Since the possible discovery of phosphine in the atmosphere of Venus two years ago, there’s been speculation that maybe life could exist in the temperate regions of the clouds of Venus. Many have investigated the possibility, but currently, it seems unlikely. The peculiar mystery of the Venusian atmosphere cannot be explained by the presence of life.

At least, that's the conclusion of a new paper published in Nature Communications testing out the "life in the clouds" hypothesis. The mystery in question is the presence of sulfur dioxide (SO₂) which is found in abundance lower in the clouds of Venus but vanishes as the altitude increases. 

One proposed possibility is that there are life forms floating about in the thick blanket of clouds, sucking up the sulfur. Life can truly do a number on planetary atmospheres, so it wouldn’t be out of the realm of the possibilities. The researchers modeled three potential ways for microorganisms to use sulfur dioxide. Each one of them violates some other observational constraint, however.   

“We looked at the sulphur-based ‘food’ available in the Venusian atmosphere – it’s not anything you or I would want to eat, but it is the main available energy source,” lead author Sean Jordan, from the University of Cambridge’s Institute of Astronomy, said in a statement. “If that food is being consumed by life, we should see evidence of that through specific chemicals being lost and gained in the atmosphere.”

“We’ve spent the past two years trying to explain the weird sulphur chemistry we see in the clouds of Venus,” added co-author Dr Paul Rimmer from the Department of Earth Sciences. “Life is pretty good at weird chemistry, so we’ve been studying whether there’s a way to make life a potential explanation for what we see.”

So these Venusian life forms should be releasing a lot of other molecules after absorbing the sulfur. But none of those molecules have been observed on Venus. The researchers found that a sulfur-sucking life form could exist and maybe it does somewhere else in the universe, but it is unlikely that it exists on Venus.

“If life was responsible for the SO₂ levels we see on Venus, it would also break everything we know about Venus’s atmospheric chemistry,” said Jordan. “We wanted life to be a potential explanation, but when we ran the models, it isn’t a viable solution. But if life isn’t responsible for what we see on Venus, it’s still a problem to be solved – there’s lots of strange chemistry to follow up on.”

New observations of Venus from upcoming missions by NASA and the European Space Agency could provide the crucial missing pieces to complete the puzzle that is the Venusian atmosphere.