Far Out Planets

About 30 years ago, the pioneering SETI (Search for Extra-Terrestrial Intelligence) work of Pat Morrison and Carl Sagan included a calculation of the probability of finding intelligent life elsewhere. Their formula is simply the multiplication of probabilities, based on an assumed sequence of development leading to intelligent life and technical civilizations. The multiplication simply represents the collective result of the odds of succeeding at each step. For example, if there is one chance in 4 that an egg will roll over, and one chance in 2 that an egg is beige, then there is one chance in 8 (2 * 4) that a beige egg will roll over.

The controversial part of the formula is the sequence of development. Just what is required to produce an intelligent creature? Will intelligent species necessarily proceed to technical civilization? Would they flourish in our time, not before or after us? Even so, would other advanced species want to talk or stalk? Obviously, no one knows the exact answers to those questions, but there have been innumerable speculations.

The current work in extra-solar planets brings us a little nearer to an answer. It looks like that at least 1/4, and maybe 1/2 or more, of stars similar to our Sun are associated with some form of solar system. This should not be surprising in view of the high probability of binary and triplet star systems among smaller stars. When a gaseous nebula collapses to form a star, not all of the material gets absorbed into one central star. The pre-solar nebula is turbulent and influenced by inter-stellar shock waves produced by nearby stars. Thus, the cloud might break down into several eddies, each of which forms a smaller star. Or, the solar nebula may precipitate chunks of material in relatively stable orbits that eventually become comets, asteroids and planets. So, planetary systems and multi-star systems are on a spectrum representing the evolutionary states of solar nebulae.

The high probability of planetary systems means there are more chances to develop life and intelligent life than previously thought. When Morrison and Sagan did their original work, it was thought we might be the only technical civilization in the Milky Way galaxy. Our galaxy has more than 100 billion stars, so that made life a pretty unlikely prospect. The work of the last decade undoes that pessimism, increasing the odds by a factor of 100 or more that we are not alone. It is clear, for example, that once Darwinian processes take hold, there will be a strong tendency for living things to evolve in our direction. So, the evolution of humans is not as chancy as once thought. Taken together, if present science suggests there are 100 or more civilizations similar to our own in our Galaxy, the Milky Way, we can have a reasonable expectation of meeting Them someday.