Iapetus, WHITE on BLACK (APOD 19 Sep 2007)

[auroradude]

Yes, it seems to be split along the equatorial ridge but south-facing slopes in the north and the north-facing slopes in the south would also be explained by this evaporation process as these slopes would get more sunlight than opposite slopes and would therefore release the water vapor and become darker. The opposite slopes that recieve less sunlight would attract this water vapor as frost and become lighter.
Did I mention two processes earlier?

[geckzilla]

I'm not quite sure what you mean, aurora.

[auroradude]

An example of what I am trying to get at was very noticable today. It was a clear blue sky day after a cold and clear night.
The temperature last night was in the high teens at our house near Homer, Alaska and it only got into the high thirties this afternoon. We had a hard frost this morning.
In the south-facing areas that the sun was hitting the frost thawed and evaporated leaving dark ground. In the shade, or north-facing areas the frost stayed all day leaving light ice-covered ground. This frost and frozen ground will most likely be around until the sun hits it again in the spring.

Couldn't the slopes of the craters of this moon with the dark deposits get more sun and turn even darker as the water ice evaporates? This water is then deposited as frost in places that recieve less sunlight making these colder areas lighter.
In the north the shadows fall on the north slopes and in the south the shadows fall on the south slopes. These would be light. Sunlight hits the south slopes in the north and the north slopes in the south. These would be dark.

[Vision]

Thats no moon!!! Nice catch andy.

[geckzilla]

Maybe if there is some odd heat source hitting the moon in that direction or emanating from the ridge? I think they probably did some thermal imaging on it and any odd heat sources would have been detected though. IIRC, the dark areas were just all slightly warmer than the white areas with some slight variations and nothing else much worth mentioning. Shrug.

Today's APOD mentioned the ridge and the possible correlation between it and the dark stuff. Coincidence?

[Danielallman]

Looking at Iapetos' location is there no chance that it has almost "Scooped up" an older outer ring of Saturn?

[Galactic Groove]

the mentioning of the north side slopes north of the equator and the south side slopes south of the equator being darker than their counters only holds true in the "transition zone." look away from this area and you'll see the craters fully dark or white (depending on which side of the transition you're looking at). If there was any evaporation taking place, then the entire white face of the moon would show greater signs of it, not just the slopes of the craters in this transition zone.

Also, is it 100% accurate that the dark side always trails like the caption says? if so, then it's all the more likely that the moon passed through some debris cloud or ring exactly like Danielallman is saying (and others). The slopes facing the debris as it went through would collect it while the slopes that didn't meet the debris head-on would collect very little.

If it did pass through a debris ring around Saturn, the craters in the white zone that are showing dark impacts would be more recent than this event since they didn't get the chance to be fully covered with the debris, if at all. The white peaks in the middle of these craters could still be in a position to collect the debris as it passed through since they are sticking out and more exposed unlike the surrounding valley below the peak which is protected by the crater walls. Simply because it's a depression in the main body of the moon, they are removed from this exposure to the debris.

[geckzilla]

Yeah Goove, I think this is the two things everyone is thinking:



Either somehow some crazy stuff flew out of the ridge, or it ran into a disc. It would have to have run into a disc or flat shaped object (or flat array of objects) for the stuff to have landed like that. I also have strange visions of a moon cracked in half and clapping together making a bunch of junk fly out but that sounds too crazy. It probably ran into a disc.

[nateleavitt]

How about another far-fetched theory ...

On object struck it with such force that it penetrated the surface and lodged itself somewhere near the core of the planet. Some core matter was ejected during the impact but the "Wound" closed up, sealing some magma and some air into the core of the planet. As the foreign body was "digested" and combined with the local material at the core of the planet, the existing air that was captured began to get superheated. Perhaps the mixture of the local magma and the new foreign material produced a gas. As the gas heated and expanded, the entire planet experienced tectonic shifting and adjustment. As the superheated gas pressure became too much for the core to contain, a giant bubble came out of the "wound" that was created upon initial impact. This carried magma with it and spewed it accross the surface of the planet. Then, with the sudden loss of pressure at the planet's core, the planet collapsed in upon itself, forming the ridge that now runs along the equator.

[geckzilla]

How would you explain that it got split perfectly in half along the equator then? One would think that if it survived a large impact, it would be deformed a lot less uniformly. And how would something strike the moon without destroying it, instead "lodging" itself in the core? It doesn't exactly seem like a marshmallow to me. Although, the color is right on one side...

[BMAONE23]

Would the current deformity be sufficient to cause a shifting in the rotational axis and force the buldge to rest at the equater?

[craterchains]

Would the current deformity be sufficient to cause a shifting in the rotational axis and force the buldge to rest at the equater?

I am doubting that BMA, but there are a couple of interesting ideas coming out.

But, I will still go with the idea that this is a destroyed space construct that has leaked it's atmosphere out onto it's surface.

That's my story, and it's sticking to me.

[JohnD]

How about another far-fetched theory ...

On object struck it with such force that it penetrated the surface and lodged itself somewhere near the core of the planet.

Large impactors usually strike with so much energy that they splash, rather than shatter, let alone stay intact. Small meteorites can land intact, as they slow enough in an atmosphere, which Japetus doesn't have. To penetrate as you suggest would require a dense impactor and very low density, or liquid object impacted.

John

[craterchains]

uhmmm , JohnD?

OOOOO000O0O0OO000

you may want to edit that post, ,

"To penetrate as you suggest would require a dense impactor and very low density, or etc"

Reads kinda funny this way, , grins

[JohnD]

We call that schoolboy humour.

Very funny,CC.

John