The theory basically posits that most of the planets and earth are moons that orbited around Saturn back in the day. The thought is that Saturn was in a "brown dwarf" mode of existence, where the moons/planets were engulfed in a semi-illuminated plasma cloud.
When Saturn got close enough to the sun, there was a discharge event removing the "atmosphere," the stars became visible, and also causing the beginning of a more pronounced day/night cycle.
Haven't read through all of it, so I'm somewhat paraphrasing. I think it's quite convincing though
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