The chances of anything living on Mars is a question puzzled over by scientists and musicians alike.
But they can all stop musing over this extra-terrestrial mystery, apparently, because a UFO hunter reckons he's found '100 percent proof' that there is life on Mars.
Scott Waring runs YouTube page UFO Sightings Daily, which does exactly as it says on the tin - and yesterday's offering was seemingly pretty massive.
The UFO detective said he spotted an alien figure watching the Mars rover; what's more, this 'alien figure' appears to be some kind of human.
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Explaining his '100 percent proof', Scott scanned over an apparent picture of the surface of Mars and honed in on a 'foot tall' figure.
He said: "There is an object right over here and I swear to God it looks like a human being, laying down on a beach.
"Can you see this person laying down on one shoulder, there arm over here, there neck exposed, you can see the pinkness, they have reddish hair there?
"There is even a trail of footprints going across the top of this rock. Can you see the trail right here of the dirt that's been disturbed?
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"That is incredible, isn't it? It shouldn't be possible and yet we're looking right at it."
So not only is there life on Mars - that life is human life. Either that or Scott has mistaken 100 percent proof of life for a rocky shadow that looks a bit like a person lying on their side. You be the judge.
You can watch the whole video here:
If you're one of those people who doesn't accept unverifiable images on YouTube channels as '100 percent proof' of alien life, then perhaps a study by NASA will be more up your street.
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Rocks collected by the Curiosity rover were reviewed by NASA and found to contain organic carbon, which could potentially have come from bugs that previously lived on Mars.
NASA analysed sediment from six different locations the rover had explored and found an ancient carbon cycle.
The samples could have a 'biological basis', according to NASA, and resemble fossilised remains of microbial life that have been found in Australia.
Professor Christopher House, the lead author of the study from Penn State University in the US, told Metro: "The samples extremely depleted in carbon 13 are a little like samples from Australia taken from sediment that was 2.7 billion years old.
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"Those samples were caused by biological activity when methane was consumed by ancient microbial mats.
"But we can't necessarily say that on Mars because it's a planet that may have formed out of different materials and processes than Earth."
So it may not be '100 percent proof', but at least Professor House understands what that actually means.
Jake Massey