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Four-and-a-half billion years ago, our planet suffered the nearest miss imaginable. Theia, a rogue planet the size of Mars, crashed into an infant Earth. Earth itself survived, but nothing was the same ever since. Tectonic plates form. Earth has a fairly large moon, the largest in relation to the parent of the entire solar system. The crash of Theia had created the moon and tipped Earth to the extent of having seasons.

To that end, for the existence of an alternate Earth with a vertical axial tilt--an axial tilt that discourages the development of seasons--how different would the moon have to be, in regards to origin, orbital trajectory, geology, chemistry, etc.?

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  • $\begingroup$ Probably "no axial tilt" would sound better than "vertical axial tilt" $\endgroup$
    – L.Dutch
    Dec 9, 2020 at 3:54

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This is simply a problem in physics. It is a matter of two large bodies colliding and the vectors adding up. Therefore the Moon could be identical in geology and chemistry.

I also note that Mars has an axial tilt similar to Earth, where Venus is just about straight up and down though inverted from Mars and Earth, and neither one has a moon as large as ours. There is no reason to think that the Earth had no tilt before the collision.

Therefore, Theia could crash at a slightly different angle, or Earth could be at a different axial tilt before it -- or both. As long as the vectors add up.

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