[BRIEF NOTE] Life on Titan?
Sep. 24th, 2005 11:33 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
rfmcdonaldWill Baird links to an interesting interview at the website of the journal Astrobiology, "The Living Worlds Hypothesis." In this interview, astrobiologist David Grinspoon explores the possibilities of life on Titan, and wonders if, in fact, the dense Titanian atmosphere might be as much of a product of life as our Earth's own dense nitrogen-oxygen atmosphere.
Will argues that we have in Titan "more a frozen Mars than a frozen Earth." This is true, and yet, even leaving aside the controversy over whether the Viking Mars landers detected life or not, life may still exist deep inside the warm Martian crust, just as it does deep inside the Earth's crust. This life just won't be complex life. The same is likely true for Titan, where A. D. Fortes' "Exobiological Implications of a Possible Ammonia-Water Ocean Inside Titan" (cached here at Google), imagines that life might take root in an ammonia-water ocean deep beneatth the planet's surface rather than on a cold and inhospitable surface. This life, Fortes argues, isn't likely to be complex, simply because a cold ammonia-water ocean without oxygen can't support large or complex ecologies.
All the large solid worlds of the Solar System--and by implication, all of the large solid worlds of other Solar Systems, and between Solar Systems--may have life. Our Earth is just uniquely the most hospitable, being warm enough to allow complex chemical reactions to take place and massive enough to hold onto its dense atmosphere and abundant water despite this temperature. Doubtless other factors can be added to this brief list.
The implications? We're alone. Titanian microbes aren't going to be building radio telescopes.
think it's possible. If there is all this energy being released by these powerful chemical reactions, with stuff raining out of the sky like acetylene and other compounds, some of that energy could be going into metabolism, the work that the organisms do to power themselves. Also, some of that energy is going to be waste heat released into the environment, but in a place like Titan, what we think of as waste heat might not be all that wasteful. Organisms can use it to melt their own little watering holes. Then you can even imagine a sort of Gaian mechanism where organisms are helping to create the environment that helps keep the organisms happy.
Taken to an extreme, you could imagine that this large-scale melting we see on Titan is the result of organisms. I'm not claiming that we can confirm it, but imagine for an instant that Titan is loaded with organisms. I don't think we can rule this out. So imagine life is all over the place, and acetylene and other compounds are being turned back into methane and heat is being released… well, that could end up melting a lot of stuff. If acetylene is concentrated in certain geologic deposits, which no doubt it will be, maybe there are places where the collective action of that life is melting a lot of stuff and helping to lead to the high degree of activity on the surface. It's pretty "out there" as an idea, but I don't think it's impossible.
Will argues that we have in Titan "more a frozen Mars than a frozen Earth." This is true, and yet, even leaving aside the controversy over whether the Viking Mars landers detected life or not, life may still exist deep inside the warm Martian crust, just as it does deep inside the Earth's crust. This life just won't be complex life. The same is likely true for Titan, where A. D. Fortes' "Exobiological Implications of a Possible Ammonia-Water Ocean Inside Titan" (cached here at Google), imagines that life might take root in an ammonia-water ocean deep beneatth the planet's surface rather than on a cold and inhospitable surface. This life, Fortes argues, isn't likely to be complex, simply because a cold ammonia-water ocean without oxygen can't support large or complex ecologies.
While certain eukaryotes have developed secondary adaptations to anaerobic environments, there are only a few examples of unicellular protists known that appear to be primary amitochondrial anaerobes (for a review of anaerobic metazoans see Fenchel 1996). However, the independent development of symbiotic relationships with methanogens in several groups of eukaryotes (Emblay and Finlay 1994) may suggest that the evolution of complex anaerobic metazoans dependent on some kind of endosymbiotic methanogen for energy is not impossible on Titan. Assuming that complex organisms could arise then the primary productivity calculated in section 3.5 indicates that a marine food chain with three trophic levels, having the Titanian equivalent of small fish at the top of the chain, could sustain in the region of 200,000 tons of the largest animals (assuming a 10% efficiency between levels). In comparison with terrestrial oceans this is extremely low and perhaps illustrates the improbability of finding such creatures in subsurface oceans on large icy satellites.
All the large solid worlds of the Solar System--and by implication, all of the large solid worlds of other Solar Systems, and between Solar Systems--may have life. Our Earth is just uniquely the most hospitable, being warm enough to allow complex chemical reactions to take place and massive enough to hold onto its dense atmosphere and abundant water despite this temperature. Doubtless other factors can be added to this brief list.
The implications? We're alone. Titanian microbes aren't going to be building radio telescopes.
