Mercury has an unusual composition: It seems to consist mostly of metal, which is otherwise common in the cores of planets. Also, Mercury's rocks are rich in volatile materials, which could not have formed as near to the Sun as Mercury is today (cf. https://www.ldeo.columbia.edu/news-events/messenger-data-reveals-evidence-ancient-carbon-rich-crust-mercury). Therefore, astronomers have conjectured that some cataclysmic event (eg. a collision) might have thrown Mercury closer to the Sun and ripped off most of its crust.

Now the question is: What became of the crust? And since the asteroid belt is not very rich in metal (or is it? Did I misunderstand?), I wonder whether its origin might have been said collision (probably with Mars, or possibly with Ceres).

Also, the asteroid belt is rather carbon-rich, just like the remnant of Mercury's crust (https://progearthplanetsci.springeropen.com/articles/10.1186/s40645-019-0312-z). Coincidence?

Perhaps, one could even make sense of it from a physical perspective: Crust and mantle might have "repelled" each other, that is, by Newton's principle of contrary motion, the two would have travelled in different directions, Mercury inwards and the debree outwards. (EDIT: To clarify this point: An object might have hit primordial Mercury, causing its crust to separate from what's now Mercury, so the crust may have first pushed Mercury, and then seperated and went off in the opposite direction.)

Also, the mass of the asteroid belt is little enough so that all could have come from Mercury's former crust. Indeed, it totals roughly twice the mass of Pluto's moon Charon.

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    $\begingroup$ Crust and mantle might have repelled each other Why would they repell each other ? $\endgroup$ Jul 31, 2021 at 3:05
  • $\begingroup$ @StephenG Of course, the motion would have been initiated by the object primordial Mercury may have collided with. $\endgroup$ Jul 31, 2021 at 9:35
  • $\begingroup$ @uhoh In case you are unable to manage to google it yourself: Here is one of the returns of a search for "messenger mission mercury volatile sulphur formation": ldeo.columbia.edu/news-events/… This is, by now, a standard fact in astronomy. $\endgroup$ Jul 31, 2021 at 9:47
  • $\begingroup$ It additionally speaks of a "carbon-rich crust", and guess which material is abundant in the asteroid belt... $\endgroup$ Jul 31, 2021 at 9:49
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    $\begingroup$ @AlgebraicsAnonymous questions should support their premises with facts supported by citing sources. Whether I know something not, we shouldn't expect every reader to go google things after reading each question. It would be better if you added a few sentences to your question citing those sources for the benefit of all readers, many folks don't go through all the comments before deciding how they are going to vote. Thanks! $\endgroup$
    – uhoh
    Jul 31, 2021 at 14:23


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