Lakes on Titan?

By Phil Plait | July 24, 2006 8:16 pm

Emily Lakdawalla from the Planetary Society blog has what might turn out to be a major scoop: possible liquid lakes on Titan!

It’s been thought for some time that liquid might exist on Titan, and given its dense atmosphere that’s loaded with hydrocarbons, methane or ethane is a good guess. But evidence has been scant. The best so far was when the Huygens probe, launched by Cassini to land on Titan, appeared to have squished down in mud!

But new evidence has just arrived. Emily posted the image above, taken using the Cassini probe’s radar. It’s the shape of the features that’s interesting: sharp-edged, yet with rounded contours. That, plus the fact that liquid methane and ethane absorb radar, making them look dark just like those features, is very provocative. Emily reports that Cassini scientists are excited about the images, so I’m sure we’ll be hearing lots more about this very soon.

People will inevitably wonder if this has any impact on life evolving on Titan. Beats me. We really have no clue how life first sparked on Earth. We need liquid water now, but as far as I know it’s not clear exactly what Earth was like when life first arose (any biologists or archaeologists wanna enlighten us physical scientist-types about this?). And does that situation apply to Titan, with twice the Earth’s atmospheric pressure and temperatures of -180 Celsius?

Still and all, liquid existing on the surface of another world is really exciting. The more we look at other worlds, the more alien we realize they are… but the more like home as well.

CATEGORIZED UNDER: Astronomy, Cool stuff, NASA, Science

Comments (34)

Links to this Post

  1. Moonage Spacedream | July 25, 2006
  2. Lakefront Property… | July 26, 2006
  1. jess tauber

    One of my long-term interests has been the origins of the genetic code, abiogenesis, etc. Even considered doing grad work in that area.

    The surviving set of genetic codes is heavily weighted towards amino acids whose side chains are polar. But I can imagine a variant where the situation is turned around. Where hydrocarbons are the solvent and polar molecules are the bases of membranes. Just extrapolate membrane-bound protein domains.

    Examining the periodic table to see which elements are utilized in living processes, one sees an interesting skew- ignoring the noble gases, p-shell elements on the upper right side of the semi-metal line, the top line of the d-shell, No f-shell elements so far as I know, and some of the s-shell elements, again ignoring helium, lithium, and beryllium.

    In the flip/flop world of hydrocarbon dominated life, would the same statistical tendencies be observed (assuming one used the same set of elements at all)?

    I wonder whether anyone has done cold hydrocarbon experiments to see if water ice particulates would have interesting properties (such as being able to be a substrate to mineral ions, etc.).

    Jess Tauber

  2. TheBlackCat

    The early Earth had water oceans with organic molecules in it. Protein folding is not my area of expertise, therefore I cannot speak with too much authority on anything but the more basic aspects regarding the kinetics and thermodynamics of the process. However, according to one of my molecular bioengineering professors, who does specialize in that, life arising based on nonpolar solvents is extremely unlikely at best. Protein folding is ultimately driven by entropy for the most part. This process is not only driver by the internal entropy of polypeptides, but also the entropy of the water they are in.

    Due to its hydrogen bonding, water has extremely high entropy relative to many liquids. Having nonpolar molecules in the water interferes with this hydrogen bonding, causing a huge entropy loss. The entropy gains or losses in the protein itself are often insignificant relative to the entropy loss in the water in which it finds itself. Thus, to preserve entropy, the protein organizes itself so that the maximum possible number of hydrogen bonds with the water are left unperturbed (this is a gross oversimplification, but gets the point across). Of course, hydrogen bonds also contain a large amount of energy, so there will also be a large enthalpy change if they are interfered with.

    The loss of a single hydrogen bond costs 5 kcal/mol, largely in entropy. By comparison, the heat of vaprization of water is a little under 10 kcal/mol. Similarly, the change in the surface area of the protein that is hydrophobic is worth 30kcal/mol per square angstrom (an angstrom being the diameter of a hydrogen atom). So for every 1 square angstrom of hydrophobic surface area you gain energy roughly equal to the heat of vaporziation of Zinc.

    The issue in non-hydrogen bonding solvents like hydrocarbons, there are no hydrogen bonds and thus the inherent entropy of the solution is extremely small relative to water. Thus, a long-chain carbon molecule like a protein may have internal entropy driving it towards a given configuration, but without the large amount of entropy from the water’s hydrogen bond there simply won’t be enough to drive the molecule towards a stable configuration in a reasonable amount of time. Additionally, even in proteins in water the stable configuration often has a very small free energy difference relative to other configurations. Without the hydrogen bonding from the water, this free energy difference very well may be too small to maintain a stable configuration.

    This isn’t a flaw in our own biology, or an adaptation to aqueous environment, it is a fundamental difference between hydrogen-bonding and non-hydrogen-bonding solvents that may be insurmountable. That is not to say it is insurmountable, as I said I lack the background to truly quantify it in a real macromolecule, but certainly life on Titan is far from given. Also remember there is much less energy available on Titan than there is on Earth, which could also put a serious damper on life’s ability to evolve.

  3. monolithfoo

    Huh, that struck a funny chord for me. It seems that more and more biologists and archaeologists resemble physicists. What with molecular genetics, Archaeometry and other cross disiplinary efforts… it’s almost as bad, sometimes, as trying to tell the difference between the astronomers and the compsci folks.

    Uh… no offence to any of the above mentioned…

  4. PK

    TheBlackCat: I don’t quite understand where the entropy comes from, because a large entropy corresponds to a large number of accessible states for a given energy (in the microcanonical ensemble, which I think is applicable here). However, the hydrogen bonds restrict the orientation and position of the molecules, which would indicate a smaller number of accessible states, and a correspondingly lower entropy.

    Surely I am missing something, can you enlighten me?

  5. ruidh

    How about some bad molecular biology to go along with your bad astromony? I don’t think we know nearly enough about how it happened on Earth to be able to predict how it might happen in places with radically different chemistries. I continue to be encouraged by an environment with sufficient energy flow for substancial erosion to occur. We measure the age of craters on Mars in the millions of years. We measure the age of visible craters on earth in the hundres of thousands of years generally — there is enough energy flow to wipe out most obvious signs of impacts in a fairly short time. I strongly suspect that the surface of Titan is similarly young. And that leads me to believe that if the chemistry is at all favorable (and we also know very little about methane and ethane and all the dlightly impure hydrocarbons) then there might be some kind of self-organized chemistry at work though probably at a greatly slowed rate of activity compared to life on Earth due to the much lower temperatures. There’s cetainly been enough time for something to have started if it is at all possible. Given enough time, even unlikely things become likely.

  6. Does Phil know what a gift he has handed creationists here with this quote

    We really have no clue how life first sparked on Earth.

    Now some creationists can show that Phil was agreeing with them just by referencing this blog.

    I just thought you ought to know

    Getting back to the Huygens probe, I recognise it is long dead due to exhausted power cells, but would the known conditions on Titan destroy it, or will it be preserved, should there one day be a human spaceflight to Titan?

  7. Grand Lunar

    I saw the “lakes” story on NASA’s website as well (it actually appeared there before it did here). It would be very interesting to have the findings confirmed once and for all.
    Perhaps in some distant future, Titan might become a fueling station.

    To Sticks,

    I think the Huygens probe might suffer some weathering, depending on what the weather conditions on Titan are. But it still might be reasonably intact, if a bit corroded. It really depends on when it is we arrive there. I suspect it may happen in the 2100s.

  8. DragonIV

    But the truth is, we don’t precisely know how life came about here on Earth. That doesn’t imply a creator, nor an intelligent designer. It just means we still have lots to learn. We can’t be mincing words over what the creationists or any other anti-science group will do with our words.

  9. dre

    dude, can i run my old mercedes diesel off of that stuff?

  10. icemith

    Re the matter of the Huygens Probe, what are the odds that it set down *in* one of those lakes?

    Would there be any tides? Or is the system far too small to have any noticeable effect on the level of the liquid lake?

    And just which fly should the angler be best advised using?

    Ivan?

  11. kingnor

    It’d be great to see some photos from the shore of one of these lakes.

    with so many oddball worlds in the solar system its too bad all the on site photos we have are of boring rocky places with features consistent with an earth desert.

    If those are lakes, what are they lakes of? water? acid? chocolate milk??

  12. liquid methane and ethane absorb radar

    Actually, they reflect, not absorb. The flat surface results in specular reflection, so they look dark unless viewed from directly above. Nick Matzke sums it up nicely at Panda’s Thumb.

    Boy it’d sure be nice if we had some preview buttons, don’tcha think?

  13. any biologists or archaeologists wanna enlighten us physical scientist-types about this?

    Ahhh Phil … archaeologists studying past HUMAN life, so this is some what (~4 billion, give or take) out of their league. I think you were thinking of paleontologist, but they aren’t much help.

  14. icemith: They had images of the landing area for Huygens. The probe itself took a few. It wasn’t a lake that it landed on, though apparently the ground was moist and muddy.

  15. Tim G

    Perhaps there are geothermal “hot spots” on Titan where it is above minus 100 Celsius. A mixture of water and ammonia may be liquid in such areas. Could life based on good old DNA survive in such an environment? Read the Astrobio.net article. Another moon of Saturn, Enceladus, may also have a mixture of liquid water and ammonia near the surface.

  16. jess tauber

    I remember many moons ago (can I say that here??) reading about electrified ammonia ice, which has a nice blue color. With ions from Saturn’s magnetic field, perhaps this would be a great energy transducer. Who needs heat?

    Jess Tauber

  17. Pro Libertate

    I wonder if Titan’s environment has been stable long enough for life to have developed? I would imagine that the answer is yes, but I haven’t run across anything discussing that aspect of the probability-of-life question.

  18. TheBlackCat

    PK says:
    “because a large entropy corresponds to a large number of accessible states for a given energy (in the microcanonical ensemble, which I think is applicable here). However, the hydrogen bonds restrict the orientation and position of the molecules, which would indicate a smaller number of accessible states, and a correspondingly lower entropy.”

    Entropy is proportional to the number of discrete states. Because each water molecule can potentially bind to dozens, maybe even hundreds of water molecules, and these bonds are broken and re-formed extremely rapidly, there is a massive number of possible discrete states. However, because the hydrocarbons do not have such hydrogen bonding, the number of discrete states they can exist in is very small. In entropy, according to my professor, continuous states such as are present in hydrocarbons do not contribute to energy, only discrete states do. Because hydrocarbons have nothing locking them into a finite number of orientations and positions but instead exist in a infinitely divisible continuum of orientations and positions they have very low entropy.

  19. That mud looks like bogs. Have you ever heard of the “Bog People” that were found buried in bogs hundreds of years ago? Hey, how about us Blog People? Have we all buried our minds inside of all this newly released data too fast? All of these recent discoveries are preliminary.

    I shall wait on the disciplines of each specialized science for their professional official reports.

    In the meantime: those pics are neat.

  20. CR

    It’s harder and harder to think of Titan as a moon, and not a planet in its own right. (Yes, I know that by definition, it’s a moon.)

    Anyway, what a cool place!

  21. Troy

    Those are very interesting pictures. Life is pretty unlikely. That was an interesting discussion polar vs. non-polar life, but ultimately Titan probably doesn’t have the energy. That excludes surface life but of course underneath you may have a water ice mantle with hot spots where you have actual liquid water. Still probably not enough energy to drive an ecology but it is useful to contemplate it.

  22. icemith

    Joshua, as there are many variations possible in the lake senario, I was curious as the craft could have set down at the edge of a lake, and if there *were* tidal, or other effects, then the said craft would be subjected to fluid inundation. It would get wet, or even be submerged.

    The images received may have been taken at a moment of low tide. Then again the depth of that lake in particular may only be measured in meters or less, even millimeters. I would doubt there would be the scale of depths we here on Earth are familar with. Can anybody shed some light on these musings?

  23. Nigel Depledge
  24. Scott

    First of all, I’d definte Titan as a satellite planet. I’m not sure which one works better, there are really various classes of celestial bodies that are not undergoing nuclear reaction, each one having the properties of the lower level (highest order being the lower number):
    1. Body with currently living lifeforms present (subdivided into evolutionary progress of said lifeforms and potentially the types of climates they thrive in);
    2. Body with all three states of matter present within a reasonable ratio–yes, that ratio would be debatable (this could also be broken into two subcategories: those that have had known life at some point which has not survived, and those that have never had any known life);
    3. Body with a complex atmosphere (i.e. an atmosphere with an apparent climate, whereas climate refers to a regular exchange of gasses and temperatures between the atmosphere and surface of the body);
    4. Body with a simple atmosphere (i.e., gasseous atmosphere with no apparent climate);
    5. Body with no atmosphere

    And then you could also classify them by other means (e.g. what they orbit). I would say any body class 4 or above would be a planet–no atmosphere, not a planet. Sorry Mecury, you’re only the sun’s moon–an honorary planet at best. Maybe I’m missing the reason they have such a hard time defining planets. Titan would be a class 2

    Moving on to life . . .
    With the myriad of locations single-cell organisms can be found living on Earth, it would not surprise me if they found some way to adopt to Titan, even if it’s at the warmest point at the bottom of the methane lakes. It’s likely they have some form of underwater vents similar to that of our oceans where we have found life flourishing. Granted, it may be very very slow moving organisms, making evolutionary processes drawn out greatly.

    The probability of life on Titan–and subsequent evolution that may have occurred–pivots on the time frame in which Titan has maintained a climate near the state it is currently at or at a more life-friendly state (if there ever was one). The other main variable in the Titan-life equation would be how likely life came from outside the planet or was induced upon the planet (if that is at all possible under any conditions that ever existed on the planet).

    That said, it would be nearly as exciting to find out that Titan at least hosted life (possibly at some more hospitable point in its history) at some point in time as finding that it currently has life.

  25. There’s a related news item at Methane makers yield to science which says:

    The genetic code of an important group of methane-producing microbes has been sequenced by German scientists.

    The archaea are probably the major source of methane emanating from rice fields, contributing up to a quarter of global emissions of the gas.

    The article goes on to say that an archaea group called Rice Cluster I (RC-I) is probably responsible and then ends:

    Some researchers hold out hope that some of the methane traces observed on Mars, for example, may be coming from organisms like RC-I.

    John Latter / Jorolat

    Evolution Research

  26. TheBlackCat

    Scott says:

    “5. Body with no atmosphere”

    How do you define “atmosphere”? Even the moon has an ambient pressure higher than that in interplanetary space. And the entire solar system has a pressure higher than that of interstellar space, which has pressure higher than that of intergalactic space, and so on. You must set some sort of arbitrary cut-off in terms of ambient pressure in order to define “presence” or “absence” of an atmosphere. Also, how do you define a “climate”? Does Mars have a climate? It certainly has weather and changing local atmospheric conditions. But then again, so would any body with any gas at all, since the body would not be recieving uniform energy at all points. Even interplanetary space has “weather” from particles streaming away from the sun and the passage of bodies like comets.

    “The probability of life on Titan–and subsequent evolution that may have occurred–pivots on the time frame in which Titan has maintained a climate near the state it is currently at or at a more life-friendly state (if there ever was one). The other main variable in the Titan-life equation would be how likely life came from outside the planet or was induced upon the planet (if that is at all possible under any conditions that ever existed on the planet).”

    It also requires a chemical environment in which life can develop. This is not by no means given. Simply having a planet stable long enough will not allow life to develop if the local environment prohibits the evolution life. Simply having solid liquid and gas does not mean life can necessary develop in that solid, liquid, and gas. It doesn’t mean it can’t, either, but it is simply not a given.

  27. Enceladus has a polar hot spot venting gas into Space, which might indicate subsurface water. Earth’s Antarctic has subsurface lakes which are considered likely homes for life. Note that all these bodies have “hot spots” located on their poles. Even Saturn herself has a polar hot spot visible at 17.65 microns; check out the photo. Makes you think, doesn’t it?

  28. George Greene

    So Titan has a temperature of 180 Celsius, huh? Amazing for a body so far from the sun. Even the earth has a mean surface temperature of only about 15 C.

  29. I discovered that if you pull these images into Photoshop and stretch the contrast, the “lake” features contain terrain that resembles craters and rivers, similar to the surrounding terrain. It appears to me that these “lakes” may actually be terrain, but with a lower radar-reflectivity than the surrounding. Possibly mud?

    See an example at http://www.smccabe.net/titan_lake1.jpg

  30. Mercury the Suns moon, Scott?!? ;-)

    Ithink thatcould apply to all theplanets if its not what you call a planet full stop.

    A planet goes round a star ie. our Sun, a moon goes round a planet -or insomecases an asteroid or planetoid.

    I’d call Titan a world – or a large moon. In fact, it is the largest moon beating Ganymede and Callisto for that honour. Its nearly as big asMars and bigger than Mercury -and yes its a very cool place.

    The finding of lakes may be old news now but its still marvellous.

    As for Phil Plait helping creationists by his “no clue how life sparked” line those excremental so-and-sos would twistsanyone’s words given thechance -bestthingany of us can do is take whatever they say with a shaker-full of salt. In truth though, we _do_ have quite a few clues on how life started just no certainities. Which puts us a considerable few steps ahead of those who claim to know with utter certainty but resort to the “God said so” fallacy of authority as their only evidence.

  31. JD

    “excremental so-and-sos”

    such deep intellect you possess.

    you have no clue how life arose.

    none.

  32. madjon

    “It appears to me that these “lakes” may actually be terrain, but with a lower radar-reflectivity than the surrounding. Possibly mud?”
    The ‘rivers’ or flow features going into these depressions point strongly to a fluid entering them, however its by no means certain, given the zoo of organic chemicals they are likely to contain, that whats in the lakes is also liquid. The material in the lakes is likely to have any impurities or dissolved chemicals concentrated by evaporation; I think the term goo would apply very well to it.

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