British and American researchers confirm the presence of phosphine, PH3, in the atmosphere of Venus. According to them, this is most likely a “biosignature” – the undeniable marker of the existence of a life form. Other scientists are still asking to see.
A pressure of 90 atmospheres at the surface for an average of 450 ° C, against 20 ° C at altitude in clouds that are extraordinarily corrosive because they are concentrated at 90% sulfur: how can we imagine the existence of life in such conditions? However, British and American researchers are now considering it through a new discovery. In a study published yesterday in Nature Astronomy, scientists at Cardiff University and the Massachusetts Institute of Technology (MIT) claim to have detected the presence of phosphine, PH3, in the atmosphere of our neighbor, Venus. Astrophysicist Jane S. Greaves and her colleagues have in fact recognized its spectral signature by studying very precisely the luminous characteristics of the Venusian atmosphere using two radio telescopes: the ALMA of the Chili and the JCMT in Hawaii.This molecule, produced in an industrial environment for fumigation (the extermination of pests by a gas), would have no other reason to be there than thanks to extremophilic microorganisms (that is to say, which resist under environmental conditions which should not guarantee the survival of the majority of living things). The researchers tried to deduce its presence from several abiotic hypotheses relating to non-organic physicochemical processes: volcanism, micrometeorite input, chain reaction due to lightning, etc.
According to them, none can justify the presence of such a quantity of phosphine measured in the atmosphere of our twin planet, namely 20 ppm (parts per million). As a result, astrophysicists and exobiologists are indeed questioning whether this Venusian phosphine is not a biosignature – a marker of life. “PH3 could come from unknown photochemical or geochemical processes or, by analogy to its biological production on Earth, from a form of life,” the study concludes.
On Earth, in an extreme natural environment, anaerobic bacteria (which survive without oxygen), able to survive in 5% acid, emit PH3 by corrosion of iron. While this extreme way of life does exist, it nevertheless remains far from the hyper-acidic conditions of the Venusian atmosphere. In addition, remember that phosphorus (P) is a chemical element essential to life on Earth,because it is an integral part of the molecules of our DNA. However, its existence is not exclusively linked to life. The atmosphere of gaseous planets where life seems definitely impossible, such as Jupiter and Saturn, also contain PH3, the non-organic origin of which is already known. By many hypotheses, phosphorus was even imported into the solar system billions of years ago, via meteorites.
Venusian phosphine: biosignature or simple anomaly?
Many scientists outside the study are therefore reluctant to speak immediately of a biosignature, or biomarker, for this Venusian phosphine. “Indeed, it is not because life can produce a molecule that the presence of this molecule implies life”, underlines the French CNRS astrophysicist, Franck Selsis, at Futura-Sciences. According to him, and other experts, the study published in Nature Astronomy is not the discovery of a biosignature but the simple discovery of an anomaly – in other words, an observation as yet unexplained.
To confirm the link between Venusian phosphine and the presence of extraterrestrial life in the clouds of Venus, scientists will need many additional elements, and in particular in situ data. The discoverers are also well aware of this and are now encouraging “the sending of an aircraft to Venus which could take samples capable of validating the presence of PH3 in the atmosphere and perhaps offering clues of its provenance.”
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