The Royal Astronomical Society has just made a potentially groundbreaking announcement. Astronomers have indeed isolated the presence of phosphine in the clouds of Venus. It is a gas which, on Earth, can be produced by anaerobic bacteria.
Venus, once our planet's twin, is now considered the worst place in the solar system. On the surface, the average temperature rises to 462°C (hot enough to melt lead) and the atmospheric pressure is 92 times higher than that of the Earth. Higher up, clouds made up of droplets of sulfur dioxide and sulfuric acid also make the environment particularly corrosive. A priori, therefore, the planet appears to be hostile to life. And yet.
As part of a press conference held this Monday at 5 p.m., researchers from the Royal Astronomical Society of London made an extraordinary announcement. These isolate the spectral signature of a rare molecule – phosphine – at an altitude where temperatures and pressures are similar to those at sea level on Earth. A first time in 2017, with the James Clerk Maxwell Telescope, then a second time using the Atacama Large Millimeter/Submillimeter Antenna Array, in 2019.
On Earth, this molecule can be produced in two ways:either synthetically in the laboratory (to be used as a pesticide), or by microorganisms evolving in an oxygen-free environment (extremophiles ). We had already isolated phosphine in the atmosphere of certain planets in the solar system, such as Jupiter or Saturn, which are rich in hydrogen. On the other hand, on a telluric planet, except the Earth, it is a first.
“When we got the first hints of phosphine in the spectrum of Venus, it was a shock “said Jane Greaves, team leader at Cardiff University in the UK, which originated the discovery. The fact of having isolated this spectral signature is all the more surprising as the atmosphere of Venus should normally oxidize this molecule. The researchers are however categorical:there is indeed phosphine on Venus, up to 20 ppm (parts per million).
These two incredible detections, made two years apart, therefore suggest the existence of a source of phosphine production on Earth's "evil twin". But which ? This is THE big question.
On Saturn and Jupiter, phosphine forms in the hot, high-pressure interiors of these gas giants, before being carried to the surface by convection. But Venus seems unable to offer the same conditions. Also, in the journal Nature Astronomy, the researchers point out that they have explored about 40 other possible "chemical" pathways for making the phosphine.
The overwhelming majority have a non-biological origin:sunlight, minerals blowing upwards from the surface, volcanism or even lightning... Yet, according to the calculations, all of these sources could only manufacture, at best, a tenth of the amount of phosphine detected by telescopes.
Obviously, the researchers do not exclude an as yet unknown photochemistry or geochemistry… but they lean towards a biological origin . Terrestrial extremophiles capable of manufacturing these molecules, they explain, would only need to work on Venus at about 10% of their maximum productivity.
Interviewed by France Inter, Emmanuel Marcq, lecturer at Versailles-St Quentin University, evokes a particularly "interesting discovery. “, but which requires confirmation with other means of detection. "For now the detection is based on the presence of a single line in the radio wave domain" , he explains. “We have to see if it is confirmed by observation in the infrared, a technique where the gases each have a specific spectral signature. That would remove any ambiguity."
According to him, "if we cannot explain the production of the gas by chemical reactions, we will have to open the door to the hypothesis of biological production , i.e. an extremophile life form living in the droplets of the clouds of Venus “.
In the meantime, the Cardiff team calls for continued research, and even to send a new probe to carry out measurements directly on site, or even collect atmospheric samples for bring them back to Earth.
