Venus is a particularly inhospitable planet for life.

SPACE – Aliens will probably never be able to come from Venus. Its clouds, which were perhaps thought to be capable of harboring life, would be uninhabitable, even for microbes, due to their lack of humidity, reveals a study by researchers from Queen’s University of Belfast published in the journal Nature Astronomy this Monday June 28.

If on its surface the planet is a real hell, with an atmospheric pressure 90 times greater than that existing on the Earth and a surface temperature around 470 ° C, its clouds seemed to offer a milder environment with a temperature around 30 degrees.

John Hallsworth, lead author of the study, and his team investigated what conditions would be necessary for clouds to support extremophiles, that is, living organisms capable of thriving even under the most hostile conditions.

They determined for that an index, the water activity, measured on a scale going from 0 to 1, which is equivalent to the relative humidity or the presence of water in the atmosphere of a planet. Scientists have established that the minimum water activity for an extremophile organism to reproduce is 0.585.

One hundred times less humidity than the threshold required for life

The authors of the study found that sulfuric acid in the clouds of Venus reduced their water activity to less than 0.004, a hundred times less than the threshold necessary for life. For comparison, the water activity of the clouds of Mars is 0.537, which is barely less than the minimum required to support life, and a value similar to what can be found in the stratosphere of the atmosphere of Earth.

Scientists at Queen’s University in Belfast reveal that Jupiter’s clouds have water activity greater than 0.585 and temperatures between -10 and 40 degrees biologically more permissive than that of Venus, although other factors such as the presence of ammonia in the Jovian atmosphere could limit his ability.

This is not the first time that scientists have questioned the possibility of life in the clouds of Jupiter: the astronomer Carl Sagan had envisaged in 1976 a hypothesis in this direction.

Cases of false detections in the past

Contacted by the HuffPost, the astronomer Francis Rocard, responsible of the solar system exploration program at CNES, is not surprised by the results of the study. The scientist is even rather skeptical on the hypothesis that life can last in a gaseous medium. “Life needs liquid which allows permanent contact [avec les molécules] allowing the complex chemistry necessary for the emergence of living things ”, he believes. This is difficult for the gaseous atmosphere where contact between molecules remains episodic.

The possibility of a life on Venus was also mentioned in September 2020 by British scientists claiming to have found phosphine in the Venusian atmosphere, recalls Francis Rocard. A news then celebrated by the director of NASA Jim Bridenstine as “the most important event to date in the search for life outside of Earth”, the gas being generally produced on Earth by the metabolism of living organisms.

But there again, “the doubt is strong enough” underlines Francis Rocard, the discovery of the British researchers not having been confirmed by other observations. What is certain is that if this gas exists on Venus, it was not produced by living beings.

“Any extraordinary discovery requires extraordinary finds” says Francis Rocard, quoting Carl Sagan. For life on Venus, the CNES researcher urges caution and recalls that “cases of false detections have taken place.”

See also on Then24: NASA announces “Davinci +” and “Veritas”, two missions to Venus

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