Surely, in this seemingly infinite Universe, aliens must be somewhere?
It turns out ET might be buried under ice caps of distant planets, unable to phone home.
One formed Nasa scientist has suggested that extraterrestrials haven't contacted Earth because they're living deep beneath the frozen oceans of sub-zero water worlds.
Alex Stern, who now works at the Southwest Research Institute in Texas, discussed the Fermi Paradox, which questions why we haven't found aliens even though it's likely they exist.
In a new paper, he wrote:
Many possible explanations have been proffered.
We suggest another - namely that the great majority of worlds with biology and civilisations are water ocean worlds.
Water would protect creatures from natural disasters; such as exploding stars and spikes of space radiation. You know, everyday problems.
Stern believes such planets are likely to be extremely chilly, forcing the aliens to live under a thick crust of ice, and making it impossible for us to contact them.
Water worlds are naturally cut off from communication by their interior nature below a thick roof of ice or rock and ice, therefore do not easily reveal themselves.
Habitable worlds are likely to be almost entirely covered in water, meaning the creatures could look like fish more than humans, suggest astronomers.
If one theory on the origin of life on Earth is anything to go by, hydrothermal vents at ocean beds can pump nutrients into their surroundings and could be a nursery for life.
HT The Sun