This word can have two meanings: referring to an object indicates any body or physical situation that is outside our planet; referred to biology, any vital form (or one of its basic elements) developed outside our planet.

One of the most debated problems by Astrobiology is the existence of living beings and intelligent forms on other planets. Astrophysics has contributed to the resolution of this problem by demonstrating that the same natural laws and chemistry predominate throughout the explored universe. Therefore, most of today's astronomers believe that the repetition of conditions analogous to those verified on the young Earth may have led, on eventual planets of other stars, to the development of living forms similar to those of our planet.

The aliens, in the sense of intelligent beings that could live in other places, have thus become exclusive characters of science fiction novels, in a hypothesis formulated on a scientific basis.

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ExplorerExtra-vehicular (activity)