Extraterrestrial life is life originating outside of the Earth. Its existence remains hypothetical; there is no evidence of extraterrestrial life that has been widely accepted by the scientific community.
Most scientists believe that if extraterrestrial life exists, its emergence occurred independently, in different places in the universe. An alternative hypothesis is panspermia, which suggests that life might emerge in one location and then spread between habitable planets. These two hypotheses are not mutually exclusive. The study and theorization of extraterrestrial life is known as astrobiology or xenobiology. Speculative forms of extraterrestrial life range from sapient beings to life at the scale of bacteria.
Suggested off-Earth locations that might have once developed or continue to host life include Mars, natural satellites of Jupiter and Saturn (e.g. Europa and Titan), and most recently Gliese 581 c, which is the only known extrasolar planet in its star's habitable zone and is predicted to have liquid water.