Concluding remarks

Abstract

This discussion on the origin of the Solar System has quite rightly focused on the chemical evidence. Harold C. Urey was fond of quoting Edward Teller’s remark about the atomic bomb: ‘ Its physical effects disappear quickly but its chemical effects are lasting’. The chemical evidence, particularly the abundance of elements and isotopes, obtained from meteorites, by ground-based astronomical methods and from space missions continues to be the starting point for inferring the processes by which the Solar System came into being and reached its present configuration. When the origin of the Solar System was first discussed it appeared a natural assumption that the material from which the planets were made came from the Sun. Similarly before the importance of radioactivity in the Earth was recognized it seemed obvious that the planets originated as liquid drops by condensation from gases drawn from the Sun. The fact that the Earth’s gravity field, for example, was almost exactly that of a hydrostatic body in equilibrium, under its self-gravitation and the centrifugal forces due to rotation, made this assumption a natural starting point. It was the discovery of the interstellar dust clouds by astronomers that first provided evidence for a nebula theory. We have been correctly reminded in this discussion that the idea of a close approach of another star from which material was drawn out by the Sun is still a possible theory, and it is entirely in the interest of a scientific approach that it should be further investigated so that its predictions can be more thoroughly tested.