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Analytical Chemistry

Phosphine, Life, and Venus

Well, as a chemist – one who does amateur astronomy on the side, yet – it’s obligatory that I write about the phosphine on Venus paper that came out yesterday. This one’s embargo was spectacularly leaky, so everyone who’s really into this stuff had various kinds of advance warning, but the news certainly has made a splash.

So what’s phosphine? It’s a simple compound, formula PH3, and if you’ve worked with it you’re likely either doing some rather funky phosphorus chemistry, or you’re in the electronics fabrication industry (where it’s used to make semiconductors). Alternatively, you could be fumigating rodents out of farm buildings; it’s good for that, too. Phosphine has a reputation as being extremely foul-smelling and flammable, but that’s largely due to it often having some diphosphane (P2H4) in it, depending on how it’s prepared. But that just makes pure phosphine an extremely toxic gas without as much foul odor to warn you, so it’s a mixed improvement.

There are small and variable amounts of phosphine in Earth’s atmosphere, and its origins have been the subject of much argument. In our oxygenated world, phosphorus just doesn’t show up in a reduced form like this without a good reason. The overwhelming majority of the phosphorus on Earth is in the form of phosphate (as oxidized as phosphorus can get), and taking that all the way back down to phosphine is an energetically costly process. One possibility is that it’s formed during lightning strikes – plenty of electrons available there for any reduction you might care to run. But it’s also become obvious since the late 1980s that phosphine can be produced in anaerobic environments like sewage sludge, with no lightning to be had. Somehow, some hard-core microorganisms (as yet unidentified) seem to come up with enough electrons to do the job enzymatically. Here’s a recent paper that looks at adding various potential nutrients for that purpose to such sludge, and they found that glucose is particularly effective at increasing phosphine production. And it’s already been reported that chemical sterilization of the sludge shuts phosphine production off entirely.

The new paper generating all the headlines reports detection of phosphine in the upper cloud decks of Venus, where there really shouldn’t be any (for the same reasons as on Earth). Everything else is oxidized: the carbon on Venus is in the form of carbon dioxide (which makes up 96% of the atmosphere and gives the place the most extreme greenhouse effect possible), and the sulfur is in the form of sulfuric acid (plenty of that, too), so the phosphorus there should be phosphoric acid/phosphate, not phosphine. The authors calculate that lightning and volcanoes could only generate enough of the gas through known processes to come several orders of magnitude short of what’s actually observed, and there aren’t any other abiotic processes (photochemistry, etc.) that are hypothesized to be able produce the gas. The paper has detailed estimates and models for phosphine production and decomposition by such routes, and none of them, all the way to delivery of reduced phosphorus minerals by meteorites, seem to get anywhere close to producing the amount that’s observed. So we’re left with either some unknown inorganic route to it, and nothing particularly plausible comes to mind. . .or we have that apparent microbial production that we’re seeing on Earth.

Now, microbes on Venus seem rather unlikely at first, because Venus is basically Hell in the sky. That was confirmed, most thoroughly, by the Soviet Venera landers in the 1970s and 1980s. That program was a major accomplishment. Venera 3 in 1966 made it to Venus’s surface (the first human object to impact another planet), but its instruments had failed on arrival in the atmosphere. Venera 4 (1967) was thought at first to have possibly survived a landing (although its communications had also ceased on the way down), but the US Mariner 5 spacecraft was arriving at nearly the same time and measured the atmospheric pressure as being at least 50x that of Earth, far beyond what the Venera probe had been built to withstand. The Soviet engineers armored up, and Venera 7 in 1970 was the first time humans landed a working probe onto the surface of another planet. But it only survived 23 minutes down there, because the pressure was indeed 91 atmospheres and the ambient temperature was 464 C (867 F), hot enough to melt lead, tin, zinc, and various alloys. And to get to this tourist trap you have to drop through kilometers of thick sulfuric-acid-laced clouds. Venera 13 (1981) set the existing record, surviving for just over two hours on the surface.

So why would anyone imagine microbial life? Well, there’s that thick cloud deck. And it’s become apparent that microbes can be isolated from the cloud droplets here on Earth. Harold Morowitz and Carl Sagan raised the possibility in 1967 of similar organisms in the temperate regions of Venus’s atmosphere, and it’s never been something to rule out. If phosphine really is a biological signature, its presence in Venus’s atmosphere is very suggestive. The authors are careful not to call it definitive evidence for life, however.

This idea has two main places it can break down: as mentioned, there could be abiotic routes to phosphine that we don’t know about. The chemistry of Venus’s atmosphere is known to some extent, but no one would claim that we have the full picture. The surface of the planet is covered in huge ancient basaltic lava flows, but the present day activity is still mysterious. It appears that Venus is somewhat volcanically active (sudden spikes global in sulfur dioxide and other such evidence), but we don’t know much more, and we certainly don’t know about the composition of hypothetical current eruptions. That said, it would have to be something pretty odd to produce the phosphine that’s been seen.

And that’s the other place this hypothesis can break down: perhaps the identification of phosphine is itself erroneous? The authors consider this at length, to their credit. The spectral band that they’re using is a rotational transition in the millimeter wave range, and the two radio telescope facilities that were used to collection data were the James Clerk Maxwell telescope on Mauna Kea and the Atacama Large Millimeter Array (ALMA) in Chile, both excellent instruments and among the best that radio astronomy has to offer. There is a nearby absorption band from sulfur dioxide, however, but the authors calculate that it could only be responsible for the data if it were twice as hot as the measured temperatures in the upper cloud decks. But that does leave an outside chance that there is something messed-up with our knowledge of sulfur dioxide in the Venusian atmosphere that led to a false call for phosphine.

The paper suggests a number of follow-up experiments to try to nail all this down, but none of them are easy (see “Strategies to confirm PH3” in the Supplementary Material). The ALMA facility could be used to search for another particular phosphine band, but that would take several days of solid data collection, which is a real challenge. There’s also a possibility for infrared observations, but ground-based ones will be complicated by absorption bands in the Earth’s atmosphere. Someone will surely try that one, though. I think eventually we’ll see proposals for aerosol sampling probes, perhaps even with a return-to-Earth component (no doubt various teams are running the numbers on this right now!)

Now for a final bit of speculation: if all of this does hang together – if there is phosphine on Venus, if we have detected it correctly, and if it is evidence for Venusian microorganisms – what does that tell us? Well, one thing you might wonder is if we brought it there ourselves, via the various probes that have entered the Venusian atmosphere. I find that unlikely, considering the conditions of travel, the conditions of atmospheric entry, and the unlikelihood of common bacterial contaminants being adapted to survive in the Venusian cloud conditions even if they did arrive in viable condition. But it’s not completely impossible.

The biggest question is what this would mean for extraterrestrial life in general. Like the arguments about methane on Mars (which have a similar profile of possible biogenic signature versus arguments about detection and abiotic sources), these things could mean that microbial life gets underway pretty readily. That would be a huge thing to prove, because it’s absolutely certain at this point that there are a huge variety of planets around a huge variety of stars. It’s likewise certain that the simple molecules of life-as-we-know-it are abundant in the universe, all the way to amino acids, carbohydrates, and nucleotides in carbon-containing meteorites and (for some cases) in interstellar clouds.

What we just flatly don’t know (and still wouldn’t know) is how easy or likely the transition to multicellular life might be, and how often any of the resulting complex organisms manage to come up with the ability to use technology to investigate their surroundings. Like we’re doing now. We’re left with some very long lines to try to connect some very important dots. . .

95 comments on “Phosphine, Life, and Venus”

  1. John Wayne says:

    For those interested in staying up to date on astronomy and physics with limited time, I recommend checking out ‘What Da Math’ by Anton Petrov on YouTube. Good stuff.

    1. Marko says:

      Thanks for the tip. It is good stuff. Bookmarked.

  2. Sok Puppette says:

    So, that sounds like quite an energy investment, for an organism to reduce phosphate all the way to phosphine. Anybody have any guess about why they do it? Desperate to get the oxygen from it for some reason? Using it for storage? Sheer perversity?

    1. Mike D. says:

      The questions I’d have before that is “how much phosphate are we observing on Venus?” and “how much would we expect absent reduction processes?”

    2. wildfyr says:

      At least on Earth, in anaerobic sludge you might indeed be right that the organisms are desperate for oxygen. Sure seems like they could rip it off of something a little easier than phosphate though.

  3. Barry says:

    Both Methane and Hydrogen Sulfide are seen in Venus’ atmosphere. But that still leave me puzzling why the Sulfur is (mostly) in the oxidized (sulfuric acid) state and why the Carbon is (mostly) in the oxidized (CO2) state. On Earth, we didn’t have an oxidizing atmosphere until the “Great Oxygenation Event” ca. 2.4 billion years ago. Only then was Ferrous iron precipitated out of the oceans as the great Iron ore deposits we know today. But the Great Oxidation Event was driven by biological (photosynthetic) processes.
    So to my mind, it is not the low-valent Phosphine that suggests the presence of life; it’s the high-valent Sulfur and Carbon that want an explanation.

    1. Marko says:

      “So to my mind, it is not the low-valent Phosphine that suggests the presence of life; it’s the high-valent Sulfur and Carbon that want an explanation.”

      Maybe what it suggests is the presence of life in the distant past , rather than the present.

      It might also offer a preview of what our atmosphere may look like some day if we keep on trashing the planet the way we are currently.

      1. Derek Lowe says:

        The thing is, the phosphine has several mechanisms to be cleared. So there seems to be some continuous source of it. . .

        1. Marko says:

          Sorry , I’m afraid I wasn’t clear. I was addressing Barry’s question about the presence of so much H2SO4 and CO2 in the absence of the sort of Great Oxidation Event as occurred on Earth.

          I’m prepared to accept that such an event is not a prerequisite , however , as I simply have no idea.

        2. Nick K says:

          If there’s abundant sulfuric acid in the clouds, why isn’t the phosphine protonated? It is a weak base, after all.

          1. Organische says:

            1. What form is sulfuric acid in the clouds? Aerosols? H2SO4 has an extremely low vapor pressure, but I suppose high enough up (i.e., at low enough pressures), some is in the gas phase.

            2. Relative concentrations of phosphine(g) and H2SO4 (g) ?

            3. Kinetics of these reactions in gas phase, or at the surface of a sulfuric acid aerosol?

            Basically, there seem to be a lot of unknown variables regarding how likely H2SO4 is to actually protonate any PH3 under these conditions.

    2. Carl says:

      Steam. Vebnus’s oceans underwent much more evaporation early on, and it has a very weak magnetic field so cosmic ray particles hit the atmosphere far more thna on earth. This breaks the steam down. The Hydregon boils off into space and the O2 goes on to combine with various things.

      Venus still leaves a trail of atmosphere behind it to this day that goes past earths orbit due to the cosmic ray bombardment and lack of a magnetic field, (another proble for high altitude microbes. They have to be really radiation hardened.

  4. LeeH says:

    Someone is preparing to do the universe’s largest Wittig.

    1. John Wayne says:

      We are going to have to chromatograph that reaction through a column full of comets.

      1. LeeH says:

        I was hoping someone would make a workup joke.

        1. John C says:

          Breaking news: Phobos and Deimos are just piles of leftover triphenylphosphine oxide.

          1. István Ujváry says:

            Witty(g)

  5. Steve Scott says:

    An aerosol sampling probe with a return to Earth could be dangerous. Imagine if the probe crash lands, the Venusian microorganisms get loose, and ravage the planet, far worse than Covid-19. Now, you might argue that such germs could not survive here, in the wild. But I suspect such a mission would never be approved. Remember the fears over potential “moon germs” that kept the Apollo 11 crew in isolation upon their return?

    1. NJBiologist says:

      Or that 1971 documentary about Project Scoop (“The Andromeda Strain”)?

      1. loupgarous says:

        Much superior to the remake from A&E Network. Robert Wise’s 1971 Andromeda Strain has never been equalled, even though the science has developed remarkably since.

    2. Anonymous says:

      Counterpoint – Venusian atmosphere cures COVID-19

      1. Marko says:

        Another counterpoint : Venusian atmosphere also great for killing rats.

        Counter-counterpoint : Pretty good at killing people , too.

        https://abcnews.go.com/Health/water-poured-rodenticide-caused-deaths-texas-home/story?id=44526042

        I think Musk and SpaceX should go for it , stat. He needs something to restore his reputation , and bringing back a sample from Venus that proved the existence of life there would wipe away all his past sins , clearing the slate for the inevitable additional ones to come.

        1. MagickChicken says:

          Bonus points to Musk if he flies the probe himself.

  6. anon says:

    It’s only been about 50 years since the first time a probe was sent to Venus. Even if phosphine-producing bacteria made it to Venus with the probes, could they have spread so successfully in such a short period of time (geologically speaking, at least) that phosphine would be found at ppb-levels?

    1. Aleksei Besogonov says:

      Well, exponential growth exists. It’s not entirely impossible that the rocket picked up atmospheric bacteria from Earth on the way up. These bacteria are already adapted for life high up, so it’s possible that they were able to colonize Venus.

      1. Eldritch says:

        Keep in mind that they’d *also* have to adapt to air that’s not only as dry as the Atacama, but where all the existing moisture is mixed in with 95% sulfuric acid.

        1. wildfyr says:

          And even more ionizing radiation than Earth due to the Sun’s proximity and Venus’ near non-existent magnetic field.

    2. Steven E says:

      Whether there’s been enough time depends entirely on how hospitable whatever bacteria that arrived would find Venus, because that sets the generation rate and maximum population for the bacteria. Given an unknown bacterium and poorly-understood conditions, estimates even from the well-informed are going to vary substantially.

      Under ideal conditions, E. coli has a generation time of fifteen minutes or so. The difference in mass between one bacterium and the whole galaxy is 30 orders of magnitude or so. As 10^3 (1,000) is just a couple percent lower than 2^10 (1,024), 10^30 is close enough to 2^100. Thus, assuming impossible ideal conditions, you could go from on E. coli to a mass the same order of magnitude as the galaxy in roughly one day.

      So the only question on whether there’s been enough time are the unknown bacterium’s biology and the poorly-understood conditions.

      Now, though we just had an ISS experiment written up in August that showed bacteria can survive three years’ exposure to space, I wouldn’t care to bet much that there’s life on Venus delivered by one of the fourteen human probes to enter its atmosphere. But the unknowns are sufficiently great that I wouldn’t rule it out.

  7. Simon Auclair the Great and Terrible says:

    Venereal life horhor.
    https://www.smbc-comics.com/comic/phosphine

  8. Dr. A says:

    I really hate “Venusian.” It sounds like mooing. Venerean and Cytherean are so much more graceful.
    But with all the sulfuric acid present, why aren’t we seeing PH4+HSO4- (phosphoronium bisulfate) or the adduct PH3:O=S=O? It seems odd the PH3 would exist in the unprotonated state under the low pH conditions.

    1. In Vivo Veritas says:

      Yes, but Venerean is such a short trip to Venereal. I’m a fan of classical etymology, but I vote for Venusian on this one……

      1. loupgarous says:

        With in vivo on this one. “Venerean” has nothing, philologically, to recommend it over its alternative, but does evoke “social diseases” too closely.

  9. Syncline says:

    Another possibility is inoculation of bacteria into the Venusian atmosphere via transport from earth impacting bolide debris. For example work by Rachel Worth at Penn State in the journal Astrobiology (2013) calculated that the K-T impactor (dinosaur killer) launched 70 billion kilograms of rock into space and distributed it throughout the solar system… And for a sense of scale, up to 20,000 kilograms of the debris could have traveled as far as Europa. Paper here (https://www.liebertpub.com/doi/full/10.1089/ast.2013.1028).

    It strikes me (ha ha, bad pun) that many bacteria in the lithosphere are sulfate eaters and anaerobes, able to handle nasty conditions. If crustal ejecta from the K-T event carrying those sulfate consuming organisms made its way to the Venusian atmosphere… breaking up upon entry… the space faring host ejecta slowing down and disaggregating into fine particles before significant killing heat was applied to the biotic passengers… the newly freed sulfate reducers would find themselves in the turbulent Venusian atmosphere with a devils cocktail of atmospheric chemistry to deal with, but not too horribly dissimilar to the conditions found at deep crustal conditions kilometers below the surface… etc… I don’t think it is completely unreasonable to develop a storyline for life on Venus, but life from Earth! ‘Hand waving’ for sure, but a logical through line is there. Rachel called it ‘Lithopanspermia’.

    How about a mission to Venus that inserts multiple inflatable balloons at various levels of the atmosphere, all carrying biological packs with growth medium dishes and miniature DNA sequencers just in case? Someone talk to Elon Musk and get Space X on a design.

    1. wildfyr says:

      This is an extremely salient point! If we ever prove there is life in the atmosphere, I too would expect ancient Earth-derived contamination before native Venusian life.

  10. PBJ says:

    I haven’t read as much as I’d like, but my understanding is that we don’t even fully understand the chemistry involved in bacterial production of PH3 on earth. So, even invoking life, the chemistry is unexplained.

    If we have to use unknown chemistry, it seems far simpler to assume it’s either reactions we don’t know or reactants that we’re unaware exist there. (Of course, maybe this chemistry has been elucidated since the last time I read about it).

    I mean, it’s awfully cool either way. But “life” seems unnecessary to the mystery. One possible explanation but a more unlikely one than that we’re missing something chemical. (If we know all the chemistry in the universe, most of us would be out of a job.)

    1. EJ says:

      Agreed.

      But that won’t be the case for long. I can already see researchers lining up to procure piles of phosphine producing sludge, and others are going to analyze every concievable metric of producing it abiotically.

  11. Barry says:

    But surely a lot of that 70 billion kgs of rock was heat-sterilized in the impact? And more of it would have been heat-sterilized by atmospheric friction on the way out, and more again upon entering the Venusian atmosphere.

    1. eyesoars says:

      Probably a lot less than you might think. Meteorites landing on Earth are usually cold. Even when they hit hard, most of the heat is created and shed in the outer layers.

      1. Barry says:

        While a meteorite core landing on Earth won’t be hot to the touch, the material that ablated off it in transit (most of the mass!) got quite hot for a while, I think.

  12. heteromeles says:

    Um, did someone say dropping a balloon on Venus? It’s been done: https://en.wikipedia.org/wiki/Vega_program#Balloon

    Did someone say something about launching a rocket from a balloon? A cool little aerospace company in California does stuff like that: http://www.jpaerospace.com/rockoons.html. Heck, they’ll carry your experiment to 100,000 feet for free, so long as you can fit it inside a pingpong ball and don’t mind waiting for their next launch next spring.

    Getting the samples and getting them back probably isn’t as hard as most people think it is. Incidentally, the Vega 2 balloon floated almost 2000 km through the Venusian atmosphere before its batteries died. It’s largely H2SO4 down there, with flavorants of HCl and HF.

  13. matt says:

    Suppose you were going to adapt a GOES weather satellite for Venus. All of the channels of the existing GOES birds are focused on wavelengths that essentially revolve around water (high and low altitude water vapor, snow, ice, etc) and heat sources based on earth background temperatures. All essentially useless at Venus. So what wavelengths would you choose to filter around?

    Overview of recent generation GOES instruments:
    https://en.wikipedia.org/wiki/GOES-16

    That’s the thought problem that occurred to me. Chances are, we’d be looking at absorption bands for sulfuric acid forms and carbon dioxide, maybe? And the IR spectrum would be dramatically different, if surface temps run 500 C and the clouds are at 30 C. Or maybe now we’d focus observations on the middle cloud layer, and phosphine. Seems like a software-definable filter system would be desirable, with the ability to reprogram it while there. Especially if you have a bunch of channels available.

    In reality, you probably wouldn’t send a GOES, of course–too much bandwidth to transmit from Venus, of information that we don’t even know what to look for yet–but the imaging wavelengths seems like an interesting problem. Tied to absorption wavelengths that chemists use frequently (although perhaps not many people focus on a thousand flavors of sulfuric acid).

    1. wayward spectroscopist says:

      Before people get too excited about where the phosphine is coming from, someone really needs to confirm that they really are observing phosphine. They detect one transition (line). It could be phosphine, or it could be a rotational line from some other molecule whose microwave spectrum hasn’t yet been measured in the laboratory. Someone needs to measure other phosphine transitions. The authors clearly know this and say so in the SI. However (as Derek relays) measuring other lines is very challenging.

      A decade ago my lab was doing optical spectroscopy on a small molecule that could, just possibly, be formed in interstellar clouds. I asked a radioastronomy colleague how precisely the rotational energy levels would have to be measured to be useful to the radioastronomers. He showed me a measured radiotelescope spectrum in the region that would correspond to a likely rotational transition. Within the <0.1 cm-1 linewidth of our laser there were about 10 microwave lines. The molecules responsible for half of them weren't known. That's why radioastronomers typically want 3 transitions before "detecting" a molecule from its radio spectrum – too many false positives. Maybe the region in the Venus observations is less cluttered, but one line is not enough for a positive ID.

      1. Marko says:

        Could the Webb telescope provide confirmation of phosphine? It seems that its exoplanet exploration mandate and capabilities fit reasonably well here , although I don’t imagine they expected to be looking at a next-door neighbor.

        Launch is still a year away , so maybe we’ll get a ground-based confirmation ( or not ) before then.

        1. anon says:

          JWST can’t even be pointed at Venus. Maximum elongation of Venus is about 45 degrees and, if I remember correctly, the minimum Sun angle for JWST (to keep the Sun from shining on the sensitive parts) is about 90 degrees.

          1. Marko says:

            Well , that’s a bummer.

  14. SteveM says:

    This could mean Life!!!

    Is the standard NASA marketing schtick for throwing it more money regardless of how improbable the claim. It’s sort of like the Pentagon fear-mongering out the wazoo for their Hundreds of Billions a year. Only somewhat more benign…

  15. In Vivo Veritas says:

    As a biologist, I get my chemistry from TV.And according to S1E1 of Breaking Bad, phosphine gas is a sign of death on earth, not life on Venus. 🙂

  16. Erik Dienemann says:

    Cool article. Speaking of triphenylphosphine, I spent months in the lab and pilot plant working with our process chemists (I’m a chem engineer) trying to optimize and scale up a very sensitive Heck Reaction using a homogeneous palladium-acetate/triphenylphosphine catalyst to produce a substituted alkene. Incredibly air sensitive reaction, especially in the lab, where it’s always far harder to keep air out vs much larger pilot plant batches (surface area to volume is one’s friend at larger scale in trying to keep out air and moisture). We eventually were able to figure out that if the catalyst prep (in THF if I recall correctly) had elevated levels of triphenylphosphine, it was an indication the catalyst had seen too much oxygen and would eventually result in elevated levels of Pd in our isolated intermediate after work-up, so air exclusion had to be exquisite (to low ppb levels in the solvent, which led to my breakthrough in utilizing membrane-based dissolved oxygen probes in solvent to measure O2 before charging the catalyst species). Fun times. Key reaction in the losartan synthesis (Cozaar).

  17. Chris Phoenix says:

    OK, so in 2020 after decades of studying Venus, we found one indication of one gas that might indicate life.

    How many other unusual gases might we expect to observe if there were life on Venus, and why haven’t we observed even a single one of them yet?

    1. confused says:

      I don’t think this is an answerable question, as we can’t constrain the possible chemistries used by extraterrestrial life.

      In fact, it’s possible we could find something happening, analyze it in great detail, and *still* be uncertain if it’s life – because I don’t think our definition of “life” is robust enough to classify all possible processes in the Universe as clearly living or clearly non-living.

      Even on Earth, people argue about whether viruses qualify, but at least those are dependent on definitely-living cells…

  18. Todd Knarr says:

    Venus may be a hostile environment, but we’ve found microbes in environments just as extreme here on Earth. Black smokers in the deep ocean, deep in the crust at temperatures high enough it’s not possible to drill past that point (the Kola borehole), even the cores of operating nuclear reactors (D. radiodurans). I’m not surprised to find microbes of some type anywhere that even-vaguely-organic-type molecules are physically possible.

    1. confused says:

      I think the difficulty in Venus’ atmosphere is the lack of water (and the destructiveness of the acid to organic molecules, but the latter might be solvable… you can keep sulfuric acid in plastic bottles, which are organic…)

    2. Oren Tirosh says:

      It is possible that life can adapt to extreme conditions where life would be unlikely to evolve in the first place. Venus used to be a milder environment and changed gradually, giving life plenty of time to adapt. Perhaps refugees from the surface survive high in the clouds.

  19. confused says:

    It’s definitely interesting, and Venus is rather under-studied. There’s a bunch of other oddities there (the radio-bright/reflective “snow” on the highest mountaintops, the UV absorption in the clouds, the apparent very close geological age of the vast majority of the surface, why doesn’t it have plate tectonics when its mass and composition are so close to Earth’s…)

    As a biosignature, though, I’m not sure it’s as convincing as Mars methane – the processes that produce it are less well understood, and Venus’ atmosphere looks less promising for life than Mars’ shallow subsurface (especially since Mars isn’t thought to be volcanically active, and the abiotic production of methane by serpentinization also requires liquid water…)

  20. milkshake says:

    1) The spectroscopic detection of phosphine on Venus is tentative, it could be also easily something else.
    2) A common abiogenic source of phosphine is reaction of metal alloys – steel for example – with acid. Phosphine is the funk you smell in released hydrogen when you put iron nails into diluted sulfuric acid, because of the phosphide impurities. One can imagine slow weathering of iron-nickel meteorites as a source of phosphine on Venus. There are even Fe,Ni-phosphide containing minerals in meteorites (schreibersite). Alternatively, Venus may still have large deposits of P in the phosphide form, as Earth had during the Hadean period

    1. Lloyd Evans says:

      I always thought that the smell cause by dipping impure iron in dilute acid was caused by sulfide impurities, either within or on the surface of the metal. These would react with the acid to produce tiny quantities of hydrogen sulfide, which is detectable by smell at ridiculously low levels – a few parts per billion if I’m not mistaken. Having done this many times in science classes, where a classic experiment is dissolving various base metals in dilute acid (including iron), the smell is definitely more sulfide-like in my estimation. I have smelled phosphines too, and they seem to be sharper and more metallic, though that may just be me.

  21. Claudio Franco says:

    Dear Derek, one big puzzle to me is if someone calculated the amount of microbial activity required to produce the detected levels of phosphine given Venus atmospheric conditions?

  22. Marko says:

    Grab your smelling salts , Dems , the Russians are coming again. They’re stealing Life On Venus. “Breakthrough Initiatives” , pet project of Russian tycoon Yuri Milner , is funding a new research project :

    “Life on Venus? Breakthrough Initiatives funds study of possible biosignature detection”

    https://www.msn.com/en-gb/news/techandscience/life-on-venus-breakthrough-initiatives-funds-study-of-possible-biosignature-detection/ar-BB193LIm

    Adam Schiff’s bulging eyeballs may pop out altogether over this one….

    1. Stranger in the Alps says:

      Further proof that right wingers can’t do comedy.

      1. fajensen says:

        *All* current flavours of “Fanatic” can’t do comedy, …. or irony, …. or self-depreciation … or fun.

  23. Otto says:

    This being 2020 I would prepare for inevitable invasion :/

  24. TallDave says:

    word I was hoping to see here is “water”

    Venus lost 99.9% of it to solar wind aeons ago

    don’t seem to be any forms of (known) life that can survive its absence

    that said, we don’t seem to know the exact variance of water vapor in the cloud deck, perhaps the bacteria bloom in the presence of enough trace vapor

    1. Marko says:

      It’s interesting to me that one of the main byproducts in the biochemical redox pathways posited by the authors is water ( bottom of p.30 ) :

      https://arxiv.org/pdf/2009.06499.pdf

      Phosphine seems like a toxic , dumb thing for a cell to make. However , if you just dump it into the recycling bin (the atmosphere) , you’re ahead by making it since you’ve managed to rehydrate for a bit while you scavenge for an energy source to allow you to regenerate your NADH ( or equivalent ) for your next round of water-making.

      I know it can’t be this simple , but it just struck me as an intriguing possibility.

      1. Marko says:

        The needed trick is a way to get from NAD to NADH for the next cycle without using up your water. If you can do that , you might be able to rehydrate the planet by running the phosphate to phosphine machine. Of course , nobody would swim on your beaches because the air would kill them.

      2. TallDave says:

        ha yes that is intriguing

        anything living in the cloud deck has to solve two major problems — don’t sink into the hotter layers (probably a bit easier than it sounds given the pressures) and scavenge every possible scarce molecule of H2O

        skeptical anything like this is possible naturally, but won’t rule out the future possibility of engineered microbes that could perhaps start the long process of locking out all that carbon so as to eventually terraform the surface while early colonists dance away the millennia in their floating cloud cities (another surprisingly viable notion)

        1. TallDave says:

          a solar shade might help speed things along, but it turns out that while the greenhouse effect on Venus does keep the planet boiling hot, it’s sort of a small flame on a very large, well-insulated pot — partly due to the fact Venus already has the highest albedo in the Solar system

          still, the first few hundred degrees of cooling are probably the easiest, given 2L, might pave the way

          presumably still going to need to rain comets for millennia to get even a tiny amount of water available

  25. Charles H. says:

    If I understand correctly, multicellular life evolved several times independently on Earth. But the transition from prokaryote to eukaryote can’t be shown to have happened more than once. Still, there’s that microbe whose Latin name means “anomalous collection of hairs” (I can’t remember the official name, but Google returned Mixotricha paradoxa) which looks like a partial reenactment of the transition. (Somewhere in Dawkins popular works.) So that may not be so infrequent either.

    OTOH, everything now detected as living on Earth uses the same genetic code (with minor variations). And ribosomes seem to have only one original source. So there may be some “narrow passages”.

    1. confused says:

      Yeah – IMO the Big Question is whether those “one time only” steps in the origin/early evolution of life were one time only because they’re very unlikely; or if it’s just because the first lifeforms took over the world ocean quickly, there was no room for separate origins of life, and so whatever they happened to use became universal due to “founder effect”; or if there were other early lifeforms that used different systems but the current one won out completely so the others have no descendants today.

    2. TallDave says:

      evolution since the Cambrian seems to happen way too fast to be explained by random mutation, fatal error rate is anomalously low (like many many orders of magnitude too small) because the degrees of freedom in folding protein are so large… suggests (at least to me) fantastically efficient code optimization to reduce that fatal error rate to something like what we observe

      while such optimization might be required to show up in our local past given that we are here to look for it, suspect it also might be so unlikely that the vast majority of 13.6B ly radius lightcones (i.e. observable universes centered on a particular planet) around today have no life in them complex enough to appreciate the view

  26. MTK says:

    Microbial life on Mars may have been detected over 40 years ago on the Viking mission. At least according to two of the NASA scientists in charge of the Labeled Release experiment aboard Viking that was developed to detect microbial activity in Martian soil. It’s all quite interesting. See the Scientific American blog entry linked and follow the links for more detail.

    https://blogs.scientificamerican.com/observations/im-convinced-we-found-evidence-of-life-on-mars-in-the-1970s/

  27. cynical1 says:

    Isn’t anyone reminded of “The Savage Curtain” episode from the original Star Trek? I feel quite certain that the phosphine is being generated by Excalbians! They lived on a volcanic planet too. Clearly, they have recently inhabited Venus and are trying to establish contact with their new neighbors. Of course, they waited until we set up our Space Force. They didn’t want to jump the gun until we were ready. After all, who needs The Federation when you have The Space Force?

    1. Steve H. says:

      Nothing Dr Who can’t handle, I presume.

  28. Sulphonamide says:

    Can anyone comment on when we stopped thinking (assuming?) that there was intelligent life on Venus and Mars? Sadly my Grandparents are no longer alive to ask (and probably would have regarded the suggestion as heretical). Presumably 200 years ago we did and maybe 100 years ago we didn’t – but what was the scientific evidence that changed our assumptions?

    1. Russ says:

      https://en.wikipedia.org/wiki/Lowell_Observatory

      A little over a hundred years ago, this facility was founded to search for life on Mars.

    2. Elliott says:

      I was nobbut a lad at the time, but there was considerable enthusiasm from both scientists and science fiction writers for life on both Mars and Venus until the 1960’s. Before then, all one could see were vague blobs at the ends of the best earth-bound telescopes. The first space probes, as was just mentioned, killed those notions.

      At the time, I read a juvenile fiction book by Asimov in which he imagined Venus to be covered by oceans (and large telepathic frogs, so there…). It was written in the early 50’s but my edition came out >10 yrs later and included a postscript in which Asimov admitted that new discoveries meant that his vision of Venus was not real.

      Similarly, the first photos of Mars from the probes showed a sterile landscape with craters, just like the Moon. There was still enough enthusiasm for life (primarily of the microbial type) from the likes of Carl Sagan that the first landers (the Viking probes) of the 1970s were aimed at detecting evidence for complex organic molecules and other signatures of life. The Viking cameras were stereoscopic and had high enough resolution that they could have detected a Martian critter (green or otherwise) hopping past. The actual photos showed a sterile and boring field of rocks, none of which showed any inclination to move, and the other experiments were ambiguous at best. NASA has taken a more conservative approach to Martian life since then.

      1. Derek Lowe says:

        The Mariner probes did indeed knock down a lot of the earlier visions for life in the solar system. But our discoveries here of the various extreme environments in which life can succeed (deep ocean vents, geological formations, clouds, hot springs, halophiles) have revived hopes that there might be plenty of environments out there that would be suitable. You have the clouds of Venus, potential underground aquifers on Mars, the definite presence of global oceans under the crusts of Europa, Enceladeus and several other moons of Jupiter and Saturn, etc.

        1. Elliott says:

          I agree that new evidence shows that some of the outer moons and maybe Ceres offer good possibilities for life, maybe better than Mars or Venus. I’m still bummed, though, that no one has picked up good evidence for intelligent life. A black monolith or two would be nice…..

          1. confused says:

            Maybe it works out to be no more than one technological (the definition of “intelligence” is arguable) species to a star system.

            The time scale to go from Paleolithic to settling/industrializing the entire solar system is probably very short on an evolutionary timescale. Behaviorally-modern humans are very new on that timescale, and we already have limited space access; IMO if our technological civilization survives the next century we will probably have most of the solar system industrialized in a thousand years.

            So probably no open niches for a new intelligent species to evolve.

            As for extra-solar intelligence… our civilization is probably not detectable at even near interstellar distances, and the Galaxy – much less the Universe – is huge; I really doubt anyone is checking on every solar system with spacecraft.

  29. Chris Ginsburg says:

    If the Venusian clouds are 95% Sulfuric Acid.. then what is the average pH? And what is the absolute lowest pH that acidophiles on Earth can endure?

    Thanks -C

    1. LdaQuirm says:

      Sulfobacillus disulfidooxidans is the most acidic loving bacterium I could find:
      “Isolate SD-11 grew between pH 0.5 and 6.0, and
      the optimum value varied between 1.5 and 2.5…” https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/00207713-46-4-1056

      But the archea “Picrophilus” sp. Found growing naturally at PH < 0.5 and apparently able to live at a PH of –0.06 are the most acidophilic organisms currently known. https://en.wikipedia.org/wiki/Picrophilus

    2. Marko says:

      pH is pretty much a meaningless metric in this context. It can only be measured accurately in more dilute solutions. As for comparables on Earth , look up “snottites”. These organisms survive in close to similar conditions by way of biofilms that shield them from the acidic environment. I see no reason why a similar mechanism couldn’t have evolved on Venus at some point. Instead of snottites in the Venusian atmosphere , it might be snot aerosols (snottasols?).

      1. Chris Ginsburg says:

        Thanks Marko — Although Snottites are interesting in that they produce sulfuric acid and survive in low pH….”The lowest pHmin -0.06 was observed for two hyperacidophilic Archaea known as Picrophilus oshimae and P. torridus (pHopt 0.7)”

        https://www.frontiersin.org/articles/10.3389/fmicb.2019.00780/full

        1. Marko says:

          That’s a nice review article on extremophiles. Thanks for the link.

  30. Tony Zbaraschuk says:

    >Can anyone comment on when we stopped thinking (assuming?) that there was intelligent life on Venus and Mars? Sadly my Grandparents are no longer alive to ask (and probably would have regarded the suggestion as heretical). Presumably 200 years ago we did and maybe 100 years ago we didn’t – but what was the scientific evidence that changed our assumptions?

    The early 1960s with the first fly-by probes. One close-up look was enough to reveal an absence of Venusian jungles and Martian canals.

  31. Uncle Al says:

    Venus’ surface is a vast supercritical CO2 extractor. Volatiles and heavy elements (including cesium) are transported to highlands where they react, condense, and crystallize into a planetary spin-orbit coupled topological superconducting hive mind connected by a phosphene (re graphene) nervous system. PH3 is a minor degradative byproduct, re methane and cow belches. As for living in concentrated sulfuric acid…

    https://en.wikipedia.org/wiki/Snottite

    More studies are needed…and modeling! Upon finding nothing, even more studies are needed.

    1. NPs says:

      Is this Pierce from the show Community?

      1. syd says:

        This sounds more like Abed, mayhaps?

      2. Matthew Burk says:

        Uncle Al is just Uncle Al. He shows up in chemistry discussions. Fun poster.

  32. Lloyd Evans says:

    It’s certainly true that most of the detectable carbon and sulfur in the atmosphere of Venus are in their oxidised forms – carbon dioxide and either sulfur dioxide or sulfuric acid. However, this in itself is not really an argument for saying that any phosphorus present must (or should) be in its oxidised form. Why? Because as far as we can tell, there is no elemental oxygen in the atmosphere of Venus. If there was, then hydrogen sulfide getting oxidised to sulfur dioxide would be mundane and expected, just as it is on earth. Same goes for methane being oxidised to carbon dioxide and water. The same again would go for phosphine being oxidised – either to phosphorus pentoxide or maybe to phosphoric acid if water was also present.

    But in the absence of oxygen in the atmosphere (which is the current situation on Venus), the existence of trace gases such as methane, hydrogen sulfide or phosphine isn’t so strange in itself. The weird part is what is producing the phosphine in the first place, not why it isn’t being oxidised. Then again, hydrogen sulfide and methane both have volcanic origins, so perhaps phosphine does as well – just by a process we don’t quite understand yet, because it hasn’t been seen on Earth.

  33. Georges says:

    Highly speculative !

  34. li zhi says:

    Snottites exist in ‘battery acid’ which is 30-50% acid, not 95%. Biogenic PH3 (here) probably is made in anaerobic and reducing conditions. DL says at the relevant altitude Venus’ atmosphere is oxidizing. Using a dubiously assigned single spectral line to connect these dots is absurdly optimistic. Excluding any discussion of life-as-we-don’t-know-it because we can’t really say anything about it (including whether it exists, anywhere (if we ignore in-silico possibilities)), life as we know it can not replicate in the conditions believed to exist there, I’d guess. Of all the places in our Solar System which we should explore to rule out life, Venus is pretty far down on the my list. I also would slightly disagree with DL that the abiotic chemistry to produce it “isn’t known”. That may be true, but it may just not be recognized, it could be fairly well-known (to some, or at some previous time). I thing saying it isn’t known is a bit too strong a claim. After all, PH3 is produced from H3PO3 decomposition, and H2S is produced in the reactions of H2SO4 which simultaneously produce SO2. (iirc, when the conditions are far from equilibrium (i.e. sufficiently energetic))

  35. JJBP says:

    The BBC’s exceptionally long running astronomy programme which is one of the few science programmes which assumes a good knowledge of science had a special on this paper.

    https://www.bbc.co.uk/programmes/m000mmjk

    The programme has a section about checking for abiotic processes which might create phosphine which goes into some detail on what’s been done.

  36. Aaron in SF says:

    Panspermia, the local version in which life arising within our own solar system once is distributed by meteor splash and similar events producing microbe-carrying ejecta, is I would guess as likely as independent genesis… maybe more so…?

  37. anon says:

    Two new papers (2010.07817 and 2010.09761 on arxiv), one already accepted and in press and the other only submitted, cast some doubt on the detection, or at least put some limits on how much phosphine there could be.

    2010.07817 (accepted to A&A) looks for phosphine signature in the IR infrared and doesn’t see anything. This is in some conflict with the earlier claimed mm detection, but the discrepancy could potentially be explained by the fact that IR and mm spectra probe different parts of the atmosphere.

    On the other hand 2010.09761 (submitted) claims that the mm line detection is not nearly as secure as originally claimed, because the data analysis that was used can easily cause spurious lines to appear.

  38. David Edwards says:

    To add to the fun and games, there are now reports that glycine has been detected in the high equatorial Venusian atmosphere … the non-technical version is here. Paper is here.

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