Sailing the Seas of Titan

The first interplanetary nautical craft may be a boat to explore the methane seas of Titan. A proposed mission to Titan would explore some of its largest seas, including Ligeia Mare (pictured) or the Kraken Mare, both of which are in the northern hemisphere of the foggy moon of Saturn. The concept has been studied for over two years by scientific team led by Ellen Stofan of Proxemy Research, Inc. in Washington DC, and has recently been submitted to NASA.

The concept is under consideration by NASA to be one of the Discovery Class missions – low-cost, high-return missions, which include the MESSENGER and Kepler missions. If chosen, the Titan Mare Explorer (TiME), could launch as early as January of 2015, and would make port at Titan in June of 2023. The total proposed cost of TiME is currently estimated at $425 million. Stofan described the proposal at this year’s American Geophysical Union meeting in San Fransisco, CA.

Lakes, seas, and rivers were discovered on Titan by the Cassini spacecraft in 2005. Since then, the weather and climate patterns of the moon have been scrutinized by scientists, leading to the discovery of both fog and rain.

Of course, the proposed boat wouldn’t be the first craft to land on Titan – that distinction is held by the Huygens probe, which as part of the Cassini mission landed on Titan on January 14th, 2005 and for three hours took images and scientific data which it sent back to Earth. Huygens touched down on dry land, though it was designed to operate on either land or ocean.

Proposed instruments for the boat include a mass spectrometer, sonar, cameras and meteorology instruments. TiME would investigate the chemical composition of the seas of Titan, as well as monitor the cycle of ethane and methane on the moon (called the “methane-ologic” cycle), a process that scientists are just beginning to understand. The sonar would be used just like it is on submarines and boats here on Earth – to map the depth of the seas, as well as get an accurate image of the sea bottom.

Since the cloudy and foggy surface of Titan sees little sunlight, the boat is proposed to be powered by an Advanced Stirling Radioisotope Generator. These types of engines, called Stirling engines after the inventor, Robert Stirling, use a radioactive source such as plutonium to heat a gas in one chamber, and as it flows to a cooler chamber the flow is turned into mechanical energy with a very high rate of efficiency.

If the boat is seaworthy, it may set a precedent to give us Earthlubbers a chance at understanding the only other body in our Solar System with lakes and seas on its surface (though Europa and Enceladus are thought to have watery oceans under their crusts). By comparing the methane-ologic cycle on Titan with the Earth’s hydrologic cycle, scientists could gain a more intricate knowledge of the large-scale impact of these cycles.

Source: Physorg, Ellen Stofan’s presentation (available here in PDF)

11 Replies to “Sailing the Seas of Titan”

  1. Thanks for presenting this extremely interesting mission! Especially the day after New Years Ewe partying, I needed something sobering and time wasting. 😉 I looked at the proposed ROI, and it’s huge, both on science and technology.

    As for the science, as a layman I would guess that establishing the hydrological cycle is of tantamount importance to understand meteorology but also climatology of the best Earth analog there is. Today we need to understand climate as never before.

    The other main line, to “look for patterns in the abundance of constituents in the liquids and analyze noble gases” and to “search for signs of self-organizing organic chemistry” as a result of ionospheric processing and what not, is no doubt every astrobiologists wet [sic] dream.

    Not that I personally have reason to see this as a likely important pathway on Earth. Any organic haze from high energy/high altitude solar energy influx would compete with surface photo-selection as an early abiogenetic driver.

    One successful test for the later pathway is that our nucleotides and amino acids have been photo-selected at some point. All that we use display optimization for fast transport of energy to the environment by vibrational and rotational states, minimizing own damage. Actually in principle the same process that photo-selects for PAH on dust in interstellar media.

    Another survived test is that our atmosphere then was mostly CO2.

    With a completely different exobase to magnetosphere conditions than say O2/N2 atmospheres I’m told. These atmospheres seem on the other hand, to a naive layman, to be rather harsh on haze production conditions as they keep their exospheres comparatively efficiently protected on Earth analogs. [“What makes a planet habitable”, Lammer et al, Astron Astrophys Rev (2009) 17.] And to boot the atmosphere then was likely methane deficient as it seems methanotrophs were late. (And accordingly methanogens seems to be the very last metabolic pathway established.)

    [I’m cribbing this from the ZnS world theory of Mulkidjanian et al and the neomura theory of Cavalier-Smith which nicely mesh together in their respective abiogenetic/phylogenetic theories, resulting in a substantially testable, and tested, complete pathway to the RNA world and beyond. As an alternative, haze production has some ways to go!]

    But organic haze production remains a process that could feasibly also lead to life further down the possible pathways.

    And these ASRGs they propose to test is ‘the latest upgrade’! Apparently they now boast an improved energy efficiency of 4 times previous RGs. They seem a lot lighter than I remember from earlier presentations. And despite my concerns for longevity, surely the mechanical engine with its friction to overcome won’t have the graceful run-down and exit of a solid state engine, the nominal lifetime is claimed to be 14 years.

    Nitpick: The text can be read as all Stirling engines being radioactively powered. Most aren’t, they are as the links tell us air-independent mechanical engines. That for example power modern non-nuclear submarines during extended subsurface runs of weeks at a time. This mission is a “return to the seas” for them. 😀

  2. “These atmospheres seem” referring to CO2 atmospheres. It’s an _N2/O2_ atmosphere like ours that much more easily can extend outside the magnetosphere at high enough EUV/FUV fluxes.

    [Gee, I _am_ tired!]

  3. I’m cool with this, but I’m worried about the possible affect of the radiation from isotope generator. Titan is the first planet we’ve visited with a large amount of standing liquid, and may harbor Titan-specific life forms.

    Would we like it if someone dropped a radioisotope craft in our “water” supply? What if something goes wrong and we poison an entire lake?

  4. A neat idea, but I would rather not put radioactive materials deliberately in space and on other planets.

  5. If NASA are responsible they will encase the plutonium in a thick metal shell that will prevent the radiation from leaking, and will survive lying at the bottom of a methane sea for a few centuries.

  6. Radioactive materials are created and present naturally everywhere in the space and even if this mission goes to the worst scenario the practical effect on the balance of what is already on Titan will be negligible.

  7. This is a bit of a sticky question. Clearly to power a probe on the murky dark environment of Titan a nuclear RTG is required. This is a sort of contamination, and the half life of plutonium is Pu_{242} is 300 thousand years. It is hard to containerized anything for that long.

    However, the contamination is hot huge. We showered Earth with a lot more Pu than this by exploding plutonium bombs.


  8. Plutonium-238 has a half-life of 88 years and emits alpha particles. It is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft.

  9. I stand corrected. This is the isotope used. So if it is contained well enough this should not be too bad a contamination problem.


  10. Nuclear radiation is the only game in town if we are to consider space travel.

    As a concept, consider this; space is saturated with radiation, (the sun RADIATES it) Uranium and all heavy atoms on the periodic table are created when stars go supernova. ALL the uranium on earth exists because a Nova went boom nearby when our solar system was forming. If it exists on earth then it will exist everywhere in our solar system. We already know its on the moon.

    To say humans should not use this material because its bad is like saying we should not swim in the ocean because we cant breathe underwater.

    Nobody seems to have a high moral ground about using hydrocarbons to generate electricity or chemical reaction rockets. These chemicals are equally bad for our meat bodies. But mention anything Radioactive and everyone has an opinion.

    Seeming as I’m on a rant here, lets also not forget that our Nuclear (power) station designs were chosen for their (weapons re-processing) capability. Not for efficiency or safety. Google “Thorium breeder reactor”

    To all those with an opinion please please research you own bias and objection. There is no excuse for ignorance.

    If we are to go to space, then this (public) armchair objection to nuclear power has to become an informed issue. Yes Ionizing radiation can damage our meat bodies, and if we go to space in our meat bodies then we will have to protect them from much worse radiation then that emitted by our engines.

    Contaminating Titan? If your really worried, hope that biology in the form of RNA or DNA is not carried by the probe, as life seems to be rather parasitic. Perhaps the Alpha radiation will scrub the probe clean.


  11. “powered by an Advanced Stirling Radioisotope Generator”

    Does this just mean power supply for the instruments or also include the ability of purposeful locomotion? Archimedes’ principle would lets the ship swim on the surface of liquid methane, but how would the ship be moved forward? Propeller? Paddle?

    And if a secure disposal of the nuclear waste is a problem, then could the ship and its Plutonium-238 brought back into space when the end of the mission comes?

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