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Thread: Testable predictions about life on Titan

  1. #31
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    Quote Originally Posted by Colin Robinson
    He says: " a biological distribution of molecules would be a series of relatively sharp spikes while an abiotic distribution would be smooth." Note that he doesn't just say "spikes", he says "relatively sharp spikes". By "relatively" he means: in comparison to an abiotic distribution.
    Its still double-talk.
    ‘Biotic’ and ‘abiotic’ molecules aren’t defined by their relative abundances (ie: ’spikes’ or no ‘spikes’, ‘smooth’ or not ‘smooth’). We’re talking about organic chemistry here.
    He’s trying to impose his fantasies onto the outcome of yet another fantasised hypothetical measurement, whilst ignoring already known chemistry.

    Quote Originally Posted by Colin Robinson
    You mention the diversity of molecules produced on Titan by abiotic processes.
    No .. the diversity of amino acids and their isomers is an outcome of organic chemistry in a natural environment.

    At the stage this becomes relevant during the detection/sample treatment process, ‘abiotic’ and ‘biotic’ is unknown.

    Quote Originally Posted by Colin Robinson
    That diversity would indeed mean lots of little spikes, but the broad outline would still be smooth. If McKay's hypothesis is correct, a series of relatively sharp spikes, corresponding to molecules favoured by Titan biology, would be present if there are biological processes happening, even if there were abiotic processes happening as well.
    Pure codswallop.

    Isomers have the same molecular weight as biomolecules.
    A subset of amino acids are classified as biomolecules.
    The distributions of amino acids and their isomers will look the same as a biomolecule distribution in a tholin dominated landscape.

    Quote Originally Posted by Colin Robinson
    The molecules showing up as relatively sharp spikes would not necessarily be those which are biologically significant on Earth, such as amino acids and lipids. They would be molecules which in Titan conditions have biologically useful properties such as functioning as catalysts (as amino acid polymers do in Earth conditions) or forming membranes (as lipids do in Earth conditions).
    They’re still organic chemicals behaving as per known physical chemistries (which can be simulated).

    The question is not how biology can use physical properties of compounds.
    The question is: Is there biology in the first place?

  2. #32
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    Quote Originally Posted by Selfsim View Post
    Its still double-talk.
    ‘Biotic’ and ‘abiotic’ molecules aren’t defined by their relative abundances (ie: ’spikes’ or no ‘spikes’, ‘smooth’ or not ‘smooth’).
    Biomolecules are defined by the criterion that they are produced and used by biota, i.e. living things.

    Therefore, in any environment with enough biota to affect the overall chemistry, these particular molecules will be more abundant than they would otherwise be.

    They’re still organic chemicals behaving as per known physical chemistries (which can be simulated).
    Of course they are organic compounds... The point is that living things contain selective catalysts which produce certain very specific organic molecules and not other (very chemically similar) ones. That is what enables biota to grow and reproduce while keeping the same chemical composition.

    The question is not how biology can use physical properties of compounds.
    The question is: Is there biology in the first place?
    The question McKay is addressing is: how can we detect biology if it is there in the first place?
    Last edited by Colin Robinson; 2019-Jul-08 at 10:04 AM.

  3. #33
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    Quote Originally Posted by Colin Robinson
    Quote Originally Posted by SelfSim
    The question is not how biology can use physical properties of compounds.
    The question is: Is there biology in the first place?
    The question McKay is addressing is: how can we detect biology if it is there in the first place?
    .. And that seems to be a good place to leave this discussion ..


    In summary, (and including my position on McKay’s pure speculations):
    Quote Originally Posted by SelfSim
    Quote Originally Posted by Colin Robinson
    1. Methanogens, if present, will affect levels of H2 in the atmosphere. Where methanogens are active, H2 levels will be lower.
    The cryovolcano mechanism is also thought to bring the mixture to the surface .. and in some models, its a continuous process for replenishing the atmospheric methane.
    McKay’s ‘prediction’ in this area is already accounted for by other variable geo-mechanisms such as winds interacting with surface materials and past cryovolcanic eruptions which bring mantle materials to the surface.


    Quote Originally Posted by SelfSim
    Quote Originally Posted by Colin Robinson
    2. Life chemistry on Titan (as on Earth) will favour the formation of the specific organic molecules it has a use for. Because of this, a graph showing relative abundance of different organics will have spikes in it, rather than being a smooth curve.
    Isomers have the same molecular weight as biomolecules.
    A subset of amino acids are classified as biomolecules.
    The distributions of amino acids and their isomers will look the same as a biomolecule distribution in a tholin dominated landscape.
    McKay’s ‘prediction’ in this area is purely dependent on his speculative premise that there are actually sizeable populations of ’living methanogens’ on the surface of Titan. Without them, his ‘prediction’ is completely useless and also flies in the face of already lab-demonstrated, understood (and expected) organic geo-chemical behaviours.

    Both of his predictions are completely moot and will only serve as an ‘I told you so’ following some other more worthy scientific investigation.

    DragonFly’s primary mission is to assess prebiotic chemistry for microbial habitability within its flight range. Its payload will include a mass spectrometer. Its visibility of such environments is thus constrained to its mass spectrometer results*, which is why my response to his ‘prediction 2’ above, is of key significance to the primary mission (whereas McKay's 'prediction 2' is not).


    * .. and its atmosphere-limited visual imaging.

  4. #34
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    Quote Originally Posted by Selfsim View Post
    Quote Originally Posted by Colin Robinson View Post
    The question McKay is addressing is: how can we detect biology if it is there in the first place?
    .. And that seems to be a good place to leave this discussion ..
    It would be a good place to start a discussion, if you were prepared to take that question seriously...

    In summary, (and including my position on McKay’s pure speculations):
    McKay’s ‘prediction’ in this area is already accounted for by other variable geo-mechanisms such as winds interacting with surface materials and past cryovolcanic eruptions which bring mantle materials to the surface.
    The prediction you're referring to here is about levels of hydrogen (H2) in different regions of the atmosphere. You've made a response which doesn't even mention H2....

    I've noticed that you said something like this earlier in the thread, when we were talking about the related question of ethane levels. Yes, it's conceivable that geological mechanisms might produce an unknown mineral catalyst affecting levels of ethane and hydrogen. But we don't yet know whether or not that is what's happening.

    McKay’s ‘prediction’ in this area is purely dependent on his speculative premise that there are actually sizeable populations of ’living methanogens’ on the surface of Titan.
    His predictions are ways of testing that model, to see whether it is actually right or not.
    Last edited by Colin Robinson; 2019-Jul-09 at 04:24 AM.

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