[AnotherUnixGeek]

What would make a moon look like a walnut? A strange ridge that circles Saturn's moon Iapetus's equator, visible near the bottom of the featured image, makes it appear similar to a popular edible nut.

I remember Arthur C. Clarke's novelization of "2001: A Space Odyssey" offered an explanation for Iapetus' appearance that was far more entertaining than reality is likely to be.

[plsvn]

I remember Arthur C. Clarke's novelization of "2001: A Space Odyssey" offered an explanation for Iapetus' appearance that was far more entertaining than reality is likely to be.

That's right, and I read somewhere that the reason why they didn't use this "more entertaining" reason at Saturn in the 2001 movie was because they couldn't make Saturn's rings authentic enough looking for the movie so they changed the original story and ended up using Jupiter (and the moon Europa).