They are often depicted as either little green men, bug-eyed creatures or terrifying monsters intent on wiping out all life on Earth.
But if aliens do exist, what might they actually look like?
MailOnline asked a number of experts what they think — both for potential extraterrestrial life within our own solar system, as well as on distant exoplanets in faraway galaxies.
Among the wide-ranging answers were features such as big brains, enormous wings and gravity-induced spindly frames, while 'crab or squid-like beasties', jellyfish-esque creatures and aliens that look almost human-like are also a possibility.
The latter might seem surprising given how aliens are often portrayed in popular culture, but some experts think if another intelligent civilisation exists, life could have evolved in a similar way to us.
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