A principal task in writing in the first edition of this book was to examine the series of events that led to the formation of the solar system. The conclusion, so greatly illuminated by the previous three decades of planetary exploration by spacecraft, was that random events had predominated in the construction of the great variety of planets and satellites. Thus it was unlikely that duplicates might be found elsewhere. This was in contrast to earlier views that the solar system was as orderly as a clock and that, given sufficient computer power, one might simulate the construction of such a clockwork system from first principles according to the laws of physics and chemistry.

In the 1992 edition, I commented that “the … common occurrence of disks around young … stars strengthens the case for the existence of other planetary systems. If so, would they resemble our own? Would we see something like the Galilean satellite system of a few equal-sized planets, systems with one giant planet, or a single brown dwarf companion?” After contemplating the satellite systems around our giant planets, I concluded that “no simple sequence of reproducible events has occurred in our solar system. Other planetary systems … will be different in detail to our own. What their satellites might look like is only for bold spirits to predict” (p. 251).