The discovery of a possible sign of life in the clouds of Venus has sparked widespread controversy. Now scientists say they have more evidence.

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Four years ago, unexpected discovery In the clouds of Venus, I encountered a gas that indicates life on Earth – phosphine. Argumentearn Reprimands In subsequent observations it failed to match its results.

Now the same team behind the discovery has returned with further observations, first presented on July 17 at a meeting of the Royal Astronomical Society in Hull, England. Ultimately, these observations will form the basis of one or more scientific studies, and that work has already begun.

The data, researchers say, provide stronger evidence of phosphine in the clouds of Venus, our closest planet, sometimes called Earth. evil twinThis planet is similar in size to our own but has surface temperatures that could melt lead, and clouds of corrosive sulfuric acid.

The work took advantage of a new receiver mounted on one of the instruments used for the observations, the James Clerk Maxwell Telescope in Hawaii, giving the team more confidence in their findings. “There’s also a lot of the same data,” said Dave Clements, a reader in astrophysics at Imperial College London.

“We've done three monitoring campaigns and in just one campaign, we got 140 times the data we got in the original discovery. What we've got so far suggests that we're getting phosphine detections again,” he said.

A separate team, also including Clements, has provided evidence for another gas, ammonia.

“This is more important than the discovery of phosphine,” he added. “We’re still a long way from saying this, but if there is life on Venus that produces phosphine, we have no idea why it would produce it. However, if there is life on Venus that produces ammonia, we have an idea why it would want to breathe ammonia.”

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

“Phosphine has been detected in Saturn’s atmosphere, but that’s not unexpected, because Saturn is a gas giant,” Clements said. “There’s a huge amount of hydrogen in its atmosphere, so any hydrogen-based compounds, like phosphine or ammonia, are the ones that dominate there.”

However, rocky planets like Earth, Venus, and Mars have atmospheres where oxygen dominates the chemistry, because they did not have enough mass to hold onto the hydrogen they had when they originally formed, and that hydrogen escaped.

So finding these gases on Venus is unexpected. “According to all normal expectations, they shouldn’t be there,” says Clements. “Phosphine and ammonia have been proposed as biosignatures, including on exoplanets. So finding them in the Venusian atmosphere is interesting on that basis as well.” “When we published the phosphine results in 2020, it came as a surprise, which is completely understandable.”

Later studies challenged the findings, suggesting that phosphine was in fact an ordinary gas. sulfur dioxideData from tools other than those used by the Clements team – such as Venus Express spacecraftthe NASA's Infrared Telescope Facility And now extinct Sofia Air Observatory – Also failed to replicate the phosphine results.

But Clements said his new data, coming from Atacama Large Millimeter/submillimeter Array, or ALMAHe ruled out the possibility that sulfur dioxide was a contaminant and that the absence of phosphine from other observations was due to timing. “It turns out that all of our observations that found phosphine were made as the Venusian atmosphere transitioned from night to day, and all of the observations that didn't find phosphine were made as the atmosphere transitioned from day to night,” he said.

During the day, ultraviolet light from the sun can break apart molecules in Venus’s upper atmosphere. “All the phosphine is baked, which is why you don’t see it,” Clements said, adding that the only exception was the Stratospheric Observatory for Infrared Astronomy, which made observations at night. But further analysis of that data by Clements’ team revealed faint traces of the molecule, strengthening the theory.

Clements also pointed out unrelated matters. research From a group led by Rakesh Mogul, professor of chemistry and biochemistry at California State University of Technology, Pomona. Mogul reanalyzed old data from NASA's Pioneer Large Venus Probewhich entered the planet's atmosphere in 1978.

“The images showed phosphine inside the Venusian clouds at parts per million, which is pretty much exactly what we were detecting,” Clements said. “So it's starting to come together, but we still don't know what's producing it.”

Using data from the Pioneer Venus Large Orbiter, the team led by Mogul in 2021 published “a compelling case for phosphine deep in the cloud layer[on Venus],” Mogul said in an email. “So far, our analyses have not been challenged in the scientific literature,” said Mogul, who was not involved in Clements’s research. “This stands in sharp contrast to telescopic observations, which remain controversial.”

The presence of ammonia on Venus would be an even more surprising discovery. The findings, presented at talks in Hull by Jane Greaves, professor of astronomy at Cardiff University in the UK, will form the basis of a separate paper, using data from the Green Bank Telescope in West Virginia.

Venus’ clouds are made of droplets, but they’re not water droplets, Clements said. There’s water in them, but there’s also a lot of dissolved sulfur dioxide, which turns into highly concentrated sulfuric acid — a highly corrosive substance that can be fatal to humans if exposed to too much. “It’s so concentrated that, as far as we know, it wouldn’t be compatible with any life we ​​know of on Earth, including extremophiles, which like very acidic environments,” he said, referring to organisms that can survive in extreme environmental conditions.

However, the ammonia within these droplets of acid can act as a buffer and lower the acidity to a level low enough that some known terrestrial bacteria can survive in it, Clements added.

“The exciting thing about this is if there is some kind of microbial life that produces ammonia, because that would be an elegant way for them to regulate their own environment,” Greaves said in the Royal Astronomical Society Lectures. “That would make their environment less acidic and more habitable, to the point where some of the most extreme places on Earth are acidic – so it’s not completely crazy.”

In other words, the role of ammonia is easier to explain than phosphine. “We understand why ammonia might be beneficial to life,” Clements says. “We don’t understand how ammonia is produced, just as we don’t understand how phosphine is produced, but if there’s ammonia there, it has a functional purpose that we can understand.”

However, Greaves cautioned that the presence of both phosphine and ammonia would not be evidence of microbial life on Venus, because there is too much information missing about the state of the planet. “There are a lot of other processes that could be going on, and we don’t have any ground truth to say whether or not this process is possible,” she said, referring to the fact that conclusive evidence can only come from direct observations from inside the planet’s atmosphere.

One way to make such observations would be to convince the European Space Agency to turn on some of the instruments on board the craft. Jupiter's Icy Moons Explorer ——A probe is on its way to the Jupiter system——when it passes by Venus sometime next year. But better data will come from da vincian orbiter and atmosphere probe that NASA plans to launch to Venus in early 1930s.

From a scientific perspective, the new data on phosphine and ammonia are interesting but warrant cautious optimism, said Javier Martin-Torres, professor of planetary science at the University of Aberdeen in the United Kingdom. He led the study. Published In 2021, a study came out that challenged the phosphine findings and suggested that life is not possible in the clouds of Venus.

“Our paper underscores the harsh and inhospitable conditions of Venus’ atmosphere,” Martin-Torres said in an email. “The discovery of ammonia, which can neutralize sulfuric acid clouds, and phosphine, a potential biosignature, challenges our understanding and suggests that more complex chemical processes may be at play. It is important that we address these findings through careful and comprehensive scientific investigation.”

The findings open up new avenues for research, he added, but should be treated with a healthy dose of skepticism. While the discovery of phosphine and ammonia in Venus' clouds is exciting, it's just the beginning of a longer journey to unravel the mysteries of the planet's atmosphere, he said.

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

The ammonia discovery would be exciting if confirmed, Patel added, because ammonia and sulfuric acid should not be able to coexist without some process — whether volcanic, biological or something yet to be considered — that drives the production of ammonia itself.

She stressed that these two results are only preliminary and require independent confirmation, but they make upcoming missions to Venus such as Jovian Icy Moons Explorer and Da Vinci interesting, she concluded.

“These missions may provide answers to questions raised by recent observations, and will certainly give us fascinating new insights into the atmosphere of our nearest neighbor and its ability to harbor life,” Patel said.