Astrogator's Logs

New Words, New Worlds
Artist, Heather Oliver             

The Sirens of Titan: Alien Life?

(Title borrowed from Kurt Vonnegut)

In the novel and film 2010, when the Monolith builders force Jupiter into nuclear ignition they also program poor put-upon HAL to broadcast, non-stop “All these worlds are yours except Europa. Attempt no landings there.”

Arthur C. Clarke was deemed uncannily prescient when he wrote this, because many astrobiologists believe that life may exist under Europa’s thick ice crust: the moon harbors an underground water ocean and has geothermal energy courtesy of its huge planet. But recent news from the Cassini-Huygens mission could prove the prophet wrong. Before we encounter life on Europa, we may find it on Titan.

The Cassini data essentially show complex surface chemistry, as the Voyager data did for Mars. They also show mysterious absences of items expected to be abundant, given Titan’s specifics – acetylene and hydrogen in particular. Such results always carry the cautionary sentence that “non-biogenic processes yet unknown” could cause these anomalies. But organisms feeding on the missing chemicals is definitely on the list of these processes, something that several astrobiologists (Chris McKay, Derek Schulze-Makuch, David Grinspoon) suggested five years ago by speculating that acetylene would be tasty to Titanian life.

Titan, unlike bone-dry Mars, has enormous lakes – although they contain liquid hydrocarbons, rather than water. The lightest in that family (methane and ethane) are poor solvents because they’re non-polar, unlike water and ammonia. Nevertheless, they do act as solvents for the rich organic soup churned by Titan’s thick atmosphere of ammonia and methane (Carl Sagan’s “tholins”, from the Hellenic word for murky). And although chemical reactions will be slow in Titan’s ambient temperature of –190 Celsius (room temperature is 24 Celsius), all bets are off once enzymes are involved.

If we can conclude definitively that there is life on Titan, we will have walked one step further to the right of the Drake equation. We share material with Mars by meteorite exchange, so any life that existed or still exists there may have shared its beginnings with us. There can be no such ambiguity for Titan, given its distance and conditions. Whatever we find there, from bacteria to placidly grazing hydrogen balloons, it will be the product of an independent genesis. And it will be very different from us, finally making it possible to rigorously determine which aspects of life are parochial and which are universal.

This brings us full circle to HAL’s warning. If life exists elsewhere in the solar system, it will be both a boon and a burden. Such a discovery will give a major boost to astrobiology, which will finally have a legitimate topic to explore beyond the armchair vaporings of famous physicists – and to crewed space exploration, beyond the depressing and trivial prospect of sending more people in fungus-infested tincans into low terrestrial orbit.

At the same time, as I wrote elsewhere, we may destroy alien life even if we are careful. Such an outcome will deprive us of precious, irrecoverable knowledge that will help us make sense of our universe and our own planet, even if the new life consists entirely of bacteria (to say nothing of the moral equivalent of genocide if it’s more advanced than that). It may be that none of these worlds are ours, except for us exploring them and becoming their stewards.

Note: The article is now also on Huffington Post, sans images and references.

Images: Huygens on Titan, Craig Attebery (NASA); “Ammonia!  Ammonia!” by Robert Grossman, The New Yorker.


C. P. McKay and H. D. Smith (2005). Possibilities for methanogenic life in liquid methane on the surface of Titan. Icarus 178, 274-276.

Schulze-Makuch, D., and D.H. Grinspoon (2005) Biologically enhanced energy and carbon cycling on Titan? Astrobiology 5, 560–564.

D. F. Strobel (2010). Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions. Icarus, in press.

R. N. Clark et al (2010). Detection and Mapping of Hydrocarbon Deposits on Titan. J. Geophys. Res., in press.

17 Responses to “The Sirens of Titan: Alien Life?”

  1. Caliban says:

    Steve Baxter’s novel “Titan” involves, not surprisingly, a journal to Saturn’s moon. He has an epilogue where life evolves on Titan billions of years from now, when the sun expands into a red giant. It is, however, an exceedingly bleak book otherwise (but that is his niche, the superscience/superdisaster subsubgenre).

  2. Caliban says:

    PS (which was actually my intended point but I forgot to add it…) Although Baxter’s “Titan” is rather bleak, it does have powerful, evocative scenes of astronauts on the surface of Titan, amind drifting dunes of frozen tholins…

  3. Athena says:

    I have to find Baxter’s novel and read it!

  4. Eniac says:

    I don’t think there will be any ambiguity if we discover life on Mars. We will know if it is related to Earth life or not.

  5. Athena says:

    Not if the differences are subtle — or even less subtle, given the possibility that life arose in earlier versions that got overtaken by the successful present one.

  6. intrigued_scribe says:

    Less subtle differences could be a tremendous possibility, in this instance.

    It may be that none of these worlds are ours, except for us exploring them and becoming their stewards.

    This fittingly sums up one of the subtler themes here. Excellent essay, as ever. 🙂

  7. Athena says:

    Yes… like the Koredháni, idealized though they may be! *smile*

  8. Eniac says:

    There are a lot of arbitrary decisions that have to be made before life reaches the point where it can conceivably jump between planets. Starting with chirality, continuing with choice of “nucleotides”, and including the genetic code. If life has jumped, all these decisions must match between the two versions (L vs. R nucleotides, nature of the nucleotides, map of code triplets to amino acids, etc.). If life is independent, the chance that all the decisions were made the same way is practically nil. There is no middle ground, and there should be no ambiguity in recognizing life as we do or do not know it.

  9. Athena says:

    As I said in my earlier brief reply to you, this is patently not true if the life that has “jumped” between planets is a very early version that gets significantly modified by local conditions, giving rise to two very divergent offshoots in each planet. Furthermore, it does not follow at all that life must first be evolved before it can fly around on meteorites. In fact, the less complex it is, the better its chances of surviving such travel. At any rate, unlike other armchair philosophizers, I won’t venture much into guessing. Also, if we’re lucky enough to find Titanian life, it will have evolved independently without a doubt, for the reasons I stated in my article (primarily, distance).

  10. Eniac says:

    “In fact, the less complex it is, the better its chances of surviving such travel.”

    I don’t think so. It does not make sense to me that early life would be more sturdy and less dependent on particulars of the environment than later forms.

  11. Athena says:

    Try bacteria versus human beings, as an exercise.

  12. Walden2 says:

    About the possible role of hydrocarbon lakes in the origin of Titan’s noble gas atmospheric depletion

    Authors: D. Cordier, O. Mousis, J. I. Lunine, S. Lebonnois, P. Lavvas, L.Q. Lobo, A.G.M. Ferreira

    (Submitted on 22 Aug 2010)

    Abstract: An unexpected feature of Titan’s atmosphere is the strong depletion in primordial noble gases revealed by the Gas Chromatograph Mass Spectrometer aboard the Huygens probe during its descent on 2005 January 14. Although several plausible explanations have already been formulated, no definitive response to this issue has been yet found.

    Here, we investigate the possible sequestration of these noble gases in the liquid contained in lakes and wet terrains on Titan and the consequences for their atmospheric abundances. Considering the atmosphere and the liquid existing on the soil as a whole system, we compute the abundance of each noble gas relative to nitrogen.

    To do so, we make the assumption of thermodynamic equilibrium between the liquid and the atmosphere, the abundances of the different constituents being determined via {\bf } regular solution theory.

    We find that xenon’s atmospheric depletion can be explained by its dissolution at ambient temperature in the liquid presumably present on Titan’s soil. In the cases of argon and krypton, we find that the fractions incorporated in the liquid are negligible, implying that an alternative mechanism must be invoked to explain their atmospheric depletion.

    Comments: 11 pages, 1 figure

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    Cite as: arXiv:1008.3712v1 [astro-ph.EP]

    Submission history

    From: Daniel Cordier [view email]

    [v1] Sun, 22 Aug 2010 18:32:07 GMT (17kb)

  13. Walden2 says:

    The mysteries of Titan

    Thirty years ago this week Voyager 1 made the first close flyby of Titan, Saturn’s largest moon and one of the most intriguing worlds in the solar system. Andrew LePage recounts the research into Titan and the planning that led up to that encounter.

  14. Athena says:

    Amazing to think what we learned from these two tiny machines! Tears come to my eyes when I think of them still flying bravely — yes, bravely and jauntily — toward the galactic core.

  15. Under Our Noses says:

    Why does all “Big Science” with regards to alien life revolve around worlds with liquid water? Life could just as easily exist in different forms other than DNA based life forms on worlds composed of liquid nitrogen, liquid hydrogen, even gaseous planets with no water components. Too much Star Trek people! Think outside the box, when we discover Aliens, they won’t be bipedal English Speaking humanoid forms.

  16. Under Our Noses says:

    We are probably already getting communications from life forms on other worlds, we just can’t understand them, or decipher them yet. Once we learn though, the floodgates of knowledge will open. Adam and Eve will have taken another bite from the apple.

  17. Athena says:

    There is no question that life elsewhere will be very different from us. However, liquid water is the best solvent, hands down. So the assumption astrobiologists make is not that other life will be based on water. The assumption is that where there’s liquid water, the chances for life increase significantly.

    As for communications, just as it’s possible that they’re happening but we can’t recognize them as such, it’s equally possible that even if we decipher we won’t be able to make sense of what they say. It’s like Etruscan: we can read it but we don’t know what it means.

    And, incidentally, there is no “Big Science” of alien life. The budgets dedicated to astrobiology are miniscule.