Last week there was a big splash (pun intended) made over some images taken by the Cassini spacecraft of Titan, Saturn’s largest moon. The images suggest that there is indeed liquid (liquid does not mean liquid water) on the surface of Titan. NASA has an excellent summary of the interpretation of the images online here, but please keep in mind that water has a number of unique properties. One of them is that water freezes from the top down, because frozen water floats in the liquid phase of water. Thus, here on Earth you can have frozen ponds with fish still swimming beneath. And on Europa you may find liquid water beneath the frozen solid surface top. Liquid ethane and methane don’t act in the same manner.
In a paper published in Nature, available online now here, an international team of astronomers, utilizing the data from the Cassini spacecraft between 2004 and 2007, announce their conclusions about the nature of the clouds of Titan, Saturn’s largest and most interesting moon. These astronomers conclude that the clouds on Titan are the result of condensation of methane and ethane. Here on Earth, our clouds result from the condensation of water vapor. The clouds on Titan are driven around the moon by global atmospheric circulation. These astronomers have developed a global circulation model for Titan, similar to the global circulation models developed for Earth.