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New preliminary evidence for phosphine and ammonia in the Venusian atmosphere deepens the mystery behind what produces these gases. The puzzling origins of phosphine, and now ammonia, mean that the idea that these chemicals could have a biological source on Venus is being seriously considered by some scientists.
Venus seems an unlikely place to find life, with surface temperatures high enough to melt lead and terrifying surface pressures. The phosphine and ammonia found in the clouds of the second planet from the Sun and the hottest planet in the solar system mean that if life could exist there, it would be found far above the surface of Venus.
The new detections of phosphine and ammonia were achieved by a team led by Jane Greaves from Cardiff University, using submillimetre radio wavelength data collected by the James Clerk Maxwell Telescope (JCMT) in Hawaii and the Green Bank Telescope in West Virginia.
“We don’t know how phosphine or ammonia are produced in an oxygenated atmosphere like Venus,” team member and astrophysicist Dave Clements of Imperial College in London told Space.com. “But it’s not clear why biology on Earth would produce phosphine.” We don’t know why bacteria produce phosphine, whether it’s in penguin poop or badger guts, but they do.”
Related: Life on Venus? Interesting phosphine molecule spotted again in planet’s clouds
Phosphine detection on Venus sparks controversy
The first detection of phosphine on Venus by Greaves and his team in 2020 at JCMT was harshly rejected by some.
The dispute centered on how the data was processed and whether this created spurious signals because observations with other telescopes had difficulty detecting phosphine.
Clements said the technical disagreements have now been resolved and the latest measurements, made using a new detector at JCMT called Nāmakanui (Hawaiian for ‘Big Eyes’), come from three observing campaigns, each providing 140 times more data than the first detection.
Clements said the technical disagreements have now been resolved and the latest measurements, made using a new detector at JCMT called Nāmakanui (Hawaiian for ‘Big Eyes’), come from three observing campaigns, each providing 140 times more data than the first detection.
“Nāmakanui is a package of three different receivers on three different frequencies,” Clements said.
One of these receptors, called ‘Ū’ū (named after a particular large-eyed fish in the waters around Hawaii that can see in the dark), can detect phosphine as well as sulfur dioxide and “semi-heavy water” (HDO), water with three hydrogen atoms instead of the normal two and one oxygen atom. Both sulfur dioxide and HDO change over time in the Venusian clouds, and Greaves and Clements’ team want to see how phosphine changes too.
“There are suspicions and possibilities that the amount of phosphine may be changing over time, but we don’t know what’s causing this variability,” Clements said.
One possibility is that ultraviolet light from the Sun breaks down molecules in Venus’s upper atmosphere, causing variations in the amount of phosphine.
Clements noted that the first detection of phosphine occurred while JCMT was observing the morning terminator on Venus, when the planet’s night side turns into its day side. At night, ultraviolet light from the sun would have no effect, allowing the phosphine to accumulate.
Other observations were made by the European Space Agency’s Venus Express spacecraft, SOFIA (Stratospheric Observatory for Infrared Astronomy), and NASA’s Infrared Telescope Facility in Hawaii. These observations showed Venus at a time when day had turned to night, and ultraviolet light from the Sun would have broken down much of the phosphine, making it difficult to detect.
Clements has since reanalyzed the SOFIA data and found a faint hint that phosphine was present. Rakesh Mogul of California State Polytechnic University also found high amounts of phosphorus when he reanalyzed mass spectrometry data from the old Pioneer Venus mission in 1978.
“If phosphine is being destroyed by the solar ultraviolet, that’s consistent with other observations not finding it,” Clements said. It also suggests that phosphine is being rapidly replenished by an unknown process.
Then there is ammonia.
Could ammonia make Venus more habitable?
The origin of the ammonia detected by the Green Bank radio telescope on Venus is as uncertain as that of the phosphine, but if its presence in Venus’s atmosphere is real, it could give microbial life a way to survive the extreme conditions there.
One obstacle to imagining how life could survive in Venus’s atmosphere is the extreme acidity of the environment, with clouds of pure sulfuric acid. Although the temperature at 31.6 to 38.5 miles (51 to 62 kilometers) is moderate, unlike the stifling 870 degrees Fahrenheit (465 degrees Celsius) on the surface, no one can see how life could survive the acidity.
Ammonia provides a way for life to do this. When mixed with sulfur dioxide, ammonia neutralizes some of the acidity.
“It’s still terribly acidic,” Clements said. “But it makes the droplets at least compatible with some acidophilic extremophile life that we know exists on Earth.”
The ability of life to survive in such conditions was also recently supported by the discovery that: amino acids can remain stable amid high concentrations of sulfuric acid.
It’s still possible that both the phosphine and ammonia detected around Venus have a more mundane explanation. After all, they’re both found in the atmospheres of gas giants. Jupiter And Saturn.
In these gas giants of the solar system, these chemicals form deep within the hydrogen atmosphere under conditions of extremely high pressure and high temperature before being carried to the cloud tops by rising convection currents.
The problem is that in hydrogen-rich atmospheres like those of Jupiter and Saturn, we would expect to find phosphine, which is made up of phosphorus with three hydrogen atoms, and ammonia, which is made up of one nitrogen atom with three hydrogen atoms.
“But if you’re in an oxygenated atmosphere like Venus or something like that, Soil“It all has to do with oxygen,” Clements said. “As soon as you have free hydrogen, it’s going to react with something that has oxygen. We haven’t explored the chemical pathways to produce ammonia as much as we have with phosphine because the results are so new, but I expect it to be exactly the same problem.”
Clements is open to the possibility that both phosphine and ammonia are produced by a rare form of photochemistry in Venus’s upper atmosphere, where solar ultraviolet light breaks apart molecules and allows phosphine and ammonia to form from the molecular debris. If that’s the case, no one has yet observed the process, even in the lab.
Another possibility that has been put forward is that phosphine could be produced as follows: Venus volcanoes.
Related Stories:
— Is there life on Venus? Phosphine, an interesting molecule, has been spotted again in the planet’s clouds
— If Venus had Earth-like plate tectonics in its distant past, was there life there too?
— Astronomers say the Magellanic Clouds should be renamed
Clements also spoke at the European Space Agency Jupiter Icy Moons Explorer (JUICE) will help launch Venus into the Jupiter system by flying by in August 2025. JUICE carries instruments that can detect phosphine and ammonia, but there is no guarantee that its instruments will be turned on and deployed to Venus.
“We’re still trying to convince engineers who don’t like to operate the devices during flight,” Clements said.
So, the presence of phosphine and ammonia in Venus’s atmosphere may remain controversial, even debatable, for some time to come. Given their potential implications for life, the stakes couldn’t be higher.
The team’s findings have not yet been peer-reviewed or published. Other scientists have not yet been able to examine them, but they were previewed in presentations at the National Astronomy Meeting 2024 in England in July.