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 user 2007-01-08 at 1:41:00 pm Views: 84
  • #16907

    ‘Proof’ of methane lakes on Titan
    Cassini probe has spotted what scientists say is unequivocal evidence
    of lakes of liquid methane on Titan, Saturn’s largest moon.Radar images
    reveal dark, smooth patches that range in size from three to 70km
    across (two to 44 miles).The team says the features, which were spied
    in the moon’s far north, look like crater or caldera lakes on Earth.The
    researchers tell the journal Nature that everything about the patches
    points to them being pools of liquid.”They look very similar to lakes
    on Earth,” explained Dr Ellen Stofan, a Cassini radar team member from
    Proxemy Research in Washington DC, US.”They have channels feeding into
    them just like you have rivers feeding into lakes on the Earth. Their
    shapes, their shore-lines, all of those geologic aspects are actually
    very familiar.”

    Northern strip
    atmospheric chemistry on Titan is dominated by nitrogen and
    carbon-based compounds.And with temperatures on the Saturnian satellite
    rarely venturing above -179C (-290F), it has long been hypothesised
    that abundant volumes of methane should pool on the surface into lakes,
    and even large seas.But evidence for current bodies of liquid material
    on the surface has until now been sparse and equivocal.Cassini must use
    radar to pierce the photochemical haze that obscures Titan’s surface
    from its optical camera system.The latest data was obtained last July,
    when the probe made its most northern radar pass of Titan to date.The
    spacecraft imaged a narrow strip about 250km wide and over 1,000km
    long. It was found to contain more than 75 lakes.Everything scientists
    know about the atmospheric chemistry on Titan suggests the liquid in
    the lakes should be predominantly methane, with some ethane also mixed
    in.Some of the liquid would be expected to rain out of the sky, some
    could have welled up from below the surface.

    Methane cycle
    methane-ethane would become transparent, the way water is on Earth; it
    would be behaving like water, the lakes could have small waves on the
    surfaces,” speculated Dr Stofan.”So if it was possible for you to stand
    on Titan and look at the lakes, you wouldn’t really know it’s this
    weird chemistry.”On Earth, the cycling of water between the atmosphere,
    the land and oceans is known as the hydrological cycle. Titan would
    appear to be the only other place in the Solar System to have a
    similar, active fluid cycle. Scientists have already dubbed it the
    “methane-ologic cycle”.Last month, it was announced that the radar
    instrument on Cassini had found an enormous mountain range on Titan.The
    range lies south of the equator and is about 150km long (93 miles),
    30km (19 miles) wide and about 1.5km (nearly a mile) high.Scientists
    told the American Geophysical Union (AGU) Fall Meeting that the range
    was probably as hard as rock, but made of icy materials.The mountains
    appeared in the radar images to be coated with layers of material that
    researchers thought could be methane “snow”.The Cassini-Huygens mission
    is a cooperative project of the US space agency (Nasa), the European
    Space Agency (Esa) and the Italian Space Agency (Asi).