[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

[tty]

I don't quite agree with your interpretation. While the relative shortage of small craters could to some extent be due to the thick atmosphere and the difficulties of detection it seems to be quite likely that it is also due to many smaller craters having eroded until they are undetectable. After all SAP radar is pretty good at detecting heavily eroded craters here on Earth. Your # 37 is a beautiful example of a (probable) crater that has eroded almost into invisiblity. On Earth (with a vastly higher erosion rate) I would guess that it is from tens to hundreds of million years old, depending on geological context. Where there are craters that have eroded to that point it seems almost certain that others have disappeared completely.

[Juramike]

It is very likely that some craters have been eroded beyond recognition. Here is a graph that shows the distribution of identified craters by erosion state:




How many craters have been eroded beyond “degraded”? There is no easy way to tell. But since the observed distribution for larger craterforms fits a 4.5 Gyr age profile, it seems likely that “not that many” craters (at least for larger craters) have been eroded or buried into obscurity.


[I take "not that many" to be within an an order of magnitude of the observed numbers - enough to still fit within the errors bars of a 4.5 Gyr crater distribution range]

Here is some evidence that craters have been obscured on Titan:


Here is a graph showing the crater distribution according to latitude zone:


It is very striking that most of the identified craters are in the Equatorial Zone, despite that fact that Polar Zone SAR RADAR coverage is pretty complete.

Assuming a uniform distribution of impactors, we would expect more craters in the polar and temperate region. I’ll leave it to a math goo-roo to calculate the surface areas of Polar Zones, Temperate Zones and Equatorial Zones of Titan. But taking the areas as equal (they’re not), we’d expect 30 more craters in the combined Temperate Zones and 30 more craters in the combined Polar Zones. Thus, about 60 extra craters or so have been “disappeared” (buried or eroded) in the non-Equatorial Zones of Titan.

This provides some observational evidence as well that burial (or erosion) is latitude dependant. Craters are more visible at low latitudes. The rates calculated from this data are weighted heavily by Equatorial Zone craters and are probably slower than those calculated for higher latitudes.

I would expect that as RADAR coverage in the Equatorial Zone increases that the number of craters will also increase. I would also expect that the identification of smaller and more degraded craters would especially increase as RADAR seems to be better at picking out the smaller and more subtle structures.

-Mike