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Adrift on Ligeia Mare

Imagine a boat from Earth drifting across an alien sea. Something like that could happen as early as 2022 if Ellen Stofan (Proxemy Research) can talk the powers that be into the venture. Stofan envisions a new mission to Titan, the only other place in the Solar System known to have bodies of liquid on its surface. The methane and ethane lakes revealed by Cassini show some bodies as large as the Black Sea or the Great Lakes of North America. Stofan’s target: Ligeia Mare or Kraken Mare, two of the larger possibilities revealed by the orbiter.


Image: Radar data from Cassini allowed the creation of this artificially colorized view of Ligeia Mare, with liquid methane/ethane shown in blue. Credit: NASA/JPL/USGS.

What an interesting off-shoot from the conventional rover concept, but then, Titan seems to inspire such things. Various types of airship designs have been put forward for studying the Saturnian moon, and at the Aosta conference in July, Giancarlo Genta described the workings of a hypothetical Titan rover that could take to the lakes as needed, converting itself into a floating research station. Stofan’s idea loses the rover capability. It is all boat, though it may not look like one.

What the planetary geologist envisions is a capsule that would be dropped directly into the target lake, with a mast to hold a camera. Drifting for months, pushed by local winds, the probe would use a nuclear-powered engine to run experiments and return data to Earth. When interviewed recently on National Public Radio, Stofan spoke about conditions in such a lake, including the possibility of a storm:

“In fact, we’d love for that to happen, to be able to return an image showing a rainy day on Titan and to see those methane raindrops falling down into the lake. The wind might kick up a little, but nothing as violent as the tropical storms and hurricanes we get here on Earth.”

The Discovery-class mission being proposed to NASA would launch around 2016 and arrive some six years later, assuming NASA chooses to go with the concept (the agency is going to be issuing a call for proposals for its Discovery missions shortly). So many good mission ideas, so little money to work with! But if by chance the Titan boat makes the cut, just imagine the view we would have from the camera mounted on its mast. You can hear Stofan interviewed on the Titan boat idea at this NPR page.

Thanks to Eric Davis for the tip on Stofan’s work. I’m also reminded that we looked not long ago at Stofan’s fine book (with astronaut Tom Jones) Planetology: Unlocking the Secrets of the Solar System (National Geographic, 2008).


Comments on this entry are closed.

  • Carl October 14, 2009, 17:50

    The boat should also have a microphone, like Huygens http://www.esa.int/SPECIALS/Cassini-Huygens/SEM85Q71Y3E_1.html

    It would be more informative to have a pair mounted for binaural recording.

  • Colin Weaver October 14, 2009, 23:12

    … and a rod, so you can drop a line in. But what to use as bait? :-)

  • Tulse October 15, 2009, 7:36

    I would think this kind of mission would be severely limited compared to a rover. A “land” vehicle could sample multiple different locations of interest, whereas presumably the liquid in the lake is pretty much homogenous. Also, the travel of a floating probe couldn’t be controlled, and it could easily become grounded or otherwise stuck. And heating a probe in constant contact with a liquid would be more challenging than one that is elevated above the surface (not to mention the possibility of liquid getting into the probe). The only benefit there seems to be is that a “splashdown” landing might be easier than landing on solid ground, but we’ve got lots of experience landing probes on solid surfaces, and the atmosphere provide a huge help in braking. I don’t see the attraction of this kind of mission.

  • keith October 15, 2009, 7:48

    There’s an Arthur C Clarke story I remember where he says Titan is the only body in the solar system where a person could walk around outside with just an oxygen mask and warm clothing. Is this still the case?

  • Doug M. October 15, 2009, 8:30

    Surface temperature on Titan is around 110 absolute, or -160 Celsius. So, no.

    Off the top of my head, I can think of three places in the Solar System that might qualify. On a hot summer afternoon in the lowlands of the northern hemisphere of Mars, the temperature might soar to nearly freezing. You’d be able to get away with an oxygen mask and warm clothing, as long as you didn’t mind getting a radiation dose roughly comparable to one medical x-ray per day.

    The other two possibilities would be on aerostats floating in the atmosphere of Venus or Jupiter. There’s a band in Venus’ atmosphere about 40 km above the surface, where temperature varies between 700 to 1000 millibars, where temperature seems to hang between 30 and 45 Celsius. You could wear light clothing, slather yourself with sunblock, and breathe from a standard SCUBA rig. Well, and you’d have to wear goggles, because sulfur dioxide is a powerful eye irritant. But otherwise, no problem.

    Then on Jupiter, there is a level in the atmosphere where there’s a comfortable temperature, and nothera level where there’s a pressure of around 1 bar. Unfortunately, the two seem to be some kilometers apart — the warm layer is lower, with uncomfortably high pressures, while the 1-bar level is a chilly 170 K or -100 C. But there is an intermediate level where the atmospheric pressure is still tolerable — four or five atmospheres — and where the temperature is a merely Siberian -40 to -60 C. SCUBA equipment again, maybe with a heliox mix, and very heavy clothing.

    Doug M.

  • Enzo October 15, 2009, 8:32

    The most incredible thing about this mission is the proposed timeline, at least when compared to the other NASA/ESA mission to Europa that it is not meant to orbit it before ~2030 (if all goes well).

  • ljk October 15, 2009, 9:02

    It’s the romance of actually being able to sail on a real alien sea, Tulse. Science would just be a bonus. :^)

    For good or bad, I can foresee future daredevils attempting to see how long they could survive with as little protection as possible in the places Doug M. mentions as well as others. How close could one get to an Io volcano, for example? Or playing chicken within the ring particles around Saturn.

  • Bob Steinke October 15, 2009, 11:20

    Tulse, a rover would be a lot more expensive. The benefit of a boat is cheap mobility. A non-self-propelled boat would be comparable in cost to a stationary lander like Phoenix, not a mobile rover like Spirit and Opportunity, and yet it would have some mobility.

  • philw1776 October 15, 2009, 14:20

    No weight of wheels or motors for wheels. Less power needed so power supply lighter. Drop 2 floating rovers into the lakes for the weight of one agile land rover. Remember the difficulty driving thru Martian sand. How many unanticipated traction hazards are there on Titan. Also a rover must be more autonomous operating without direct human control due to the couple hours one way light travel time.

  • Tulse October 15, 2009, 15:33

    But why a floating probe rather than a regular lander? I can’t imagine that the “mobility” one gets is all that valuable, since you don’t actually go to anyplace new that you can sample — at best you get closer to some “shores”. And that unpowered mobility also comes with a cost — risk of liquid getting into various parts of the probe, increased need for insulation/heating due to contact with the liquid, and risk of “grounding” or even capsizing in strong winds or currents.

    If the idea is to travel unpowered without sampling, a balloon probe would do better.

    I love the romance of the notion of a ship on a sea of Titan, but I’m not convinced that it would give us the best science for the money.

  • Bounty October 15, 2009, 16:53

    Well, do you want a sample from the solid areas of Titan or the wet ones? Or from the air? I’m guessing wet might be more interesting since it’s a nice place to mix things.

  • keith October 16, 2009, 7:34

    Doug M, I don’t quite agree with your analysis. On Mars, you would need a pressure suit. Admittedly, there are concept designs for kind of Lycra pressure suit, so an Apollo moon suit may not be fully necessary, but those concepts have not been proved. Also, like you say the thin atmosphere on Mars does not provide sufficient radiation shielding.

    The atmospheric layers on Venus and Jupiter are a bit of a cheat, because I did say “walk around”. In any case both atmospheres have severe irritants in their compositions, even tiny leaks would be very uncomfortable.

    The only apparent difficulties on Titan are the cold and lack of oxygen. It is VERY cold, but I am sure thermal clothing of the required insulation value could be made. Unfortunately I guess it might be necessary to wear eye protection because your tears could freeze (however it gets down to -90 C on Earth, so that’s not too far off).

    I wonder if it smells like an organic chemistry lab though?

  • ljk October 16, 2009, 9:55

    Space fact of the day: The first Soviet Venera probes with landing capsules
    were designed to float in a liquid medium. Some of their scientists still thought
    and hoped that the planet was covered in seas of liquid water, seltzer, or even
    oil as conjectured in the 1950s.


  • James M. Essig October 16, 2009, 12:56

    Hi Folks;

    The methane and ethane lakes revealed by Cassini are fascinating and whimsical to say the least.

    I can imagine at some future time a nuclear powered manned vessel plying the depths of the methane/ethane oceans with the caveat being that the submarine could be boyant enough yet with a thick enough hull to avoid dangerous pressures that might be reached within the lakes.

    Although we have only one star system as a data point where planets have been shown to provide us with about 200 moons in total, it seems likely that our solar system is typical of G class stars in terms of the wide variety of moons that can develop within associated solar systems.

    There is much fascinating territory to explore as we do manned missions out to the depths of our solar system and then on to our local stellar nieghboors and beyond.

  • Adam October 16, 2009, 17:54

    An RTG powered floater will need efficient insulation so the methane/ethane doesn’t evaporate overly and fog everything up. Seems a shame that a proper sailing vessel isn’t contemplated – propulsion ‘for free’ and a chance to reconnoiter the whole of the shoreline.

  • NS October 17, 2009, 2:08

    I’d guess that for Adam’s idea you’d need a streamlined hull, and a sailing rig and rudder with controls. Given the distance from Earth it would have to be semi-autonomous too — unlike a drifter or land rover, it might have to respond to hazards in real time instead of just riding it out or waiting for instructions. Sounds cool, actually. But I have to reluctantly agree with Tulse that a balloon probe would give better coverage with less risk.

  • Andrew W October 20, 2009, 1:03

    I noticed this on wiki: “Evidence of volcanic activity from the Cassini mission suggests that temperatures are probably much higher in hotbeds, enough for liquid water to exist.”

    So perhaps there are places where Keith could go for his stroll.

  • keith October 20, 2009, 13:52

    Andrew W, the “hotbeds” might be the more hazardous locations -there seems to be cyanogen in the surface material. If that gets volatilised I might be in trouble. Another thing I have thought of about going walkabout on Titan is I would need an umbrella in case it rained liquid methane. That could be bad news not only because of the cold, but also because it could bring down solid hydrogen cyanide crystals from the upper atmosphere.

  • Andrew W October 20, 2009, 16:57

    Geez, there are some people you can never please :)
    Probably, somewhere between the boiling hot pools and the frigid wastelands, we’ll be able to find a spot (around -25C) where it’s not raining, that is, like Baby Bear’s porridge, just right for Keith (aka Goldilocks).

  • keith October 21, 2009, 7:42

    Sorry Andrew I didn’t intend to come across as negative ! I had not actually heard of these warm spots until you mentioned them, I will have to look into that. I still find it fascinating that survival on Titan is potentially so “low tech”, at least in comparison with other the other planets and moons, even Mars.

  • Andrew W October 21, 2009, 14:01

    All in good humor Keith, I was going to suggest a swim in a hot spring, and perhaps that would be possible if the water was fresh to the surface, with cyanogen about, older surface water could be hazardous.


  • ljk October 27, 2009, 22:44

    A robot armada to Titan and elsewhere in the Sol system:


    Nice idea, but when will it become a reality? Computer graphics are
    much cheaper to produce than real spacecraft that go somewhere.

  • ljk November 21, 2009, 18:21


    Thursday, November 12, 2009

    The Surprising Contents of Titan’s Lakes

    The lakes on Titan have some surprising chemical contents, according to the latest data from the Cassini spacecraft.

    One of the exotic attractions of Saturn’s moon Titan is the possibility that it has oceans and lakes, with waves and breakers not unlike those on Earth. In the 1990s, astronomers ruled out the possibility of a global ocean using radar measurements taken from Earth but the possibility of lakes remained.

    And sure enough, in 2005, the Cassini spacecraft spotted a large lake-like feature called Ontario Lacus near the south pole and has since spotted numerous smaller ones.

    So what are these lakes made of? The conventional thinking is that the lakes must be made of a mixture of liquid ethane, methane and nitrogen. However, the amount of methane in the atmosphere makes it difficult to see in liquid form at ground level and only liquid ethane has been directly spotted in Ontario Lacus.

    The only other way to infer the composition of the lakes is by creating a thermodynamic model of the atmosphere using spacecraft and laboratory data and theoretical calculations. And of course, data from Cassini is revolutionising these calculations.

    Today, Daniel Cordier from the Ecole Nationale Superieure de Chimie de Rennes, France, et amis, present the latest take on the data. Their number crunching reveals that:

    “the main constituents of the lakes are ethane ( 76-79%), propane (7-8%), methane (5-10%), hydrogen cyanide (2-3%), butene (1%), butane (1%) and acetylene (1%).”

    That’s a rich and somewhat unexpected mix. But it’s also useful because it allows more detailed calculations about the role of liquid on the surface of Titan. “Our results provide the chemical data needed to compute the amount of deposition of various hydrocarbons and nitriles in fluvial valleys in the Titan’s midlatitudes,” says the team.

    And that should allow planetary geologists to build and test a new generation of models that show how rivers and streams have carved the surface of Titan. Geologists will be waiting with baited breath. The differences as well as the similarities with the processes that occur on Earth should make fascinating reading.

    Ref: http://arxiv.org/abs/0911.1860: An Estimate of the Chemical Composition of Titan’s Lakes

  • Patrick December 18, 2009, 12:31

    Let’s got there. One way or another. Only temperature is a problem, nothing else. The pressure is stable at 1.5 Bar, the gravity low. A light weight airplane could easily glide over the Titan landscape. This world is really astonishing. There is no other world (except Earth) which is so divers and beautiful at the same time. The romantic vision of a Titan lake in the evening, with calm and serene waves and a gloaming Saturn near the horizon. It would be all perfect.