Rev 49 - Aug 9-Sep 14, 2007 - Iapetus I1, The only close flyby of Iapetus Options

[David]

Uhhh... whaddaya call *this*???

I'd call 'em channels or fissures of some sort. The surrounding landscape seems to have been compressed or folded. Perhaps Iapetus wasn't always dead as a doornail! And the odd thing is that it isn't peppered over with craters. Mystery upon mystery...

And on second thought, it looks to me like the fissures are going through craters that were already there before the fissures formed. Unless there's a crater-producing process that also creates fissures?

[tasp]

(I got caught on this earlier today)

Invert the picture.

The 'cracks' are actually the edges of a landslide.

The 'bumps' are craters.

These pictures are so, for lack of a better word, alien, that it is easy to get confused.

[tasp]

Regarding the black and white:

Any white surface perpendicular to the sun (with some of the other angular constraints I have been outlining in other posts) turns black.


That's it.


Surface of Iapetus is covered in silver nitrate.

[David]

(I got caught on this earlier today)

Invert the picture.

The 'cracks' are actually the edges of a landslide.

The 'bumps' are craters.

These pictures are so, for lack of a better word, alien, that it is easy to get confused.

I did invert the picture. (Or rather, I inverted myself relative to the picture ). Still look like fissures to me. Didn't see any bumps.

Any white surface perpendicular to the sun (with some of the other angular constraints I have been outlining in other posts) turns black.

That can hardly explain the global distribution!

[tasp]

OK, it's late, the silver nitrate thing is a joke.

But, the surface of Iapetus behaves similarly.

I think the coating is everywhere, but only when the level of insolation (not insulation) exceeds a certain value, the stuff turns black.

[tasp]

The amount of the 'silver nitrate' is maximum halfway between the sub-Saturn and the anti-Saturn points, on the leading hemisphere.

The 'silver nitrate' is 'applied' every Iapetan month when Iapetus traverses the Saturnian magnetotail. It almost totally dissipates in ~ 40 days, but can persist in low spots.

[David]

Here's a remarkable one: white field spattered with black lake-like forms. (I am not suggesting there are lakes on Iapetus! Sheesh.) Some of them are obviously crater-related, but not all of them.

[tasp]

It really is a landslide. The edges of the flow have 'banked' themselves a bit.

The flow looks, um, er, 'flowy'. Might be mostly pulverized, or granular materials.

[tasp]

Try not to think about spraying black powder on a white surface, or spraying white powder on a black surface.

We have something sprayed everywhere (on a white surface!), but it only turns black when it gets hot in the sunlight.

(and recall 'hot' on Iapetus is still a bit on the chilly side of dry ice)

[David]

It really is a landslide. The edges of the flow have 'banked' themselves a bit.

So how does a landslide get sharp ridges at the sides? Not challenging you, just curious.

[JRehling]

[...]

[tasp]

Same stuff is all over Hyperion too.

But the only place it gets hot enough there is at the bottoms of the craters that have walls steep enough to focus the sunlight on those crater bottoms.

And why are virtually all the crater bottoms on Hyperion black ??

Chaotic rotation eventually points all the craters directly at the sun.


So what is the 'stuff' ??

It's gaseous.

It's a gaseous photo-thermal reactive, er, um, gas.

It 'ponds' in craters and low spots on tiny grav places like Hyperion. It persists around more massive Iapetus for about half (40 days) the orbit about Saturn. That's why Cassini Regio is on the leading hemisphere.

Toot sweet.

I am going to bed, a happy camper tonight.

[David]

Try not to think about spraying black powder on a white surface, or spraying white powder on a black surface.

We have something sprayed everywhere (on a white surface!), but it only turns black when it gets hot in the sunlight.

(and recall 'hot' on Iapetus is still a bit on the chilly side of dry ice)

It's a fascinating idea, but it doesn't explain (to me) the shape of the black-white boundary -- which reminds me of nothing so much as early spring snowmelt. I think the distribution you note could be explained otherwise: the white stuff melts away where it's hottest, exposing a black layer underneath. On other parts of Iapetus, it either never existed, or has been covered over with darker materials. (I'd love to see if there's any evidence of dark-light-dark layering).

[tasp]

JRehling:

Wait till we get a Uranus orbit and look at Ariel!

[David]

It's final: the Saturn system does beat the Jupiter system. Iapetus blows Ganymede away, Dione beats Callisto, Enceladus ties Europa, Titan crushes Io, and there are a handful of other moons to run up the score against Amalthea and jovian rubble. And then there are the rings.

It's not really a fair comparison; Saturn has seven larg(ish) moons, Jupiter only four, so Saturn has more opportunities for wackiness; and we now have much better coverage of the Saturn system. I'm not entirely convinced that Dione beats Callisto, or that Enceladus and Europa are even comparable; but there's only one Titan in the solar system, and of course Iapetus deserves some record for having presented precisely the same mystery, without solution, for over 300 years.

And there are, as you say, the rings.