Generations of scientists have tried to explain how the solar system began. None of the explanations is wholly adequate. The trouble is that the solar system is not a haphazard collection of planets buzzing around the sun. It has remarkable "regularities" which indicate that all its major members had a common and systematic origin.
The planets, for instance, revolve in the same direction and in almost the same plane. The four inner ones (Mercury, Venus, Earth, Mars) are smaller and denser than the outer ones (Jupiter, Saturn, Uranus, Neptune). Perhaps the most remarkable peculiarity is that the outer planets possess almost all...