Since the discovery of a chemical called phosphine on Venus was announced last September, the scientific community has been confused. Scientists have back and forth published articles to either debunk or reinforce the claim.
With two new papers coming in this week, some claim the nails are being hammered into the phosphine box. However, we suspect the detection will be explored and discussed for a while.
So what’s the actual deal? Read on for a brief introduction.
Phosphine on Venus? Why does it matter?
The discovery itself is quite fascinating. Using two different instruments at different times – the James Clerk Maxwell Telescope (JCMT) in 2017 and the Atacama Large Millimeter / submillimeter Array (ALMA) in 2019 – a team led by astrobiologist Jane Greaves of Cardiff University in the UK discovered the spectral signature of a chemical called phosphine in the atmosphere of Venus, at 20 parts per billion. The findings are published in Nature astronomy.
As we reported at the time, phosphine has been found in abundance here on Earth in anaerobic (oxygen-poor) ecosystems. It is found in swamps and silt, where anaerobic microbes thrive. It’s found in intestines and, well, farts. Somehow anaerobic microorganisms produce phosphine. And the clouds of Venus are anaerobic.
While Greaves and her team ruled out many possible abiotic pathways for phosphine formation in Venus, they noted very well that there could be other ways the chemical could appear. First, volcanoes here on Earth produce phosphine, and we have evidence that Venus is still volcanically active. (A volcanic origin was later found plausible in a different preprint.)
Regardless, the detection was fascinating, but the mention of a microbial origin sparked much speculation and a lot of follow-up research from other scientists.
What happened next?
Well, it all got a bit complicated. First, a team of scientists looked at historic Venus data and found that the Pioneer probe could have detected phosphine way back in 1978. That paper has not yet been accepted for publication. Another, submitted to the magazine Science and also not yet peer-reviewed, claimed to have detected the amino acid glycine – a protein building block – on Venus.
Other scientists began to look at the data. Three separate articles – one since published in Astronomy and Astrophysics on the ALMA data, another published in the Monthly Communications from the Royal Astronomical Society on the JCMT data, and the other who re-analyzed both datasets and is still awaiting peer review – found no significant detection of phosphine in Venus’ atmosphere.
Then it turned out that there was an error processing the data from the ALMA observations. Greaves requested reprocessing of the data; those reprocessed data were made public in November 2020.
Greaves and her team analyzed the new data and found that they could still detect phosphine on Venus, but in smaller quantities – a global average of 1 to 4 parts per billion, with local peaks of 5 to 10 parts per billion.
Since sulfur dioxide and phosphine both absorb radiation near the frequency of 266.94 gigahertz, some suggested that Greaves and her team may have detected sulfur dioxide (also produced by volcanic activity), and not phosphine. In their new paper, Greaves et al. Excluded sulfur dioxide. The spectral absorption line, interpreted as the chemical fingerprint of phosphine, they said, was too wide to be sulfur dioxide, and there was not enough on Venus to produce the observed signal.
A third paper by Greaves and her team followed, defending the robustness of the phosphine signal.
OK, so why is it back in the news now?
Two new articles have been deleted, one of which has been published in The Astrophysical Journal Letters, and the other of which has been accepted for publication in The Astrophysical Journal Letters, re-analyze the data. Both papers contribute to the anti-phosphine stack.
In the first article, both sets of ALMA data were re-analyzed, before and after they were reprocessed. The team found a spectral line at 266.94 gigahertz in the earlier data set, but no significant signal after the reprocessing. They also found that sulfur dioxide could be in at least 10 parts per billion and cannot be detected by ALMA, suggesting it could be more abundant than Greaves and her team thought.
The second paper used data from decades of Venus observations to model conditions in the Venusian atmosphere and determine how phosphine and sulfur dioxide would behave. They found that the 266.94-gigahertz signal fits best with an origin at about 80 kilometers (50 miles) above the cloud decks, rather than 50 to 60 kilometers, as suggested by Greaves and her team.
At this altitude, phosphine wouldn’t last very long at all, so the best explanation would be sulfur dioxide, they concluded.
Is that the end of it? Is the Venus Phosphine Detection dead?
Not even close! For starters, Greaves and her team will likely respond to the new articles, which will lead to more responses, with more simulations and models and number cracking and maybe even experiments to determine the possibilities and probabilities.
Plus, nothing we’ve seen so far is decisive. It’s more than likely that the only way we can put the controversy to rest is to make more detailed observations with more powerful tools. We might wait for that for a while. Several proposed missions to Venus are in the pipeline, but there is often a long time between proposal and execution.
However, this is science at its best. There is a ‘true’ and a ‘false’ here. Either there is phosphine on Venus or there is not. Scientists will use their creativity to solve the problem, which will lead to sophisticated techniques and analysis tools.
Ultimately, we will learn the truth. And whatever that truth is, it will teach us something new about our universe.