Biological Agent Phosphine Found on Venus

  • #26
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The problem I have with neutron capture to make this phosphine is, according to the Nature Astronomy paper, under the most favourable reasonable phosphine lifetimes, a million molecules have to be made every second per cm^2. That is a rather severe neutron flux. Which raises a further question for me: if the star is throwing out that flux of neutrons, why are the stellar levels of 16O and 14N higher (or the heavier isotopes lower) than anywhere else in the solar system?

As to where the deuterium came from, that is another very important question. The usual answer is that Venus once had as much water as Earth (No evidence is offered for that, though) and photochemistry knocked the hydrogen atoms off and these were lost to space. The deuterated water was slightly heavier, so ordinary water was slightly favoured. I do not believe that because it raises the question, where is the oxygen? If it is in the CO2, that would mean there had to be a lot less water to start with, and the carbon had to be something like methane (to react with the oxygen).

Sulphur and phosphorus will be quite plentiful on Venus, but they will be solids, the phosphates dispersed in rocks, while much of the sulphur binds with iron and forms an iron sulphide layer around the iron as part of the core, at least that is what models suggest.

My answer to why the high levels of deuterium go like this. Where do the elements that are in the atmosphere come from? There is a variety of reasons why comets or chondrites cannot be the answer. For comets, there should be at least 20,000 times more 36Ar. For chondrites, the isotopes are wrong, and as an example the isotope ratios of oxygen in chondrites are quite different from Earth. If the volatiles came from chondrites, the Moon should also have been struck, and while you can argue that the volatiles would be lost, the rocks are not. Now Earth's rocks have been tectonically recycled, so those chondritic isotopes would be dispersed into the mantle, but not on the Moon, so why does the Moon have the same ratio as Earth? Also, why do the atmospheres of the rocky planets all have different ratios of components, and none have the xenon expected of chondrites?

As I see it, the simplest explanation is that the planets only accreted solids. The water came from hydration of silicates, and especially aluminosilicates, while the carbon and nitrogen came as carbides and nitrides, made from standard chemistry expected in the accretion disk while the star was forming. That requires the solids NOT to get swept into the star then, but at least it explains why the planets contain most of the system's angular momentum. The solids then react with water to generate reduced gases, and these involve hydrogen transfer. The deuterium is retained by the water through the chemical isotope effect, and any hydrogen formed is preferentially lost to space.
 
  • #27
Astronuc
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That is a rather severe neutron flux. Which raises a further question for me: if the star is throwing out that flux of neutrons, . . .
Neutrons in the planetary atmosphere do not come from the sun (stars), but the neutrons to which I refer originate in spallation reactions from high energy protons, or deuterons, and even alpha particles, with light elements such as C, N, O in the respective atmosphere.

One raises many other issues related to element and isotope abundance and ratios.
 
  • #28
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Thanks, but it is still a puzzle to me why the same sort of reactions do not increase the heavier isotopes in the sun. Is it reasonable to assume that any such neutrons made would react preferentially with hydrogen simply because there is so much more of it?
 
  • #29
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Does phosphorus in the atmosphere get lost to some process, or why does it need a good source of new material?
1) Dilute sulphuric acid is not a kinetically good oxidant (which is why active metals give off hydrogen from dilute sulphuric acid) but hot concentrated sulphuric acid is oxidant and oxidizes metals such as Cu, Hg and Ag. Which is why it might oxidize phosphine:
H3P+H2SO4=H3PO4+H2S
H3P+4H2SO4=H3PO4+4SO2+4H2O
3H3P+4H2SO4=3H3PO4+4S+4H2O
All the ways you end up with H3PO4 dissolved in strong sulphuric acid.
2) While exploring what happens to strong acids in Venus´´ lower atmosphere is a bother, what happens to strong acids when heated in a pot in a laboratory is reasonably well known, if not so well published.

Basically, at 1 bar total vapour pressure, sulphuric acid loses mostly water vapour till it is concentrated to over 90 % and 200 Celsius. Then it starts giving off appreciable fraction of sulphuric acid vapour as well, till at 338 Celsius it boils at constant composition of 98,3 % (by mass) sulphuric acid.
Azeotropic mixture compositions depend on pressure. When sulphuric acid is evaporated away at lower pressure (as would be the case in Venus´ atmosphere, mostly carbon dioxide not sulphuric acid vapour), the evaporation temperature is of course lower - and the azeotropic concentration of sulphuric acid is higher.

Now, phosphoric acid is less volatile than sulphuric acid. When boiled off by itself, again under 1 bar vapour pressure, the azeotropic mixture is slightly towards P2O5, near HPO3, at 869 Celsius.
Therefore, when sulphuric acid with phosphoric acid admixture rains down and is evaporated in hot lower atmosphere of Venus, HPO3 should remain, at first.
What would become of HPO3 that rains on Venus? Any way to return it?
 
  • #30
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Is it reasonable to assume that any such neutrons made would react preferentially with hydrogen simply because there is so much more of it?
I plotted the cross-sections for radiative capture (n,γ) and elastic scattering (n,el). They show a greater probability of scattering over the energy range 0.001 eV to 100 MeV. For the radiative capture, the probability is greater for H until about 200 keV where the capture cross section of O becomes greater. I do not know the neutron energy spectrum of solar neutrons, but the following might provide an answer: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JA015930

Based on the cross-sections, it would appear that a neutron is more likely to scatter than be captured such that it would eventually decay (t1/2 = 613.9 s) to a proton, electron and antineutrino.
 

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  • #31
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I plotted the cross-sections for radiative capture (n,γ) and elastic scattering (n,el). They show a greater probability of scattering over the energy range 0.001 eV to 100 MeV. For the radiative capture, the probability is greater for H until about 200 keV where the capture cross section of O becomes greater. I do not know the neutron energy spectrum of solar neutrons, but the following might provide an answer: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JA015930

Based on the cross-sections, it would appear that a neutron is more likely to scatter than be captured such that it would eventually decay (t1/2 = 613.9 s) to a proton, electron and antineutrino.
Thanks for the information.
 
  • #32
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As for recycling phosphorus in the Venusian atmosphere, the phosphorus oxide systems are very complicated because they tend to condense and dehydrate, but if they dehydrate to phosphorus pentoxide, that sublimes at 1 atmosphere at 300 degrees C (according to my copy of the Handbook of Chemistry and Physics) so if sulphuric acid could be revolatalised from the surface of Venus, so could phosphorus, but this presupposes it has not formed a solid salt. If it could form something like a phosphoryl halide it would volatalise. Phosphorus would normally be expected to be some calcium salt on a rocky planet and dispersed in the silicates. I am unaware of any detection of phosphorus in the Venusian atmosphere, but that may reflect more my ignorance than anything else.
 
  • #33
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@Astronuc , I agree with you that the neutrons in question are secondaries produced by spallation. However, I don't see how the primary cosmic ray flux can be high enough. I don't have a good definitive reference for this number at a few MeV, but it's got to be of order a few per square meter per second. That's quite a jump to the million per square centimeter per second that @Ian J Miller cites.
 
  • #34
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As for recycling phosphorus in the Venusian atmosphere, the phosphorus oxide systems are very complicated because they tend to condense and dehydrate, but if they dehydrate to phosphorus pentoxide, that sublimes at 1 atmosphere at 300 degrees C (according to my copy of the Handbook of Chemistry and Physics) so if sulphuric acid could be revolatalised from the surface of Venus, so could phosphorus, but this presupposes it has not formed a solid salt.
SO3 boils at 45 Celsius, but for one it is liable to polymerize to solid in which case it sublimes t 62 Celsius, and for another, it is highly hygroscopic, forming azeotrope H2SO4 with a small amount of H2O, which boils at 338 Celsius.
P4O10 boils at about 360 Celsius, but is also liable to polymerize (then boils round 700 Celsius) and is highly hygroscopic, forming azeotrope HPO3 with small amount of P2O5, which boils at 869 Celsius.
 
  • #35
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Based on the cross-sections, it would appear that a neutron is more likely to scatter than be captured such that it would eventually decay (t1/2 = 613.9 s) to a proton, electron and antineutrino.
Neutrons won't survive that long unless you carefully prepare a trap for them in the lab. A cross section for scattering that's 100 times as large just means you get an average of 100 scattering processes before a capture (+- something because the energy changes from the scattering processes). That's still tiny fractions of a second.
 
  • #36
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Another team attempted to confirm the presence of phosphine in the atmosphere of Venus by examining IR spectra and did not observe signals at the wavelengths expected for phosphine:

A stringent upper limit of the PH3 abundance at the cloud top of Venus
https://arxiv.org/abs/2010.07817

Abstract
Following the announcement of the detection of phosphine (PH3) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the infrared range.
Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO2 and H2O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm−1 where a PH3 transition is present.
From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-σ upper limit of 5 ppbv for the PH3 mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths.
Our result brings a strong constraint on the maximum PH3 abundance at the cloud top and in the lower mesosphere of Venus.
 
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  • #37
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That's seems to be to be at least a moderate confirmation of one or more of Fred Hoyle's speculations.

Quote
I think the guy really deserves a retrospective break. At the time he favoured the Steady State solution, he was by no means the only one and the CMBR measurements were only available after he published his views. Not surprisingly, he didn't go down without a struggle. And he did invent the term "Big Bang" (though it was in an attempt to put the idea down.)

Mainstream Science can often be pretty unforgiving of 'good Scientists'. Take poor old Eric Laithwate, who was a very competent Electrical Engineer but just wasn't allowed to suggest that reactionless drive might be needed in order to 'explain' the results of some of his dodgy Maths.

Science is a rough business and shows no sympathy for people who rock the boat. Paradigm changes do occur though but history is written by the winners, as in all of life.
 
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  • #38
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I would be very nervous of assigning a signal at 950 cm-1 to phosphine. Acid chlorides, phosphates, and certain nitrogen-oxygen bonds can give signals in this region, and when talking about the upper atmosphere, as seen in Earth's atmosphere, some rather strange molecules are formed in very low concentration due to UV photochemistry. Phosphine is not the only molecule that could give the signal.
 
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  • #39
sophiecentaur
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I would be very nervous of assigning a signal at 950 cm-1 to phosphine. Acid chlorides, phosphates, and certain nitrogen-oxygen bonds can give signals in this region, and when talking about the upper atmosphere, as seen in Earth's atmosphere, some rather strange molecules are formed in very low concentration due to UV photochemistry. Phosphine is not the only molecule that could give the signal.
I talked to Emily Darnell Maunder, who was a member of the team. I asked her about the sort of signal to noise ratio for their measurement and she quoted well above 10dB. So that is a Reasonable confidence limit, I would have thought.
 
  • #40
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I don't doubt they properly recorded a signal. The question is, what caused it?
 
  • #41
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I would be very nervous of assigning a signal at 950 cm-1 to phosphine. Acid chlorides, phosphates, and certain nitrogen-oxygen bonds can give signals in this region, and when talking about the upper atmosphere, as seen in Earth's atmosphere, some rather strange molecules are formed in very low concentration due to UV photochemistry. Phosphine is not the only molecule that could give the signal.
The significance is not that they observed a signal at 950 cm-1, it's that the did not observe a signal at that wavenumber (especially not the intensity of signal they would expect to see if phosphine were as abundant as claimed in the Nature Astoronomy paper). This would seem to suggest that either phosphine is much less abundant than claimed or that the signal observed by the Nature Astronomy paper is not due to phosphine.

To quote Encrenaz et al. pre-print:
the detection of at least one other PH3 transition, in the infrared or in the millimeter/sub-millimeter range, is definitely needed to confirm the PH3 detection in Venus.
 
  • #42
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Yes, the upper limit is significant. I was more concerned with whether there was any? I noticed the factor of 4, but again could it be something else there as well? The something else does not have to be equivalent at both frequencies. We still don't know, and I guess I am simply suspicious of phosphine being there.
 
  • #43
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I don't doubt they properly recorded a signal. The question is, what caused it?
The thing about spectroscopy is that frequency can be measured with more accuracy than any other quantity (it goes wit time). ‘They’ used a lot of previous data as well and the the probability of another explanation for the (precise) frequency arising any other way was considered to be very low.
It’s a system that’s been used for finding the components of all astronomical objects. If you doubt it’s veracity then you need to doubt an awful lot of other discoveries.
I’m not sure there is actually any alternative explanation for the line.
 
  • #44
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Yes wavelength is accurately measured but assignments us a different problem. There are many lines in high resolution spectra and a single line is not reliable proof . Hence the need for confirmation. This is standard practice and does not challenge all of spectroscopy.
Regards Andrew
 
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  • #45
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Yes wavelength is accurately measured but assignments us a different problem. There are many lines in high resolution spectra and a single line is not reliable proof . Hence the need for confirmation. This is standard practice and does not challenge all of spectroscopy.
Regards Andrew
That is a reasonable statement but absolute frequency gives an absolute Energy transition and, if there are no other possible candidates for the phenomenon then what alternatives are there? I know that the various series are often used for identifying elements and that can be used when the light levels are very low.

Have there been any challenges, other than yours, though? The practical details are very important here - also the precise values of measurements which were obtained from a vast amount of existing data. The team stopped, once their confidence in the result was high enough. I think the data is all public domain so you could, in principle, do the same analysis yourself. (Domestic data connection might be a bit limiting, I suppose.

I'm always impressed with the apparent certainty that spectroscopy gives us; the numbers seem to be reliable.
 
  • #46
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If I recall correctly they did consider sulphur dioxide as a possibility but dismissed it. You also have to consider the conditions which can broaden the lines, various relative velocities (wind speed, Earth Venus relative velocity) which can shift the lines so it is not as absolute as you might think.

It may well be PH3, but it could be a line from an unnconsiders molecule hence the need for confirmation. I did see a paper where it was detected in retrospect in a Venus probes data. I don't have the reference to hand.

Many lines in the solar spectrum remain unidentified even today after years of study.

Regards Andrew

PS I think only the reduced data is available and in any case without experience of the telescopes involved and the necessary calibration data it is not possible to check.
 
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  • #47
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Although I am not too familiar with these fields, I am surprised that the authors could claim detection of phosphine based detection of only a single spectral line, especially since the presence of phosphine on Venus is quite unexpected. Is this standard of evidence common across astronomy? Perhaps this limitation of the paper is why it appeared in Nature Astronomy (a relatively new journal published by a for-profit publisher that was likely looking for publicity) rather than a more prestigious journal.
 
  • #48
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An infrared signal is generated by an energy transition between two states, usually vibrational states, and in chemistry the frequency is often set by what happens in a functional group, and modifed by "the rest of the molecule". If you check a chart of infrared signal possibilities, you will see that a number of molecules could generate a 950 cm-1 line. You need the rest of the signals to be more certain. What concerns me more is that nitrogen-oxygen species can give signals there, and in the Venusian atmosphere it is unclear what could be generated by photochemistry. I am not saying it is not phosphine, but simply that given the difficulties in forming enough phosphine to be stable sufficiently long to generate that signal I suggest a little caution.
 
  • #49
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A re analysis of the alma data finds no evidence for phosphine Re analysis
Regards Andrew
 
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  • #50
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Without Alma, the JCMT data is not very convincing. (If you turn it upside down, you see signals at least as significant)
 

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