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> People dismiss that as astronomically unlikely, but it must have happened many times somewhere in the universe

It's hypothesised that a Mars-sized planet once collided with Earth in the early history of the solar system (about 4.5 billion years ago), creating our moon today:

https://en.wikipedia.org/wiki/Giant-impact_hypothesis

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Right, and a more recent paper suggests the reason for the seas on the near side of the moon is that the earth temporarily shone like a star, whereas the moon being smaller cooled faster overall. So the moon was melted by earthshine.

Not sure that quite meets this definition, but there's a newly named object Synestia that sounds pretty similar.

https://en.wikipedia.org/wiki/Synestia

A very close sub-brown dwarf: https://en.wikipedia.org/wiki/WISE_0855%E2%88%920714

> So the moon was melted by earthshine.

Do you have any links with more info on this?

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