Leslie puts forth is that the earth might be struck by a comet or an asteroid: “Of comets and asteroids whose orbits are such that they might some day hit the Earth, there appear to be around two thousand measuring between half a mile and six miles [1 and 10 km] in diameter.
” Aptuveni diviem tūkstošiem komētu un asteroīdu, kuru diametrs ir no viena līdz desmit kilometriem, orbītas ir tādas, ka tie kādu dienu varētu sadurties ar Zemi.