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352 never had sent such signals, as well as societies that had ceased doing that long ago. Probes also might reveal future habitats for humans—Earth-like planets, or asteroidal and cometary resources that could support artificial worlds. After the initial detection of another civilization, we would want to gather as much additional information as possible—their proximity, their technological capabilities, their intentions. Only their proximity would be relatively easy to determine. We also would want to know if there are additional extraterrestrial societies. Other technological civilizations are potential competitors, particularly if they are relatively nearby. They also are potential allies who might help us to improve our prospects for long-term survival. The more we learn about civilizations that may exist elsewhere in the Galaxy, the better our policy decisions will be. Only fools do not surveil their surroundings, for opportunities as well as for dangers. Exploring the solar system and homesteading other worlds constitutes the beginning, much more than the end, of history. Dad On ~.- 100424 Shall we be forever one people, or shall we be a million intelligent species exploring diverse ways of living in a million different places across the galaxy? Te we Tee 107025 We humans will use the information we gather in formulating policies for human activities beyond the Earth. One policy decision may be to accelerate the expansion of human presence and influence into the solar system and beyond. Spaceflight advocates have argued for decades that human expansion is not a frivolous waste of money, but a survival strategy. All life on Earth, including its most intelligent species, will come to an end some day due to changes in the biosphere or the Sun, or an astrophysical accident. Sagan, who earlier in his career had questioned the utility of sending humans into space, came to advocate expansion and colonization late in his life. Every planetary society is obliged to become spacefaring, he argued, not because of exploratory or romantic zeal, but for the most prac- tical reason imaginable: staying alive. The spread of Humankind through the solar system would be the best insurance against any fatal catastrophe arising from external or internal threats. The more of us beyond the Earth, the greater the diversity of worlds we inhabit, the more varied the planetary engineering, and the The Human Role Expansion —Carl Sagan, 1994” —Freeman Dyson, 19797