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Thread: Phosphine, a strong biosignature, has been detected in the atmosphere of Venus

  1. #61
    Join Date
    Aug 2010
    Perhaps it's worth contextualising the reported phosphine by looking at whether other simple hydrogen compounds, such as methane (CH4), ammonia (NH3) and hydrogen sulfide (H2S) have been detected in the atmosphere of Venus...

    It turns out that space probe data has given apparent indications of all these compounds. Venera 8 (1972) found indications of NH3. Pioneer Venus Large Probe (1978) found indications of NH3 and H2S.

    These are the papers I found

    Ammonia in the atmosphere of Venus

    Venus methane and water

    Composition of the atmosphere of Venus below the clouds

    The apparent indications of NH3 and CH4 were treated with scepticism by scientists. But considering how little research has been done on Venus in the last few decades, can probe data from the seventies be disregarded?

    If all these simple hydrogenated molecules are there, how does it relate to the phosphine finding?

    Methane, ammonia and hydrogen sulfide, like phosphine, are produced on Earth by micro-organisms in conditions which are anoxic (lacking O2 molecules) yet comparatively oxidising (rich in oxygen compounds). The microbial chemistry breaks bonds between oxygen and another element (carbon, nitrogen, sulfur, or phosphorus), and bonds the C, N, S, or P with hydrogen instead. This makes oxygen atoms available for energy-producing reactions (anaerobic respiration).

    So the apparent presence of CH4, NH3, and H2S is consistent with the hypothesis that the apparent presence of PH3 is due to life. But doesn't necessarily rule out geothermal activity either, as this can produce a range of hydrogen-rich molecules.

    Another reason methane (CH4) is interesting... Compared to other simple carbon compounds, such as CO2, CH4 is chemically more similar to biomolecules, which typically contain large numbers of carbon-hydrogen bonds (as well as carbon-carbon bonds).
    Last edited by Colin Robinson; 2020-Oct-01 at 08:11 PM.

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