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Astrobiologist tries to set the record straight about extraterrestrial life on Titan

The views expressed are those of the author and are not necessarily those of Scientific American.


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Saturn's largest moon, TitanTitan, Saturn’s largest moon and the second-biggest natural satellite in the solar system, is an unquestionably interesting place. It’s a world with a thick atmosphere and with lakes, fog and rainfall—only with liquid hydrocarbons rather than liquid water.

Titan would be even more interesting if a speculation made five years ago proved out: that the moon could be teeming with extraterrestrial life. Titan-based (Titanate? Titanic?) life could dwell in liquid methane and breathe gaseous hydrogen, just as so much Earthly life dwells in liquid water and breathes gaseous oxygen. Such organisms would consume hydrocarbons such as acetylene near Titan’s surface, so their presence might be recognizable by a dearth of acetylene and hydrogen at the surface, Chris McKay and Heather Smith noted in Icarus in 2005.

A pair of new studies provide evidence for such depletions of acetylene and hydrogen, stirring up a sudden frenzy of public interest in Titan, including a characteristically bombastic treatment from the British press. The Telegraph grabbed readers’ attention with the headline, "Titan: Nasa scientists discover evidence ‘that alien life exists on Saturn’s moon’." On Twitter, Carolyn Porco, lead scientist on the imaging team for NASA’s Cassini spacecraft, bemoaned the headline and reported that she "just got an e-mail from someone ‘applying’ to be among those folks we send to Titan."

Now McKay, of the NASA Ames Research Center in Moffett Field, Calif., has seen fit to clear the air himself, making plain that extraterrestrial life on Titan is but one possible explanation of many—and far from the most likely.

The astrobiological significance of the lack of acetylene at Titan’s surface, as measured by Cassini, rests on the finding that hydrogen seems to be disappearing at the surface as well, McKay wrote on the Cassini imaging team’s Web site. "This is the key that suggests that these depletions are not just due to a lack of production but are due to some kind of chemical reaction at the surface." (Ethane, another possible fuel for methanogenic life on Titan, is also depleted.)

Nevertheless, the key finding that hydrogen is vanishing at ground level on Titan needs to be confirmed before jumping to any conclusions. The most plausible explanation for the new results, according to McKay? "The determination that there is a strong flux of hydrogen into the surface is mistaken." Other possible mechanisms for the presumed hydrogen loss include atmospheric processes that transport hydrogen out of the upper atmosphere, or nonbiological chemistry at the surface, driven by some unknown catalyst.

The existence of methane-based life churning through hydrocarbons and gaseous hydrogen is the fourth most likely explanation out of four, according to McKay. "This is a still a long way from ‘evidence of life’," he wrote. "However, it is extremely interesting."

Photo of sunlight glinting off a Titan lake: NASA/JPL/University of Arizona/DLR

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  1. 1. hotblack 11:44 am 06/8/2010

    I can’t remember where I first read about Titan possibly harboring life, or possibly being the nursery to life in our solar system, but it was a long time ago, in a very old book. I look forward to seeing more data roll in.

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  2. 2. SDR 12:24 pm 06/8/2010

    Fascinating findings, indeed. However, at the extremely low surface temperatures present on Titan, I would suspect that most chemical reactions would proceed there very slowly. Assuming that Titan is at least a few billions years old, would this allow enough time for an exotic primitive life form to evolve?

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  3. 3. Ekimmu Shrgnien 2:07 pm 06/8/2010

    SDR

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  4. 4. Ekimmu Shrgnien 2:13 pm 06/8/2010

    I don’t think a few billion years would be enough for an exotic primitive life form to evolve, or at least not in the form of lizards or something similar to small apes…. i believe it would be more like a plant-like species, in my opinion that would explain the depletion of hydrogen and the slow process… if there were a slow process, which probably is due to the low temp. i think.

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  5. 5. roozbeh6 8:25 pm 06/8/2010

    something is not making sense, lets assume that there are some form of titanish living things, but why would the process of depletion of hydrogen and acetylene have recently been speeding up to that extent which would trigger our sensors, I want to ask if the mass production of plant like creatures is sudden ? this cant be, the depletion curve should have a very shallow gradient, accounting for evolution and scale of reproduction to the extent which could bring about a sudden change in the amount of hydrogen and acetylene,
    im an engineering student, i do not have any background in this type of universal sciences, but couldnt help but noticing this strange hole in the findings,

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  6. 6. roozbeh6 8:25 pm 06/8/2010

    something is not making sense, lets assume that there are some form of titanish living things, but why would the process of depletion of hydrogen and acetylene have recently been speeding up to that extent which would trigger our sensors, I want to ask if the mass production of plant like creatures is sudden ? this cant be, the depletion curve should have a very shallow gradient, accounting for evolution and scale of reproduction to the extent which could bring about a sudden change in the amount of hydrogen and acetylene,
    im an engineering student, i do not have any background in this type of universal sciences, but couldnt help but noticing this strange hole in the findings,

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  7. 7. Ekimmu Shrgnien 10:53 pm 06/8/2010

    It could be some sort of fungus then…. that would explain the fast reproduction and the depletion of the elements in question. However, i do believe that if there was a plant-like being in Titan it wouldn’t grow one at a time thus explaining your point (roozbeh6) about a slow reproduction, i would think about a mass of these beings growing at relatively the same speed and depleting more and more hydrogen and acetylene as they grow larger. This would explain that these chemical reactions are larger and drawing our attention. But then again, this is only a possibility, i am not (yet) implying the existence of life in Titan.

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  8. 8. jgrosay 2:45 am 06/9/2010

    I remember having read about some earth bacteria being able to thrive and multiply in a simulated Jupiter atmosphere environment. It is worth repeating such experiment on a Titan model? Is it worth selecting strains of bacteria being able to take advantage of such toxic planets?

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  9. 9. oldvic 3:19 am 06/9/2010

    Will "The Telegraph" publish a clarification, giving it the same exposure as the misleading headline it used before? Many in the press seem to forget that power comes with responsibility, while at the same time loudly demanding the latter from anyone who wields the former.
    The "fourth estate" must exercise its power correctly, otherwise it becomes just another problem for society to contend with.

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  10. 10. homerj 10:47 am 06/9/2010

    Methane-based life? Extremely cold temps?
    How likely?
    How about methane-eating, very cold temp-based life:
    Methane Eaters in Canada’s extreme North
    http://www.astrobio.net/pressrelease/3519/methane-eaters-at-lost-hammer

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  11. 11. roozbeh6 8:34 pm 06/13/2010

    Ekimmu Shrgnien ! of course they dont grow one at a time, my point is that the process of reaching to a point where these creatures could convey a significant amount of consumption would most probably be something in the order of millions of years, or generally not in human scale time, so how is it that they are suddenly showing some major amount of consumption ? it would be more logical to see the depletion very slowly, or yes, as you imply the speed of the hydrogen depletion should most definitely be a function of them becoming more complex and growing more, hence its almost impossible for us to just see this depletion, unless there is something kinky going on and they are not covering it, or are trying to covering it,

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  12. 12. RickMan 1:36 am 06/16/2010

    If we could only get some of those hypothetical hydrocarbon consuming Titan organisms to the BP oil spill…(:>))

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  13. 13. QuantumQualifax 2:56 am 06/23/2010

    If there is life on Titan, we can only hope it is not currently causing climate change there. That would be unfortunate. It also begs the question – would we be morally required to eliminate that sort of life from Titan? Many times I have wished for xenonauts to come and just stop us from warming the planet beyond all hope of recovery.

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