Why did the Moon form differently on the near side and the far side? The near side has many mare, where the crust was thinner and lava came out after the moon was impacted by meteors. But why was the crust on the near side thinner?

Related: Why is the Far Side of the Moon so different from the Near Side?

(Note: The above explains that the crust is thinner, but not why.)


1 Answer 1


It has been proposed that Earthshine, i.e. light and heat from the molten Earth after the Moon forming impact when the Moon was much closer, heated the near side of the tidally locked Moon and that this caused the differences in crust thickness by allowing different materials accrete and condensate as the Moon cooled. Basically, more of the crusty materials condensated on the colder far side, to put it in the blunt way that I can relate to.

I (not being a scientist) would think that tidal forces played an important part too. Causing different volcanic activities on the near and far sides. The only somewhat similar system is the tidally locked Pluto/Charon system and maybe something could be learned from how their crusts are differentiated from facing and opposing hemispheres.

Mars too has a basic dichotomy in its topography, although not obviously related to any companion present or past.

  • $\begingroup$ That's interesting! It looks like the use of the term "Earthshine" in that paper refers to thermal radiation from an earlier, hotter Earth, and is not to be confused with the other use of the word which refers to reflected sunlight that for example makes the dark part of a crescent moon still visible at night. $\endgroup$
    – uhoh
    Commented Jan 11, 2017 at 2:24

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