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132 Such scenarios raise their own risks. Would these young humans have any sense of connection with those who sent them? Children developing without committed human parents, warned Mauldin, may lack some essen- tial qualities.*° Human voyagers might not need to travel all the way to another sun. The space between the stars is not empty; there are stepping stones. Our solar system and others extend much farther into interstellar space than we once thought. There could be huge numbers of icy planetoids far beyond Pluto, including some that are Pluto’s size or larger. Beyond the Kuiper Belt, the enormous cloud of icy bodies hypothesized by astronomer Jan Oort may reach out an estimated 3 light-years; other sun-like stars may be girded by similar clouds.*! If Alpha Centauri has a cloud of similar scale, its cloud will overlap with ours. “Any civilization that spans our Oort Cloud,” wrote space coloniza- tion advocate Mark Hopkins, “also will expand into the Alpha Centauri Oort Cloud.” He described this as “a star bridge” between stellar systems.” Bodies similar to comet nuclei may pervade our Galaxy; the average distance between them might be only light-days instead of light-years. This would make the Galaxy a much friendlier place for interstellar travelers.** Extraterrestrials too could take advantage of such stepping stones. The Last Migration When the sun has exhausted its energy, it would be logical to leave it and look for another, newly kindled star still in its prime. —Konstantin Tsiolkovskii™ Why would we send humans, in whatever form? MacVey concluded in 1977 that were fusion drives permitting interstellar transit times of about a century to the nearest stars the ultimate in propulsion tech- niques, manned interstellar flight could probably never be made for purposes other than colonization. Your present author independently published a similar conclusion during the same year. Even if migration seems like a remote prospect now, one factor may drive our descendants to journey away from their star. Roughly a billion years in our future, our Sun will expand to consume the Earth and the other inner planets. Long before then, physical conditions on the Earth would become intolerable (some predict that the Sun’s increased lumi- nosity will make the Earth uninhabitable sooner, in about 500 million years). Mautner suggested that survivors could continue to exist by adjusting their distance from the star as it evolved. However, migrating farther Direct Contact