Are aliens real or are we alone in our universe?
FOR thousands of years humans have asked whether we are alone in our universe. But could extraterrestrial life exist on other planets?
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?
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NASA believes that exoplanets – planets that orbit stars other than our Sun – have the best chance of hosting alien life.
Scientists have discovered more than 3,300 exoplanets, and are looking for Earth-like bodies that are capable of having liquid oceans.
The US space agency is also looking at four celestial bodies within our solar system that they think could host microscopic life forms.
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."
But he has insisted that humans are unique and ruled out intelligent life existing anywhere else but Earth.
“There is only one advanced technological civilisation in this galaxy and there has only ever been one – and that's us,” he said.
Professor Cox believes that humanity’s evolution from single-celled organisms to intelligent beings was a “an incredibly unusual fluke” that could not be repeated anywhere else.
Professor Stephen Hawking has warned that humans are not likely to discover alien life within the next 20 years. He says “the probability is low”.
The cosmetologist has backed a new Russian venture that hopes to send miniature spacecrafts to other universes to search for life.
UFO captured over space progress capsule
Is there any proof of aliens?
While there has never been any official proof of extraterrestrial life, many have claimed to have spotted aliens and UFOs.
Most recently, a video emerged which allegedly shows two spacecrafts flying around the International Space Station (ISS).
NASA has announced that it will no longer stream the ISS camera online. Conspiracy theorists called the move a “cover-up”.
Others have claimed to have spotted extraterrestrials who have visited Earth with some even reporting alien invasions.
Scott C Waring, editor of UFO Sightings Daily, claims to have found an alien base in Argentina, South America.
As well as pictures and videos, many scientists have found mysterious radio signals coming from space.
Just this week, Russian astronomers picked up an unknown signal that some think could have originated from an advanced civilisation.
Scientists have been discovering space signals since 1968, when Jocelyn Bell Burnell picked up radio beams that were exactly three seconds apart. They turned out to be from a pulsar star.