Evidence of extraterrestrial biochemistry ?

[SW VandeCarr]

Evidence of extraterrestrial "biochemistry"?

The linked article claims the apparent depletion of H2, acetylene and ethane from the surface of Titan might be evidence of "life" since (the authors claim) there seems to be no likely simple set of chemical reactions that would account for for this at 95K. Biochemistry, as we know it, generally requires enzymes composed of proteins. Clearly, complex metabolic pathways would require some type of enzyme system that could function at 95K. Any opinions on life as we don't know it?

http://www.spacedaily.com/reports/Have_We_Discovered_Evidence_For_Life_On_Titan_999.html

 

[Ygggdrasil]

I heard about this story on the radio today. Although these observations are consistent with methane-based life on Titan, there are other abiotic explanations for the observations. For example, Jonathan Lunine, one of the authors on the 2010 J. Geophys Res. papers, said:

one attractive thing about the biological hypothesis is that it explains three things at once: the sink of hydrogen, the dearth of acetylene and also the relative lack of the primary product of methane chemistry, which is ethane.

However, you can explain all three of these with separate mechanisms, abiotically. So let me just offer one quickly: There is a catalyst that we're not aware of at the surface that is fixing the hydrogen with methane. The acetylene is just converting to plain old benzene, abiotically. We have evidence for that. I mean, that's something that in fact we see in some of the Cassini data.

And finally, the ethane, after being produced by methane, is simply being buried in the crust. It's percolating through the icy crust of Titan.

That set of hypotheses requires no life whatsoever, and in fact given the fact that an extraordinary explanation, which would be a biological one, requires extraordinary evidence, one really ought to focus, I think, on developing the abiotic explanations and trying to test those.

(Source)

Indeed, the author of the Space Daily echoes some of these sentiments at the end of the article.

 

[SW VandeCarr]

I heard about this story on the radio today. Although these observations are consistent with methane-based life on Titan, there are other abiotic explanations for the observations. For example, Jonathan Lunine, one of the authors on the 2010 J. Geophys Res. papers, said:(Source)

Indeed, the author of the Space Daily echoes some of these sentiments at the end of the article.

Yes. I agree. Life "as we don't know it" is not the stuff of conservative science. The weakest argument Lunine makes for abiotic processes is that "some" catalyst is fixing H2 at the surface. If it's not an enzyme-like analogue and/or co-factor, what might it be?

If there were some kind of metabolism, without replication as we understand it, would it still be considered life? Viruses exhibit host dependent replication without metabolism. Perhaps such quasi-lifelike or pre-biotic entities are common in the universe.

 

[Ygggdrasil]

It is reasonable to think that some type of inorganic substance could catalyze the fixation of hydrogen. The reaction is thermodynamically favorable, but the energy barrier is too high to allow the reaction to occur at a reasonable rate at the temperatures on Titan. While we often think of catalysts as complicated, exquisitely designed (or evolved) molecules, a catalyst can be something a simple as a surface. Indeed, a simple platinum surface can be used to recombine hydrogen with oxygen or simple organic molecules (like methanol and ethanol). In fact, this chemistry forms the basis for fuel cell technology.

Luckily, the molecules involved in this reaction (acetylene, hydrogen, and methane) are all relatively simple, so I'm sure some computantional chemists will be able to come up with testable hypotheses about the identity of such a mystery catalyst. I should note that part of the reason why we don't already know of a catalyst could be simply that no one has bothered to look yet. We currently produce acetylene from methane, so there isn't really any point in figuring out how to make methane from acetylene. It remains possible that this catalyst could indeed be of biological origin, but if this is the only evidence in support of that theory, I'm not betting the farm on it.

 

[SW VandeCarr]

It remains possible that this catalyst could indeed be of biological origin, but if this is the only evidence in support of that theory, I'm not betting the farm on it.

I wouldn't either, but I find it very interesting. Thanks for your views and observations.