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The "science" is called Astrobiology, the famous "science in search of a subject". You can keep up on the latest news, but for now if you want aliens, you are going to have to create them yourself.Suggested reading includes The Encyclopedia of Science Fiction's entry on "Aliens", Steve Colgan's Worlds of Possibility blog, Life Everywhere by David Darling, The Science of Aliens by Clifford Pickover and Aliens and Alien Societies by Stanley Schmidt.[first use unknown, but goes back at least to 1940s]General SF term for an extraterrestrial or alien possessing human-level intelligence (see sophont).Exosemanticists have their work cut out understanding them, and exopsychologists in figuring out what they're all about.Relations between humans and Really Aliens are necessarily limited, since we have so little in common with them.
Much more common - especially in HOLLYWOOD SCIFI - than Really Aliens, these are species that look almost exactly like Earth Humans, except for some distinguishing visible feature such as, well, forehead ridges, or odd-shaped ears, or whatever.
Sometimes they look rather less like humans, in which case (if friendly) they often resemble large teddy bears.
Not only do Aliens with Forehead Ridges mostly look like Earth Humans, they tend to act like Earth Humans as well, or at least one particular (real or speculative) Earth Human culture.
A particular race of Aliens with Forehead Ridges may all have a culture like that of medieval Japan, or one based entirely on music, but you will very rarely find more than one culture per species.
(The Vulcans and Romulans of Trek fame are a rare exception.)Because of the similarity (or at least comprehensibility) of cultures, Earth Humans can have far more complex and intimate relations with Aliens with Forehead Ridges than with Really Aliens.