[X] My Assistant

[RPascal]

The images of Hyperion are fascinating, and its appearance with the many dark crater bottoms and the very steep crater walls seems to be unique, never seen on any other Solar System body before (?). For this reason I wanted to start a special topic solely about Hyperion and the origin of its appearance here.
(By the way: phantastic mosaics and color images, Jason!)

In most discussions here I have read the idea, that the dark crater bottoms is material that slides down the steep crater walls after the volatile icy component has evaporated or sublimated away. But looking at the many images I could not find a single (small or large) crater in the dark material that would expose bright material beneath. Shouldn't we expect this? If the dark component would indeed be a more or less thin layer deposited on the crater bottoms one should find many small craters were this thin layer was blasted away by the impact.
Because of this, my impression is that the dark stuff is the material from inside Hyperion, exposed by impacts, and the bright material is the crust.

[alan]

I suspect the perceived cone shape of the craters is due to the landslides visible in many of them. The landslides have buried the dark material in the outer part of the crater so it is only visible near the center or more often just on one side of the crater. The contrast makes the dark areas appear deeper than it actually is. Look at some of the high resolution images, the dark areas don't appear much lower than the surrounding bright areas in them.

[RNeuhaus]

I suspect the perceived cone shape of the craters is due to the landslides visible in many of them. The landslides have buried the dark material in the outer part of the crater so it is only visible near the center or more often just on one side of the crater. The contrast makes the dark areas appear deeper than it actually is. Look at some of the high resolution images, the dark areas don't appear much lower than the surrounding bright areas in them.

It is strange that there is landslides on the world where the temperature never rises above than 0 centigrades...I don't think that Hyperion might have landslides since the ice is very hard and firm on their surfaces.

Rodolfo

[JRehling]

[...]

[tasp]

I will go out on limb for this;

The dark stuff on Iapetus, is exactly the same dark stuff in the crater bottoms of Hyperion.

?

Yep. Same stuff.

How......

Major impacts on Titan that exceed Edward Tellers criteria for blasting atmospheric materials into space (from the old H-bomb days) send methane and nitrogen to Hyperion and Iapetus via Saturn's magnetotail. As we have seen on Enceladus, even low grav objects can have some atmospheric retention capabilities. The gases persist in the deep holes of Hyperion, and are polymerized by solar radiation. In the case of Hyperion, the steep crater walls make a hot spot at the crater bottom whenever the sun is over head. Due to the chaotic rotation, the sun is eventually overhead everywhere on Hyperion.

On Iapetus, the long orbit period around Saturn implies a 'day' 40 days long. After Iapetus transits through the magnetotail of Saturn, the leading hemisphere is turning sunward and the photo- or thermo- chemical reaction processes the methane and nitrogen into dark brown goo. Same stuff in Titans atmosphere, aerosolized is orange, puddled, its dark brown. The spot is symetrical north and south due to the symetrical insolation of the surface. The trailing hemisphere doesn't develop the dark coating because the methane and nitrogen are lost to the void or used up in 40 days and when that side of Iapetus is exposed to the sun, no gas, no darkening.

[tasp]

Major impacts on Titan that exceed Edward Tellers criteria for blasting atmospheric materials into space (from the old H-bomb days) send methane and nitrogen to Hyperion and Iapetus via Saturn's magnetotail. As we have seen on Enceladus, even low grav objects can have some atmospheric retention capabilities. The gases persist in the deep holes of Hyperion, and are polymerized by solar radiation. In the case of Hyperion, the steep crater walls make a hot spot at the crater bottom whenever the sun is over head. Due to the chaotic rotation, the sun is eventually overhead everywhere on Hyperion.

Was poking around at the Cassini website looking at pictures of Hyperion.

Noticed something about picture N00040336.jpg (there are some similar frames of this picture available too)

The photo shows a typical Hyperion crater, except that it is on the edge of a depression and a good chunk of the crater wall is 'open' to the depression.

While the crater has a small dark shadow at its bottom due to angle of illumination, it does not appear to have the black stuff virtually all the other craters do.

Why?

The crater, open on one side, can not trap a pool of gas to be polymerized (or whatever, maybe thermo-catalyzed) at the bottom like all the other intact craters do. The gas runs (wafts? whatever word you wish to describe it exiting the crater) out and 'pools' in other craters downslope. The darkening effect does not occur here because even though there is enough crater left to focus the sun at the bottom, there is no material for the UV or heat to process.

I am doing a great job of convincing me I know what is going on on Hyperion and Iapetus, ( ), but I don't know about the rest of you . . . .