26 July, 2006

Lakes on Titan

Finally, what we've all been waiting for: possible evidence of liquid hydrocarbons on the surface of Titan:

According to the JPL press release linked to above, these images were taken by the Cassini radar in synthetic aperture mode, which means that the dark and light areas on the image correspond to smoother and rougher areas on the surface, respectively. The dark patches on these images are therefore quite smooth, as you'd expect if they represented liquid; their irregular shape is also quite suggestive. Each of these radar images covers and area of about 450 x 150 km, so if they are lakes they're fairly sizeable ones.

These images are from the north polar regions of Titan, which makes sense; it's colder there, so any methane and ethane would evaporate into the atmosphere less quickly. However, it's not completely clear to me why the scientists are so sure that these features represent currently filled lakes rather than dried up ones, as is the case on most of the surface we've studied so far. Perhaps the radar data indicate a particularly high value of smoothness for these features. Insider gossip from Emily Lakdawalla at the Planetary Society Blog indicates that this might be the case:

Cassini RADAR team member Rosaly Lopes [said that t]he lake-like features are "circular or kidney-shaped and very radar-dark -- the darkest things we have seen. Morphologically, they look much like lakes on Earth. There are drainage features around the sides of lakes."

The rest of the article has a very interesting discussion about the possible origin of the topographic lows that these features seem to represent. There's some evidence that they are collapse structures, so may represent cryovolcanic calderas. The evidence for that is presently fairly equivocal, but if that is the case then these would be the Titanian equivalent of lava lakes. How cool is that?

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