Astrobiology and the Search for Life

Concepts from the study of whether, and how, life might exist elsewhere in the universe and how humanity might detect or become such a civilization itself: the Drake equation estimating the number of communicating civilizations, the Fermi paradox asking why none has been detected, the Great Filter proposed to explain that silence, the habitable zone in which liquid water can persist on a planet's surface, and the hypothetical Dyson sphere and self-replicating Von Neumann probe as signatures a civilization might leave. Belongs here: a concept from the search for extraterrestrial life or the reasoning behind it. Does not belong here: a concept about the universe's origin or structure, grouped under Cosmology and the Early Universe, or a concept about spacecraft maneuvers, grouped under Orbital Mechanics and Spaceflight Engineering.