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Cassini Spies a Possible ‘Oasis’ on Titan

Saturn’s rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. Image Credit: NASA/JPL-Caltech/Space Science Institute

From a JPL press release:

New data from the Cassini spacecraft shows enduring methane lakes in the equatorial regions on Saturn’s moon Titan. Previous models of the frigid liquids on Titan’s surface showed standing bodies of liquid would only exist at the poles, but one of the newly found “tropical” lakes appears to be about half the size of Utah’s Great Salt Lake, with a depth of at least 3 feet (1 meter).

Where could the liquid for these lakes come from? “A likely supplier is an underground aquifer,” said Caitlin Griffith, the paper’s lead author and a Cassini team associate at the University of Arizona, Tucson. “In essence, Titan may have oases.”

Understanding how lakes or wetlands form on Titan helps scientists learn about the moon’s weather. Like Earth’s hydrological cycle, Titan has a “methane” cycle, with methane rather than water circulating. In Titan’s atmosphere, ultraviolet light breaks apart methane, initiating a chain of complicated organic chemical reactions. But existing models haven’t been able to account for the abundant supply of methane.

“An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life.”

Global circulation models of Titan have theorized that liquid methane in the moon’s equatorial region evaporates and is carried by wind to the north and south poles, where cooler temperatures cause methane to condense. When it falls to the surface, it forms the polar lakes. On Earth, water is similarly transported by the circulation, yet the oceans also transport water, thereby countering the atmospheric effects.

The latest results come from Cassini’s visual and infrared mapping spectrometer, which detected the dark areas in the tropical region known as Shangri-La, near the spot where the European Space Agency’s Huygens probe landed in 2005. When Huygens landed, the heat of the probe’s lamp vaporized some methane from the ground, indicating it had landed in a damp area.

Areas appear dark to the visual and infrared mapping spectrometer when liquid ethane or methane are present. Some regions could be shallow, ankle-deep puddles. Cassini’s radar mapper has seen lakes in the polar region, but hasn’t detected any lakes at low latitudes.

The tropical lakes detected by the visual and infrared mapping spectrometer have remained since 2004. Only once has rain been detected falling and evaporating in the equatorial regions, and only during the recent expected rainy season. Scientists therefore deduce the lakes could not be substantively replenished by rain.

“We had thought that Titan simply had extensive dunes at the equator and lakes at the poles, but now we know that Titan is more complex than we previously thought,” said Linda Spilker, the Cassini project scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini still has multiple opportunities to fly by this moon going forward, so we can’t wait to see how the details of this story fill out.”

The findings appear in this week’s issue of the journal Nature.

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Jon Souter June 14, 2012, 12:14 PM

    Interesting future location to investigate the possibility of simple life evolving, based on very different chemistry to that found on Earth.

    Earth’s extremophiles have arguably managed stranger feats.

    • KnappHerbert June 14, 2012, 12:15 PM

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    • lcrowell June 14, 2012, 3:00 PM

      Any self organizing chemistry on Titan is likely very different from life on Earth. We might have trouble identifying it as life if it is found to exist. Also remember that chemical reactions occur at a rate dependent upon temperature. Very cold systems tend not to permit much chemical activity.
      LC

      • Jon Souter June 14, 2012, 3:24 PM

        Agree fully – but would still like to think this moon is on NASA’s and ESA’s shortlist for future long-term astrobiology missions.

        Who knows… where there are liquid methane aquifers, there could also be geological processes that generate enough thermal energy for methane-based micro-organisms to flourish.

        The article suggests liquid methane was unexpected at equatorial latitudes, so who knows what other surprises this smoggy moon harbours?

        • lcrowell June 14, 2012, 4:21 PM

          I am not saying life is known to be ruled out. It does seem pretty unlikely to me. Titan is curious because it is an analogue of Earth geology, oceanography and atmosphere. It has volcanoes of liquid water and ammonia, and a crust of largely water and ammonia. Methane seems to be the analogue of water on Earth.

          I am not sure about chemical analogues. At around -180C or 93K Titan’s surface is “classical low temperature physics” and what ever chemistry there might be there. The atmosphere is mostly nitrogen, and on average is less than 20K above its liquid phase.

          LC

          • Jon Souter June 15, 2012, 10:20 AM

            Recent studies have found microbial life flourishing deep in cores extracted from terrestrial polar ice. If I recall correctly, these single-cell organisms have evolved clever mechanisms that liquify small pockets within the ice.

            I like to keep an open mind about what is possible – as life’s diversity and ability to carve unexpected niches on Earth continues to surprise biologists.

          • lcrowell June 15, 2012, 12:40 PM

            Ice at freezing temperatures on Earthis not that hard. The lattice of molecules is loosely bound and the molecules can flip around. Water ice is then in a transient liquid state. Cryro-bacteria can then maintain a level of cellular activity. In order for molecular pathways to operate it is necessary for molecules to be in a solution so they can move and transform their physical state. If ice is warm enough there is enough floppiness in the molecular lattice due to vibrations so that can happen at a low rate.
            On Titan temperatures of -180C are such that ice is as hard as steel. The molecular lattice has much lower energy states of vibrations and the lattice is locked hard into place. I leave it to your physical sense of things to determine if much molecular activity can occur in ice at that temperature.
            LC

          • Jon Souter June 15, 2012, 5:42 PM

            @lcrowell

            With the greatest respect, we’re not talking about (Water) ice on Titan’s surface though.

            If life could exist, based upon some crazy form of methane-centric chemistry, the fact that methane exists on the surface of Titan in a liquid state suggests that there is *some* potential, however remote.

            I’d imagine we still have gaps in our knowledge regarding Titan’s potential for generating thermal energy beneath it’s chilly surface.

            Can anyone be certain that thermal vents, geysers, smokers, etc are an impossibility on Titan?

            Can we offer anything more than ‘best guesses’ regarding the effects of tidal heating, both on and within Titan?

            There may be a number of current & ideal habitats there for very different kinds of life to that which we are accustomed?

            What about past events in Titan’s history, such as meteor impacts? Can we rule these out as having
            generated enough prolonged heat to act as a catalyst for chemical processes that might underpin simple methane-based life?

          • lcrowell June 16, 2012, 3:15 PM

            I can’t disprove these speculations. Whether liquid methane can serve as a medium for complex self-replicating chemistry is pure speculation. I will say this; the principle energy mechanism for life is ATP —> ADP + P phosphorylation, and water is a polar molecule which plays an important chemical physics role in permitting that phosphorus to bind onto amino acid residues in polypeptides. Water as a polar molecule plays an important role in the mediation of chemical processes involving other molecules with charges or polarizations. Building a case for how a nonpolar molecule such as methane can function the same way water does is in it full extent hard to do.
            LC

          • Torbjörn Larsson June 16, 2012, 4:00 PM

            This thread seemed to hone in on liquid methane metabolism, which is a big jump from what we know, but if we get back to general possibilites I repeat what I said in an earlier comment: Titan is differentiated and believed to have an (unfortunately ammonia soaked) ice covered ocean.

            With this, liquid water, organics, minerals and heat energy from the core, you can potentially have liquid water metabolism habitats from the crust on down.

            If that is “methane-centric” (say, using methane as source of organic and/or enerty) or not, I dunno. But at a guess a water cell would kick a methane cell’s membrane any time, due to water’s versatility. Hence with these observations I would surmise most Titan life would be water based, if any.

          • Torbjörn Larsson June 16, 2012, 4:31 PM

            What the fuss on Titan has been about. Most importantly perhaps, purely from an energetic viewpoint, methane as solvent is possible.

            Considering other solvents than water is, as considering other energy sources than the observed used, part and parcel of astrobiology. I recommend an introductory book if you want to get the gist of it.

            Mostly, it is more unlikely because of a) less availability b) most often more constrained temperature and pressure ranges c) less versatility. Add the unknowns that lcrowell mentions, as opposed to water we have no type case of extant metabolism to look at.

          • Jon Souter June 15, 2012, 10:29 AM

            Recent studies have discovered microbial lifeforms deep in terrestrial polar ice cores – so the liquid phase of water is not strictly a pre-requisite for simple life even here on Earth. Just 3 years ago – such possibilities were deemed highly improbable.

            Certainly think it pays to keep an open mind at this early point in our exploration of off-world environments.

    • Torbjörn Larsson June 14, 2012, 10:43 PM

      Between Mars, Titan, and Enceladus, Titan is the planet that tests best for extant life.

      Methane based life would IIRC consume hydrogen and produce acetylene, which are both observed and in the case of hydrogen unambiguously so as no atmospheric or surface process has been found as alternative yet.

      For Mars solely methane is ambiguously observed, active mantle (which now seems a fairly robust conclusion from recent signs of landshakes) can produce the same.

      Enceladus tests negative, observed organics are pristine cometary. But it does have water and organics, and the vents are partly remelted ice so concealing any extant or extinct life fossil. Hence better tests are needed.

      But going from water to methane based chemistry is a big jump.

  • Kathleen Sisco June 14, 2012, 12:50 PM

    The entire solar sysem is being deluged with neutrinos. This deluge is not only heating the gas of Fluff of which our solar system, possibly one of many, is embedded; it is expanding and therefore compressing our heliosphere. The neutrino deluge is also heating the cores of the planetary bodies. This heat is held captive as it cannot expand while the heliosphere is undergoing this ‘shrinking’ down closer to the sun. An analogy would be the lid on a heated pressure cooker. Further out the heliosphere no longer exists as it has been contracted toward the sun due to compression. This is why the heated cores of planetary bodies can radiate the heat upwards and produce such things a oases and liquid where formerly there was none. All this temporary compression will vanish when 2013 arrives. Is a body of antimatter briefly broaching the ORT shell shedding massive neutrinos before being repelled? OR is the Milky Way a giant capacitor storing charge up to saturation and then will discharge in an energy pulse currently misinterperted as a run away black hole? OR is it both?

    • lcrowell June 14, 2012, 2:53 PM

      Neutrinos interact very weakly and a flux of neutrinos through a planet deposits very little energy. A trillion neutrinos pass through each of us every second and we generally don’t complain.
      It is best to try to learn a bit about real physics. To be honest little of what you write here makes much sense.
      LC

    • Aqua4U June 14, 2012, 2:53 PM

      Ha Ha Ha! I like the part about ‘the gas of Fluff’. Is this gaseous ‘Fluff’ related to ‘Flubber’?

    • zetetic elench June 14, 2012, 3:12 PM

      of all the gin joints in the world, you had to show up in this one.

    • Jon Souter June 14, 2012, 3:29 PM

      Uh-oh… the Nutrinos have mutated!

      http://www.youtube.com/watch?v=DGf0AHky0Os

      ;-)

      • magnus.nyborg June 14, 2012, 8:47 PM

        Just waiting for the sequel – Return of the mutant Ninja Neutrinos, no more hide and sneak, this time they are using full contact eastern combat techniques, and full frontal nudity.

    • Olaf2 June 14, 2012, 4:36 PM

      This is the most pathetic explanation I ever heard. I can’t find anything that is scientifically true in the comment.

  • Aqua4U June 14, 2012, 2:56 PM

    Comparing the similarities between Earth’s water based hydrological cycles and Titan’s assumed methane based hydrological cycles is downright fascinating… and hints at further comparisons to be discovered. Even stuff that wiggles in the ‘Fluff’…..?

  • Torbjörn Larsson June 14, 2012, 10:53 PM

    All the time we looked for cryovolcanoes predicting the needed methane source, when we should have looked for cryooases!

    In any case, hopefully one less mystery and – even better – perhaps another place for a biosphere. Titan is differentiated and is believed to have a deep ocean analogous to Europa. If it has organics and not too much ammonia it could well be an abode for water based life.

  • Martin_Lambert June 14, 2012, 11:26 PM

    How about letting Cassini fly around Enceladus for a couple of times and then sending it back to Earth instead of dumping it into the Saturn. I guess it is probably impossible due to lack of the “fuel”, but maybe using Saturn’s gravitational assistance we could get somewhere near Earth’s orbit. Even if it takes a long long time I’m pretty sure that it is going to be quicker then the actual new Enceladus sample retrieval mission… and btw just imagine seeing a “real Cassini” in a museum :)

    • squidgeny June 15, 2012, 11:59 AM

      Saturn’s gravitational assistance would be of no use, since the craft is already deep down Saturn’s gravity well. The craft would need a lot of energy to get back out, and that energy is best used for continuing to visit the moons. However, I do wonder if it’s possible to climb out of Saturn’s gravity well by using a gravity assist from one of the moons… perhaps someone with more knowledge of the Saturn system could enlighten us?

      • Torbjörn Larsson June 16, 2012, 4:12 PM

        Intriguing idea – the Cassini craft would work as an Enceladus probe sampler. The “interplanetary highways” (here and here) that may exist between planets use Lagrange points to reduce needed fuel to virtually steering:

        “Each planet and moon have five points near them where gravity balances out, called Lagrange points – by networking them together, Lo has worked out paths which will use very little fuel to travel from planet to planet. The first spacecraft to take advantage his work will be NASA’s Genesis mission, which will collect solar particles and then return them back to Earth.”

        “Most missions are designed to take advantage of the way gravity pulls on a spacecraft when it swings by a body such as a planet or moon. Lo’s concept takes advantage of another factor, the Sun’s pull on the planets or a planet’s pull on its nearby moons. Forces from many directions nearly cancel each other out, leaving paths through the gravity fields in which spacecraft can travel.”

        “Lo and his colleagues have turned the underlying mathematics of the Interplanetary Superhighway into a tool for mission design called “LTool,” using models and algorithms developed at Purdue University, West Lafayette, Ind. The new LTool was used by JPL engineers to redesign the flight path for the Genesis mission to adapt to a change in launch dates. Genesis launched in August 2001.” [ref 1]

        “Spaceflight typically requires the expenditure of considerable quantities of propellant. But after it blasted off from Earth, the Genesis probe was able to travel 1.5 million kilometers toward the Sun (green portion of the trajectory), which is some four times farther than the Moon’s orbit (gray circle). Genesis then orbited the Earth’s Lagrange point (white cross in foreground) collecting particles of the solar wind for two and a half years before traveling millions of kilometers along a circuitous path (blue) that looped by another Lagrange point,
        before returning to Earth in September 2004. Amazingly, Genesis completed this vast trek using hardly any fuel.” [ref 2]

        I assume the remaining lifetime of Cassini, set by steering thruster remaining fuel, is too small by now. And we would need an (SLS?) mission to one Lagrange point timed to pick the probe up sometime soon after arrival, if we want it and its gathered plume material intact.

  • I3VI5 June 16, 2012, 5:51 AM

    Titan is the best place to search for life since if there is life there it will be completely different from ours and it will prove that life is really common around the universe.

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