Why Titan’s Lakes Have Been Smooth so Far – and May Be about to Get Rough

Introduction: Observations of Titan’s polar lakes and seas to date suggest that their surfaces have been qualitatively smooth. Yet it might be expected from the thick atmosphere and low gravity that lakes on Titan would have wave-roughened surfaces. Here we show results (discussed in more detail in a submitted paper [1]) that there are two possible explanations. First, that some or all of Titan’s lakes are viscous and thus never have waves. A second possibility is that observations to date in both hemispheres have been during seasons when winds may have been relatively weak. In contrast, upcoming observations of the north (including SAR imagery of Ligeia Mare on T64 in December 2009, to be reported at this meeting) will instead be during the windier summer, and thus northern lakes may display much brighter, windroughened surfaces than have been seen so far. Windroughening is readily apparent in radar images of terrestrial lakes as a modest brightness enhancement, identifiable either morphologically (it is suppressed in the sheltered lee of topographic obstacles such as islands) and by comparison with previous imagery. Figure 1 shows a radar image with obvious windroughening on Lake Janisjarvi, an impact crater lake in Karelia, Russia that illustrates what might be soon visible on Titan.