A group of scientists has detected phosphine – a gas that on Earth can be produced by the decomposition of organic matter – in the atmosphere of the neighbouring planet

A group of scientists has detected phosphine in the atmosphere of Venus. The news published this Monday by the magazine ‘Nature’ is an astronomical milestone for several reasons, but it is still very unlikely that it has anything to do with the existence of extraterrestrial life on the neighbouring planet.

The phosphine (PH3) is a colorless gas with a characteristic odor of garlic, which can be formed in small amounts by the degradation of organic matter. Does this mean that if there is phosphine on Venus it is because there has been life? No. Decay is the main source of phosphine on Earth, but this does not mean that it can form abiotic – without life influencing – on other planets. In fact, for more than 30 years it has been known to be present in some layers of the atmospheres of Jupiter and Saturn.

As experts explain that phosphine is not a biomarker. “In my opinion, the prefix ‘bio’ should not be used until there is clear and unequivocal evidence that it is something related to life,” says Jesus Martinez-Frias, an expert in meteorites and Planetary Geosciences at the CSIC’s Geosciences Institute and the Complutense University of Madrid. Jorge Pla-Garcia agrees with him, a researcher in Planetary Sciences at the Astrobiology Center of the CSIC (associated with NASA): “The chemistry of the cosmos gives many more options to form this compound in addition to the decomposition of organic matter. Phosphine is a gas that can be produced by inorganic reactions (in fact it is done every day in laboratories). It would not be unusual for it to occur on Venus due to strong pressures and temperatures.”

Conditions on the surface of Venus are hostile to life. Due to the intense greenhouse effect produced by the gases in its atmosphere, the average temperature is around 464 degrees. However, in the environment of its upper cloud layer – between 53 and 62 kilometers high – the climate is temperate. In any case, the composition of the clouds is very acidic, so it could only provide a suitable habitat for certain Extremophilic microbes. And there is no proof of it either.

Furthermore, habitable is not synonymous with inhabited. “A planet has habitability characteristics does not mean that for that reason it will have life. Here on Earth, we know that habitability and life are related to the presence of liquid water and the chemistry of carbon. Probably in other places it is the same. So far, the only guidelines for the search for life are these: carbon and water,” Martinez-Frias distinguished in an article published in 2017, following the bombastic headlines about a possible habitable zone around the star TRAPPIST-one.

As Carl Sagan said, “extraordinary claims require extraordinary evidence. And to this day we do not have such extraordinary evidence yet on the detection of extraterrestrial life. This evidence must be unique, ruling out false positives using multiple different techniques with independent instrumentation from research groups. Moreover, to confirm this once you have this so-called unequivocal evidence, there must be consensus throughout the global scientific community,” Pla-Garcia says.

The study authors themselves, led by Jane S. Greaves of Cardiff University, acknowledge that phosphine detection is not strong evidence of microbial life and only indicates potentially unknown geological or chemical processes occurring on Venus. Greaves and his colleagues observed the planet using the James Clerk Maxwell Telescope and the Atacama Large Millimeter in 2017 and 2019, respectively. They came across a spectral signature that is unique to phosphine and estimated an abundance of 20 parts per billion of phosphine in the clouds of Venus. The scientists weighed up different ways that phosphine could have been produced: from sources on the planet’s surface, micrometeorites, lightning, or chemical processes that occur inside clouds. In the end, they couldn’t determine the source of the traces.

What is important about this discovery?

The discovery of phosphine on Venus opens a horizon of questions. “There are several geochemical and photochemical possibilities, which I hope will be explored in detail from now on thanks to this finding”, encourages Martinez-Frias. “It is a very interesting discovery, especially in terrestrial-type planets like Venus. We know that on Venus the volcanic activity was very important. There are phosphorus minerals in volcanic rocks as well as in meteorites and lunar rocks. The implications, according to one of the probabilities suggested in the article itself is that there is a geochemical or photochemical process that could lead to the formation of phosphine”.

For Pla-Garcia, it is also an announcement of special relevance. Firstly, because there is still a great lack of knowledge about the chemistry of atmospheres, in such a way that knowing more details about the elements that make up those of other planets can help to take steps in this field of study. Likewise, thoroughly analyzing atmospheric conditions can be key to ‘following the trail’ of life: “The study of the evolution of the atmospheres of Venus, Earth and Mars since their origins (everything indicates that their initial conditions were similar) it is key to understanding the different destinies that the three planets followed and how life could have arisen on all three but only last on Earth.”

NASA’s upcoming mission

Life on Venus? The discovery of phosphine, a byproduct of anaerobic biology, is the most significant development yet in building the case for life off Earth. About 10 years ago NASA discovered microbial life at 120,000ft in Earth’s upper atmosphere. It’s time to prioritize Venus. https://t.co/hm8TOEQ9es

— Jim Bridenstine (@JimBridenstine) September 14, 2020