A question regarding the scenario where H2 and acetylene get incorporated in a solid precipitate...
As you've mentioned, an acetylene-hydrogen mixture is a source of chemical energy. So, what happens to that energy in the long term as the precipitated materials keep building up? Does it simply sit there indefinitely? Or, could some of that energetic mixture of hydrogen, acetylene (and whatever else) eventually find its way down to the subsurface liquid water-ammonia environment, and provide an energy source for chemistry or biology there?
Is this a possibility to consider in planning future missions to Titan - a naked gene able to catalyse, or a naked catalyst able to propagate itself - that might made of something other than RNA?
Your article mentions that when we eat chocolate, we use catalysts to get energy out of it,
Which (by the Occam's Razor principle) seems to support the conclusion that Titan more likely just has catalysts, rather than catalysts plus chocolate-eaters making use of them.
But maybe there is another way of thinking about the relation between organisms and catalysts. Rather than living cells using catalysts, what if we think in terms of the catalysts using the cell as a space to work in?
Natural carbon-based catalysts here on Earth seem to need these little workshops to do their catalysing.
To assume that Titan's catalysts need no such spaces is to assume that Titan's ones are smarter, at least in the sense that we speak of smart machines.
Questions for Chris... I know there has been some discussion about how Titan might change in the future. But what about Titan in the past? If its atmosphere used to be substantially richer in hydrogen atoms (more H2, and perhaps NH3 instead of N2) what would that mean for how easily acetylene and ethane could be hydrogenated into methane? Could less effective catalysts have done the job, back then, than would be required now? And would molecules with catalytic properties have been more, or less, likely to form in such conditions? Has anyone experimented with this? Is it possible that an evolutionary scenario -- more sophisticated catalysts gradually appearing as an adaption to decreasing availability of hydrogen -- will turn out to be the most economical explanation? Even though that scenario of course implies existence of systems capable of evolving, and thus meeting one definition of life?
Chris. Thanks for your reponse! Yes, I enjoy the thought of life on Titan also. Are the findings about hydrogen, acetylene and ethane the chemical footprints of life? At any rate, it would seem more likely that the carbon cycle depends on an organic catalyst rather than a metal one, given that Titan's surface (unlike that of Mars) is rich in organics rather than in compounds of metals. Have you considered that the answer might lie between the non-biological explanation and the biological one? Is it conceivable, for instance, that there are systems of catalytic molecules which are carbon-based without being enzymes, and those systems can maintain themselves and observably affect their environment without necessarily having all the bells and whistles of a living cell? -Colin
To Chris McKay: I can understand the note of caution in your article... But it does look like you and your colleagues have found something that is indeed (as you put it) "extremely interesting"... Even if the explanation isn't a population of organisms... Levels of ethane, acetylene, as well as hydrogen all seem to imply that Titan's carbon chemistry is not a one-way street (compounds forming in the atmosphere, sinking to the ground and accumulating there), but a true carbon cycle. This in a world that also has a liquid cycle of evaporation and precipitation... Isn't a carbon cycle important in itself? Which other place in the solar system has a liquid cycle plus a carbon cycle?