korwynkim

A team including two of the original authors looked at a different spectral frequency for phosphine and found an upper bound of only 5 ppb: https://arxiv.org/abs/2010.07817 Another team disagrees with a part of the methodology used for the original data analysis and says the results are invalid: https://arxiv.org/abs/2010.09761 A possible detection of glycine on Venus: https://arxiv.org/abs/2010.06211

Some researchers went through the old Pioneer Venus mass spectrometer data and found that it probably detected phosphine: https://arxiv.org/abs/2009.12758 Others came up with a set of assumptions under which volcanism could explain the phosphine amount: https://arxiv.org/abs/2009.11904

Hmm. I just learned about the Martian labeled release experiment done in the 70s by the Viking landers. They took soil samples and injected nutrients tagged with Carbon-14, then monitored for evolved gas which could result from metabolism. This produced positive results with multiple samples from both landers. Control tests were done to eliminate the effect of UV-chemistry and samples were heated at different temperatures to help distinguish biology from chemistry. Results were dismissed due to the lack of detection of organic compounds (at the time) and the lack of water, along with the result of chemical experiments carried out involving gamma ray interactions with perchlorate which could partially explain the results. This seems like it was possibly stronger evidence of life than phosphine on Venus. I wonder how the phosphine discovery will turn out.

I never said it meant that life is everywhere. It gives us a starting point. Whether or not life needs things beyond just the presence of building blocks to start is the Big Question, isn't it? On one hand, life on Earth started almost as soon as it was able. On the other hand, we have no evidence of the steps leading up to the first microbe, and we don't know how it would have happened.

In general, I think speculation is helpful or even necessary for generating hypotheses. In the case of this interview, the whole point was to discuss and speculate about the possibility and nature of life on Venus. Nobody is denying that we should locate the source of phosphine. As for the origin of life, many complex organic molecules like amino acids and other building blocks of RNA/DNA have been found in comets, meteorites, the interstellar medium, and even a protostar. The gap between these molecules and microbes is still a big mystery, but at the very least, it seems like the ingredients for life as we know it are abundant or easily formed.

Here is a detailed interview with one of the authors about the possibility of life on Venus: https://youtu.be/vnLqUiaWXnA A few of the topics covered: Correlation of phosphine with the unknown UV absorbers Implausibility of contamination from Soviet probes It would have to be "life as we don't know it" even if it uses water based biochemistry or has DNA Possibility of silicon based life using sulfuric acid as a solvent Photosynthesis isn't limited to fixing carbon Whether oxygen is required for complex multicellular life Whether we could tell if life on Venus and Earth shares the same origin Also, going through past data from the ExoMars TGO orbiter suggests there is little to no phosphine on Mars: https://orbiterchspacenews.blogspot.com/2020/09/russian-spectrometer-did-not-detect.html

Interesting. Here is a relevant quote from this paper (https://arxiv.org/abs/2009.06499) The measurements suggest that the Venus’ crustal composition is extremely similar to terrestrial tholeitic basalts. Terrestrial basalts contain very low amounts of phosphorus (0.08% - 0.45%). If phosphorus is present on the surface of Venus, it is likely to be in the form of phosphate salts. We have considered phosphate salts of Mg, Ca, Al and K, with fluorapatite included as well as HF is probably present in the atmosphere. Phosphate minerals were assumed to be present as differentiated minerals, i.e. as pure solids whose activity is 1. The presence of pure solids is geologically unlikely, but (as with many other assumptions in this paper) presents a ‘best case scenario’ for making phosphine chemically. This independent paper seems to agree that the phosphorus concentrations of basalts is low, at least on Earth (https://link.springer.com/article/10.1007/s11104-012-1490-2)

We do need all the data we can get. This is true in general. If you know anyone with a decent telescope and imaging setup, let them know that scientists are looking for help from amateur astronomers to gather data on Venus: http://pvol2.ehu.eus/bc/Venus/

I doubt Akatsuki will be getting that much more attention. I don't think too many people really suspect anything about how the weather and climate might help sustain microbial life in the clouds. If anything, old data might get reanalyzed within that context. Much more attention will be focused on the BepiColombo flybys. I don't think Dragon01 - or anyone for that matter - was ever assuming there was life, just arguing how it might not be outright impossible. Of course, this is built upon a tower of assumptions stacked on top of assumptions, but most things we can infer about Venus are.

Point taken. Either way, Pioneer could detect water very accurately. I wasn't disagreeing with you that we don't know in detail how water is distributed on Venus. I got the impression that you thought our level of confidence in the general water level at every altitude was less than was merited by the evidence, and was trying to clear that up. The Akatsuki observation only shifts my prior slightly toward there being times of high enough humidity in some areas. I suppose we could continuously observe Venus from the ground to try to detect fluctuations, then corroborate with Akatsuki? Important for anything resembling known life. If we're considering unknown processes, then perhaps those can be used to form chemical bonds. Maybe unknown life would only need the amount of water we observe. Maybe they wouldn't need it at all. I admit I don't really know enough to say, and it's hard to evaluate the probability given one example. Maybe there are aliens somewhere, looking for planets with sulfuric acid because that's the only way they know of forming life.

Absolutely. More data is always better. We are able to do look at spectral lines for water all the way down to the surface using ground based telescopes, let alone from orbit (https://arxiv.org/abs/0901.3869). The humidity level does seem to vary leading to some different measurements, but it's all within a small range. You generally don't equip a probe with an instrument specifically designed to find water. Just one of the spectrometers on the Pioneer had the capability to measure the level of a wide range of components with better than 1 ppm precision (https://www.researchgate.net/publication/224457637_Pioneer_Venus_large_probe_neutral_mass_spectrometer) I believe we were discussing water within the context of Earth-like microbes? If we're considering unknown life, then yeah water is not a factor. It would be adapted to the conditions. The only example of life we have requires water, but that's only one sample. How important you consider water is on Venus depends on how strongly you weigh this evidence.

What I meant by our models being wrong was more about our assumptions about the conditions on Venus than our estimations given those assumptions. I find this more likely than finding an unknown process or life, though I haven't tried to estimate the probabilities. A good place to start would be to examine all the times where we found a phenomenon that we couldn't explain at first, then figure out how many of those were because our models weren't good enough vs how many were due to discovering an unknown process. We obviously haven't found life yet and that would be the least likely by far. (does anyone know of such a list?) The Pioneer multiprobe made several direct measurements of the atmosphere. Venera 15 measurements line up with ground based measurements (https://doi.org/10.1016/S0273-1177(99)00170-2) and the earlier Venera data was reanalyzed and agree as well (https://doi.org/10.1016/S0032-0633(96)00143-2). Galileo also made remote measurements during its flyby. I'm sure other probes collected whatever data they could as well. It's not a requirement but it does make it harder. The high winds would eventually spread any dried out microbes around, exposing them to acid. They also wouldn't produce phosphine when dried out which means there would need to be a higher biomass to make the same amount. We don't know how often these separate air masses form, whether it really is due to water or CO or COS or something else, and how much of a difference there is in humidity. But if areas of high enough humidity do occur regularly, it would certainly be a good place to look for life.

Wrong. High temperature and pressure as found in gas giants is only one way to make phosphine. In the second paper from my last post, the authors exhaustively list out all the relevant abiotic pathways they can think of. They calculate how much each of these processes might be producing based on our models (some don't produce any). The issue is that the estimated amount produced would be orders of magnitude lower than what we detected. This is very true but besides the point. We don't exactly know what organisms are producing it or how, but we can be pretty sure that they are. However, this tells us nothing about what unknown life might or might not produce. On top of Venus Express, we also have data from Pioneer, the Venera landers, and many ground based observations on atmospheric composition. So we have a pretty good idea about the acidic content of the clouds and the average humidity level at various altitudes. Sure, it's possible there are areas of higher humidity. Images from the currently orbiting Akatsuki showed what looks like a boundary between two air masses, similar to what we find on Earth between drier and more humid air. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6954018/ But the boundary dissipates within 2-10 days so it's not really stable.

KerikBalm already mentioned that Venus is way too dry for any life we know of to grow and replicate. It's also the case that the acidity of the sulfuric acid droplets is at least 10^11 times more acidic than the most acidic place on Earth where we might find life (which has negative pH). In fact, the pH scale doesn't even make sense here because it's not dilute enough. https://www.liebertpub.com/doi/10.1089/ast.2020.2244 This precludes any life similar to what we know about. This means if there is life, it would have to be completely different, having arisen through independent abiogenesis. But presents a bit of a dilemma since we can't use phosphine as a biosignature for any unknown life. It's suitability as a biomarker is based only on known anaerobic life. So this discovery doesn't increase my probability for life, except in the sense that "we found something in space that we can't explain" (big surprise), and it could be anything. Here is a quote from a preprint paper written by most of the same authors as the original discovery paper: "We conclude that, while we cannot rule out life as a source of the phosphine on Venus, the hypothesis that the phosphine is produced by life cannot a priori be favored over the hypothesis of unknown photochemistry or unknown atmospheric chemistry. All seem equally unlikely, and hence all call for further investigation. We note, after (Catling et al. 2018), that the extraordinary claim of life should be the hypothesis of last resort only after all conceivable abiotic alternatives are exhausted." https://arxiv.org/abs/2009.06499 The most likely explanation is that our models and estimates are wrong. We have seriously limited information about Venus. We don't even know the composition of crust and mantle rocks, although all the plausible types based on what is known about rocky planets in general were considered. There is the extremely slim chance that life arose when Venus was much nicer and had water oceans up to 4 billion years ago. My favorite wild speculative theory is that there used to be a civilization on Venus much like ours, but they destroyed themselves through nuclear war and global warming, leading to the current runaway greenhouse atmosphere. Volcanic activity caused magma to ignite abundant fossil fuel deposits leading to the formation of phosphorous-rich pyrometamorphic rocks (like zuktamrurite). The above paper briefly mentions these types of rocks as a source of phosphorus.