Oxygen Isotope Fractionation Due to Non-Thermal Escape of Hot O from the Atmosphere of Mars

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is written at a good scientific level and the author relies on the measurements of the MAVEN mission. A comparison of different isotope systematics has made it possible to better assess the complex evolution of the Martian atmosphere. The author also points out some discrepancies with the isotopy of Martian meteorites and identifies possible ways to solve them. The minor disadvantages of the article include only a small list of references. Only the most basic and necessary papers are listed. It will be difficult for readers interested in this topic to understand the advantages of this model.

Author Response

I thank the reviewer for their report. I have not added any additional references, but I have added some new calculations and figures which I believe improve the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

It is a very interesting work. Author addressed the issue of loss of the atmosphere of Mars over the age of the planet, an issue crucial to our understanding of how Mars evolved to its present mostly dessicated state. The manuscript could be accepted in present form. If possible, I hope authors can answer my questions below:

 1.     Author used Rayleigh fractionation model to compute the results.

It seems like one model is not enough.

Could author try multiple models?

 

 2.     ‘ The fractionation factors (Figure 4) and the delta-values for the remaining atmosphere (Figure 7) are both dependent on the assumed temperature profile, which is from [6] (Figure S1).’

Are the assumptions here reasonable?

Comments on the Quality of English Language

good

Author Response

I thank the reviewer for their helpful comments. I have added a new model calculation, as suggested by the reviewer. The new model more properly accounts for the altitude dependence of gravity and temperature, as pointed out in point 2 raised by the reviewer.

Reviewer 3 Report

Comments and Suggestions for Authors

This is certainly a very interesting debatable theoretical study that provides important results about the mechanisms of oxygen isotope fractionation in the Martian atmosphere. This manuscript may be published in the journal "Atmosphere" in its current form. The research design is logical, the conclusions are reasoned, although debatable. This is a good example of qualitative research that should be read by the wider audience of journal "Atmosphere".

Author Response

I thank the reviewer for their comments. I'm not sure which results the reviewer considered to be debatable, but I've added new calculations that directly address the unexpected result of a 17O depletion resulting from hot O escape.