He also maintained that planets were expelled, one at a time, from the Sun, specifically from an equatorial bulge caused by rotation, and that one hypothetical planet shattered in this expulsion, leaving the asteroid belt. The Kuiper Belt was unknown at the time, but presumably it, too, would have resulted from the same kind of shattering. The moons, like the planets, originated as equatorial expulsions from their parent planets, with some shattering, leaving the rings, and the Earth was supposed to eventually expel another moon.