In short, if ‘Oumuamua was a natural object, it had to have been generated by planet formation. It also has to belong to an unknown class of objects generated by planet formation whose size, shape, and composition make them deviate from a path shaped solely by our Sun’s gravity without any visible outgassing. At the time of this writing, we know of no other object that fits the second set of criteria. But we know of at least one that fits the first.
