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Four years ago, the unexpected discovery in the clouds of Venus of a life-signaling gas – phosphine – was controversial, earning relics in subsequent observations that failed to match its findings.
Now, the same team behind that discovery has come back with more observations, presented for the first time on July 17 at a meeting of the Royal Astronomical Society in Hull, England. Eventually, they will form the basis of one or more scientific studies, and that work has already begun.
The data provide even stronger proof, say the researchers, that phosphine is present in the clouds of Venus, our closest planetary neighbor. Sometimes called Earth’s evil twin, the planet is similar in size to ours but has surface temperatures that can melt lead and clouds made of corrosive sulfuric acid.
The work benefited from a new receiver installed on one of the instruments used for the observations, the James Clerk Maxwell Telescope in Hawaii, which gave the team more confidence in their results. “There’s also a lot more of the data itself,” said Dave Clements, reader in astrophysics at Imperial College London.
“We had three observing campaigns and in one run, we got 140 times more data than we got in the original detection,” he said. “And what we have so far shows that we have detected phosphine again.”
A separate team, which also includes Clements, presented evidence of another gas, ammonia.
“That is arguably more significant than the discovery of phosphine,” he said. “It’s a long shot to say this, but if life on Venus is producing phosphine, we have no idea why it’s producing it. However, if there is life on Venus that produces ammonia, we have an idea why it wants to breathe ammonia.”
A sign of life?
On Earth, phosphine is a foul, toxic gas produced by decaying organic matter or bacteria, while ammonia is a pungent-smelling gas that occurs naturally in the environment and is produced primarily by bacteria at the end of the decomposition process. of plant and animal waste.
“Phosphine has been found in Saturn’s atmosphere, but that’s not unexpected, because Saturn is a gas giant,” Clements said. “There’s a lot of hydrogen in its atmosphere, so any hydrogen-based compounds, like phosphine or ammonia, dominate there.”
However, rocky planets such as Earth, Venus and Mars have atmospheres where the chemistry is dominated by oxygen, because they did not have enough mass to hold the hydrogen they had when they first formed, and the hydrogen that after escaping.
Therefore these gases are not expected to be found on Venus. “By normal expectations, they shouldn’t be there,” Clements said. “Phosphine and ammonia have been proposed as biomarkers, including on exoplanets. So finding them in the atmosphere of Venus is interesting on that basis as well. When we published the phosphine results in 2020, understandably, that was a surprise.”
Subsequent studies challenged the findings, suggesting that the phosphine was ordinary sulfur dioxide. Data from instruments other than those used by Clements’ team — such as the Venus Express spacecraft, NASA’s Infrared Telescope Facility and the now-defunct SOFIA airborne observatory — failed to replicate the phosphine results.
But Clements said his new data, coming from the Atacama Large Millimeter/submillimeter Array, or ALMA, rules out that sulfur dioxide could be a contaminant and that the lack of phosphine from other observations is due to timing. “It turns out that all of our observations that detected phosphine were taken while the atmosphere of Venus was moving from day to night,” he said, “and all the observations that did not detect phosphine were taken while the atmosphere was moving from day to night. .”
During the day, ultraviolet light from the sun can break up molecules in the upper atmosphere of Venus. “All phosphine is baked out, and that’s 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, confirming the theory.
Clements also cited unrelated research by a group led by Rakesh Mogul, a professor of chemistry and biochemistry at California State Polytechnic University, Pomona. Mogul reanalyzed old data from NASA’s Pioneer Venus Large Probe, which entered the planet’s atmosphere in 1978.
“It showed phosphine inside the clouds of Venus at about the part-per-million level, which is exactly what we were mostly detecting,” Clements said. “So it’s starting to hang together, but we still don’t know what’s producing it.”
Using the Pioneer Venus Large Probe data, the team led by Mogul published in 2021 “a very strong case for phosphine deep in the cloud layer (of Venus),” Mogul confirmed in an email. “So far, our analysis remains unchallenged in the literature,” said Mogul, who was not involved in Clements’ team’s research. “This is in sharp contrast to the telescopic observations, which are still controversial.”
Breathing microbes?
Ammonia on Venus would make an even more surprising discovery. Presented at the talks in Hull by Jane Greaves, professor of astronomy at Cardiff University in the United Kingdom, the findings will form the basis of a separate scientific paper, using data from the Green Bank Telescope in West Virginia.
The clouds of Venus are made of droplets, Clements said, but they are not water droplets. They contain water but also so much dissolved sulfur dioxide that they become highly concentrated sulfuric acid — a highly corrosive substance that can be fatal to humans with heavy exposure. “It’s so concentrated that, as far as we know, it wouldn’t be compatible with any life we know of on Earth, including extremophile bacteria, which like very acidic environments,” he said. , referring to organisms that can. survive in extreme environmental conditions.
However, the ammonia inside these acid droplets can buffer the acidity and bring it down to a low enough level that certain agricultural bacteria can survive, Clements added.
“The exciting thing behind this is if it’s some sort of microbial life making the ammonia, because that would be a neat way of controlling its own environment,” Greaves said at the Astronomical Society talks. Royal. “It would make its environment a lot less acidic and a lot better to last, to the point where it’s only as acidic as some of the most extreme places on earth – so it’s not crazy.”
The role of ammonia, in other words, is easier to explain than phosphine. “We understand why ammonia might be useful for life,” Clements said. “We don’t understand how the ammonia is produced, just like we don’t understand how the phosphine is produced, but if ammonia is there, it would have a functional purpose that we can understand.”
However, Greaves warned that even both phosphine and ammonia would not be evidence of microbial life on Venus, because so much information is missing about the planet’s condition. “There are many other processes that could go on, and we have no absolute truth to say whether that process is possible or not,” she said, referring to the hard evidence that can only come from direct observations. from the inside. the atmosphere of the planet.
One way to make such observations is to convince the European Space Agency to put some instruments on board the Icy Moons Explorer —– a probe on its way to the Jupiter system —– when it flies by Venus sometime next year. But even better data would come from DAVINCI, an orbital and atmospheric probe that NASA plans to send to Venus in the early 2030s.
Cautious hope
From a scientific point of view, the new data on phosphine and ammonia are interesting but cautious optimism is needed, said Javier Martin-Torres, professor of planetary sciences at the University of Aberdeen in the United Kingdom. He led a study published in 2021 that challenged the phosphine results and claimed that life is not possible in the clouds of Venus.
“Our paper highlighted the harsh and inhospitable conditions in the atmosphere of Venus,” Martín-Torres said in an email. “The discovery of ammonia, which could neutralize the sulfuric acid clouds, and phosphine, a potential biosignature, challenge our understanding and suggest that more complex chemical processes may be at work. It is imperative that we investigate these findings carefully and thoroughly.”
The findings open new avenues of research, he said, but it is necessary to treat them with a healthy dose of skepticism. Although the detection of phosphine and ammonia in the clouds of Venus is exciting, it is only the beginning of a longer journey to solve the mysteries of that planet’s atmosphere, he said.
Scientists’ current understanding of the atmospheric chemistry of Venus cannot explain the presence of phosphine, said Dr Kate Pattle, a lecturer in the Department of Physics and Astronomy at University College London. “It is important to note that the team behind the phosphine measurements is not claiming to have found life on Venus,” Pattle said in an email. “If phosphine is really present on Venus, it could indicate life, or it could indicate that there is atmospheric chemistry of Venus that we don’t yet understand.”
The discovery of ammonia would be exciting if confirmed, Pattle added, because ammonia and sulfuric acid should not be able to exist without some process — whether volcanic, biological or something that has not yet been accounted for — producing ammonia. drive yourself.
She emphasized that these two results are only preliminary and would require independent confirmation, but they make upcoming missions to Venus such as the Icy Moons Explorer Jupiter and DAVINCI interesting, she concluded.
“These missions may provide answers to the questions raised by the recent observations,” said Pattle, “and will certainly give us interesting new insights into our nearest neighbor’s atmosphere and its potential for life. nurture.”
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