[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

[titanicrivers]

"Fluvial channels on Titan: Initial Cassini RADAR observations"
The Cassini Radar Team; Lorenz, Ralph D.; Lopes, Rosaly M.; Paganelli, Flora; Lunine, Jonathan I.; Kirk, Randolph L.; Mitchell, Karl L.; Soderblom, Lawrence A.; Stofan, Ellen R.; Ori, Gian; Myers, Melissa; Miyamoto, Hideyaki; Radebaugh, Jani; Stiles, Bryan; Wall, Stephen D.; Wood, C. A

(Not having the actual paper to read what follows may be a bit off base!). Interesting abstract but I wonder if the"1% prominent channel area" figure significantly underestimates the amount of fluvial erosion happening on Titan. Of course not all the moon has been imaged and some channels that we know exist (from Huygens) seem not to be resolved from Cassini's height above Titan on the flybys. A good example is the Huygen’s landing site where we know channels are eroding highlands and lowlands, yet Cassini imaging of the landing site (A: PIA03569) doesn't give much of a hint (at least to my eyes) of any fluvial channels, say like appear at 10 degrees south latitude and 292 degrees west longitude, an area showing a probable fluvial erosion at a highland-lowland interface. (see PIA03568 in b below)

To emphasize the point in C) are Huygen's DISR images of its landing site and even at the resolution shown (which seems greater than the radar images of Cassini) the highland channels we know to be present are not prominent.

Even if there is some under-estimating, do the sand seas have to come from eroded highlands? Can we view them as dried up ocean/sea bottoms from a "wetter" Titan of the past that are now being blown around be Titanian winds?(apologies for the simplification). Or if the sand-seas are from atmospheric deposition are there other mechanisms besides rainfall and fluvial erosion keeping the higher landforms relatively free of deposits?
A) b C)

[rlorenz]

"Fluvial channels on Titan: Initial Cassini RADAR observations"

(Not having the actual paper to read what follows may be a bit off base!). Interesting abstract but I wonder if the"1% prominent channel area" figure significantly underestimates the amount of fluvial erosion happening on Titan.

(Sorry - been a bit off-line for the last 2 months - travel to Pasadena, Rome, Korea, Atlanta, Paris, Corpus Christi,
Montreal, ESTEC, Crater Lake and now London....)

for the paper, see http://www.lpl.arizona.edu/~rlorenz/fluvial.pdf

Yes, this 1% is a very preliminary number. Obviously Huygens shows that there are channels present
at scales too small to be resolved by the Cassini radar. Further, there are some areas of Titan (which hadnt
been seen, e.g. T39 in the south, when this paper was written) which show a lot more eroded volume.

So, like many Titan results, this number - and possibly even the conclusion - may need to be revised.

[Juramike]

Taking figure 7 in Lorenz et al, 2008 as a rough guide, I made my own interpretation of the channel network observed in W Xanadu:
(I traced curvilinear lines that showed neighboring bright and darker pixel sets - it came out pretty close to that described in the text).



There seems to be an overlying trellis pattern. There are parallel major channels spaced 200 km along a NNE-SSW (major?) and also a WNW-SSE (minor?) direction. This spacing is consistent with the "dark lanes" indicating possible broad graben or undulations (Equatorial Sand Seas thread, post 332)

This spacing and orientation is also similar to the orientation and spacing of the roughly N-S undulations previously indicated on Titan.

The side channels lie parallel to the EW tectonic ridges and have a much tighter spacing (50 km).

This seems pretty similar to the drainage pattern observed in the Appalachian mountains.

I'll speculate that the overall drainage pattern was set up in the roughly NS undulation, and that the tectonic ridges rose later.

If I understand the superposition right, we get:
1. Undulations set up
2. Drainages set up
3. Tectonic ridges rise
4. Smaller side drainages set up.

If this pattern repeats across a broad region of Titan, we would predict that the major drainages will follow the gradient along roughly NS parallel axes with regular spacing. The EW ridges will constrain the side channels into tighter valleys.

(Another interesting thing I noticed when doing this exercise is that there are several places where a major channel makes a complete circle. One of these is visible in the NE corner of the graphic. There is another near center.)

-Mike

[Jason W Barnes]

On this erosional topic, there's a new VIMS paper by Ralf Jaumann that's recently been published online in _Icarus_. It won't be out in the dead-tree version of the journal for some months, I suspect, but in the meantime I thought that you all might be interested in getting a leg up.

Someday I will feel comfortable enough doing something more than just posting papers as they come out. Maybe . . . but not today

- VIMS Jason