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ftp://ftp.lpi.usra.edu/pub/outgoing/lpsc2009/full254.pdf

A GLOBAL SUB-SURFACE ALKANIFER SYSTEM ON TITAN?



NUMBERS, DISTRIBUTION AND MORPHOLOGIES OF IMPACT CRATERS ON TITAN

Introduction: Titan has very few impact craters [1]. With more than 30% of the surface now imaged by Cassini Radar through data take T44 there are only seven certain impact structures known. Fifty additional possible craters also have been identified. The certain craters have two distinct morphologies, and the probable craters appear to mostly be more degraded version of these two types. The craters do not appear to be randomly distributed.

Crater Distribution: The distribution of Cassini Radar swaths is uneven, with little coverage south of 30°S, and more over the leading hemisphere (0-180°) than for the trailing. Presently, cartographic mapping is complete only through the T39 data take, which includes 49 craters. Based on those craters and the actual areal cover of data takes up through T39 we make the
following observations. Craters are found in proportion to the areas of coverage in equal area latitude bins, except there is a 17% deficiency between 42°N and 90°N. There is a 14% excess of craters between 42°N and 19.5°N. Again, these are deviations in the expected distribution of craters of all diameters based upon the actual areas of Radar coverage.
The paucity of impact craters in the northern polar region may be due to the abundance of lakes and seas which may submerge craters; indeed, a 10 km diameter crater is revealed by its circular rim rising above a lake surface. A large area of the surface north of 60° is also composed of circular and irregular depressions that may be of karstic origin [3]. In any case, few other types of landforms exist in these northern areas, implying that these surfaces may be relatively young.
Longitudinally, there is an excess of 20% of craters on the leading hemisphere compared to the trailing.
Although Titan has few craters, there are many areas with Radar coverage that lack any craters so this may be evidence for a significant leading-trailing hemispheric difference. Further statistical testing is required at the end of the mission when presumeably more craters will have been discovered and we will have detemined the areal coverage of all data takes.