Mini-Throughput: Life on Venus Edition


Michael Siegel

Michael Siegel is an astronomer living in Pennsylvania. He is on Twitter, blogs at his own site, and has written a novel.

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4 Responses

  1. Avatar Oscar Gordon

    We need to do an atmosphere scoop.Report

  2. Avatar George Turner

    I would rate the theory as slightly less plausible than finding a plesiosaur in Loch Ness, which is what came to mind when I watched the BBC “The Sky at Night” episode on the discovery.

    Among the problems are:

    No known biological processes produce phosphine. There is anecdotal evidence that biological processes might produce phosphine, but nobody knows what such mechanisms might be.

    Earth’s atmospheric phosphine doesn’t seem particularly associated with biological life. It can be detected at ground level, so one assumption is that some kind of organic decay must produce it, but radon gas likewise bubbles up through the subsoil and nobody thinks that’s biological.

    Phosphine concentration in the Earth’s atmosphere various by about a factor of 100,000. You can find it over the arctic tropospheric concentrations that are almost a thousand times higher than you might find over a swamp. If phosphine did have a short atmospheric half life, this would indicate no correlation to biological processes. (See figure 1 of this January paper on phosphine detection in “Astrobiology”.

    Phosphine can be produced by lightning. The Journal of Atmospheric Environment published a 2004 paper titled “Phosphine and methylphosphine production by simulated lightning—a study for the volatile phosphorus cycle and
    cloud formation in the earth atmosphere” (Link is https colon // – I’m avoiding the spam filter)

    From the abstract:

    These results suggest evidence that phosphine and methylphosphine (detectable in the field by intense garlic odor) are produced when atmospheric lightning strikes the ground or aerosol which is containing oxidized forms of phosphorus and chemical reductants.

    Additional reviewed data show that laboratory lightning was able to reduce a much more significant portion of phosphate to phosphite (up to 25% yield), methylphosphonic acid (up to 8.5% yield) and traces of hypophosphite in a matter of seconds.

    The atmosphere of Venus includes H2O, HCl, and HF, and it rains H2SO4. Most of the atmospheric phosphorus is phosphorous anhydride, P4O6, at 2 ppm below 25 km, which reacts with sulfuric acid to form phosphoric acid (H3PO4) and sulfur dioxide (SO2) in the lower cloud decks. As it sinks lower, it should form P4O10.

    One reaction with phosphine is:
    sulfuric acid + phosphine –> water + phosphoric acid + sulfur dioxide
    4H2SO4 + PH3 –> 4H2O + H3PO4 + 4SO2

    And as the above paper shows, lightning can produce phosphine in an atmosphere, and all the atmospheric ingredients are present for the above reaction to run in either direction, along with intense Venusian lightning storms.

    One question nobody has investigated is whether phosphine could also be produced above lightning storms by sprites and blue jets.

    So my problem with the theory claiming evidence of life on Venus is that phosphine isn’t known to be evidence of life, but it is known to be evidence of lightning. And it also is the equilibrium form of phosphorus at temperatures above 800 K (as on Jupiter and Saturn), while Venus is already at 737 K.Report

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