[X] My Assistant

[Juramike]

Recently released article on RADAR interpretations of Titan's mountains.

"Mountains of Titan observed by Cassini Radar"

J. Radebaugh, R. Lorenz, R. Kirk, J. Lunine, E.R. Stofan, R. Lopes, S. Wall
Icarus (2007) doi:10.1016/j.icarus.2007.06.020

[Only accessible via Icarus website? I have no clue how to link to a free abstract. Sorry, y'all!]


This is the full paper following the 2006 LPS abstract (which is freely available):

Radebaugh et al LPS 37 (2006) Abstract 1007. “Mountains on Titan Observed by Cassini Radar”. Abstract freely available here.

-Mike

[Juramike]

In the article, Radebaugh et al describes tectonic ridges in the Belet Equatorial Sand Sea as seen from the T8 RADAR swath. The ridges in T8 have a mean height of 420 m. The ridges are also “typically surrounded by radar-bright diffuse blankets of material, often to several tens of kilometers from the mountain base. These are materials that have perhaps been eroded off the mountain and then deposited in a gently sloping mantle that becomes thinner with greater radial distance. The blankets to not appear to have substantial topography or raised edges, so we consider theslopes of the blankets to be 2 degrees or less.”



As seen from the graphic above, the T8 tectonic ridges are spaced sorta regularly about 50 km apart. In the next graphic, the T28 tectonic ridges are spaced very regularly about 60 km apart.




The margins in the T8 tectonic ridges extend approximately 20 km from the ridges. The margins in the T28 tectonic ridges are spaced very nicely and extend about 15 km from the ridge center. The margin is considered to be the border of the RADAR medium dark material (green in post above) with the RADAR medium light material (uncolored in the post above). Like the tectonic ridges, in the T28 swath the margins are regularly spaced.
Assuming the tectonic ridges have similar heights and other characteristics, we would expect a similar mantle of material to have eroded from the ridge. If material was then deposited on this, the mantle should extend out farther. [Mountain erodes, stuff dumps on, valley gets cleared by unknown mechanism]. Since the T28 margins are less than the T8 margins, it seems that the any deposit was not preferentially placed on the slopes (wind loading).

I’ll assume that the pre-deposition margin spacing in T28 was 20 km, in analogy with T8 ridges.



If there was an even coating of material, the margin spacing would be the same after deposition . This is shown in the first graphic above. If there was a preferential loading of material on the slopes, the margin would decrease, as shown in the second graphic. If the valleys were preferentially filled with deposited material, the margins will get buried and tend to creep closer to the ridge. Assuming ridge margins the same as in T8, this is exactly what we see.




Assuming the angle of repose for the eroded material and the deposited material is the same (2 degrees), trigonometry (uh-oh, math) can estimate the depth of the deposited materials. The key is that after deposition the margins have pulled back 5 km. (This result is independent of the actual ridge height).

For a 5 km pullback and 2 degree slope, we get an estimate of 350 m of deposited organics in the valley. The thickness of the organic deposit blanket on the slope is approximately 175 m.

The numbers are pretty close (actually spot-on) for the estimated 200 m of organics on the surface of Titan.

-Mike