Four years ago, the unexpected discovery of phosphine gas that signifies life on Earth- in the clouds of Venus sparked controversy, as subsequent observations failed to replicate the findings. The same team behind the original discovery has returned with more observations, presented for the first time on July 17 at a Royal Astronomical Society meeting in Hull, England. These observations will eventually form the basis of one or more scientific studies, and the work has already begun, CNN reported.
The researchers claim that the new data provides even stronger evidence of phosphine in the clouds of Venus, Earth's closest planetary neighbour. Often referred to as Earth's "evil twin," Venus is similar in size to our planet but has surface temperatures capable of melting lead and clouds of corrosive sulfuric acid.
The team's confidence in their findings has been bolstered by a new receiver installed on the James Clerk Maxwell Telescope in Hawaii, one of the instruments used for the observations. "There's also a lot more data itself," said Dave Clements, a reader in astrophysics at Imperial College London.
"We had three observation campaigns and in just one run, we collected 140 times as much data as we did in the original detection," he explained. "And what we've got so far indicates that we once again have phosphine detections."
Additionally, a separate team, which Clements is also part of, presented evidence of another gas, ammonia.
"That is arguably more significant than the discovery of phosphine," he added. "We're a long way from saying this, but if there is life on Venus producing phosphine, we have no idea why it's producing it. However, if there is life on Venus producing ammonia, we do have an idea why it might be wanting to breathe ammonia."
On Earth, phosphine is a foul-smelling, toxic gas produced by decaying organic matter or bacteria, while ammonia, a pungent gas, occurs naturally in the environment and is primarily produced by bacteria during the decomposition of plant and animal waste.
"Phosphine has been discovered in the atmosphere of Saturn, but that's not unexpected because Saturn is a gas giant," Clements explained. "Its atmosphere contains a lot of hydrogen, so hydrogen-based compounds like phosphine or ammonia dominate there."
However, on rocky planets like Earth, Venus, and Mars, the atmospheres are oxygen-dominated since they lack the mass to retain their original hydrogen, which escaped over time.
Finding these gases on Venus is unexpected. "By all normal expectations, they shouldn't be there," Clements said. "Phosphine and ammonia are both suggested as biomarkers, even on exoplanets. So finding them in Venus's atmosphere is intriguing. When we published the phosphine findings in 2020, it was understandably a surprise."
Subsequent studies questioned the results, suggesting the phosphine was ordinary sulfur dioxide. Data from other instruments, such as the Venus Express spacecraft, the NASA Infrared Telescope Facility, and the now-defunct SOFIA airborne observatory, also failed to replicate the phosphine findings.
However, Clements stated that new data from the Atacama Large Millimeter/submillimeter Array (ALMA) rules out sulfur dioxide contamination and suggests the lack of phosphine in other observations is due to timing. "All our observations that detected phosphine were taken as Venus's atmosphere moved from night into day," he said, "and all the observations that didn't find phosphine were taken as the atmosphere moved from day into night."
During the day, ultraviolet light from the sun can break up molecules in Venus's upper atmosphere. "All phosphine is baked out, and that's why you don't see it," Clements said, adding that the Stratospheric Observatory for Infrared Astronomy (SOFIA), which made nighttime observations, detected weak traces of the molecule upon further analysis by his team.
Clements also referenced unrelated research led by Rakesh Mogul, a professor of chemistry and biochemistry at California State Polytechnic University, Pomona, who reanalyzed old data from NASA's Pioneer Venus Large Probe, which entered Venus's atmosphere in 1978.
"It showed phosphine inside the clouds of Venus at around the part-per-million level, which is exactly what we have largely been detecting," Clements said. "So it's beginning to hang together, but we still don't know what's producing it."
Using the Pioneer Venus Large Probe data, Mogul's team published a "compelling case for phosphine deep in the cloud layer (of Venus)" in 2021, which remains unchallenged in the literature, according to Mogul. "This is in sharp contrast to the telescopic observations, which remain controversial," Mogul said.
Clements said that the clouds of Venus are made of droplets, but they're not water droplets. The researchers said that there is water in them but also so much dissolved sulfur dioxide that they become extremely concentrated sulfuric acid.
