A trace of life on Venus? 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, qualified by NASA chief Jim Bridenstine “Most important event” in the search for extraterrestrial life, stimulated research on the subject. Especially since the study by Prof. Greaves cautiously recalled the importance of confirming its unique detection of phosphine.
“We can say that we don’t see any”
The team coordinated by Thérèse Encrenaz, astrophysicist at the Paris-PSL Observatory, took her at her word, looking for a « signature » of the molecule in the infrared range. She concluded, in the review Astronomy & Astrophysics on October 27, that his results were incompatible with those of Prof. Greaves’ team.
According to Thérèse Encrenaz, “What Greaves actually saw is 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”, says Thérèse Encrenaz.
Under these conditions it is “Extremely difficult to make the two measures 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.
“Distorted results”
A second study, still published in Astronomy & Astrophysics Tuesday, December 1, drives home the point by attacking the method of Professor Greaves.
For Ignas Snellen, astrophysicist at the Dutch University of Leiden, this method leads to “Distorted results”. His team calls into question the use of a “Polynomial of degree 12”, an equation allowing 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, finds results “ below the generally accepted statistical acceptance threshold ‘. It concludes that these data do not provide “No statistical proof for the presence of phosphine in the atmosphere of Venus”.
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