What happens with this detection of phosphine on Venus?

Since the discovery of a chemical called phosphine on Venus was announced in September of last year, the scientific community has been in a state of mind. Scientists have published papers back and forth, trying to debunk or strengthen the claim.

With the arrival of two new newspapers this week, some are claiming the nails are hammered into the phosphine coffin. We suspect, however, that the detection will continue to be reviewed and discussed for some time to come.

So what’s the problem? Read on for a brief overview.

Phosphine on Venus? Why is this important?

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 has detected the spectral signature of a chemical called phosphine in the Venusian atmosphere, at a rate of 20 parts per billion. The results were published in Nature astronomy.

As we reported at the time, here on Earth, phosphine has been found in abundance in anaerobic (oxygen-poor) ecosystems. It is found in swamps and sludges, where anaerobic microbes thrive. It is found in the intestines and, finally, in farts. One way or another, anaerobic microorganisms produce phosphine. And the clouds of Venus are anaerobic.

Although Greaves and his team ruled out many abiotic pathways of Venusian phosphine formation, they were careful to note that there could be other ways the chemical could appear. On the one hand, here on Earth, volcanoes produce phosphine, and we have proof that Venus is still volcanically active. (A volcanic origin was later found plausible in another preprint.)

Regardless, the detection was fascinating, but the mention of a microbial origin sparked much speculation and many follow-up reviews from other scientists.

What happened next?

Well, it all got a bit complicated. First, a team of scientists looked at historical data from Venus and discovered that the Pioneer probe could have detected phosphine since 1978. This article has not yet been accepted for publication. Another, submitted to the review Science and also not yet peer reviewed, claims to have detected the amino acid glycine – a protein building block – on Venus.

Other scientists have started looking at the data. Three separate articles – one since published in Astronomy and astrophysics on ALMA data, another published in the Monthly notices from the Royal Astronomical Society on the JCMT data, and the other reanalysis of the two datasets and still pending peer review – found no significant detection of phosphine in the atmosphere of Venus.

Then, it turned out that an error had occurred while processing the data of the ALMA observations. Greaves requested that the data be reprocessed; these restated data were made available to the public in November 2020.

Greaves and his team analyzed the new data and found they could 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 frequency of 266.94 gigahertz, some have suggested that Greaves and his team may have detected sulfur dioxide (also produced by volcanic activity) and not phosphine. In their new article, Greaves et al. excluded sulfur dioxide. The spectral absorption line interpreted as the chemical fingerprint of phosphine, they said, was too large to be sulfur dioxide, and there was not enough of it on Venus to produce the observed signal.

A third paper by Greaves and his team followed, defending the robustness of the phosphine signal.

OK, so why is this back in the news now?

Two new articles were dropped, one of which was published in Letters from the Astrophysical Journal, and the other of which has been accepted for publication in Letters from the Astrophysical Journal, reanalyze the data. Both papers contribute to the mounting stack against phosphine.

The first article reanalyzed the two ALMA datasets, before and after their reprocessing. The team found a spectral line at 266.94 gigahertz in the previous data set, but no significant signal after reprocessing. They also found that sulfur dioxide could appear in at least 10 parts per billion and go undetected by ALMA, suggesting it may be more abundant than Greaves and his team believed.

The second paper used data from decades of Venus observations to model the conditions of the Venusian atmosphere and determine the behavior of phosphine and sulfur dioxide. They found that the 266.94 gigahertz signal best matched an origin about 80 kilometers (50 miles) above the clouds, rather than 50 to 60 kilometers, as proposed by Greaves and his team.

At this altitude, phosphine wouldn’t last long at all, so the best explanation would be sulfur dioxide, they concluded.

Is this the end? Is Venus Phosphine Detection Dead?

Not even close! For starters, Greaves and his team will likely respond to the new articles, which will elicit more responses, with more simulations and modeling, calculating numbers, and maybe even experimentation to figure out what the possibilities and probabilities are.

Furthermore, nothing that we have seen so far is conclusive. It is more than likely that the only way to end the controversy is to take more detailed observations with more powerful instruments. We may be waiting for that for a while. There are several missions offered to Venus in the pipeline, but there is often a significant amount of 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 try to solve the problem, which will lead to sophisticated analysis techniques and tools.

Eventually we will learn the truth. And whatever this truth may be, it will teach us something new about our Universe.