"We know that the moon Charlie was on was our Moon—because we found him there, because we can identify the areas of terrain he described, because we have ample evidence of a large-scale Lunarian presence there, and because we have proved that it was the scene of a violent exchange of nucleonic and nuclear weapons. But that same place must also have been the satellite of Minerva. It was only a two-day flight from the planet—Charlie says so and we're confident we can interpret his time scale. Weapons were sited there which could pick off targets on Minerva, and observations of hits were almost instantaneous; and if all that is not enough, Charlie could stand not ten yards from where we found him and distinguish details of Minerva's surface. These things could only be true if the place in question was within, say, half a million miles of Minerva.

"Logically, the only explanation is that both moons were one and the same. We've been asking for a long time whether the Lunarian civilization developed on Earth or whether it developed on Minerva. Well, from the account I've given, it's obvious it was Minerva. We thought we had two contradictory sets of information, one telling us it was Earth and the other telling us it wasn't. But we had misinterpreted the data. It wasn't telling us anything to do with Earth or Minerva at all—it was telling us about Earth's or Minerva's moon! Some facts told us we were dealing with Earth's moon while others told us we were dealing with Minerva's moon. As long as we insisted on introducing, quite unconsciously, the notion that the two moons were different, the conflict between these sets of facts couldn't be resolved. But if, purely within the logical constraints of the situation, we introduce the postulate that both moons were the same, that conflict disappears before our eyes."

Shock seemed to have overtaken the audience. At the front somebody was muttering, "Of course . . . of course . . ." half to himself and half aloud.

"All that remains is to reconcile these propositions with the situation we observe around us today. Again, only one explanation is possible. Minerva exploded and dispersed to become the Asteroid Belt. The greater part of its mass, we're fairly sure, was thrown into the outer regions of the Solar System and became Pluto. Its moon, although somewhat shaken, was left intact. During the gravitational upheaval that occurred when its parent planet broke up, the satellite's orbital momentum around the Sun was reduced and it began to fall inward.