Astronomers have searched for extraterrestrial civilizations in planetary systems for sixty years, to no avail. In the paper published by International Journal of Astrobiology, Cambridge University Press, and titled “Migrating extraterrestrial civilizations and interstellar colonization: Implications for SETI and SETA,” Irina K. Romanovskaya proposes that the search for extraterrestrial intelligence (SETI) may have more chances to become successful when including the search for migrating extraterrestrial civilizations. For example, extraterrestrial civilizations may leave their home planetary systems when they face existential threats. One of the ways to do so is to ride free-floating planets. Free-floating planets can offer space and resources, as well as protection from space radiation, for very large populations embarking on interstellar travel. It is most likely technically impossible that huge starships, also called world ships, can offer the same.
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