There was a serious point to Moore's joke. Jupiter is massive, but it's far away from us. Our Moon has more of a gravitational effect on Earth than Jupiter does. As for Pluto, it's smaller than the Moon and about six times as far away from us as Jupiter. Moore was ridiculing a popular book that predicted the dire consequences of a rare planetary alignment that would happen in 1982. All of the planets would be on the same side of the Sun as the Earth and the tidal effects would create massive earthquakes. In particular, Los Angeles would be destroyed.