udy of the idea in the nineteenth and twentieth centuries (Dick 1-2).
Dick notes how science has examined each of the planetary bodies in this solar system over the centuries and come to the conclusion that they could not be inhabited, at least at this time. This led to an even broader problem, the issue of other planetary systems and whether they could harbor life:
As the Copernican theory generated the search for an inhabited moon and solar planets, so theories of the origin of solar systems--passing beyond the mere analogy that the stars were sunlike--generated a search for other solar systems. So great were the difficulties of this search, that serious observations were not undertaken until the first half of the twentieth century, with results that even then were ambiguous, controversial, and laden with different interpretations (Dick 184).
Plank notes the assessment scientists have given to the possibility of life on other planets and in other solar systems and finds that there is some reason to assume that there could be intelligent life beyond our world. Attention has been given to the number of possible suns there may be in the universe, the number of worlds that may be circling those suns, the number of those planets with the proper configuration of circumstances to support life, the number that may actually do so, and so on, up to how many may have life at least at our level of intelligence. Plank cites Dr. Frank Drake of Cornell University "that by the most optimistic reckoning we may expect communication signals form one-fourth of all stars, while Shapley thinks that life may exist near but one star in a million" (Plank 62). This makes a difference in estimates of 250,000 times from highest to lowest.
Plank points out the difficulties involved in communicating with beings from another solar system, let alone in having them visit. A trip to the nearest star at the present speed of our fastest rockets wo...