Rather than forming in place, Triton is thought to have been captured by Neptune from the Kuiper Belt, a sort of cosmic junkyard beyond Neptune's orbit.
When I was very young, that was the battle between them: Mother trying to hold school every morning, and Dad herding the boys into the junkyard the moment her back was turned.
I pictured my brothers pushing out the door to search for me. They'd try the junkyard first, hefting iron slabs in case some stray sheet of metal had shifted and pinned me.