Alternative hypotheses for making the Moon

Stevenson replies: I thank these letter writers for their alternative suggestions. Actually, neither is really new, and my failure to mention them—or others—is not because I was unaware of their existence, but rather because of the major challenges that these alternatives must overcome. In the Lagrange point scenario, which is widely known in the community, the challenge is to devise a story in which such bodies naturally arise in the context of a model that explains the planetary system, not just Earth–Moon. It is not sufficient to postulate them. A new paper¹ might suggest that the similarity of the impacting body and target is not so unreasonable. In the more astonishing fission story, the challenge lies in the basic physics of the proposed process, which is questionable.