Venus atmosphere shows potential signs of life — again

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4 years ago, Unexpected discovery In the clouds of Venus there is phosphine, a gas that means life on Earth. Controversyearn income smack down Subsequent observations were inconsistent with those findings.

Now, the same team that made that discovery has brought back further observations, which they presented for the first time at a meeting of the Royal Astronomical Society in Hull, UK, on ​​July 17. Ultimately, those results will form the basis of one or more scientific studies, which have already begun.

The researchers say the data contains even stronger evidence for the presence of phosphine in the clouds of Venus, the planet closest to Earth. Evil TwinThe planet is similar in size to Earth, but has surface temperatures hot enough to melt lead and clouds made of corrosive sulfuric acid.

The study benefited from a new receiver on one of the instruments used in the observations, the James Clerk Maxwell Telescope in Hawaii, which has given the team more confidence in their discovery. “We now have a lot more data,” says Dave Clements, a lecturer in astrophysics at Imperial College London.

“We’ve carried out three observation campaigns and, in just one run, we’ve obtained 140 times more data than we had at the time of the first detection,” he said, “and the data we have so far shows that phosphine has been detected again.”

Another team, including Clements, presented evidence for another gas: ammonia.

“This is probably more significant than the discovery of phosphine,” he added. “We can’t say that yet, but if there is life on Venus that produces phosphine, we don’t know why it would be produced. But if there is life on Venus that produces ammonia, we now have some idea of ​​why it would want to breathe ammonia.”

On Earth, phosphine is a foul-smelling, toxic gas produced by decaying organic matter and bacteria, while ammonia is a pungent-smelling gas that occurs naturally in the environment, primarily produced by bacteria at the end of the decomposition process of plant and animal waste.

“The discovery of phosphine in Saturn’s atmosphere is not unexpected, as Saturn is a gas giant,” Clements said. “There is so much hydrogen in Saturn’s atmosphere that hydrogen-based compounds such as phosphine and ammonia dominate Saturn’s atmosphere.”

But the atmospheres of rocky planets like Earth, Venus, and Mars have oxygen-dominant chemistry because they didn’t have enough mass to hold onto the hydrogen they originally had when they formed, so that hydrogen escaped.

Finding these gases on Venus is therefore unexpected. “You wouldn’t normally expect them to be there,” Clements says. “Phosphine and ammonia have been proposed as biomarkers, including for exoplanets, so finding them in the atmosphere of Venus is intriguing in that respect as well.” When we published our findings on phosphine in 2020, it was understandably a surprise.”

Subsequent studies have disputed this result, showing that phosphine is in fact a common Sulfur dioxideData from instruments other than those used by Clements’ team, e.g. Venus Express spacecraft, NASA Infrared Telescope Facility And now it has been abolished Sofia Aerospace Observatory — They also couldn’t replicate the phosphine findings.

But Clements said: Atacama Large Millimeter/submillimeter Array (ALMA)He rules out sulfur dioxide as a contaminant and attributes the failure to detect phosphine in other observations to timing: “It turns out that all of the observations that detected phosphine were made when the Venus atmosphere was transitioning from night to day,” he says, “and all of the observations that didn’t find phosphine were made when the atmosphere was transitioning from day to night.”

During the day, ultraviolet light from the sun breaks down molecules in Venus’ upper atmosphere. “You don’t see the phosphine because it’s all burned up,” Clements said, adding that the only exception is the Stratospheric Infrared Observatory, which observes at night. But when Clements’ team analyzed its data further, they found faint traces of the molecule, supporting the theory.

Clements also spoke to an unrelated the study The study was conducted by a group led by Rakesh Mogul, a professor of chemistry and biochemistry at California State Polytechnic University, Pomona. Mogul is a NASA Pioneer Venus Large-Scale ProbeIt entered the Earth’s atmosphere in 1978.

“We’ve detected phosphine in the clouds of Venus at levels around parts per million, which is exactly what we’ve been detecting,” Clements said. “So it’s starting to come together, but we still don’t know what’s producing the phosphine.”

Using data from the Pioneer Venus probe, Mogul and his team published “compelling evidence for the presence of phosphine deep within the cloud layers” of Venus in 2021, Mogul confirmed in an email. “So far, our analysis has not been challenged in the literature,” says Mogul, who was not involved in Clements’ team’s work. “This contrasts with the telescope observations, which remain controversial.”

The presence of ammonia on Venus would be an even more surprising discovery, announced in a talk in Hull by Jane Greaves, professor of astronomy at Cardiff University in the UK, and which forms the basis of a separate scientific paper using data from the Green Bank Telescope in West Virginia.

Clements said Venus’ clouds are made of water droplets, but they’re not water droplets. The clouds contain not only water, but also very high amounts of dissolved sulfur dioxide, resulting in very high concentrations of sulfuric acid, which is highly corrosive and can be deadly to humans with severe exposure. “It’s so highly concentrated that it would be incompatible with any life known on Earth, as far as we know, including extremophiles, which prefer very acidic environments,” Clements said, referring to organisms that can survive in extreme environments.

But the ammonia in these acid droplets could act as a buffer against the acidity, reducing it to a level where known terrestrial bacteria could survive, Clements added.

“The interesting thing behind this is whether it’s some kind of microbial life form that’s producing ammonia, because that would be a clever way of regulating its environment,” Greaves said in a speech to the Royal Astronomical Society. “The environment would be much less acidic and much more survivable. The acidity would be comparable to some of the harshest places on Earth, so it’s not a completely far-fetched idea.”

In other words, ammonia’s role is easier to explain than phosphine’s. “We know why ammonia is useful for life,” Clements says. “We don’t know how ammonia is produced. We don’t know how phosphine is produced, but if it’s there, there must be a functional purpose that we can understand.”

But Greaves cautioned that even if both phosphine and ammonia were present, it wouldn’t be evidence of microbial life on Venus, because we lack so much information about the conditions on Venus. “There could be lots of other processes going on, and we have no basis to say whether they’re possible,” she said of the hard evidence that can only come from direct observations from inside Venus’ atmosphere.

One way to make such observations would be to convince the European Space Agency to activate some of the instruments on board a spacecraft. Jupiter Icy Moons Explorer The probe is headed for the Jupiter system as it passes Venus next year. But there’s even better data. Da VinciIt is an orbital satellite and atmospheric probe that NASA plans to launch to Venus in 2020. Early 2030s.

From a scientific standpoint, the new data on phosphine and ammonia are intriguing but call for cautious optimism, said Javier Martin-Torres, a professor of planetary science at the University of Aberdeen in the UK, who led the study. Published In 2021, a paper was published that disputed the phosphine findings and hypothesized that it is impossible for life to exist in the clouds of Venus.

“Our paper highlighted the harsh and seemingly inhospitable environment of Venus’ atmosphere,” Martín-Torres said in an email. “The discovery of ammonia, which could neutralize sulfuric acid clouds, and phosphine, a potential biological signature, challenge our understanding and suggest that more complex chemical processes may be at work. It is important that these findings are addressed with careful and thorough scientific investigation.”

“The discovery opens up new avenues of research, but it’s essential that it be treated with a healthy dose of skepticism,” he added. “The detection of phosphine and ammonia in Venus’ clouds is exciting, but this is just the beginning of a long journey to unlock the mysteries of Venus’ atmosphere.”

Dr Kate Pattle, a lecturer in the Department of Physics and Astronomy at University College London, said scientists’ current understanding of Venus’ atmospheric chemistry cannot explain the presence of phosphine. “It’s important to note that the team that made the phosphine measurements are not claiming to have found life on Venus,” Dr Pattle said in an email. “If phosphine is truly present on Venus, it could indicate the presence of life, or it could indicate that there is something in Venus’ atmospheric chemistry that we don’t yet understand.”

The discovery of ammonia, if confirmed, would be very exciting, Pattle added, because ammonia and sulfuric acid cannot coexist unless ammonia itself is being produced by volcanic, biological, or some other process yet to be considered.

She stressed that all these results are only preliminary and require independent confirmation, but concluded that they could be of interest for future Venus exploration missions, such as the Jupiter Icy Moons Explorer and Da Vinci.

“These missions may provide answers to questions raised by recent observations,” Pattle said, “and will undoubtedly give us fascinating new insights into our closest neighbor’s atmosphere and its capacity to harbor life.”