On a ring origin of the equatorial ridge of Iapetus Options

[Guest_AlexBlackwell_*]

Wing Ip just had an interesting Iapetus-related paper published in GRL.

[jsheff]

Would this process also explain the albedo assymetry on Iapetus?

[tasp]

Would this process also explain the albedo assymetry on Iapetus?

The dark staining on portions of Iapetus might be attributed to gaseous materials containing perhaps hydrogen, nitrogen, and carbon being introduced into the Iapetan vicinity at a fixed segment of it's orbit about Saturn.

Let's assume for the moment, that atmospheric leakage from Titan only encounters Iapetus when Iapetus encounters the Saturnian magnetotail as it traverses the far side of Saturn.

What would we see?

We might expect a very tenuous cloud of N2 and CH4 to persist around Iapetus for a while before it dissipates into the void.

What does the Titanian atmospheric constituents do when exposed to solar radiation of sufficient intensity?

They apparently tholinize.

Where do the necessary conditions for this occur on Iapetus?

The leading hemisphere, and within 40 to 50 degrees of the equator. Also, north and south of of that zone, crater bowls with appropriate slopes on their poleward sides will also collect and intensify the distant suns flux, causing dark spots outside the main 'blotch'.


Is this what we see?


I will suggest we do.

Aparently in the roughly 40 days till Iapetus passes between the sun and Saturn, the gas dissipates completely, or is tholinized completely (actually both processes probably occur together) so as Iapetus continues on around Saturn back around to the far side, that hemisphere now sunward doesn't darken.



Would we expect this wafting gas in the Saturnian system to evince itself anywhere else?

Perhaps the dark crater bottoms of Hyperion are dark for the same reason as Cassini Regio? The gas ponds in the craters, the distant sun is roughly focused by the crater walls and makes a warm enough spot for the gas to tholinize.

Why do all the crater bottoms of Hyperion seem to be dark? Hyperions' chaotic rotation eventually aims all its' craters sunward at one time or another, so they all darken.

BTW, there is one largish crater, seen clearly by Cassini, with a broken rim. It did not form much of a dark spot at all, perhaps because that crater cannot pond gas to tholinize as it runs out downslope . . . .