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Pondering an Ocean Beneath Titan

An underground ocean on Titan? The apparent detection of low frequency radio waves makes liquid water beneath the surface of the huge Saturnian moon a possibility, according to research led by Fernando Simoes (Centre d’Etudes Terrestres et Planetaires, Saint Maur, France). Simoes and team have been studying what New Scientist is describing as an ‘enigmatic radio signal’ that the European Space Agency’s Huygens probe detected as it descended to Titan’s surface in 2005.

The signal seems not dissimilar to what lightning produces on Earth, where low frequency signals bounce between the ground and the upper atmosphere, in the process attenuating some frequencies while enhancing others. But Titan’s surface seems to be a poor reflector, meaning there may be a better one below. Thus the talk of an ocean, although it’s just one candidate. “We do not need a subsurface ocean but require a subsurface reflector,” Simoes told New Scientist. “If a subsurface ocean exists, the solid-liquid interface would be a good reflector.”

Still in question is the possibility of extraneous vibrations within the radio instrument itself, although the team’s testing has so far failed to reveal any evidence of this. If a body of water is there, it’s probably deep, perhaps fifty kilometers down. A vast ocean rich in ammonia is an exciting prospect indeed, but waiting for future Cassini flybys is necessary for confirmation. If an ocean can be found by analyzing Titan’s behavior under the gravitational pull of Saturn, we’ll have yet more reason for astrobiologists to ponder the outer icy moons as abodes of life.

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  • Adam June 13, 2007, 4:39

    Hi Paul

    Dominic Fortes examined the astrobiological potential of this idea a few years ago – Titan’s ocean looked more hospitable than Europa’s in some respects, though that was before the discovery of oxygen-charged ice on Europa. Solid-phase “electrolysis” (well ion bombardment) means Europa’s ocean has a bit of oxygen supplied to it. Titan’s is highly unlikely to have any free oxygen, but ammonia-water might have surprising effects on biochemistry too. But a whole lot of weird inorganic biochemistry has been suggested too – for example, that big blobs of plastic might exist in the ice crust’s base, rising slowly through the “soft” ice like giant polyethylene diapirs.

    Need I say it, but Titan will be a stranger world the more we explore it. Arthur Clarke’s “wax worm” and Stansilaw Lem’s “glass menagerie” might have even stranger analogues in the real world.

  • Administrator June 13, 2007, 16:55

    Adam, what’s the reference on Lem’s ‘glass menagerie’? I’m not familiar with that one, although I’ve read some Lem.

  • Adam June 14, 2007, 7:14

    Hi Paul

    In the first part of Lem’s 1986 novel “Fiasco” the protagonist must cross a dangerous part of Titan in a giant teleoperated robot. The region is volcanic and the cryolava is basically plastic glass, solidified into shapes like the skeletons of once living things, like some huge elephant graveyard, or a giant’s glass menagerie. The weird organic chemistry colours it all with streaks of blood red making it even more eerie, and unstable.

    “Fiasco” is also a story of a SETI contact going horribly wrong because the humans trying to contact the aliens totally misread what’s occurring on the alien home planet. Has a certain humour through out the story though, making it one of my favourite SETI tales.

  • ljk June 14, 2007, 10:25

    Earth’s Future Glimpsed on Titan

    http://bcast1.imaginova.com/t?r=2&ctl=14056:4A48D

    A desert moon suggests how our planet might end up.

    Trickle of Planet Discoveries Becomes a Flood

    http://bcast1.imaginova.com/t?r=2&ctl=14053:4A48D

    Alien worlds, once hidden from knowledge, are now being discovered in droves.

  • ljk August 17, 2007, 0:10

    arXiv:0708.2158

    Date: Thu, 16 Aug 2007 08:58:16 GMT (87kb)

    Title: Clathrate hydrates as a sink of noble gases in Titan’s atmosphere

    Authors: C. Thomas, O. Mousis, V. Ballenegger and S. Picaud

    Categories: astro-ph

    Comments: Astronomy & Astrophysics Letters, in press

    We use a statistical thermodynamic approach to determine
    the composition of clathrate hydrates which may form from a
    multiple compound gas whose composition is similar to that
    of Titan’s atmosphere. Assuming that noble gases are initially
    present in this gas phase, we calculate the ratios of xenon,
    krypton and argon to species trapped in clathrate hydrates.

    We find that these ratios calculated for xenon and krypton
    are several orders of magnitude higher than in the coexisting
    gas at temperature and pressure conditions close to those of
    Titan’s present atmosphere at ground level. Furthermore
    we show that, by contrast, argon is poorly trapped in these
    ices. This trapping mechanism implies that the gas-phase is
    progressively depleted in xenon and krypton when the
    coexisting clathrate hydrates form whereas the initial
    abundance of argon remains almost constant.

    Our results are thus compatible with the deficiency of Titan’s
    atmosphere in xenon and krypton measured by the Huygens
    probe during its descent on January 14, 2005. However, in
    order to interpret the subsolar abundance of primordial Ar
    also revealed by Huygens, other processes that occurred
    either during the formation of Titan or during its evolution
    must be also invoked.

    http://arxiv.org/abs/0708.2158 , 87kb

  • ljk February 8, 2008, 10:54

    Sequestration of ethane in the cryovolcanic subsurface of Titan

    Authors: Olivier Mousis, Bernard Schmitt

    (Submitted on 7 Feb 2008)

    Abstract: Saturn’s largest satellite, Titan, has a thick atmosphere dominated by nitrogen and methane. The dense orange-brown smog hiding the satellite’s surface is produced by photochemical reactions of methane, nitrogen and their dissociation products with solar ultraviolet, which lead primarily to the formation of ethane and heavier hydrocarbons. In the years prior to the exploration of Titan’s surface by the Cassini-Huygens spacecraft, the production and condensation of ethane was expected to have formed a satellite-wide ocean one kilometer in depth, assuming that it was generated over the Solar system’s lifetime. However, Cassini-Huygens observations failed to find any evidence of such an ocean.

    Here we describe the main cause of the ethane deficiency on Titan: cryovolcanic lavas regularly cover its surface, leading to the percolation of the liquid hydrocarbons through this porous material and its accumulation in subsurface layers built up during successive methane outgassing events. The liquid stored in the pores may, combined with the ice layers, form a stable ethane-rich clathrate reservoir, potentially isolated from the surface. Even with a low open porosity of 10% for the subsurface layers, a cryovolcanic icy crust less than 2300 m thick is required to bury all the liquid hydrocarbons generated over the Solar system’s lifetime.

    Comments: accepted for publication in Astrophysical Journal

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.1033v1 [astro-ph]

    Submission history

    From: Olivier Mousis [view email]

    [v1] Thu, 7 Feb 2008 18:16:11 GMT (153kb)

    http://arxiv.org/abs/0802.1033

  • ljk February 14, 2008, 10:22

    Saturn’s orange moon Titan has hundreds of times more
    liquid hydrocarbons than all the known oil and natural gas
    reserves on Earth, according to new Cassini data. The
    hydrocarbons rain from the sky, collecting in vast deposits
    that form lakes and dunes.

    More at:

    http://www.esa.int/esaSC/SEMCSUUHJCF_index_0.html

  • ljk March 20, 2008, 15:33

    CASSINI SPACECRAFT FINDS OCEAN MAY EXIST BENEATH TITAN’S CRUST

    PASADENA, Calif. – NASA’s Cassini spacecraft has discovered evidence
    that points to the existence of an underground ocean of water and
    ammonia on Saturn’s moon Titan. The findings made using radar
    measurements of Titan’s rotation will appear in the March 21 issue of
    the journal Science.

    “With its organic dunes, lakes, channels and mountains, Titan has one
    of the most varied, active and Earth-like surfaces in the solar
    system,” said Ralph Lorenz, lead author of the paper and Cassini
    radar scientist at the Johns Hopkins Applied Physics Laboratory in
    Laurel, Md., “Now we see changes in the way Titan rotates, giving us
    a window into Titan’s interior beneath the surface.”

    Members of the mission’s science team used Cassini’s Synthetic
    Aperture Radar to collect imaging data during 19 separate passes over
    Titan between October 2005 and May 2007. The radar can see through
    Titan’s dense, methane-rich atmospheric haze, detailing
    never-before-seen surface features and establishing their locations
    on the moon’s surface.

    Using data from the radar’s early observations, the scientists and
    radar engineers established the locations of 50 unique landmarks on
    Titan’s surface. They then searched for these same lakes, canyons and
    mountains in the reams of data returned by Cassini in its later
    flybys of Titan. They found prominent surface features had shifted
    from their expected positions by up to 19 miles. A systematic
    displacement of surface features would be difficult to explain unless
    the moon’s icy crust was decoupled from its core by an internal
    ocean, making it easier for the crust to move.

    “We believe that about 62 miles beneath the ice and organic-rich
    surface is an internal ocean of liquid water mixed with ammonia,”
    said Bryan Stiles of NASA’s Jet Propulsion Laboratory (JPL) in,
    Pasadena, Calif. Stiles also is a contributing author to the paper.

    The study of Titan is a major goal of the Cassini-Huygens mission
    because it may preserve, in deep-freeze, many of the chemical
    compounds that preceded life on Earth. Titan is the only moon in the
    solar system that possesses a dense atmosphere. The moon’s atmosphere
    is 1.5 times denser than Earth’s. Titan is the largest of Saturn’s
    moons, bigger than the planet Mercury.

    “The combination of an organic-rich environment and liquid water is
    very appealing to astrobiologists,” Lorenz said. “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.”

    Cassini scientists will not have long to wait before another go at
    Titan. On March 25, just prior to its closest approach at an altitude
    of 620 miles, Cassini will employ its Ion and Neutral Mass
    Spectrometer to examine Titan’s upper atmosphere. Immediately after
    closest approach, the spacecraft’s Visual and Infrared Mapping
    Spectrometer will capture high-resolution images of Titan’s southeast
    quadrant.

    The Cassini-Huygens mission is a cooperative project of NASA, the
    European Space Agency and the Italian Space Agency. The mission is
    managed by JPL, a division of the California Institute of Technology
    in Pasadena. The Cassini orbiter also was designed, developed and
    assembled at JPL.

    For information about Cassini visit: http://www.nasa.gov/cassini/