Strange Shadows: Saturn's Two-Faced Moon (space.com)

[On the Road]

Clear as black and white, Saturn's moon Iapetus is two-faced. One half is dark as coal and the other is as bright as fresh linens. Astronomers have puzzled over the stark difference since late in the 17th Century. New radar observations hint at what's going on, but the mystery is far from solved:

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Oddly, the side of Iapetus that always faces forward as it moves along its orbital path -- think of the front of a race car on a circular track -- reflects just 5 percent of the sunlight that hits it. The trailing hemisphere is much brighter, reflecting 50 percent of sunlight.

---snip

Astronomers have theorized that perhaps the front face is dark because it picks up debris, just as the front bumper of the race car is peppered with tire rubber, grease and whatever else the other cars cast off. With Iapetus, the debris might be bits of another moon, Phoebe, whose whole surface is relatively dark. The material might be kicked up from Phoebe by small meteor impacts, the thinking goes.

----snip

And there's another puzzling fact: The dark material on Iapetus seems also to be concentrated in the bottoms of some craters. That led to speculation long ago that the chemical or mineral or whatever it is perhaps oozes from within.... Now scientists have scanned the moon with radar, using the Arecibo Observatory in Puerto Rico. The picture is not a whole lot clearer, but some interesting twists emerge.



http://www.space.com/scienceastronomy/mystery_monday_040426.html

[liarliartieonfire]

1. Does the darker side resemble George? The lighter side Kerry???

Ominous, yes.
Can someone photoshop this?

[tridim]

2. The dark side is a bunch of Monoliths

It's where stargates are born, each one having the ratio of the squares of 1,2 and 3.

[Dogmudgeon]

3. Mars is almost the same way

Mars is divided into two uneven hemispheres. One of them is several kilometers higher than the other, and has much different features.

Some scientists think that there was a disaster early in the history of the solar system -- perhaps a planetary collision. Mars and Iapetus are probably not the only members of the solar system to show this kind of effect.

--bkl