Saturn’s moon Titan is only the fourth planetary body we have
explored that has both a solid surface and a significant atmosphere. I
will talk about new discoveries that have come from the Visual and
Infrared Mapping Spectrometer instrument aboard the Cassini spacecraft
regarding the nature of Titan’s surface/atmosphere interactions.
Photolysis of methane in the moon’s atmosphere drives chemical reactions
that lead to ethane and other higher-order hydrocarbons that form smog
layers. However, when we peered through that smog we did not see the
predicted 300-meter deep ocean of liquid ethane that would result from 4
billion years’ worth of methane photolysis. Instead we see relatively
small seas of methane/ethane clustered near both the north and south
poles. At the equator lies a vast desert covered in the solar system’s
largest field of sand dunes. The dunes’ spectral signature indicates that
the sand is made of solid hydrocarbons, which account for a portion of the
missing ethane. Confronted with only enough methane to last for 10
million years, and faced with extensive networks of gullies and channels
carved over a much longer period, it seems that Titan’s methane must be
being replenished. I will show our best candidates for places where
eruptions may have taken place that could help resupply the atmosphere’s
methane, and discuss the implications that these have for Titan’s
 evolution.