Titan has an abundance of hydrocarbons. Earthbound animals live on carbohydrates that are metabolised by elements like Oxygen that is found on Earth. Is there a possibility of different metabolism that will allow living beings to live off hydrocarbons instead of carbohydrates. If so, then living on Titan becomes relatively easy. Is this something even remotely possible? Curious.

  • $\begingroup$ I think there are bacteria and possibly other organisms already on Earth that can metabolize hydrocarbons. Not sure though, I don't have a reference for you. $\endgroup$ – uhoh Aug 17 '19 at 15:15
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    $\begingroup$ It's worth keeping in mind that the low temperatures will cause chemical reactions to be very slow, which I would expect to cause evolution to happen much more slowly or fail to start at all. Still worth considering the chemical possibilities in case this analysis is wrong. $\endgroup$ – Mark Foskey Aug 19 '19 at 4:54

There are bacteria on Earth which get energy from hydrocarbons and oxygen. See for example this article. Many of them need oxygen which is not freely available on Titan. Some (thank's to @Calcutta for pointing this out) can use sulphate as an oxidising agent instead. However, as far as I can find out, essentially all the oxygen on Titan is in the form of water, which is a rock hard solid at local temperatures. There do not appear to be any oxidising agents available in the Titan surface environment.

We can speculate on an artificial ecosystem for Titan. It must ultimately be powered either by the Sun, or by the heat of Titans core. A sun-powered system probably begins with a population of microbes of some kind in the haze layers at the top of the atmosphere. They could store energy (for example) by converting methane into higher hydrocarbons and hydrogen, or cracking ethane into ethene and hydrogen. This isn't a hugely energy-dense form of storage, but it might work. A heat-powered system would begin with vents (which might need to be made artificially) where hot liquid water came to the surface. Since it would be cooling and depressurising quite fast, it might well contain chemicals that were not in equilibrium (this is what happens at Earth's deep ocean events). Those chemicals can be exploited for energy by life forms. In this case they could break water into hydrogen and oxygen, or perhaps water and ethane into methane and oxygen.

Either way, you then have scope for a second stage in the life cycle that exploited that stored energy.

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  • $\begingroup$ Thank you for your answer. However it seems that even anaerobic bacteria -- that do not need oxygen -- exist mpg.de/257961/Oil_degrading_bacteria $\endgroup$ – Calcutta Aug 18 '19 at 12:39
  • $\begingroup$ @Calcutta I have edited $\endgroup$ – Steve Linton Aug 18 '19 at 21:51

As an alternative, there is the possibility of an oxygen-free metabolism. Let us look at some standard enthalpies of formation from the various Wikipedia articles for a few simple species

$\text{H}_2 = 0$ kJ/mol (definition for elements in their standard state)

$\text{CH}_4 = -74.87$ kJ/mol (Wikipedia)

$\text{C}_2\text{H}_6 = -84$ kJ/mol (Wikipedia)

$\text{C}_2\text{H}_4 = +52.47$ kJ/mol (Wikipedia)

$\text{C}_2\text{H}_2 = +226.88$ kJ/mol (Wikipedia)

Taking account of the fact that reducing each of the last three hydrocarbons with hydrogen, to give methane ($\text{CH}_4$), gives two moles of methane per mole of "fuel", we see that in all cases the reduction yields a net energy output and thus could drive other processes, especially with acetylene ($\text{C}_2\text{H}_2$). Energy is also evolved by hydrogenating acetylene to the other two-carbon molecules, notably ethane ($\text{C}_2\text{H}_6$) which is present in Titanian lakes along with methane.

Where does Titan fit in? According to JPL, the surface of Titan is acting as a sink for acetylene and hydrogen, the above pair with the largest potential energy for forming methane. Could it be a biological process? Of course, prudence demands that nonbiologicsl sources must be given priority, but these preliminary findings open up the possibility of hydrogen-"breathing" organisms.

Whatever process is driving this apparent acetylene-hydrogen reaction is likely driven by solar energy. Sunlight can break down Titan's methane molecules, leading to the formation of less stable products that could be recovered to methane.

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  • $\begingroup$ hydrogen 'breathing' organisms is an excellent idea .... $\endgroup$ – Calcutta Aug 19 '19 at 0:10

It would have to be vastly different to earth physiology but there are exothermic chemical reactions possible with compounds found on Titan. This may well not be the only hurdle though. For example without having a solvent for the redux reaction and a functional group for what ever the analog of enzymes would b in this system: using this energy would be tricky.

Impossible: maybe not. Those a lot more knowledgeable than I haven't ruled it out. But 'easy'... I don't think its fair to call any creation of life easy.

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