Paris (AFP)

A study announcing the discovery of a gas possibly related to a life form in the atmosphere of Venus, is disputed this week by two studies questioning this discovery, even denying its reality.

The study by Professor Jane Greaves, of the British University of Cardiff, published in mid-September, had made the headlines, with the "apparent presence" of phosphine on Venus.

This gas, which is not linked to living things in the giant planets of the solar system, comes exclusively from microbial or human activity on Earth.

The announcement, called by NASA chief Jim Bridenstine "the most important event" in the search for extraterrestrial life, has stimulated research on the subject.

Especially since the study by Prof. Greaves cautiously recalled the importance of confirming its unique detection of phosphine.

The team coordinated by Thérèse Encrenaz, an astrophysicist at the Paris-PSL Observatory, took it at its word, looking for a "signature" of the molecule in the infra-red range.

She concluded, in the journal Astronomy & Astrophysics on October 27, that her results were incompatible with those of Prof. Greaves' team.

According to Ms. Encrenaz, "what Greaves actually saw was a signature which, if real, formed at an altitude of 80 km, in the upper mesosphere, well above what we observed. above the clouds ".

However, the Cardiff scientist assumed that the phosphine detected found its source in these clouds, 20 km below, which assumes a constant gas mixture at these two altitudes.

"We are observing what is happening at cloud level, approximately 60 km away, at the top of the cloud layer, and we can say that we do not see any," Encrenaz told AFP.

Under these conditions it is "extremely difficult to make the two measurements compatible", according to the astrophysicist, a specialist in planetary atmospheres, who says "for the moment" not to believe in the presence of this gas in that of Venus.

A second study, still published in Astronomy & Astrophysics on Tuesday, drives home the point by attacking Professor Greaves' method.

For Ignas Snellen, astrophysicist at the Dutch University of Leiden, this method leads to "false results".

His team particularly calls into question the use of a "polynomial of degree 12", an equation making it possible to "clean" a detection signal, but at the risk of corrupting it if the degree is too high.

Prof. Snellen's team, using the data and method of Prof. Greaves, found results "below the generally accepted threshold of statistical acceptance".

She concludes that these data do not provide "statistical evidence for the presence of phosphine in the atmosphere of Venus".

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