June 15, 2012 | David F. Coppedge

Titan Lake News: Throwing Caution to the Wind

Planetary scientists this week cautiously suggested the possible presence of an equatorial lake on Saturn’s moon Titan.  You wouldn’t know that from the headlines.

In Nature this week (486, 14 June 2012, pp. 237–239, doi:10.1038/nature11165) Griffith et al., announced the “Possible tropical lakes on Titan from observations of dark terrain” (italics added).  “Possible” is the operative word; the discovery depends on interpretation of spectral signatures obtained by the Cassini orbiter flying by the giant moon of Saturn.  Most lakes have been found in polar regions.  This would be the first semi-permanent body of liquid methane found in “tropical” (e.g., equatorial, not “warm,” since Titan is -290 degrees Fahrenheit).  Most of Titan’s mid-latitudes are covered with sand dunes made of icy grains coated with hydrocarbons.

In short, if the scientists interpret the color bands correctly, within the margin of error, a dark oval patch about the size of Great Salt Lake might be a lake of liquid methane.  But other options are possible from the data – for instance, it could be a mudflat, a rain puddle, or a patch of dry hydrocarbon-coated sand.  Cautiously, the scientists could only state that the data are consistent with it being a liquid methane lake as the best explanation – but even that hypothesis raises new problems, because lakes in tropical regions on Titan are thought to be unstable due to prevailing winds that pile up grains into giant dunes.  So if it is a lake, the scientists surmised that the methane would have to come from below, like groundwater in marshes or oases on Earth, instead of from the atmosphere.  But they can’t tell (if it is a lake) how deep it is, or how long it has been there, other than to note it has been observed since 2004 (eight years).

A lake – an oasis – a marsh – tropics – those suggestive words were all the news media needed to go nuts with visions of certainty.  Here’s how it got reported:

  • Live Science: “Giant Tropical Lake Found on Saturn Moon Titan” (Charles Q. Choi).
  • PhysOrg: “Lake detected near equator of Saturn’s moon Titan.”
  • New Scientist: “Titan’s tropical lake hints at hydrocarbon wells.”
  • National Geographic: “Saturn Moon Has Tropical “Great Salt Lake,” Methane Marshes” (Andrew Fazekas).  This one even had artwork.
  • CNN: “A moon of Saturn may have ‘tropical’ lakes.”
  • Nature News: “Tropical lakes on Saturn moon could expand options for life” (Maggie McKee)

All but Live Science tied the report in with “building blocks of life,” but what they didn’t report is that even if this is a methane lake, it is a paltry pittance of one, compared to what scientists expected in the 1990s to find: a global ocean of liquid ethane and methane several kilometers deep.  And only Live Science went into any detail about the problems with the lake hypothesis.

The problem gets even worse.  Nature‘s final paragraph pointed out that scientists are puzzled how any methane could still remain after the presumed 4.5 billion years of Titan’s existence, given that methane is destroyed rapidly:

General circulation models demonstrate that long-lasting tropical lakes several metres deep must be replenished, depending on the ethane content, within a ten-thousand-year timescale. Taken together, tropical lakes and studies of Titan’s lakes suggest that, currently, subterranean liquid supplies methane to Titan’s surface and atmosphere. A supply of on average 6 × 10−4 kg m−2 yr−1 is needed to explain the composition of Titan’s atmosphere, because methane, the progenitor of the moon’s organic species, is destroyed in 10–100 million years through solar ultraviolet photolysis. More observations are needed to determine whether this 4.5-billion-year-old moon is undergoing a specific recent flourish of geological activity, because it is freezing and its orbit decaying.

What that last sentence implies is that scientists are being forced by the evidence to consider special conditions – “a specific recent flourish of geological activity” – to account for the presence of methane on Titan at all.  At most, the methane on this bizarre moon would all be gone in 100 million years, one fortieth the assumed age of Titan, unless it were constantly being supplied from somewhere.  Underground reservoirs might provide a convenient (unobservable) hiding place for the stockpile, but that solution arouses geological puzzles about how deep the methane would need to be, how it would form, and how it could erupt onto the surface.  Added to that are indications that since Titan is freezing and its orbit is decaying, there should be less geological activity, not more.

Secular scientists are generally reluctant to invoke any “specific recent flourish” of activity occurring right at the time humans are around to observe it.  Why now, and not throughout Titan’s lifetime?  The contrast between scientific caution in the paper and media exuberance provides a case study in how science is communicated to the public.

If reporters are this reckless with a non-biological story like methane on Titan, how careful do you think they are reporting Darwin fables?

Enjoy Space.com‘s Titan picture show with its real, observable data from the historic Huygens landing (January 14, 2005), a welcome escape from hyped-up stories.


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