[X] My Assistant

[Decepticon]

Here's a nice look at Rhea. http://saturn1.jpl.nasa.gov/multimedia/ima...9/N00030797.jpg


Tethys @
http://saturn1.jpl.nasa.gov/multimedia/ima...9/N00030798.jpg

[volcanopele]

a paper by Jeff Moore et al. in Icarus (I can send it to any who wish to have a copy), suggested that fractures like Pu Chou Chasma (the upper right most of dvandorn's outlines) are radial to a 250-km wide crater near 25S, 155W, west of the ray crater in DEChengst'a second Rhea mosaic.

[dvandorn]

a paper by Jeff Moore et al. in Icarus (I can send it to any who wish to have a copy), suggested that fractures like Pu Chou Chasma (the upper right most of dvandorn's outlines) are radial to a 250-km wide crater near 25S, 155W, west of the ray crater in DEChengst'a second Rhea mosaic.

I have a hard time believing the crater chains are simply lines of secondaries. The dynamics are all wrong.

I assume Moore et. al. are suggesting these crater chains / chasma are basically cracks caused by a large impact? Some of the chains are indistinct enough that I could believe it, but the younger ones (especially the one in upper left of the image being discussed) are obviously chains of circular depressions. And while diatremes could form a series of circular depressions along a fault line, how do you get diatremes without volcanic activity? I don't see any other evidence of cryovolcanism on Rhea (unlike what we see on Enceladus, for example).

Remember, a lot of people were absolutely convinced that the Davy crater chain on the Moon *must be* an endogenically-controlled chain of diatremes, but the data indicate that they'r really just a chain of impact craters. I think Occam's razor suggests these chains on Rhea are also chains of primary impact craters.

Both of my main concepts for how Rhea could develop such crater chains as direct primary impacts -- streams of outflung ring material and/or tidally shattered fragments -- can account for such chains seeming to lie radially away from a central larger impact. All you have to do is postulate a stream of roughly similar-sized fragments with one significantly larger fragment embedded within it.

Besides, it really looks to me like many of these crater chains are closer to parallel than being arrayed radially to a given point -- though until we get better global coverage, that's harder to pin down.

-the other Doug