I was reading an article about a ring that was destabilized out of orbit on one of Saturns moons. I got there by looking for mountains because of this question (unrelated mostly). Here's a picture of a mountain range on Iapetus that this article claimed could be a mountain range formed by a ring that crashed to the planet:

enter image description here

Same moon, zoomed out more:

enter image description here

I want to ask how a ring would get destabilized and collide with a planet's surface to create a mountain range that is 20km tall and along a linear path. I can't really picture how it would be disrupted in a way that would cause it to be pulled toward the planets surface all at once.

  • If there are misconceptions in my question, that's an answer (if it is bigger than a comment).

My hypothesis on what I misunderstood:

  • The mountain range may not encircle the planet entirely, I didn't find info on that. does not seem to encircle the whole planet.
  • If the mountain range is only on 1/2 of the moon, would a planetary pass between the moon and Saturn cause additional pull on the ring and allow a collapse to the surface? Below is an image of the terrain annotated to point out why I think this.
  • Is there still a partial ring in orbit? Or would a destabilization as I've described it pull the other half away and out of a local orbit of Iapetus?

enter image description here

Original image here, without my red marks...

If this is better served to astronomy-- migrate (I will not be offended and cannot do it myself)...

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    $\begingroup$ This shape looks familliar; Separating fact from fiction, how to get from this radar image to this GIF? $\endgroup$
    – uhoh
    Commented May 23, 2019 at 22:49
  • $\begingroup$ @uhoh- 1994KW4 alpha rotates in 2.8 hr, which is near its rotational stability limit (so its equatorial ridge is actually 'downhill'), whereas Iapetus rotates in 79 days and is tidally locked (like our moon). Being far from Saturn, it has a large Hill sphere so it could have had its own ring system at one time. It once rotated much faster, but the hemispheric distribution of the ridge (on the dark side) fits with formation after tidal lock. The high inclination of its orbit is a mystery, and bothers me as far as ring accretion resulting in a ridge so well aligned with its equator. $\endgroup$
    – amI
    Commented May 24, 2019 at 5:02
  • $\begingroup$ Also, I would guess that the ridge is mostly ice (and some did fall on the light side), and the darkening occurred later. Maybe the darkening protected the ridge from later 'erosion', although I doubt it. $\endgroup$
    – amI
    Commented May 24, 2019 at 5:16
  • $\begingroup$ @aml if nobody answers this within 2-3 days can your write what you said in an answer- perhaps with the signifigance of the tidal lock explained in terms of the question? Id appriciate that- I feel like I dont understand your comment $\endgroup$ Commented May 25, 2019 at 2:59
  • $\begingroup$ @aml ...poke... $\endgroup$ Commented May 28, 2019 at 18:55


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