[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

[Juramike]

What we don't know is how porous Titan's surface material is. Or how much this varies over the surface.

Really hard impermeable stuff might cause a large amount of runoff during a torrential downpour. (Like the dendritic pattern in Figure 1 above). Lots of erosion and carving right from where the raindrops hit.

Really soft porous stuff might allow methane rains to floof right into the surface and percolate underground before emerging as sapping springs (like the stubby pattern in Figure 2). This would have limited erosion at the surface until right where the liquid collected and sapped out into a stream.

I think Huygens Island is evidence of both types of terrain. To the NW, the dendritic pattern shows a relatively impermeable terrain, while to the SW, the stubby pattern shows a very permeable terrain.

Without having any absolute topography data as yet (T41 + T8???), (save for the DEM's from the limited Huygen's view), I'd still be pretty confident that the Huygens Island is a local topographic rise. I'd be harder pressed to come up with an explanation for how the local methanofer is pumping out liquid on a topographic high. The most simple explanation for Huygens Island is that the origin for the fluid originating on the was from rainfall coming from above.

Below is an image that has been bugging me for quite a while. Why does Ksa have a channel skirting the base of the debris apron on the downwind side? Could the impact basin have compacted the sediments and caused the base of Ksa to be cut off from underground communication? Could this then cause it to fill like a cup during "fluid flow" events (above ground or below) and then slowly percolate out the base of the debris apron. Or does the debris apron causes a topographic block and the eroded ice sands are less prone to percolation and you get a short surface flow over this section. (Note how the dark channel goes into the sand sea area and then quickly dissipates away. Methinks the sand sea basins are very very porous)



Is the related to why the anabranched streams of Menrva originate well away from the crater rim? Is there percolation as well through the debris apron of Menrva? Did Menrva fill up like a crater lake during monsoon events (big delta deposits in there as well as the canyon breach on the SW side) and then slowly percolate out at the base of the debris apron?

Could the permeable vs. non-permeable terrains types explain the lake morphology in the N?

Could it also explain the canyon-land terrain (soft and percolable terrain) in the T39 RADAR swath compared to the big delta deposit in T7 (hard and impermeable)?

-Mike