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According to a study backed by Nasa, aliens could be living in the acid clouds of Venus - the second planet from the Sun and thought to be among the most inhospitable.
Researchers have said they've spotted dark patches in Venus' clouds, which have been detected by space probes and appear to resemble the light-absorbing properties of the bacteria found on earth.
However, the alien life is likely to only be microbes.
"Venus shows some episodic dark, sulfuric rich patches, with contrasts up to 30-40 percent in the ultraviolet, and muted in longer wavelengths," says study leader, Sanjay Limaye, who is from the University of Wisconsin-Madison's Space Science and Engineering Center.
These patches persist for days, changing their shape and contrasts continuously and appear to be scale dependent."
The research was published earlier this week in a peer-reviewed journal called Astrobiology, and suggests that the extra-terrestrial microbes could survive by being blown around by winds in Venus' cooler clouds tops.
Professor Rakesh Mogul - paper co-author and biological chemist at California State Polytechnic University, Pomona -said: "On Earth, we know that life can thrive in very acidic conditions, can feed on carbon dioxide, and produce sulfuric acid."
Co-author David J Smith, of Nasa's Ames Research Center, has also said that similar bacteria and other organisms on Earth have been found alive at altitudes of 25 miles.
While Venus is of a similar size to Earth, it has an incredibly inhospitable surface - with a temperature that's twice the maximum setting in a kitchen oven.
It also rains sulphuric acid, so, y'know', not ideal.
"Venus has had plenty of time to evolve life on its own," explains Limaye, noting that some models suggest Venus once had a habitable climate with liquid water on its surface for as long as 2 billion years. "That's much longer than is believed to have occurred on Mars."
In the paper, the authors explain: "Our comparative analyses support the blended hypotheses that terrestrial-type biology can survive within and contribute to the spectral signatures of Venus' clouds.
"To test the ideas presented here, we propose the need for an integrated chemical, biochemical, and microbiological study focusing on the survival and spectroscopy of terrestrial microorganisms under Venus' cloud conditions."
The scientists have also said that further research is needed to investigate.
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