The signs of a possible life on Venus fade

So goes science. One day a team of researchers announced an astonishing result. Their colleagues set in motion and challenge it, defend it but above all try to confirm it. A few weeks later, new work arrives and… deflates the initial enthusiasm.

This is what happens with the story of the presence in the clouds of the planet Venus of an unexpected gas, phosphine, with the formula PH₃ (one atom of phosphorus, three atoms of hydrogen). This announcement made on September 14 in Nature Astronomy by an international team led by Jane Greaves, from Cambridge University (UK), was intriguing. After eliminating the usual physico-chemical scenarios to explain their origin, the remaining hypothesis was to consider that these molecules could be created by living organisms. In short, it would be the index of extraterrestrial life.

But very quickly, before seizing this extraordinary conclusion, many researchers doubted the very presence of phosphine. Two articles, one published, the other under evaluation, have just confirmed these doubts. The first article is co-authored by… Jane Greaves herself (and two more of the September co-authors). Accepted for publication in Astronomy & Astrophysics (A&A) On October 14, he estimated there would be four times less phosphine than advertised in the original article. And this is only a theoretical maximum because, in fact, nothing was detected. The September article had spotted the phosphine using radio waves picked up by two telescopes.

Overestimated signals

This new article focuses on infrared wavelengths. Thérèse Encrenaz, from the Paris Observatory, co-author of the article, had, several months ago, looked at how to identify phosphine in this part of the electromagnetic spectrum because it was planned, with Jane Greaves, to observe the instrument. Texts, in the spring, in Mauna Kea (Hawaii). But the Covid-19 epidemic canceled the operation. The Frenchwoman and her colleagues therefore analyzed “old” data from March 2015 in infrared to see if the phosphine was there. Without finding anything.

“This remains compatible with our measures, Jane Greaves believes. Either the phosphine concentration changes over time and it could not have been there during infrared measurements. Either phosphine is in a thin layer of the atmosphere that only radio waves can see. “ Indeed, the two types of radiation do not probe the same altitudes. Radio waves make it possible to observe layers at an altitude of 80 kilometers, when it is rather 60 kilometers for infrared. “These results make me more skeptical about the presence of phosphine”, believes Thérèse Encrenaz. Even if the chemistry and atmospheric circulation of Venus are still mysterious, scenarios allowing the existence of this “reservoir” of phosphine at altitude seem very unlikely.

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