What is Extraterrestrial Life?

Extraterrestrial life is defined as life which does not originate from Earth. It is the subject of astrobiology and its existence remains hypothetical, because there is no credible evidence of extraterrestrial life which has been generally accepted by the mainstream scientific community. Hypotheses regarding the origin(s) of extraterrestrial life, if it indeed exists, are as follows: one proposes that it may have emerged, independently, from different places in the universe. An alternative hypothesis is panspermia, which holds that life emerges from one location, then spreads between habitable planets. These two hypotheses are not mutually exclusive. The study and theorization of extraterrestrial life is known as astrobiology, exobiology or xenobiology. Speculated forms of extraterrestrial life range from life at the scale of bacteria to sapient or sentient beings.