Hot enough to melt metal and covered in a toxic, crushing atmosphere, Venus is among the most hostile locations in the solar system. But astronomers have reported discovering two gases that could indicate the presence of life forms lurking in Venus’ clouds.
The findings, presented on Wednesday at the National Astronomical Meeting in Hull, support evidence for a strong-smelling gas, phosphine, whose presence on Venus has been hotly contested.
Another team revealed the preliminary detection of ammonia, which on Earth is mainly produced by biological activity and industrial processes. According to scientists, its presence on Venus cannot be easily explained by known atmospheric or geological phenomena.
The so-called biosignature gases are not evidence of alien life. But the observation will increase interest in Venus and raise the possibility that life arose and even flourished in the planet’s more temperate past and lingers in parts of its atmosphere to this day.
“It could be that Venus went through a warm, wet phase in the past and that runaway global warming increased [life] would have evolved to survive in the only niche left – the clouds,” Dr Dave Clements, a lecturer in astrophysics at Imperial College London, told the meeting.
The surface of Venus reaches about 450C, hot enough to melt lead and zinc, the atmospheric pressure is 90 times that of Earth’s surface, and there are clouds of sulfuric acid. But about 50km (31mi) above the surface, the temperature and pressure are closer to conditions on Earth – and potentially just survivable for very hardy microbes.
On Earth, phosphine gas is produced by microbes in oxygen-poor environments, such as badger guts and penguin poop. Other sources, such as volcanic activity, are often so inefficient that on rocky planets the gas is considered a marker for life.
A high-profile claim of phosphine detection on Venus in 2020 was followed by controversy after subsequent observations failed to replicate the finding. Clements and colleagues’ latest observations using the James Clerk Maxwell Telescope (JCMT), based in Hawaii, aimed to resolve the dispute. By tracking the phosphine signature over time, they were able to strengthen the evidence for the gas’s presence, finding that its detection appeared to follow the planet’s day-night cycle.
“Our findings suggest that when the atmosphere is flooded with sunlight, the phosphine is destroyed,” Clements said. “All we can say is that phosphine is there. We don’t know what’s producing it. It could be some chemistry we don’t understand. Or it could be life.”
In a second lecture, Prof. Jane Greaves, an astronomer at Cardiff University, presented preliminary observations from the Green Bank telescope that pointed to ammonia. Ammonia is produced on Earth through industrial processes or by nitrogen-converting bacteria.
Greaves said: “Even if we were to confirm both claims, [findings]“It’s not proof that we’ve found these magical microbes and that they’re still there today,” he said, adding that there were no “ground truths” yet.
According to Professor Nikku Madhusudhan, an astrophysicist at the University of Cambridge, who was not involved in either study, evidence of a biosignature generally requires that the signal is robust and that the molecules are convincingly linked to life.
“When it comes to Venus, those are both open questions,” he said. “If they really solidify phosphine and ammonia, that raises the possibility of biological origins. The natural next thing that will happen is that new people will look at it and provide support or counterarguments. The story will be solved by more data.”
He added: “All of this is cause for optimism. If they can show that the signals are there, that is good for them.”
Dr Robert Massey, Deputy Director of the Royal Astronomical Society, said: “These are very exciting findings, but it must be stressed that the results are only preliminary and more research is needed to find out more about the presence of these two potential biomarkers in the clouds of Venus. Nevertheless, it is fascinating to think that these detections could indicate possible signs of life or unknown chemical processes. It will be interesting to see what further studies reveal in the coming months and years.”