The Ancient Greek philosopher and scientist Aristotle first suggested the Earth was not alone in 350 BC.
Since then, man has grown more curious and science more advanced, with countless experts dedicating their lives to searching for life beyond our planet.
But could there be aliens out there?
Without any definitive proof, experts have speculated if alien life exists and where it could be.
A NASA scientist recently confirmed that the space agency is looking for signs of extraterrestrial life and hopes to have an answer within the next 10 years.
James Green, the agency’s planetary science director, said: "We're hot on the pursuit. We're concentrating our attention on four locations - the planet Mars and then three moons of the outer planets: Titan, Europa and small Enceladus."
NASA believes the four celestial bodies have the best chance of hosting microscopic forms of life.
Professor Brian Cox said that Pluto could also be home to basic lifeforms after new photos proved the planet is still geologically active.
But he has insisted that humans are unique and ruled out intelligent life existing anywhere else but Earth.
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