Is there any theory that prohibits planets that are not in solar systems?
I see we keep looking for planets in other galaxies.
Couldn’t there be some between us and the next star, just floating free?
Maybe formed on their own without enough mass to become even dead “stars”.
Or maybe ejected from an exploding star.
Whatever the case, they should be possible. And they could have enough internal heat for volcanic action and thus sustain life without a sun.
But I’ve never heard anyone looking for something like that.