Modern sovereignty is anthropocentric, constituted and organized by reference to human beings alone. Although a metaphysical assumption, anthropocentrism is of immense practical import, enabling modern states to command loyalty and resources from their subjects in pursuit of political projects. It has limits, however, which are brought clearly into view by the authoritative taboo on taking UFOs seriously. UFOs have never been systematically investigated by science or the state, because it is assumed to be known that none are extraterrestrial. Yet in (...) fact this is not known, which makes the UFO taboo puzzling given the ET possibility. Drawing on the work of Giorgio Agamben, Michel Foucault, and Jacques Derrida, the puzzle is explained by the functional imperatives of anthropocentric sovereignty, which cannot decide a UFO exception to anthropocentrism while preserving the ability to make such a decision. The UFO can be "known" only by not asking what it is. (shrink)