Hot enough to melt metal and blanketed by a toxic, crushing atmosphere, Venus ranks among the most hostile locations in the solar system. But astronomers have reported the detection of two gases that could point to the presence of life forms lurking in the Venusian clouds. Findings presented at the national astronomy meeting in Hull on Wednesday bolster evidence for a pungent gas, phosphine, whose presence on Venus has been fiercely disputed. A separate team revealed the tentative detection of ammonia, which on Earth is primarily produced by biological activity and industrial processes, and whose presence on Venus scientists said could not readily be explained by known atmospheric or geological phenomena. The so-called biosignature gases are not a smoking gun for extraterrestrial life. But the observation will intensify interest in Venus and raise the possibility of life having emerged and even flourished in the planet’s more temperate past and lingered on to today in pockets of the atmosphere. “It could be that if Venus went through a warm, wet phase in the past then as runaway global warming took effect [life] would have evolved to survive in the only niche left to it – the clouds,” said Dr Dave Clements, a reader 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 the Earth’s surface and there are clouds of sulphuric acid. But about 50km (31 miles0 above the surface the temperature and pressure are closer to conditions on Earth – and potentially just about survivable for very hardy microbes. On Earth, phosphine gas is produced by microbes in oxygen-starved environments, such as badger guts and penguin faeces. Other sources, such as volcanic activity, tend to be 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 with 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 evidence for the presence of the gas and found that its detection appeared to follow the planet’s day-night cycle. “Our findings suggest that when the atmosphere is bathed in sunlight the phosphine is destroyed,” Clements said. “All that we can say is that phosphine is there. We don’t know what’s producing it. It may be chemistry that we don’t understand. Or possibly life.” In a second talk, Prof Jane Greaves, an astronomer at Cardiff University, presented preliminary observations from the Green Bank telescope indicating ammonia, which on Earth is made through either industrial processes or by nitrogen-converting bacteria. Greaves said: “Even if we confirmed both of these [findings], it is not evidence that we have found these magic microbes and they’re living there today,” adding that there were not yet “any ground truths”. Prof Nikku Madhusudhan, an astrophysicist at the University of Cambridge, who was not involved with either paper, said that in general proof of a biosignature required the signal to be robust and the molecules to be convincingly tied to life. “When it comes to Venus, both of those are open questions,” he said. “If they really confirm phosphine and ammonia robustly it raises the chances of biological origin. The natural next thing will be new people will look at it and give support or counter-arguments. The story will be resolved by more data.” He added: “All of this is grounds for optimism. If they can demonstrate the signals are there, good for them.” Dr Robert Massey, the deputy executive director at the Royal Astronomical Society, said: “These are very exciting findings but it must be stressed that the results are only preliminary and more work is needed to learn more about the presence of these two potential biomarkers in Venus’s clouds. Nevertheless, it is fascinating to think that these detections could point to either possible signs of life or some unknown chemical processes. It will be interesting to see what further investigations unearth over the coming months and years.”