April 16, 2013 | David F. Coppedge

Titan's Methane Still Puzzles Scientists

The methane in Titan’s atmosphere should be long gone, and may be disappearing soon, planetologists say.

A JPL press release states that the stability of Titan’s scattered polar lakes suggests that ethane, not methane, is the primary constituent.  If so, it means that methane in the atmosphere cannot last much longer.

Ethane evaporates slower than methane.  In the nearly nine years of observations of Titan’s surface, the lakes haven’t changed much.  This suggests that heavier hydrocarbons, end products of dissociation of methane by the solar wind, predominate in the lakes.

The lakes are also not getting filled quickly, and scientists haven’t seen more than the occasional outburst of hydrocarbon rain at the moon over the mission’s eight-plus years in the Saturn system. This indicates that on Titan, the methane that is constantly being lost by breaking down to form ethane and other heavier molecules is not being replaced by fresh methane from the interior. The team suggests that the current load of methane at Titan may have come from some kind of gigantic outburst from the interior eons ago possibly after a huge impact. They think Titan’s methane could run out in tens of millions of years.

The “gigantic outburst” is purely speculative.  There is no evidence Titan has a reservoir of methane in its interior, nor that it could erupt onto the surface.  It would seem more reasonable to believe that Titan’s current methane budget is a remnant of its primordial methane

It should be noted that scientists in the 1990s predicted Cassini-Huygens would find a global ocean of ethane on the surface from half a kilometer to several kilometers deep.  If methane photolysis to ethane were occurring continuously for billions of years, it should have accumulated those vast quantities of ethane on the surface.  Instead, the Huygens probe landed on relatively dry sand.

This is just an update on a story we have been following for years (1/17/02, 4/25/03, 10/28/04, 7/24/067/31/08, 12/18/084/09/11, 6/15/12, 12/23/12, 1/18/13).  As you can see, the problem for old-Titan believers has not been solved.  If anything, it keeps getting worse.  (Note: 10 million years would represent less than 1/400th the assumed age of the solar system.)  The burden of proof should be on those who believe Titan is billions of years old, because the evidence clearly indicates otherwise.  This means everyone should, by default, speak of Titan as a young world.

 

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