Phosphine is a potential indicator of life on our extremely inhospitable neighboring planet.

And now the researchers who stunned the scientific community in 2020 when they announced the detection of phosphine in the atmosphere of Venus have detected it again, twice.

The team of scientists, led by Jane Greaves of Cardiff University in Wales, used the James Clerk Maxwell Telescope (JCMT) in Hawai’i to observe Venus’ atmosphere in February 2022 and May 2023 and found phosphine in both observing runs. 

Speaking at the Royal Astronomical Society's National Astronomy Meeting (NAM) 2023 in the UK on July 6, 2023, Greaves said her team was able to look deeper into the Venusian atmosphere, finding traces of phosphine, even down into Venus’ clouds, lower in the atmosphere than previous measurements. 

Phosphine was a completely unexpected finding on Venus, a place known to be bleak and uninhabitable. In one paper, Greaves and colleagues called the detection a “Wow! Signal in chemistry,” — referring to the famous “Wow!” signal, the strongest candidate for a genuine alien transmission. 

Phosphine is made from one phosphorous and three hydrogen atoms (PH3). It is flammable and toxic. On Earth, it is often thought of as swamp gas, produced by microorganisms living in a very low oxygen (anaerobic) environment.  On Venus, it is not obvious how it could be produced, which initially led some scientists to question the findings of Greaves’ team.

However, even though the phosphine was observed in low quantities at Venus, the fact that it has been found several times since its initial detection in 2017 infers the molecules are surprisingly persistent. Sunlight or the sulfuric acid in Venus’ clouds should annihilate the gas before it can accumulate. Repeated detections mean the phosphine must exist with some type of replenishing source, or there’s some odd type of unknown chemistry going on in Venus’ atmosphere. 

In her talk at NAM, Greaves said the several detections over the last few years, from three different sets of instruments, and from many methods of data processing keep providing more and more clues that there must be some sort of steady, replenishing source.

The initial detection was based on observations at JCMT in 2017, and the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in northern Chile in 2019. As we reported in September 2022, even though other scientists questioned the observations and conclusions, Greaves’ team detected the gas again in 2020 and 2021, both times using JCMT. 

Additionally, Greaves said a reanalysis of data from NASA’s airborne SOFIA (Stratospheric Observatory for Infrared Astronomy) observatory, which was previously thought to show a non-direction of phosphine, in fact, does show phosphine in the data. 

“By-passing some instrumental effects, we extract a detection with 6.5 [omega] confidence from the same data,” Greaves and her team wrote in their paper, published on arXiv. They also noted how observations during “mornings in Venus’ atmosphere” would show higher abundances of phosphine versus observations in the afternoon, since sunlight destroys phosphine. They said that all observations should be noted with a type of timestamp, which might explain differences in the amount of phosphine. “If the six available datasets can be reconciled in this way, further modeling of possible sources of PH3 (e.g. volcanic, disequilibrium chemistry, extant life) seems worthwhile,” the team wrote.

As they noted, one potential source for the phosphine would be active volcanism on Venus. While it has long been known that Venus is covered in volcanoes, whether any of them are still active has been highly debated. However, in March 2023, two researchers announced they had found evidence for recent active volcanos on Venus, using archival radar images taken in the 1990s by NASA’s Magellan spacecraft. 

Adding to the volcanism possibility, another paper, published in 2021, concluded that volcanism could provide an adequate amount of detectable phosphine. The authors said that small amounts of phosphides from deep inside Venus’ mantle could be brought to the surface by volcanism, then ejected into the atmosphere in the form of volcanic dust by explosive volcanic eruptions.

The question regarding phosphine in Venus’ atmosphere is likely to be debated for some time. Astronomer Chris Lintott from the University of Oxford told Supercluster that more observations are needed. 

“I’m shocked that that team hasn’t been awarded more time with ALMA; checking what’s going on with this more powerful instrument seems essential,” said Lintott, who is not involved with the Greaves team study. “The hope is to make a better case with new JCMT data that might show whether the phosphine appears in Venusian morning, evening, or daytime.”

But the debate continues, with some scientists still questioning the phosphine findings.

“Of course, even if the Phosphine is real,” Lintott said, “understanding what is causing it is another matter. My guess would be exotic chemistry in the atmosphere - but isn’t that exciting too?”

However, until a spacecraft can go to Venus to make in situ observations, the back and forth on this finding will likely remain. Even though only one space mission has gone to Venus in the past 30 years, the recent resurgence of interest in Earth’s closest neighbor has NASA and ESA committing to three new missions to Venus, all due to launch by the early 2030s.

NASA has DAVINCI (Deep Atmosphere Venus Investigation of Noble Gases, Chemistry, and Imaging) and VERITAS (Venus Emissivity, Radio Science, InSAR, Topograph, and Spectroscopy), and Europe has the EnVision orbiter.