[X] My Assistant

[Juramike]

I made a list of 42 putative impact craters on Titan to try to estimate erosion rates of craterform features.

This list has the “typical” craterform features all characterized by an ISS or RADAR circular bright rim with either a RADAR or ISS dark central portion or a RADAR or ISS bright inner portion (dome or peak) and a darker inner circle. Several of these have been previously reported in the literature. Due to the extensive rim erosion, some of these are broken or incomplete circles.

These (broken)circular features have been classified into five groups depending on the level of erosion evident (from most pristine in appearance to the most used and abused):

- Fresh craters - with little to no erosion evident on the crater rim or debris apron.

- Recent craters – with some evidence of fluvial erosion on the rim, some crenellation being present.

- Eroded craters – with a single breach of the rim or with severe erosion of the rim wall.

- Multiple breached craters – with several complete breaks in the rim structure.

- Degraded craters – with collapse or removal of large sections of the rim structure with extensive invasion of new materials (e.g. dune sands).

Here is a map showing the approximate locations of these features on Titan:



-Mike

[volcanopele]

The other issue is that a number of the crateriforms that Mike has identified, while intriguing, might not be impact features. For example, I don't believe that the "Sliced carrot" feature is caused by an impact feature. Impact structures of that size, if you look at Callisto and Ganymede, are typically multi-ring structures. The sliced carrot feature appears to only be a single, partial arc. I don't think we can rule out a tectonic origin with that feature.

[Juramike]

The other issue is that a number of the crateriforms that Mike has identified, while intriguing, might not be impact features. For example, I don't believe that the "Sliced carrot" feature is caused by an impact feature. Impact structures of that size, if you look at Callisto and Ganymede, are typically multi-ring structures. The sliced carrot feature appears to only be a single, partial arc. I don't think we can rule out a tectonic origin with that feature.

As structures become more degraded, they are much more difficult to positively identify as impact craters.

I have tried to pair up the images so that similar shapes and erosion levels are in each graphic. For example, the "Sliced Carrot" (entry 32) looks similar to a craterform feature in S Senkyo basin (entry 31). [In retrospect, these should have paired up in the same graphic, as they are done below:]




For both features, I would agree that tectonics has played a very important part in the evolution of the structure. (Either impact-->tectonic modification-->erosion or tectonic modification-->impact-->erosion)


Looking at all the images listed in this thread, it seems that there is a diverse variety of crater shapes. Final crater shape should be function of impactor energy, crustal structure, and viscosity of target material. A study of impacts into slurries (Bingham materials) shows that even small changes in viscosity (or impact energy) can have a dramatic effect on crater shape, particularly on spacing and appearance of secondary ring structures.

I strongly suspect that the crustal structure and viscosity of target material is not uniform around Titan. The different shapes of lakes (fractal w/rivers vs. pothole/sinkholes) in the two regions of the north polar area demonstrate that at least the near surface geology varies regionally. So it would seem to reason that the shapes of craters resulting from a similar impactor energy may also vary regionally.

-Mike