Hot enough to melt metal and covered by a toxic, crushing atmosphere, Venus is one of the most hostile places in the solar system. But astronomers have reported the detection of two gases that could indicate the presence of life forms lurking in the Venusian clouds.
Findings presented at the National Astronomy Meeting in Hull on Wednesday strengthen evidence for a pungent gas, phosphine, whose presence on Venus has been hotly contested.
A separate team revealed the preliminary detection of ammonia, which on Earth is produced mainly by biological activity and industrial processes, and whose presence on Venus, scientists say, cannot be readily explained by known atmospheric or geological phenomena.
The so-called biosignature gases are not a smoking gun for extraterrestrial life. But the observation will heighten interest in Venus and raise the possibility that life emerged and even flourished in the planet’s more temperate past, remaining in pockets of the atmosphere until today.
“It could be that if Venus went through a warm, wet phase in the past, if runaway global warming kicked in [life] would have evolved to survive in the only niche left to it – the clouds,” 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 sulfuric acid. But about 50 km (31 mi0) above the surface, the temperature and pressure are closer to conditions on Earth – and possibly just about survivable for many hardy microbes.
On Earth, phosphine gas is produced by microbes in oxygen-starved environments, such as badger intestines and penguin feces. Other sources, such as volcanic activity, tend to be so inefficient that the gas on rocky planets 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 at resolving 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 we can say is that phosphine is there. We do not know what it produces. It could be chemistry 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 that indicate ammonia is made on Earth either by industrial processes or by nitrogen-fixing bacteria.
Greaves said: “Even though we both confirmed [findings]it’s not proof that we’ve found these magic microbes and that they’re living there today,” adding that there haven’t been “any ground truths” yet.
Prof Nikku Madhusudhan, an astrophysicist at the University of Cambridge, who was not involved in either paper, said that proof of a biosignature generally requires that the signal be robust and that the molecules be convincingly linked to life be.
“When it comes to Venus, both are open questions,” he said. “If they really strongly confirm phosphine and ammonia, it increases the chances of a biological origin. The natural next thing will be for new people to look at it and give support or counterarguments. The story will be resolved by more data.”
He added: “All this is grounds for optimism. If they can demonstrate that 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 emphasized that the results are only preliminary and that more work is needed to learn more about the presence of these two potential biomarkers in Venus’ clouds. Nevertheless, it is fascinating to think that these detections could indicate either possible signs of life or some unknown chemical processes. It will be interesting to see what further investigations come to light over the coming months and years.”
