Claim: Hints of life on Venus: Scientists detect phosphine molecules in high cloud decks


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Hints of Life On Venus - Scientists detect phosphine molecules in high cloud decks

An international team of astronomers, led by Professor Jane Greaves of Cardiff University, today announced the discovery of a rare molecule—phosphine—in the clouds of Venus. On Earth, this gas is only made industrially, or by microbes that thrive in oxygen-free environments.

Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes—floating free of the scorching surface, but still needing to tolerate very high acidity. The detection of phosphine molecules, which consist of hydrogen and phosphorus, could point to this extra-terrestrial 'aerial' life. The new discovery is described in a paper in Nature Astronomy.

The team first used the James Clerk Maxwell Telescope (JCMT) in Hawaii to detect the phosphine, and were then awarded time to follow up their discovery with 45 telescopes of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Both facilities observed Venus at a wavelength of about 1 millimeter, much longer than the human eye can see—only telescopes at high altitude can detect this wavelength effectively.

Professor Greaves says, "This was an experiment made out of pure curiosity, really—taking advantage of JCMT's powerful technology, and thinking about future instruments. I thought we'd just be able to rule out extreme scenarios, like the clouds being stuffed full of organisms. When we got the first hints of phosphine in Venus' spectrum, it was a shock!"

Naturally cautious about the initial findings, Greaves and her team were delighted to get three hours of time with the more sensitive ALMA observatory. Bad weather added a frustrating delay, but after six months of data processing, the discovery was confirmed.

Team member Dr. Anita Richards, of the UK ALMA Regional Centre and the University of Manchester, adds: "To our great relief, the conditions were good at ALMA for follow-up observations while Venus was at a suitable angle to Earth. Processing the data was tricky, though, as ALMA isn't usually looking for very subtle effects in very bright objects like Venus."

Greaves adds: "In the end, we found that both observatories had seen the same thing—faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below."

Hints of life on Venus Synthesized false colour image of Venus, using 283-nm and 365-nm band images taken by the Venus Ultraviolet Imager (UVI). Credit: JAXA / ISAS / Akatsuki Project Team
Professor Hideo Sagawa of Kyoto Sangyo University then used his models for the Venusian atmosphere to interpret the data, finding that phosphine is present but scarce—only about twenty molecules in every billion.

The astronomers then ran calculations to see if the phosphine could come from natural processes on Venus. They caution that some information is lacking—in fact, the only other study of phosphorus on Venus came from one lander experiment, carried by the Soviet Vega 2 mission in 1985.

Massachusetts Institute of Technology scientist Dr. William Bains led the work on assessing natural ways to make phosphine. Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning, but none of these could make anywhere near enough of it. Natural sources were found to make at most one ten thousandth of the amount of phosphine that the telescopes saw.

To create the observed quantity of phosphine on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity, according to calculations by Dr. Paul Rimmer of Cambridge University. Any microbes on Venus will likely be very different to their Earth cousins though, to survive in hyper-acidic conditions.

Earth bacteria can absorb phosphate minerals, add hydrogen, and ultimately expel phosphine gas. It costs them energy to do this, so why they do it is not clear. The phosphine could be just a waste product, but other scientists have suggested purposes like warding off rival bacteria.

Another MIT team-member, Dr. Clara Sousa Silva, was also thinking about searching for phosphine as a 'biosignature' gas of non-oxygen-using life on planets around other stars, because normal chemistry makes so little of it.

She comments: "Finding phosphine on Venus was an unexpected bonus! The discovery raises many questions, such as how any organisms could survive. On Earth, some microbes can cope with up to about 5% of acid in their environment—but the clouds of Venus are almost entirely made of acid."

Other possible biosignatures in the Solar System may exist, like methane on Mars and water venting from the icy moons Europa and Enceladus. On Venus, it has been suggested that dark streaks where ultraviolet light is absorbed could come from colonies of microbes. The Akatsuki spacecraft, launched by the Japanese space agency JAXA, is currently mapping these dark streaks to understand more about this 'unknown ultraviolet absorber.'

The team believes their discovery is significant because they can rule out many alternative ways to make phosphine, but they acknowledge that confirming the presence of "life" needs a lot more work. Although the high clouds of Venus have temperatures up to a pleasant 30 degrees centigrade, they are incredibly acidic—around 90% sulphuric acid—posing major issues for microbes to survive there. Professor Sara Seager and Dr. Janusz Petkowski, also both at MIT, are investigating how microbes could shield themselves inside droplets.

The team are now eagerly awaiting more telescope time, for example to establish whether the phosphine is in a relatively temperate part of the clouds, and to look for other gases associated with life. New space missions could also travel to our neighboring planet, and sample the clouds in situ to further search for signs of life.

Professor Emma Bunce, President of the Royal Astronomical Society, congratulated the team on their work, "A key question in science is whether life exists beyond Earth, and the discovery by Professor Jane Greaves and her team is a key step forward in that quest. I'm particularly delighted to see UK scientists leading such an important breakthrough—something that makes a strong case for a return space mission to Venus."

Science Minister Amanda Solloway said, "Venus has for decades captured the imagination of scientists and astronomers across the world."

"This discovery is immensely exciting, helping us increase our understanding of the universe and even whether there could be life on Venus. I am incredibly proud that this fascinating detection was led by some of the UK's leading scientists and engineers using state of the art facilities built on our own soil."
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This is my first new post, I'm trying to follow the posting guidelines correctly.
In my opinion the claim that phosphine molecules is indicative of possible alien life is so ridiculous, that it rises to the level of needing debunking. It looked to me like they detected signatures of phosphine molecules at concentrations of around 2 PPB (parts per billion).
The article said:
Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning, but none of these could make anywhere near enough of it.
With the lack of knowledge that we have about the surface of Venus and the types of chemical reactions that could be in play, to so quickly dismiss these in complete ignorance but yet give preference to an Alien Life hypothesis is unbelievable to me.

Furthermore, if phosphene is a byproduct of a microbial reaction, and it can be detected at 2 PPB, then we should be able to detect the change in sulfuric acid or hydrogen sulfide concentrations that would result from it. They also keep saying "so much phosphene! too much to explain!" But 2 PPB is nothing.

From Wikipedia


Composition of the atmosphere of Venus. The chart on the right is an expanded view of the trace elements that all together do not even make up a tenth of a percent.
The atmosphere of Venus is composed of 96.5% carbon dioxide, 3.5% nitrogen, and traces of other gases, most notably sulfur dioxide.[12] The amount of nitrogen in the atmosphere is relatively small compared to the amount of carbon dioxide, but because the atmosphere is so much thicker than that on Earth, its total nitrogen content is roughly four times higher than Earth's, even though on Earth nitrogen makes up about 78% of the atmosphere.[1][13]

The atmosphere contains a range of compounds in small quantities, including some based on hydrogen, such as hydrogen chloride (HCl) and hydrogen fluoride (HF). There is carbon monoxide, water vapour and atomic oxygen as well.[2][3] Hydrogen is in relatively short supply in the Venusian atmosphere. A large amount of the planet's hydrogen is theorised to have been lost to space,[14] with the remainder being mostly bound up in sulfuric acid (H2SO4) and hydrogen sulfide (H2S). The loss of significant amounts of hydrogen is proven by a very high D–H ratio measured in the Venusian atmosphere.[3] The ratio is about 0.015–0.025, which is 100–150 times higher than the terrestrial value of 1.6×10−4.[2][15] According to some measurements, in the upper atmosphere of Venus D/H ratio is 1.5 higher than in the bulk atmosphere.[2]

In September 2020, it was announced that phosphine, a potential biomarker indicating the presence of life, had been detected in the atmosphere of Venus. No known abiotic source present on Venus could produce phosphine in the quantities detected.[10][16]

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"No known source". So why not hypothesize a new abiotic source? Why hypothesize an unknown biological source instead? This type of nonsense is why lay people distrust the scientific community. I guarantee within a few months or years someone will either fail to repeat the observations or come up with a far more plausible abiotic theory. I get so annoyed when the answer to anything knew is always "aliens". I guess this isn't a complete debunk scientifically since I can't prove a negative, but so many of the alternative theories such as lightning and volcanoes are so much more plausible, that I can actually imagine a chemical mechanism for how they can produce phosphine, far more readily than some weird living organism high up in the atmosphere with almost no access to hydrogen.

There's at least a few abiotic methods for producing phosphine on earth. Tell me why this couldn't happen in the atmosphere of Venus instead of by aliens.

A.V. Lyubimov, V.F. Garry, in Hayes' Handbook of Pesticide Toxicology (Third Edition), 2010
104.1.1 Physical Properties
Pure phosphine is an odorless and colorless gas with a molecular weight of 34.00 and density of 1.17 at 25°C. Commercial grade phosphine derived from aluminum or magnesium phosphide can contain to a variable degree higher molecular weight phosphines including diphosphines. These higher phosphines give commercial grade fumigants containing aluminum or magnesium phosphide odor characteristics described as decaying fish or “garlic-like.” Commercial grade phosphine containing diphosphines can ignite and form explosive mixtures at concentrations exceeding 1.8% phosphine in air. The rate of conversion of the phosphide to phosphine is temperature and humidity dependent. Similarly, metal phosphides readily hydrolyze in water to yield phosphine, which is poorly soluble in water.
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Again from Wikipedia

Preparation and occurrence[edit]
Phosphine may be prepared in a variety of ways.[10] Industrially it can be made by the reaction of white phosphorus with sodium or potassium hydroxide, producing potassium or sodium hypophosphite as a by-product.

3 KOH + P4 + 3 H2O → 3 KH2PO2 + PH3
Alternatively, the acid-catalyzed disproportionation of white phosphorus yields phosphoric acid and phosphine. Both routes have industrial significance; the acid route is the preferred method if further reaction of the phosphine to substituted phosphines is needed. The acid route requires purification and pressurizing. It can also be made (as described above) by the hydrolysis of a metal phosphide, such as aluminium phosphide or calcium phosphide. Pure samples of phosphine, free from P2H4, may be prepared using the action of potassium hydroxide on phosphonium iodide (PH4I).

Laboratory routes[edit]
It is prepared in the laboratory by disproportionation of phosphorous acid[11]

4 H3PO3 → PH3 + 3 H3PO4
Phosphine evolution occurs at around 200 °C. Alternative methods involve the hydrolysis of aluminium phosphide, calcium phosphide, and tris(trimethylsilyl)phosphine.

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Amber Robot

Active Member
Although I agree that it is more likely an unknown abiotic source, none of your criticisms seem to actually address their arguments quantifiably. If you “can actually imagine a chemical mechanism for how they can produce phosphine” then you should write a paper showing how your mechanism accounts for the concentration observed. I haven’t fully read their paper yet but my understanding is that they considered abiotic sources but couldn’t account for the observed concentration. They address quantitatively various methods of production (with citations) in their paper. Which calculation of theirs do you take issue with? Having a qualitative objection akin to argument from incredulity won’t cut it in a scientific argument.


Senior Member.
"No known source". So why not hypothesize a new abiotic source? Why hypothesize an unknown biological source instead? This type of nonsense is why lay people distrust the scientific community.

But every professional comment I have heard on this has acknowledged the possibility that there might be other explanations, while also acknowledging that the researchers have addressed the known possible abiotic sources. Even the team leader, Jaane Greaves, said this in a TV interview I saw. So why should this cause anyone to distrust the scientific community, when they seem to be taking exactly the correct fallibilistic approach?

Unless you have evidence to the contrary, both the Greaves group and those examining seem to be doing just what scientific approaches would require.

By chance I was just listening to this excellent podcast on philosophy of science which used the Venus phospine issue as an very good instance of a the way science should address unconceived alternatives.

Edit: I thought I should add a link to the original paper:
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Senior Member.
There are no extraordinary claims in the original scientific report. It is just a media hype.
This here.

The original report emphasizes volcanism as a possible source. It's very hard to pin down how much volcanic activity Venus has, because while it appears to be none right now, it also appears to have been incredibly huge not long ago. Earlier this year there was a report of rising and receding magma domes in the crust - Venus doesn't have tectonic plates and has a thicker crust than Earth, but it has the same mantle activity with nowhere for it to break through. Evidence suggests when an eruption happens it's cataclysmic, the most recent one seems to have resurfaced much of the planet and nothing on the surface is as old as most of Earth's continental crust, meaning its likely happened more than once.

That said, our current beliefs about the planet don't account for the current phosphine levels, but our understanding of volcanoes on Venus is pretty speculative. We don't have a great estimate for how old the surface is, only that it's younger than Earth's continents and the other terrestrial planets, or exactly what happened to renew it.

One of the things happening after this paper is a "prediscovery" search, looking for existing data that also shows phosphine that was missed or ignored (planetary astronomy produces immense data sets and a scientist looking at, say, sulphur reaction chains in the clouds can't chase down every random trace gas signature or they'd never get anywhere), to see if this might be declining, rising, or temporary, all of which would point to geological sources, or if it's steady, which would be the real puzzle.


Senior Member.

So the follow-ups have been coming in. Several other groups have failed to find any phosphine, and going through archival data for pre-discovery detections has come up empty (except for Pioneer-Venus, which tentatively supported phosphine but did not have sufficient data for conclusive results).

Two groups reprocessed the raw data from the original observations, and also did not find phosphine. Both groups identified possible data analysis glitches.

The first group, comprising more than two dozen researchers, failed to find evidence for phosphine in both the JCMT and ALMA data. JCMT did detect a spectral line at the right frequency, but the team suggests it can be explained by sulfur dioxide gas in the atmosphere of Venus, which happens to generate a spectral line in the same place.
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One group suggests an identification error matching a spectral line for sulfur dioxide (abundant in the upper atmosphere of Venus) to phosphine. The original paper *did* address this overlap, this particular line was stronger than it should be relative to other lines from sulfur dioxide, suggesting an additional source (i.e. phosphine) with a line at that frequency. The strong line, however, goes to the other group's reanalysis:

To make matters more complicated, the ALMA observatory recently identified an error in its calibration system that produced a spectrum of Venus with a lot of noise for Greaves and her colleagues to work with. “This data is messy, and noisy, and delicate,” Sousa-Silva says. (ALMA has removed the original Venus data from the archive and is reprocessing it now.)
Using a technique called polynomial fitting, the original discovery team looked for phosphine’s spectral line by mathematically removing background noise around the region in the spectrum where phosphine should be. In principle, this type of analysis allows astronomers to predict which parts of the observations are noise and which are real signals.
Butler downloaded the ALMA data and started from scratch, redid some of the initial calibrations, and then processed the data as he normally would. He didn’t find any evidence of phosphine in the planet’s spectrum
Another analysis of the ALMA data, led by Leiden Observatory’s Ignas Snellen and colleagues, also failed to find any sign of phosphine. Similarly, that team reported that high-order polynomial fitting could create multiple spurious spectral lines.
“They’ve shown that this fitting process can be really problematic,” Nixon says. “It’s very temperamental and it can produce features as easily as it can remove them. In the end, you’re not really sure what you’re looking at anymore.”
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The other suggests a more complicated data processing error, the raw data was unusually noisy and a very high order polynomial was used to filter for noise. The more noise you need to filter, the more complex the math and the greater chance for the processing to introduce artifacts. Using different filtering processes cancelled out the phosphine detection.

And for fun, one of the best sentences I think I've read in a science article:
Humans make [phosphine] too, in meth labs and as part of the semiconductor industry.
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That's quite the Venn diagram right there.

The short version: This currently appears to be a false alarm caused by poor raw data.
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NorCal Dave

Senior Member.
Just the musings of a non-scientist, but is this more a sign of our current culture? A world of "influencers". Everybody has to be on Instagram, Facebook, Twitter, LinkedIn, Tumbler, ok, maybe not Tumbler. You have to Google your business, have it listed on Alexa and check your Yelp reviews. You always need more followers and subscribers.

You think you found phosphine? You want a good write up? More money for more research? You better get the hype going.
The team first used the James Clerk Maxwell Telescope (JCMT) in Hawaii to detect the phosphine, and were then awarded time to follow up their discovery with 45 telescopes of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.
Right from beginning, finding phosphine on the big telescope leads to being "awarded" time on the really big telescope.

After that, how do they proceed? "Hey, we think we found some phosphine. Anybody else seeing this? And if you do, while it's known to be linked to certain micro-organisms, we should first rule out abiotic sources, especially ones that may happen someplace as different as Venus. Again, assuming anyone can replicate the finding in the first place." Zzzzzz. No, they announced that they found it, speculated on why, advance alien life as distinct possibility and, by listing abiotic sources, but showing that they can't account for amount found, kinda give weight to the alien idea. That's something that's goin to be picked up in the press.

It's like Scientific Instagramming. Maybe? We all want hype. Not "Metabunkers", but in general.

I'm not condemning or excusing. Scientists are people and are part of our culture. They want followers too. Fortunately science, unlike the world of influencers, is ultimately self correcting, as appears to be the case above.


Senior Member.
If anything the influencer era has actually calmed it down because scientists can actually participate and actively knock down stories about their work - generally an article in the journals is noticed in a keyword search and a journalist with a high school understanding (if we're lucky) writes it up, pulling answers to any "questions" from scholarly articles rather than obtaining them directly.

A good example was the "cephalopods are panspermia aliens" hype from a couple years ago, the scientists involved were right there on every social media platform to explain that in fact their work was the exact opposite. Similar claims that hit the mainstream media cycle even ten years ago were basically unanswerable for the scientists who never made the outlandish claims they were getting attached to them, something that actually ruined a few careers.

Alexandria Nick

Active Member
Right from beginning, finding phosphine on the big telescope leads to being "awarded" time on the really big telescope.
Observation time is a pretty big battle to win, but there's perfectly valid reasons to prioritize one project over another. For instance, they could have pitched it to the observatory that they're is a potential seasonality to the observation.

Amber Robot

Active Member
Right from beginning, finding phosphine on the big telescope leads to being "awarded" time on the really big telescope.

yes. A promising detection on one telescope is quite often a good justification for award for follow up on another telescope. Nothing out of place there. However, it appears that the original detection was very likely a misidentification.

NorCal Dave

Senior Member.
If anything the influencer era has actually calmed it down because scientists can actually participate and actively knock down stories about their work - generally an article in the journals is noticed in a keyword search and a journalist with a high school understanding (if we're lucky) writes it up, pulling answers to any "questions" from scholarly articles rather than obtaining them directly.
Good point. It cuts both ways. I guess I got caught up in the negative aspect of it.
yes. A promising detection on one telescope is quite often a good justification for award for follow up on another telescope. Nothing out of place there. However, it appears that the original detection was very likely a misidentification.
I'm sure that's true. I guess my takeaway, from the way the quoted article was written, is that, to get more time, one must, understandably, give a good reason. It just seemed like, "hey, we may have found phosphine, but not sure" wasn't going to cut it. "Hey we found phosphine, and that might mean alien life! Can we get on the big 'scope?" is the way it seemed to come across. Again, just from reading the original article as posted.


Senior Member.
but it took CNN only six sentences to get to ALIENS:
They don't write "aliens", they write "life", and ever since the news from Mars, we know that that's going to mean possibly single-cell organisms at best.

"Aliens" is your own interpretation. CNN simply talks about whether Titan may be habitable.
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Senior Member.
"Hey we found phosphine, and that might mean alien life! Can we get on the big 'scope?" is the way it seemed to come across.
The people who decide these telescope allocations are astrophysicists. They'd know there aren't any "aliens" there. They'd understand, "hey, we found phosphine, and that might mean organic chemistry!" It's big news.

The original article quoted in post #1 talks about "microbes".

Alexandria Nick

Active Member
They get to "life" that fast because it isn't the first time it has come up. Titan as potentially populated by microorganisms has been conceptualized for a while now. Modeling biochemistry that uses hydrocarbons as a solvent instead of water produces observable atmospheric markers and those markers have already been detected in Cassini data.


Senior Member.
The people who decide these telescope allocations are astrophysicists.
Also: It wasn't the original team who got time on the better telescopes. The original team hasn't gotten follow up chances yet, only their original set of observations. The follow ups have been from other teams.

Considering how quickly some of the follow ups followed the publication, they probably already had the time booked and noting they had an angle on Venus took time out of their own projects to take a quick set of observations.

Amber Robot

Active Member
I don’t think there have been follow up observations since that paper. One team looked at archival data and another reprocessed the same data and determined a non-detection.


Senior Member.
Nature reports that the original scientists have repeated their analysis and found an error:
The reanalysis, based on radio-telescope observations at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, concludes that average phosphine levels across Venus are about one part per billion — approximately one-seventh of the earlier estimate. Unlike in their original report, the scientists now describe their discovery of phosphine on Venus as tentative

This is it:
To summarise: we tentatively recover PH3 in Venus’ atmosphere with ALMA (~5σ confidence). Localised abundance appears to peak at ~5 parts-per-billion, with suggestions of spatial variation. Advanced data-products suggest a planet-averaged PH3 abundance ~1 ppb, ~7 times lower than from the earlier ALMA processing.

How confident is that?
In the social sciences, a result may be considered "significant" if its confidence level is of the order of a two-sigma effect (95%), while in particle physics, there is a convention of a five-sigma effect (99.99994% confidence) being required to qualify as a discovery.

So the phosphine is definitely there. The question is, which sources can account for that quantity? And why does the analysis show regions with more PH3?
One group suggests an identification error matching a spectral line for sulfur dioxide (abundant in the upper atmosphere of Venus) to phosphine.
From the re-analysis paper:
SO2 contamination was already considered in detail by G2020 (see Methods and Figure 4). Because the two transitions are separated by 1.3 km/s but both lines are expected to be a few 2 km/s wide, they will not appear as two separate minima at any spectral resolution. The limit in identification here is the precision of the centroid of the line minimum (calculated in Table 1 of G2020). The intrinsic spectral resolutions of the datasets are 0.034 km/s (JCMT) and 0.069 km/s (ALMA), and the centroids are measured to precision as good as 0.3 km/s. The spectra were shown in G2020 with larger velocity-bins for clarity, but this does not affect the precision. [..] We describe below our conclusion that the feature identified as PH3 can not be explained as SO2, because of the extreme-outlier SO2-abundance this would require, and the incompatibility of the observed line width.
As an analogy, imagine if you had two partially overlapping dartboards and a fuzzy picture of darts sticking in the board, and you're trying to figure out which board the darts were thrown at. Obviously, for each single dart, you won't be able to decide that, but if you consider which bullseye the darts are centered on, you can tell, if your picture shows enough detail. If you see the darts centered on the PH3 target, you'll conclude that this is unlikely to happen by chance ("extreme outlier") if someone throws darts at SO2.

Then the idea is, maybe somebody threw very many darts at the SO2 board, and you're looking at the PH3 board and seeing lots of darts and then wrongfully conclude that that's what they aimed at. But for that to work, you'd have to have very many darts thrown at SO3:
V2020 consider that the JCMT feature can be fully reproduced by a mesospheric abundance of ~100 ppb of SO2, reading such a value off the altitudinal molecular-abundances plot shown as Extended Data Figure 9 in G2020.

To address this point, we re-examined the JCMT data. Figure (f2) shows the spectrum obtained by G2020 (in the mid-range |v| = 5 km/s reduction), overlaid with a linearly-scaled version of our radiative transfer model of the proposed SO2 line, after baseline-subtracting this model in the same way performed as on the data. The required SO2 abundance to reproduce the whole feature would in fact need to be ~150 ppb, not 100 ppb.

This value of ~150 ppb would be an extreme outlier in millimetre-waveband monitoring observations. (We note some higher literature abundances derived from UV/IR observations; see discussion of data tracing the cloud top1 and over time3 .). Comparing to a large compilation of millimetre-derived SO2 abundances4 , a value of 150 ppb would be a > +6σ outlier – in fact, the highest value recorded over several years was only 76 ppb, half this value. SO2 would also need to be sustained at this very high level over the week of the observations, while it is normally seen to vary on timescales of hours to days.

When I saw the phrase “twelfth order polynomial” I knew it was over.
The re-analysis covers this:
Extended Data Figure 4b in G2020 showed that new features were not produced in the ALMA spectra by polynomial subtraction (however, there were issues with the bandpass calibration, see Section 2 below). Specifically, in G2020 we applied the same reduction procedures to regions of the passband offset by 400 spectral channels either side of the phosphine’s expected location. This produced narrow artefacts spanning only ~2 channels, much less broad than the real line, and comprising only ~18% of the real line’s line-integrated signal. Narrow artefacts of this sort are not physically representative of spectral lines from Venus’ clouds.

In their point S2, V2020 applied a polynomial fit to their reduction of the ALMA data. They included all the antenna baselines, whereas G2020 omitted baselines that were substantially noisier, of <33m. Figure FS1 of V2020 demonstrates fitting a 12th -order polynomial baseline, with the residual creating an artifical “line” feature.

This procedure used by V2020 is not correct in context. G2020 noted the very strong ripple when all the ALMA antenna-baselines were included, and page 3 of the SI describes the decisions made in excluding short baselines (balancing random noise and systematic ripple). When V2020 include all the antenna-baselines, they recover this very strong ripple. It is then inevitable that they can produce a “fake line” by fitting across a section of the passband, ignoring the actual shape of the data.

Further, the correct polynomial order is defined by the number of changes of direction of the spectral baseline within the passband. As this value appears to be 7 in V2020’s Figure FS1 (left), the correct order would be 8. By fitting a 12th order polynomial designed for different data, they have given the polynomial function excess freedom, generating an unstable solution.

Fitting polynomials is not a method we would use when the spectrum is dominated by large systematic ripples. These ripples are produced on the short antenna-baselines, and including these also raises the noise substantially.

In short, the researchers are accusing their critics of using a bad method that creates an erroneous signal from noise, and then using that as evidence against them. They say that they didn't use that method at all; if they use their own methods, they're finding smaller artifacts that can't be mistaken for a signal.

There is another reference to 12th-order polynomials on page 9 that I don't fully understand. It seems to be part of the calibration of the sensor using Jupiter's moon Callisto. The team is hoping to get a better calibration with next year's observations:
The intent is to re-observe Venus with optimum settings after the re-opening of ALMA in 2021. Such observations can include optimising the selection and use of calibrators; using a small mosaic and total power observations if Venus fills the primary beam; and applying a more recent higher-precision primary beam model, needed to accurately extract faint absorption lines across the planet. In the meantime, the data gathered in March 2019 has been reprocessed to resolve some of the processing issues in the data used in G2020.

The data sets that have turned up in the meantime are apparently quite diverse.
Temporal variation is now required to reconcile all the available PH3 data. [..] The overall compilation of data could thus be reconciled with a PH3 profile decreasing with altitude, and temporal variations of at least an order of magnitude.

The diversity is such that you'd have to assume that the PH3 concentration changes strongly over time and with altitude for all the detected values to be correct, which feels like a cop-out.

Hopefully, next year's observations can provide more insight here.
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Active Member
A new study pours cold water on Venus phosphine. It's on ArXiv at the moment but from what I've read it's been accepted for publication by the Astrophysical Journal.

Claimed detection of PH3 in the clouds of Venus is consistent with mesospheric SO2​

Andrew P. Lincowski, Victoria S. Meadows, David Crisp, Alex B. Akins, Edward W. Schwieterman, Giada N. Arney, Michael L. Wong, Paul G. Steffes, M. Niki Parenteau, Shawn Domagal-Goldman

The observation of a 266.94 GHz feature in the Venus spectrum has been attributed to PH3 in the Venus clouds, suggesting unexpected geological, chemical or even biological processes. Since both PH3 and SO2 are spectrally active near 266.94 GHz, the contribution to this line from SO2 must be determined before it can be attributed, in whole or part, to PH3. An undetected SO2 reference line, interpreted as an unexpectedly low SO2 abundance, suggested that the 266.94 GHz feature could be attributed primarily to PH3. However, the low SO2 and the inference that PH3 was in the cloud deck posed an apparent contradiction. Here we use a radiative transfer model to analyze the PH3 discovery, and explore the detectability of different vertical distributions of PH3 and SO2. We find that the 266.94 GHz line does not originate in the clouds, but above 80 km in the Venus mesosphere. This level of line formation is inconsistent with chemical modeling that assumes generation of PH3 in the Venus clouds. Given the extremely short chemical lifetime of PH3 in the Venus mesosphere, an implausibly high source flux would be needed to maintain the observed value of 20±10 ppb. We find that typical Venus SO2 vertical distributions and abundances fit the JCMT 266.94 GHz feature, and the resulting SO2 reference line at 267.54 GHz would have remained undetectable in the ALMA data due to line dilution. We conclude that nominal mesospheric SO2 is a more plausible explanation for the JCMT and ALMA data than PH3.

In practice, what they say is that the spectral line detected at 266.94GHz and attributed to phosphine (which has a line at 266.944GHz) has been confused with the sulphur dioxide line at 266.943GHz. The authors of the original phosphine detection (Greaves et. al.) article were of course well aware of this possibility, which they ruled out because observations made at ALMA observatory failed to find a nearby sulphur dioxide line. They deduced SO2 concentration had to be low and not able to explain the 266.94GHz line without phosphine.

Lincowski et. al. (the new study) reanalysed the ALMA data and found contradictions with the known abundance of SO2 on Venus. From this they deduced (modelling Venus atmosphere) that the signal at 266.94GHz did not come from Venus clouds, but much higher, where phosphine would be destroyed by solar radiation with a lifetime less than 1 second (this does not happen to SO2).

These are the conclusions of the paper of Lincowski et. al.:

5.CONCLUSIONS We simulated millimeter-wavelength Venus spectra to ex-plore the vertical distribution and detectability of PH3andSO2in the Venus atmosphere. We find that the observa-tions of the 266.94 GHz absorption line are insensitive to theabundance of PH3and SO2within the cloud deck. Instead,the observed absorption at this wavelength originates fromthe mesosphere at altitudes above 80 km. At these altitudes,PH3would be rapidly destroyed, such that 20±10 ppb of PH3 would require a flux of PH3to the Venus mesospherethat is∼100 times higher than the global production rate of photosynthetically-generated O2on Earth. Because PH3and SO2both absorb within the width of the line detectedat 266.94 GHz, we emphasize that the identification of this absorption line as due to PH3in both the ALMA and JCMTdata relies heavily on the apparent low abundance of SO2inferred from the non-detection of an SO2reference line at267.54 GHz in the ALMA data. However, we show thatSO2absorption is likely heavily suppressed in the ALMAdata. Using SO2vertical profiles within the range of previ-ous observations (from 30 ppb at 78 km to 400±150 ppb at100 km)—including SO2observations taken within a monthof the JCMT data—our model can fit the depth and widthof the 266.94 GHz feature without PH3. We also show thatALMA line dilution suppresses the values for nominal Venusmesospheric SO2to below the corresponding detectabilitylimit set by Greaves et al. (2020a). Given the mesospheric al-titude range, short chemical lifetime of PH3, and consistencywith existing mesospheric SO2abundances observed within amonth of the JCMT observations, we argue that SO2provides a more self-consistent explanation for the 266.94 GHz feature than PH3. Single dish observations optimized for Venusand used to assess the PH3detection and SO2abundance inthe Venus upper mesosphere should be prioritized to discrim-inate between PH3or SO2as the source of the 266.94 GHz line.

It looks like another case of 'crying life', of which we had already too many from Lovell's Mars canals to meteorite ALH84001.