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….
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