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Earth's Moon is thought to have been created in a glancing collision with a Mars sized planet.

I've just seen an expose on Mercury which claimed Mercury: formed in the region between Earth and Jupiter, migrated to it's current orbit through an unknown interaction, consist of 60% core material which was explained as the result of a glancing blow with a planet sized object.

Has anyone looked in to whether a Mercury/Earth collision could be the creator of our Moon?

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  • $\begingroup$ That Mars-sized planet destroyed. Mercury now exists. Maybe if the collision created three major bodies (Earth, Moon and Mercury), and Mercury has somehow got a trajectory what slowly shifted it into its current orbit... I would not say that it is impossible, but extreme unlikely. Here is the orbit of the Parker Solar Probe, it uses the Venus to get near to the Sun, imagine the probability of this to happen randomly. $\endgroup$ – user259412 Jul 26 at 19:13
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There's a principal in science that a strong hypothesis doesn't depend on numerous improbable factors. I read that somewhere, I think it was Phil Plait who created the bad astronomy website, but I can't find it right now.

For Mercury to have done what you claim, a 2nd planet would have needed to form between Earth and Jupiter, OK, maybe that happened, in fact, the young solar system was probably full of protoplanets.

This planet would then have needed to change it's orbit. This usually takes a more massive planet to toss the smaller one, but there's two problems here. Could Mars push Mercury all the way into Earth's orbit? Probably not. Could Jupiter? Sure, but then, where did Mercury get all it's Iron if it formed between Mars and Jupiter. It's becoming problematic.

Planet on planet collisions are rare, obviously not impossible.

Then there's the problem of how did the collison result in Mercury flying off, losing some material, the moon forming and Earth rapidly rotating. Planet on planet collisions tend not to be glancing blows because planets are too big, and gravitational wells are pretty deep. I don't want to say it's impossible but that's an odd scenario which seems highly unlikely.

And then, Mercury changes it's orbit again, perhaps gravitational assist from Venus and it ends up where it is.

A hypothesis like that depends on that many rare events all happening isn't not going to be a popular one. Building a hypothesis on a single improbable event is fine. The giant impact theory began like that.

A good hypothesis also has evidence behind it. Mercury looks like it formed about where it is now, clearing out it's orbital neighborhood and being made up of denser material that was more likely to orbit closer to the sun. There's very little reason to stand behind the Mercury impacted Earth idea and there's no evidence to support it.

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  • $\begingroup$ Thank you for your answer. I thought it was an interesting question and put it here as the answers are most often well thought out. $\endgroup$ – Kevin Burke Jul 27 at 22:25
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It is highly improbable that the moon was created by a collision between Earth and Mercury, or that there has ever been such a collision. The idea that Mercury was formed in what sounds from your description like the asteroid belt and from there migrated to its present orbit, striking the Earth on the way, is pure speculation and there is no evidence for it. Nobody has ever taken the idea seriously enough to spend a lot of time and effort and possibly money looking into it. And if Mercury can go blundering about the solar system, bumping into obstacles on its way, how do we know that Mars won't do the same thing one day?.

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