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Musings on Titan’s Sub-Surface Ocean

The recent news that there may be an underground ocean on Titan tantalizes us in astrobiological terms. It also brings us up against the question of how to define a habitable zone. The standard definition involves the presence of liquid water at the surface, a reasonable requirement when you’re looking for carbon-based life. But it’s also true that exobiology may one day be studying forms of life that are nothing like us, living in environments we would at first dismiss from our list of living places. Just how far does a habitable zone extend?

First, a short defense of the status quo. As we expand our exoplanet hunt and become capable of detecting the signature of life on distant planets, we need a target list to optimize our search time. It’s entirely reasonable to fine-tune that list toward conditions similar to what we find on Earth because the life on our planet is the only kind we’ve been able to study. Detecting its biomarkers in an alien atmosphere is a sensible goal. We know what we’re looking for (within reasonable parameters), and trying to identify such life doesn’t mean that we’re not aware that far more exotic possibilities may occur elsewhere.

So calling a habitable zone a region where liquid water is possible helps us keep our focus as we begin to learn what possibilities the universe presents. But it’s also clear that even here in our own Solar System there may lurk surprises. Enceladus reminds us of that, as does Europa, and now we learn that Titan may be even more interesting from an astrobiological perspective. Thus Ralph Lorenz (Johns Hopkins Applied Physics Laboratory), lead author of the recent Titan paper, commenting on the possible presence of liquid water mixed with ammonia 100 kilometers down:

“The combination of an organic-rich environment and liquid water is very appealing to astrobiologists. Further study of Titan’s rotation will let us understand the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, we might see seasonal variation in the spin in the next few years.”

Lorenz mentions Titan’s rotation because Cassini’s science team has been using the spacecraft’s Synthetic Aperture Radar to collect data, establishing fifty unique landmarks on the moon’s surface. The intriguing result is that when earlier data are compared to more recent flybys, some of these features seemed to shift as much as thirty kilometers from their prior positions. There was no actual movement at the surface — the apparent ‘shift’ was the result of the fact that Titan was spinning about its axis in a different way than expected. An internal ocean is almost demanded as a way of explaining how the moon could move in such a way. Couple deep water with all those useful chemical compounds that preceded life on Earth and things get interesting.

One day we will discover whether places like Titan or Europa do contain life. Once confirmed, even simple bacteria become reason for us to extend the search for life into even more remote territory, surveying possible biospheres in the Edgeworth/Kuiper belt, for example. Life may prove astoundingly adaptive, even if conditions in the outer Solar System cannot support the complex fauna of Earth.

And that’s really what the notion of habitability comes down to. The question philosophers and scientists have asked for centuries is whether there are other places in the universe where humans could live. The term ‘habitable zone’ is a way of phrasing such a region, but we’ll need to start talking about ‘biozones’ as we adapt our astrobiological thinking to more extreme environments. Humans would be out of their element on Hal Clement’s Mesklin (the world of his novel Mission of Gravity), but bizarre creatures might still evolve there.

And we might as well push this as far as possible: If some form of string theory proves out and we do live within a multiverse containing as many as 10100 universes, we may have to extend our idea of biozone zone to our entire universe. Some theorists suggest we live in one of the few out of the multitude of universes that could sustain life, its parameters — the precise strength of the nuclear force, for example — exquisitely tuned for life. Many of the others could be lifeless, formless, inimical to organization.

The poet John Dryden’s lovely line ‘And music shall untune the sky’ comes to mind, this theory suggesting that we inhabit a universe whose harmonies keep all essential forces in balance. Just hope nothing happens to put us off-key.

If we’re living within a single living bubble amidst a froth of dead universes, then in the ultimate scheme of things life of any kind whatsoever may be an extreme rarity. But before we go quite that far, let’s find out whether we’re not looking at potential biospheres much closer to home. The Titan paper is Sotin and Tobie, “Titan’s Hidden Ocean,” Science Vol. 319. no. 5870 (21 March 2008), pp. 1629-1630.

Comments on this entry are closed.

  • Edg Duveyoung March 24, 2008, 11:29

    Any chance of life thriving by using outer orb superconductivity?

    Perhaps a bit goofy to ask, but do our outer orbs reach such low temperatures that the materials they’re made of become superconductors? I’m thinking about the thriving bacteria in the underground lakes of Antarctica and whether their example of hardiness indicates that life could find a way to hack it at extremely lower temps.

    If such a superconductive environment were possible, would such extremophile life-chemicals have a chance to communicate over great distances? Recent studies on DNA/RNA processes are examining the electronic attractions that various chemicals have which “draw in” other chemicals which then react chemically with them.

    So, could a bacterium that’s splashed off Earth find its way to an outer orb, plunge through the icy crust to an inner ocean that’s composed of superconducting liquid, and find itself able to interact with other life forms because it’s natural electronics are extended by superconductivity? Or, at the least, would a bacterium enjoy massively “better” inner chemistry since all its parts would be speaking to each other much “better?” Or, would superconductivity immediately “short out” life processes?

    Has there been enough time for, say, some interstellar cloud of material could give rise to life because of superconductivity? Oh, I know I’m getting all star-trekky here, but it seems to me that superconductivity is a dynamic that should play much larger than it seems to be doing in the imaginations of scientists that I come across in the mundane venues I frequent.

    Maybe nanobots will find that superconductivity gives them the ability to communicate “for free” and thus there’s be very low power requirements to run a nanobot swarm.



  • philw1776 March 24, 2008, 11:29

    I too would like to better define HZ and develop more specific terminology alternatives. If HZ includes only such places as moderately re-enginered standard humans could inhabit, these water moons are out. Although we have virtually no data, probably many here believe that subsrface oceans might well support active biological system, so I like the term bio-zone to encompass such environments. Upon reflection, we don’t know enough about biology to tell if (a) we’re the only biology in the solar system, and maybe much further, or (b) thinkers like Freeman Dyson are right and the Oort cloud could support some (possibly engineered) life forms.

    After 50 years of planetary exploration by robots, we still do not have an inkling if anything else living resides outside the Earth-moon system.

  • dad2059 March 24, 2008, 12:45

    It’s looking less and less plausible that Terran-life is the only biology in the Solar System. One should look at the possibility of protecting these potential eco-systems from exploitation, or accidental extinctions.

    Yes, until we actually discover a native extraterrestrial biology, the statement is moot, but these are issues that bear future consideration.

    Human history in this matter isn’t exactly sterling y’know.

  • Ron S March 24, 2008, 22:44

    Edg, try not to hope for magical attributes of superconductors. If it were so wonderful for life, you might expect that any run-of-the-mill metal would be better than carbon. Yet the elements that appear to be most suited as a basis for life are right down the center line of the periodic table: carbon, silicon and germanium – the semiconductors – with a strong bias on carbon for biochemistry and the others for electronics. Semiconductors seem to be more conducive to develop variety and complexity.

  • Adam March 25, 2008, 5:21

    Hi All

    Edg, as far as I know superconductivity only occurs in solids, so perhaps not.

    As for Titan’s ocean, a 100 km of ice means the pressure down there is the equivalent of ~ 14 km of water here. No sunlight, intense cold, but all the right ingredients for making biomolecules. “Discover” magazine has an article on the icy origins of life – as advocated independently by Leslie Orgel and Stanley Miller, late heavyweights of the Origins of Life field.


    …which has incredible implications, that I’ve noted in another post. In summary what is found is that firstly, RNA enzymes work better at joining chunks of RNA when in frozen conditions, and secondly, very large sequences of RNA can form in freezing conditions which would otherwise be impossible. Published work has shown RNA sequences up to 400 bases long, while unpublished work has gotten up to 700 bases long. This is very exciting news for origins-of-life research, and for the odds of life on icy worlds like Titan, Enceladus, Europa and Mars.

    Perhaps, if Earth was never frozen as imagined by Miller and Orgel, Life here began Out There. Hypervelocity impacts on Mars, Europa or Titan could have sent the seeds of life here aeons ago.

  • djlactin March 25, 2008, 8:07

    “Liquid water 100 km down?”
    Consider us humans, on a planet with a molten iron core. 4000K or so.
    Consider methane-base life forms on Titan, considering a ‘molten ice’ core 100 km down. What’s the difference?
    To a methane-based life-form, adapted to a biosphere at -140C, liquid water would be as inhospitable as molten siderophiles are to us.
    But take this idea another step: what would a life-form based on molten iron think about our core: “Possible conditions for life?”

    “The universe is not only stranger than we imagine, it’s stranger than we can possibly imagine”

  • James M. Essig March 25, 2008, 9:09

    Hi Paul;

    Thanks for posting this fine article. The idea that life might exist in the sub-surface oceans of Titan absolutely tantalizes me. We really must send probes to melt through the ice and have a look.

    Finding an extraterrestrial fish or other animal in Titan’s oceans would be astounding from a exobiology standpoint. The possibility of such lifeforms within Titan’s subsurface aquatic environment is I believe strong. Discovery of extraterrestrail animal lifeforms on Titan is a very real possibility that requires only chemical rockets for the probe to reach Titan. We are talking about mission success potentially within the life times of just about all of us here at Tau Zero.

    There is a very real possibility that the high school class of 2030 will be using biology textbooks with units on Titan’s life forms. I can imagine a full color image of an ET fish as an insert within the text book. The same I am sure would apply to National Georgraphic Magazine.

    I have always been intrigued as to the shapes, habits, psychology, etc., of any animal life forms we might discover on other planets. The universe just might be teeming with interesting animals.



  • Doug M. March 25, 2008, 13:03

    One problem: what would be the energy source for these hypothetical deep-ocean organisms?

    There would have to be some equivalent to “deep smoker” volcanic vents here on Earth. Is that even plausible?

    Also, apropos of the pressure — wouldn’t the pressure be lower due to Titan’s lower gravity? “Only” equivalent to 5 km of water instead of 14?

    Doug M.

  • tacitus March 25, 2008, 13:18

    There is a very real possibility that the high school class of 2030 will be using biology textbooks with units on Titan’s life forms.

    I admire your optimism, Jom, but finding life on Titan 2030 is extremely unrealistic. In fact, unless the rate of space exploration has a sudden and massive uptick, we’ll be lucky to have more than one or two more orbital missions to the Saturn as a whole by then. I think you’re looking at more like 2100 at the earliest as the time when we will have the technology and resources to drill down below Titan’s surface (and then only if there we still believe there is a chance of finding something).

    The Jupiter system, and Europa in particular will almost certainly be the first target for subterranean (subeuropan? sublunar?) mission. Jupiter is easier to get to, and Europa is probably an easier first target than the much more distant Saturn. Even then, I doubt we will have done more than land on Europa by 2030 and sampled the surface ice (if that). Drilling beneath the surface probably won’t happen for at least another 10 – 20 years beyond that.

    It’s all painfully slow, I know, but while in the long run I am an optimist, one only needs to take a look at the pace of exploration over the past 40 years to realize that it takes an awful long time to do anything significant, and that one failure can set the whole program back a decade or more (especially if you’re talking about missions to the outer planets).

  • Enzo March 26, 2008, 1:36

    Have a look at Cassini’s CHARM site. There are presentations and lectures about various results of Saturn’s exploration:

    Relevant to this topic is “Organics on Titan, Water on Enceladus: Worlds of Possibilities for Life” dated March 25, 2008. the audio is not available yet. However, the presentations in pdf, at the end, show possible reactions on Titan using Hydrogen that could be used by life. The presentation concludes that this is testable (in part) using Huygens’ results but that calibration will take a while.
    Basically it assumes that H2 would be depleted near the surface where Titan’s life would make use of it.

  • Adam March 26, 2008, 4:54

    Hi All

    djactin, good point. Europa is a much better prospect, but Titan in its early days would’ve been ideal for making Life, albeit the small and cellular variety. Dominic Fortes has suggested that the sub-surface ocean is actually ammonium sulfate, or very rich in it, and this might actually be a better medium for life than ammonia/water. An exciting possibility is life existing in porosities within a few kilometres of the surface, and/or brought up to the surface (and frozen) via cryovulcanism.

    Jom, I’m afraid Doug’s point does rule out very active life-forms – to have a vigorous biosphere the ocean needs a powerful energy surface, and there’s nothing indicating it has that. Europa has a source of oxygen, and Enceladus might too, so active life is possible on either, but deep ocean moons like Callisto, Ganymede and Titan just don’t.

    Tacitus, Titan is much easier to get to than Europa for any surface mission because it has an atmosphere for aerobraking – it wins hands down for practicality, even more so when you factor in the electronics wrecking radiation environment on Europa’s surface (except on the wake side of the moon.)

  • Adam March 26, 2008, 5:13

    BTW the gravity on Titan is 14% of Earth’s, thus the pressure 100 km down (ice and seawater being roughly equivalent in density) is equivalent to 14 km of ocean. The pressure down there is ~ 1400 atm, which might be endurable by microbes. Fish are seen at ~ 1100 atm in the bottom of Earth’s oceans, so it doesn’t seem a great hindrance.

  • Athena March 26, 2008, 13:17

    I think that right now the definition of a habitable zone is narrow by necessity, due to the lack of a second life sample. If any variant of a multiverse theory proves correct, it is almost certain that we will still be confined to our own universe in terms of being able to exchange information with other “bubbles” in the foam.

    There are two reasons why carbon is the best basis for complexity by several orders of magnitude: because its outer electron orbital is half-full, it is an equal-strength electron donor and acceptor, an attribute shared by its cousins in the fourth column of the periodic table (silicon, etc). Uniquely, however, the distance of that outer orbital from the nucleus enables strong carbon-carbon bonds, a feature not shared by silicon et al. Hence the amazing diversity of organic compounds, which outnumber the combined combinations of all other elements.

    Water is also the best general solvent because of its unique bipolarity and freezing properties, but carbon compounds can use other tetrahedrally shaped relatives in a pinch (ammonia being the most prominent).

    Although there is general consensus that RNA preceded DNA, whether it started and evolved in ice, in fire or on “helper” clay substrates (the Cairns hypothesis) is unclear. RNA is heat-stable but water-labile. So all bets are equal at this point.

    If Europa, Titan or Enceladus harbor life, we will have to be very careful about how we design and deploy our probes. The heat they generate by drilling alone may annihilate cryo-life. I discuss this briefly in an essay, You Only Find What You’re Looking For. Here are two excerpts from it:

    Even after the discovery of terrestrial extremophiles, it took heroic measures to propagate them once they left their native habitats. Also unknown were the thriving communities of fragile, gelatinous animals living in the ocean depths: the methods used to capture samples shredded them to confetti.
    Now we are aware that even terrestrial life pushes the boundaries of what was once considered possible. We should put that experience to use. Otherwise we may literally step on alien life and deprive ourselves of unique, irreplaceable knowledge.

  • James M. Essig March 26, 2008, 15:59

    Hi Doug M., tacitus, Exciting News from Saturn | Ultratech Memes, Adam, and Athena:

    Thanks for the comments. I am actually a little disturbed about the slow pace of our space program. As a U.S. citizen, I have been proud of America’s sucess in space but it still seems a wee bit too slow with far too little funding.

    I would love to see other technological powers such as Russia, the EU, China, India, Japan etc., really ramp up their space programs as well. Some one’s got to fund more in depth exploratory missions to the moons of the gas giants.

    I will be very happy simply to see man return to the moon by 2020, and then onward from there.

    It is interesting to speculate what if any bazaar life forms we might find on the various large moons within our solar system. Heck, on Europa under the ice, I will settle for any hydrothermal vent based tube worms.



  • andy March 26, 2008, 16:47

    Excluding worlds like Europa from the definition of the HZ makes sense if you consider observing an extrasolar system. Detecting subsurface oceans at a distance of tens or hundreds of light years is pretty much impossible, let alone detecting signs of life in them.

  • James M. Essig March 26, 2008, 23:23

    Hi andy;

    I have to agree on the essentially impossible detectiion of subsurface oceans at a distance of tens or hundreds of lightyears. The only way to detect such oceans let alone any existent life in them would be to send probes or manned craft for a visit.

    However, given the incredibly large number of such potential moons, I am intregued by the possibility that ETI lifeforms may have developed in the sub-surface oceanic environments of such moons. Perhaps they evovled technology to leave there home planet or should I say home moon to travel into interstellar space.

    I can imagine that creatures with durable bodies at least as mechanically strong as octopuses and squid, as well as sharks might exist in these subsurface extrasolar environments.

    I have allso wondered about the existence of mobile or stationary organisms that posess both plant and animal properties.



  • ljk April 7, 2008, 15:47

    Earth’s Crust Shows Long-Term Wiggle Room

    Discovery Channel


    Larry O’Hanlon, Discovery News

    April 7, 2008

    A new, long-term look at the Earth’s crust suggests that the
    continental plates — including the one underlying the Western
    United States — are not completely rigid after all. Rather, when
    viewed on very long time scales, they can behave with
    surprising fluidity, report scientists.

    “As usual, things are more complicated” than thought, said
    earthquake researcher ROLAND BÜRGMANN OF THE UNIVERSITY
    OF CALIFORNIA AT BERKELEY, of the classic view of stiff plates
    over a more fluid mantle.

    It may be that sometimes the Earth’s crust behaves as if its
    plates are rigid and strong all the way down — with only the
    underlying mantle showing any jelly-like elasticity. On longer
    time scales, however, the same area of crust can act more
    like pudding, with only the top few miles — the rocky
    lithosphere — staying consistently strong and rigid.

    “We’re tying to take a new look at an old problem,” said
    Wayne Thatcher, a geologist with the U.S. Geological Survey

  • ljk May 21, 2008, 17:14

    What Lies Beneath (pdf)

    A self-professed Caltech “lifer,” JPL Director Charles Elachi has
    spent 40 years using spaceborne radar to explore such exotic
    places as the Sahara, Venus, and Titan. More…


  • ljk June 3, 2008, 10:28

    Saturn’s Titan has Implications for Understanding of Life
    Throughout the Galaxy

    NASA’s Cassini spacecraft buzzed Titan last month, coming
    close enough to taste the Saturnian moon’s atmosphere. The
    data acquired has implications for our understanding of life
    throughout the galaxy, as well as Earth’s own past.

    Full article here:


  • ljk April 7, 2009, 22:58

    Titan may have subsurface ocean of hydrocarbons, says Stanford researcher


    “Saturn’s largest moon, Titan, may have a subterranean ocean of hydrocarbons and some topsy-turvy topography in which the summits of its mountains lie lower than its average surface elevation, according to new research.”