New preliminary evidence for the presence of phosphine and ammonia in the atmosphere of Venus deepens the mystery of what exactly makes up 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 for life, with its surface temperature high enough to melt lead and its terrifying surface pressure. The second planet from the Sun and the hottest planet in the Solar System has phosphine and ammonia in its clouds, meaning that if life existed there, it would be far above Venus’s surface.

The new detections of phosphine and ammonia were achieved by a team led by Jane Greaves from Cardiff University, using submillimetre radio waves 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 can be produced in an oxygen-saturated atmosphere.
“Venus,” team member and astrophysicist Dave Clements of Imperial College London told Space.com. Again, it’s not clear why the biology
The world produces phosphine.” We don’t know why bacteria produce phosphine in penguin feces or badger guts, but they do.”

Discovery of phosphine on Venus is controversial

The first detection of phosphine on Venus by Greaves and his team in 2020 with JCMT was met with fierce disagreement from some quarters, with some focusing on how the data was processed and whether it created false signals because observations with other telescopes failed to detect phosphine.

Clements said those technical differences have now been resolved, and the latest measurements, made using a new detector at JCMT called Nāmakanui (which means “Big Eyes” in Hawaiian), come from three observing campaigns, each providing 140 times more data than the first detection.

Clements said those technical differences have now been resolved, and the latest measurements, made using a new detector at JCMT called Nāmakanui (which means “Big Eyes” in Hawaiian), come from three observing campaigns, each providing 140 times more data than the first detection.

“Nāmakanui is a set of three different receivers at three different frequencies,” Clements said.

One of these receptors, called `Ū’ū (named after a large-eyed fish in the waters around Hawaii that can see in the dark), is capable of detecting phosphine as well as sulfur dioxide and “semi-heavy water” (HDO), water with three hydrogen atoms instead of two and the usual one oxygen atom. Both sulfur dioxide and HDO change over time in Venus’s clouds, and Greaves and Clements’ team also wanted to see how phosphine changes.

“There is a suspicion, a possibility, that the amount of phosphine may be changing over time, but we don’t know what’s causing that variability,” Clements said.

One possibility is that ultraviolet light from the Sun breaks down molecules in Venus’s upper atmosphere, causing phosphine to volatilize. Clements noted that the first detection of phosphine occurred when JCMT observed the morning terminator on Venus, when the night side of the planet turns into day. At night, the Sun’s UV light would have no effect, causing the phosphine to accumulate.

Other observations by the European Space Agency’s Venus Express spacecraft SOFIA (Stratospheric Observatory for Infrared Astronomy) and NASA’s Infrared Telescope Facility in Hawaii observed Venus as day turned into night, and the sun’s ultraviolet radiation may have been significantly scattered by phosphine, so it was difficult for them to detect it.

Clements later reanalyzed the SOFIA data and found a faint hint of phosphine. Rakesh Mogul of California State Polytechnic University also found large amounts of phosphorus when he reanalyzed mass spectrometer data from the old Pioneer Venus mission in 1978.

“If phosphine is destroyed by the sun’s ultraviolet rays, that’s consistent with other observations that don’t detect it,” Clements said. It also suggests that phosphine is being rapidly replenished by an unknown process.

Could ammonia make Venus more habitable?

The origin of ammonia detected on Venus by the Green Bank radio telescope is as uncertain as the origin of phosphine, but if its presence in the Venusian atmosphere is real, it could enable microbial life to survive in the extreme conditions there.

One obstacle to the idea of ​​how life could survive in Venus’s atmosphere is the sheer acidity of the atmosphere, which consists of clouds of pure sulfuric acid. Although temperatures are mild at 31.6 to 38.5 miles (51 to 62 kilometers) above the Earth, unlike the sweltering 870 degrees Fahrenheit (465 degrees Celsius) on the surface, no one understands how life could survive in the acidity. Ammonia provides it. When mixed with sulfur dioxide, ammonia neutralizes some of the acidity.

“It’s still very sour,” Clements said. “But this makes the droplets at least compatible with the acidophilic extremophiles that we know exist on Earth.”

The ability of life to survive in such conditions was confirmed by the recent discovery that amino acids can remain stable in high concentrations of sulfuric acid. It is still possible that there is a more prosaic explanation for both the phosphine and ammonia found around Venus. After all, both are found in the atmospheres of the gas giants Jupiter and Saturn.

In the 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 upward convection currents.

The problem is that we would expect to find phosphine (consisting of phosphorus with three hydrogen atoms) and ammonia (consisting of one nitrogen atom with three hydrogen atoms) in hydrogen-rich atmospheres like those of Jupiter and Saturn.

“But when you’re in an oxygen-rich atmosphere like Venus or Earth, it’s all about 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 for ammonia production as much as we have for phosphine because the result is so new, but I think it’s exactly the same problem.”

Clements suggests the possibility that both phosphine and ammonia are produced by some rare photochemistry in Venus’s upper atmosphere, involving solar ultraviolet light splitting molecules and allowing phosphine and ammonia to form from the molecular debris. If so, no one has yet observed this process, even in the lab.

Clements also noted that the European Space Agency’s Jupiter Ice Orbiter Explorer (JUICE) will fly past Venus in August 2025 to help guide it toward the Jupiter system. JUICE has instruments that can detect phosphine and ammonia, but there’s no guarantee its instruments will be turned on and deployed on Venus.

“We’re still trying to convince engineers who don’t like to include certain things in flight,” Clements said.

Therefore, the presence of phosphine and ammonia in the atmosphere of Venus may remain controversial, even debatable, for some time to come. Given the possible consequences for life, the risk could not be higher.

The team’s findings have not yet been peer-reviewed or published. While other scientists have not yet been able to examine them closely, they were presented in presentations at the 2024 National Astronomy Meeting in England in July.