New Iapetian image series Options

[TritonAntares]

Hi,
CASSINI has transmitted 184 pics (!) over the last days.
Here five takeouts, 3-4x enlargement:



Date: 2009-09-06
Distance: 2.228.548 km
Filters: CL1 and CL2


Date: 2009-09-08
Distance: 3.215.284 km
Filters: P120 and GRN


Date: 2009-09-08
Distance: 3.216.610 km
Filters: P60 and GRN


Date: 2009-09-09
Distance: 3.390.271km
Filters: P60 and GRN


Date: 2009-09-09
Distance: 3.427.313 km
Filters: P120 and GRN

Maybe somebody is able to combine some of those images to show more details.

Bye.

[tasp]

I suspect a thermo-reactive gas is introduced into the Iapetan environment at a fixed point in its' orbit about Saturn. Most likely when Iapetus traverses the Saturnian magnetotail.

The gas persists in the vicinity of Iapetus, and in equatorial to the midlatitudes the Iapetan surface temperatures are sufficient for the gas to 'tholinize' and coat the surface. The gas is used up (or dissipates into the void) in less than the ~80 days it takes for Iapetus to return to the place in it's orbit where the gas is replenished, thus, we do not see the darkening extending further around in longitude than we do.

That there is some 'ponding' of the gas in low areas seems apparent, there is some darkening outside of the main areal extent of Cassini Regio in the lower latitudes.

Additionally, the more directly perpendicularly sunward facing segments of crater bowls north and south of Cassini Regio also show the darkening, as expected, the local heating conditions being sufficient for the chemical staining reaction to occur.


The gas also appears to interact with Hyperion. Quantities of it appear to pond in the craters, and when the chaotic rotation of Hyperion causes the sun to shine perpendicularly into a given crater, the crater bowl reflects enough solar radiation onto the crater floor to make a local warm spot. The gas reacts, and we get dark crater bottoms all over Hyperion.

The same basic mechanism, a thermo-reactive gas being introduce into the Hyperionian and Iapetan environments, explains the dark areas of each moon.