Since the discovery of a chemical called phosphine on Venus in September last year, the scientific community has been in a dilemma. Scientists have published articles back and forth, trying to ward off or reinforce the claim.
With two new papers landing this week, some claim the nails are being hammered into the phosphine coffin. However, we suspect that the detection will take some time to be reviewed and discussed.
So, what is the actual transaction? Read on for a brief cover.
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 United Kingdom detected the spectral signature. a chemical called phosphine in the Venusian atmosphere, at 20 parts per billion. The findings were published in Natural Astronomy.
As we reported at the time, phosphine was found in abundance here on earth in anaerobic (low oxygen) ecosystems. It is found in swamps and sludge, where anaerobic microbes thrive. It is found in intestines and, well, vessels. Somehow anaerobic microorganisms produce phosphine. And the clouds of Venus are anaerobic.
Although Greaves and her team ruled out many possible abiotic venous phosphine formation pathways, they were very careful to note that there are other ways the chemical can occur. 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 another preprint.)
Either way, the detection was fascinating, but the mention of a microbial origin caused much speculation and much follow-up investigation by other scientists.
What happened next?
It all got a little complicated. First, a team of scientists looked at the historical data of Venus and found that the Pioneer probe was able to detect phosphine as early as 1978. The article has not yet been accepted for publication. Another submitted to the journal Science nor has he yet been peer-reviewed, claiming to have detected the amino acid glycine – a protein building block – on Venus.
Other scientists began looking at the data. Three separate papers – one since its publication in Astronomy & Astrophysics on the ALMA data, another was published in the Monthly notices from the Royal Astronomical Society on the JCMT data, and the others reviewed both data sets and were still awaiting peer review – found no significant detection of phosphine in the atmosphere of Venus.
Then it turned out that there was an error processing the data from the ALMA observations. Greaves requested that the data be re-processed; these processed data were made available to the public in November 2020.
Greaves and her team analyzed the new data and found that they can still detect phosphine on Venus, but in lower amounts – a global average of 1 to 4 parts per billion, with localized peaks of 5 to 10 parts per billion.
Since sulfur dioxide and phosphine both absorb radiation near the 266.94 gigahertz frequency, some suggested that Greaves and her team detected sulfur dioxide (also by volcanic activity) and not phosphine. In their new paper, Greaves et al. sulfur dioxide excluded. According to them, the spectral absorption line was interpreted as the chemical fingerprint of phosphine, too wide to be sulfur dioxide, and there was not enough of it on Venus to provide the observed signal.
A third article by Greaves and her team follows, defending the robustness of the phosphine signal.
OK, so why is it in the news again now?
Two new articles have fallen, one of which in The astrophysical journal letters, and the other one was accepted for publication in The astrophysical journal letters, review the data. Both papers contribute to the mounting stack against phosphine.
The first article reviewed both sets of ALMA data, before and after it was re-processed. The team found a spectral line at 266.94 gigahertz in the previous dataset, but no significant signal after the rework. They also found that sulfur dioxide could be present in at least 10 parts per billion and could not be detected by ALMA, suggesting it could be more prevalent than Greaves and her team thought.
The second paper uses data from decades of Venus observations to model the conditions in the Venus atmosphere and to determine how phosphine and sulfur dioxide will behave. They found that the 266.94-gigahertz signal best suited an origin about 80 kilometers (50 miles) above the cloud cover, rather than 50 to 60 kilometers, as suggested by Greaves and her team.
At this level, phosphine would not last long at all, so sulfur dioxide would be the best explanation.
Is this the end of it? Is the detection of Venus phosphine dead?
Not even close! To begin with, Greaves and her team are likely to respond to the new papers, which will elicit more responses, with more simulations and modeling and number matching and perhaps even experimentation to determine what the possibilities and probabilities are.
Moreover, nothing we have seen so far is conclusive. It is likely that the only way we can calm the controversy is to make more detailed observations with more powerful instruments. We may be waiting for that for a while. There are several proposed missions to Venus in the offing, but it often takes a long time between proposal and execution.
However, this is science at its best. Here’s a ‘true’ and ‘false’. There is phosphine on Venus, or not. Scientists will use their creativity to solve the problem, which will lead to refined techniques and analytical tools.
Eventually we will learn the truth. And whatever the truth is, it will teach us something new about our universe.