They’re on Europa, they’re already dead or they’re walking among us… here are the top theories about alien life

IT sounds like science fiction, but aliens are almost certainly out there somewhere, given the possibly infinite size of our universe.

But if extraterrestrials do exist, that begs the question: why haven’t we found them yet?

There are actually plenty of exciting theories about where aliens are lurking – and some scientists even believe that alien life is lurking in our solar system.

Other theories are a bit more wild, such as the suggestion that we’ll never find aliens because they’ve already died out.

Given that they are (or at least were) out there, here are the best guesses about where we can find extraterrestrials.

They’re walking among us
It sounds a bit too out-there to be true, but maybe aliens have already found us – and we just don’t know it yet.

Super-intelligent aliens could have disguised themselves as humans to live alongside us on Earth, where they study and experiment on humans.

And if not fully-evolved aliens, extraterrestrial bacteria or single-celled life may have made it to our planet by hitching a ride on an asteroid.

Physicist Paul Davies believes that this claim isn’t as crazy as it sounds, saying that alien life may be “right under our noses, or even in our noses.”

They’re on Mars

For hundreds of years, scientists and alien enthusiasts have looked to Earth’s neighbouring planet as part of the search for extraterrestrial life.

Some researchers claim that microscopic life could have once existed on the Red Planet, which still has small amounts of liquid water – a key ingredient for life – on its surface.

Others claim that life is still there, after a 2005 study suggested that Mars’ atmosphere has methane in it which could have been produced by primitive Martians.

They’re on Europa
Even better than the small reserves of water on Mars, Jupiter’s moon Europa is believed to have entire oceans underneath its icy surface.

This means that life could exist around underwater vents, which would allow simple lifeforms to evolve – similar to those at the bottom of Earth’s oceans.

NASA intends to take samples from the icy moon to see if it’s possible that life could be thriving in our own solar system.

They’re in another star system
As exciting as alien life in out own solar system is, it’s far more likely that we’ll find developed extraterrestrials further afield.

Three Earth-sized planets were recently found orbiting a star known as Trappist-1, and the planets are all roughly the right distance from their star that they could sustain life.

Alternatively, life could be lurking on an Earth-like planet orbiting our neighbouring star, Proxima Centauri, after scientists found it was also in the sweet spot for sustaining life.