Chaotic Capture of a Retrograde Moon by Venus and the Reversal of Its Spin

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review Report:

The manuscript entitled `Chaotic Capture of a Retrograde Moon by Venus and the Reversal of its Spin’ is a beautiful contribution in the planetary science of observational level though is lacking a bit in connection to the theoretical aspects as well as mathematical techniques. However, the manuscript overall has been presented and written very clearly based on the simulation done by the authors and I therefore do recommend its acceptance in the journal Universe.

Comments for author File: Comments.pdf

Author Response

We thank the anonymous referees for the review reports.
As for the mathematical foundation of our manuscript, the tidal part is solidly based on the fundamental publications, which are quoted in the manuscript. We chose to enlighten our presentation avoiding copying the massive mathematical background on this topic. The frictional decay in a circum-Venus disk is our novel theoretical derivation, we believe, and it is presented in a greater detail.
In response to the second review, the point about the current obliquity of Venus on the ecliptic is a valid one, and we inserted a new paragraph in Summary addressing this issue. In our opinion, it strengthens the case for a retrograde moon that tidally decayed reversing Venus' spin in the process. Indeed, the angular momentum conservation principle dictates that the latitudinal component of tidal torque should equalize the initial obliquity of the captured moon on the equator of Venus, which was very likely different from the exact 180 degrees. This also points at a gaping hole in the current theory of tidal orbit evolution, which routinely omits the equatorial components of tidal libration and is approximately valid for small obliquity anyway. The updated text (v2) with new references is attached.

Reviewer 2 Report

Comments and Suggestions for Authors

Venus is an amazing planet of the Solar system and understanding its origin and evolution is certainly interesting. The authors used a well-developed mathematical apparatus and obtained reasonable conclusions. But, nevertheless, a number of questions remained unanswered. Perhaps the main thing is the tilt of the axis of planet' rotation (2.7 to the plane of the ecliptic). Its magnitude is not explained in any way in the calculations given. I think the paper is incomplete without this consideration.

Author Response

We thank the anonymous referees for the review reports.
As for the mathematical foundation of our manuscript, the tidal part is solidly based on the fundamental publications, which are quoted in the manuscript. We chose to enlighten our presentation avoiding copying the massive mathematical background on this topic. The frictional decay in a circum-Venus disk is our novel theoretical derivation, we believe, and it is presented in a greater detail.
In response to the second review specifically, the point about the current obliquity of Venus on the ecliptic is a valid one, and we inserted a new paragraph in Summary addressing this issue. In our opinion, it strengthens the case for a retrograde moon that tidally decayed reversing Venus' spin in the process. Indeed, the angular momentum conservation principle dictates that the latitudinal component of tidal torque should equalize the initial obliquity of the captured moon on the equator of Venus, which was very likely different from the exact 180 degrees. This also points at a gaping hole in the current theory of tidal orbit evolution, which routinely omits the equatorial components of tidal libration and is approximately valid for small obliquity anyway. The updated text (v2) with new references is attached.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

After adding new material, the conclusions of the article became better substantiated. Venus is a special case of the planets motion at the Solar system and the obtained results are of interest.