Introduction
Mankind has always wondered, "Are we alone in the Universe? Isn't there life out there somewhere?" With an estimate around 300 billion stars in the Milky Way galaxy alone, many with their own satellites, the possibilities seem likely that some form of life should exist somewhere in the Universe. This search for life begins with a definition of life itself, followed by possible candidates both within and outside our solar system, and also includes what measures are being taken to find these life sources and justify their existence.
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