aliens

Aliens is a term with multiple meanings. In law and immigration contexts, an alien is a person who is not a citizen of the country in which they reside. In astronomy and popular culture, the word is used to describe life that did not originate on Earth.

Exobiology or astrobiology studies the possibility of extraterrestrial life, ranging from microbial organisms to intelligent civilizations. To date, no confirmed discovery of life beyond Earth exists. Scientists search for life by assessing planetary habitability, detecting biosignatures in atmospheres, and studying the chemistry that could support life.

Efforts to find evidence of intelligent life include the Search for Extraterrestrial Intelligence (SETI), which examines signals from space for non-random patterns. Exoplanet surveys identify planets in or near the habitable zone of their stars, and missions such as Mars rovers, the Europa Clipper, and Dragonfly investigate environments that could harbor life. The Drake equation and the Fermi paradox are theoretical tools used to frame questions about the prevalence and detectability of extraterrestrial civilizations.

Speculation about alien life often ranges from microbes to sophisticated societies. Most scientific discussions emphasize broad possibilities, noting that life—if it exists—could feature different biochemistries or reside in oceans beneath ice, on planets with extreme conditions, or on moons with chemical energy sources.

In popular culture, aliens are frequent subjects of science fiction, film, and literature, often reflecting human hopes and fears about contact, coexistence, and the ethics of exploration. The term itself remains controversial and context-dependent, underscoring distinctions between official terminology and storytelling.