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New preliminary evidence for phosphine and ammonia in Venus’ atmosphere deepens the mystery of what produces these gases. The enigmatic 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 because of its extremely hot surface temperatures, enough to melt lead, and its terrifying surface pressure. The presence of phosphine and ammonia in the clouds of the second planet from the sun and the hottest planet in the solar system implies that if life were possible, it would be found high above the surface of Venus.
The new detections of phosphine and ammonia were obtained by a team led by Jane Greaves of 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 you make phosphine or ammonia in an oxygen-rich atmosphere like Venus,” team member and astrophysicist Dave Clements of Imperial College London told Space.com in an interview. But then again, it’s not clear why biology on Earth produces phosphine. “Whether it’s in penguin poop or badger guts, we don’t know why bacteria make phosphine, but they do.”
Related: Life on Venus? Intriguing molecule phosphine spotted again in planet’s clouds
Phosphine detection over Venus sparks controversy
The first detection of phosphine on Venus by Greaves and her team at the JCMT in 2020 sparked fierce controversy in some quarters.
The disagreements focused on the way the data was processed and whether this produced erroneous signals, since observations by other telescopes failed to detect the phosphine.
Clements said the technical differences have now been resolved and the latest measurements, using a new detector on the JCMT called Nāmakanui (meaning “Big Eyes” in Hawaiian), come from three observing campaigns, each of which provided 140 times as much data as the first detection.
Clements said the technical differences have now been resolved and the latest measurements, using a new detector on the JCMT called Nāmakanui (meaning “Big Eyes” in Hawaiian), come from three observing campaigns, each of which provided 140 times as much data as the first detection.
“Nāmakanui is an array of three different receivers on three different frequencies,” Clements said.
One of those receivers, called ‘Ū’ū (the name of a particular large-eyed, dark-seeing fish in the waters around Hawaii), can detect phosphine, as well as sulfur dioxide and “semiheavy water” (HDO), water with three hydrogen atoms instead of two and the usual one oxygen atom. Both sulfur dioxide and HDO vary over time in the clouds of Venus, and Greaves and Clements’ team wants to see how phosphine varies, too.
“There are suspicions and possibilities that the amount of phosphine can vary over time, but we don’t know what causes that variation,” Clements said.
One possibility is that ultraviolet light from the Sun breaks apart molecules in Venus’s upper atmosphere, creating variations in phosphine.
Clements pointed out that the first detection of phosphine came when JCMT observed the morning terminator on Venus, where the night side of the planet turned into the day side. At night, the ultraviolet sunlight would have no impact, allowing phosphine to build up.
The other observations, made by the European Space Agency’s Venus Express spacecraft, SOFIA (Stratospheric Observatory for Infrared Astronomy) and NASA’s Infrared Telescope Facility in Hawaii, were made on Venus as day was turning to night. The sun’s ultraviolet light would have already broken down most of the phosphine, making it difficult to detect.
Clements has since reanalyzed the SOFIA data and found a faint hint of phosphine. Rakesh Mogul of California State Polytechnic University also found phosphorus in large quantities when he reanalyzed mass spectrometer data from the old Pioneer Venus mission from 1978.
“If phosphine is destroyed by ultraviolet sunlight, that’s consistent with these other observations that don’t find it,” Clements said. It also suggests that the phosphine is being rapidly replenished by some unknown process.
And then there’s the ammonia.
Can ammonia make Venus more habitable?
The origins of ammonia, discovered on Venus by the Green Bank radio telescope, are as murky as those of phosphine. However, if its presence in the Venusian atmosphere is real, it could provide a way for microbial life to survive in the extreme conditions there.
One barrier to imagining how life could survive in Venus’ atmosphere is the sheer acidity of the environment, with clouds of pure sulfuric acid. Although the temperature at an altitude of 31.6 to 38.5 miles (51 to 62 kilometers) is moderate, in contrast to the sweltering 870 degrees Fahrenheit (465 degrees Celsius) on the surface, no one can imagine how life could survive the acidity.
Ammonia provides a way for life to do this. When mixed with sulfur dioxide, the ammonia neutralizes some of the acidity.
“It’s still terrifyingly acidic,” Clements said. “But it makes the droplets compatible with at least some acidophilic extremophilic life forms that we know exist on Earth.”
The ability of life to survive such conditions has also recently been supported by the discovery that amino acids can remain stable amid high concentrations of sulfuric acid.
It is still possible that both phosphine and ammonia found around Venus have a more mundane explanation. After all, both are found in the atmospheres of the gas giants Jupiter And Saturn.
In these gas giants of the solar system, these chemicals are formed deep in the hydrogen atmosphere under extremely high pressures and temperatures, and then carried to the cloud tops by upwelling convection currents.
The problem is that we would expect to find phosphine (made of phosphorus with three hydrogen atoms) and ammonia (made of one nitrogen atom with three hydrogen atoms) in hydrogen-rich atmospheres like those of Jupiter and Saturn.
“But if you’re in an oxygen-rich atmosphere, like Venus or Soil“Everything should be bound to oxygen,” Clements said. “Once you have free hydrogen, it will react with something that has oxygen in it. We haven’t explored the chemical pathways to produce ammonia as thoroughly as we did with phosphine because the result is so new, but I expect it will be exactly the same problem.”
Clements is open to the possibility that both phosphine and ammonia are produced by a rare photochemistry in the upper atmosphere of Venus, where ultraviolet sunlight breaks apart molecules and phosphine and ammonia can form from the molecular debris. If so, no one has yet observed this process, even in the lab.
Another possibility that has been suggested is that the phosphine could be produced by Volcanoes on Venus.
Related Stories:
— Life on Venus? Intriguing molecule phosphine spotted again in planet’s clouds
—If Venus had plate tectonics similar to Earth’s in the distant past, would there be life there too?
— The Magellanic Clouds need a new name, astronomers say
Clements also pointed out that the European Space Agency Jupiter icy moons explorer (JUICE) will fly by Venus in August 2025 to slingshot it toward the Jupiter system. JUICE carries instruments that can detect phosphine and ammonia, but there is no guarantee that the instruments will be turned on and deployed to Venus.
“We’re still trying to convince the engineers because they don’t want things turned on during flight,” Clements said.
So the existence of phosphine and ammonia in the atmosphere of Venus may remain up for debate, even controversy, for some time to come. Given the potential implications for life, the stakes could not be higher.
The team’s findings have not yet been peer-reviewed or published. Although other scientists have not yet been able to examine them, they were presented in presentations at the National Astronomy Meeting 2024 in the UK in July.