ALIEN life could be lurking under frozen water to survive on Mars, Nasa scientists have suggested.
Living on the Red Planet is near impossible on the surface because of extreme ultraviolet radiation.
Earth is protected by harmful radiation thanks to the magnetic field - which Mars does not have.
But scientists have proposed that staying beneath thick ice could shield microbial life from this danger.
Experts haven't uncovered any evidence that aliens are there - the study outlines such spots as a possibility worth exploring for clues.
They say that the amount of sunlight that can shine through dusty ice could be enough for photosynthesis to occur in shallow pools of meltwater below the surface of that ice without high levels of radiation getting through.
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It's plausible because back home on Earth similar pools of water that form within ice are known to be teeming with life, including algae, fungi, and microscopic cyanobacteria.
Nasa's Aditya Khuller, who led the study, said: "If we’re trying to find life anywhere in the universe today, Martian ice exposures are probably one of the most accessible places we should be looking."
Using computer modeling, scientists looked at water ice, most of which formed from snow mixed with dust that fell on the surface during a series of Martian ice ages in the past million years.
If there is dust within ice it can create something known as cryoconite holes, Nasa explains.
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These are small holes that form in ice when particles of windblown dust fall there.
They take in sunlight and melt farther into the ice each summer on Earth.
Over time, they lower further down but eventually reach a point where they stop sinking.
However, they still generate enough warmth which creates a pocket of meltwater around them, which life can feed off.
"This is a common phenomenon on Earth," explained co-author Phil Christensen, from Arizona State University in Tempe.
"Dense snow and ice can melt from the inside out, letting in sunlight that warms it like a greenhouse, rather than melting from the top down."
The full study was published in the Nature journal Communications Earth & Environment.
Mars facts
Here's what you need to know about the Red Planet...
- Mars is the fourth planet from the Sun
- It is named after the Roman god of war
- The landmass of Mars is very similar to Earth but due to the difference in gravity you could jump three times higher there than you can here
- Mars is mountainous and hosts the tallest mountain known in the Solar System called Olympus Mons, which is three times higher than Everest
- Mars is considered to be the second most habitable planet after Earth
- It takes the planet 687 Earth days to orbit the Sun
- So far, there has been 39 missions to Mars but only 16 of these have been successful