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Iapetus, satellite of Saturn, has a huge mountain range along about half its equator.

On this list of our solar system's biggest mountains, it is the only entry with uncertain origin.
..The unmeasured peaks of the nameless range are estimated nearly as high as Olympus on Mars.

Here are 4 hypotheses for the equatorial ridge's formation: wiki again
(To me, the 4th sounds right but incomplete, & the rest seem unlikely)

This Guardian article says Earth's equatorial mountains are taller than lower-latitude mountains because cold-erosion has a huge effect on mountain height & snowlines etc.
..Is this part of the reason for Iapetus' high equatorial mountain range?
...Iapetus IS mostly ice...Does/Did it have glaciers?
Is Iapetus an extreme case of cold-erosion seen on Earth?

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An explanation to the equatorial ridge of Iapetus must also explain the similar, yet even more striking feature of two other Saturn moons, Atlas and Pan.

AtlasPan

This may rule out the explanations involving geological activity, because Atlas and Pan are too small to have any. This leaves the explanation that the ridges are material from the rings of Saturn swept up by the moons.

To address the second part of your question, regarding cold-erosion, this is due to glaciers. Glaciers consist of ice, like Iapetus, but this ice is not moving like on Earth, thereby causing no erosion due to friction. Water in the outer solar system is best viewed as just another type of rock. Like most objects in space, the mountain range of Iapetus has not received any notable erosion.

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  • $\begingroup$ If the ridge was due to accretion, it would be continuous around the entire equator. Instead it exists only on the dark side of Iapetus. $\endgroup$ – kim holder Dec 16 '15 at 15:38
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    $\begingroup$ @kimholder Not necessarily, Iapetus is tidally locked to Saturn, and that may cause the material to only hit a part of the equator. $\endgroup$ – Hohmannfan Dec 16 '15 at 15:42

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