article resolved the flaw previously noted and in consequence, I think the paper should not be published in its present form.