Iapetus equatorial ridge fell from the skies

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In summary: The equatorial ridges are unique to the Saturnian system because they are the only instance of a ring system that is not confined to a planet's equator.
  • #1
PhysicoRaj
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Moons of Saturn have always been mysterious. The Iapetus equatorial ridge is now seen as exogenic, according to these people:Discover_Magazine-Iapetus.
Researchers believe the mountain range formed after Iapetus collided with another large planetary body, similar to the collision that created our moon. The crash ejected material into orbit that formed a temporary ring around Iapetus, but the unstable ring eventually collapsed and smashed back to the surface, creating the mysterious mountain range.

A massive planetary collision could also help explain Iapetus’ lopsided orbit, and why one side of the moon always faces away from Saturn.
What makes a ring system unstable?
Also, the wiki says that equatorial ridges are unique to the Saturnian system.
 
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  • #2
PhysicoRaj said:
What makes a ring system unstable?
There is viscous spreading(http://arxiv.org/abs/1006.0633), which is basically the rings getting gravitationally flattened like a pancake and falling onto the surface or escaping past the Roche limit(to eventually form moons), depending on whether it's the inner or outer edge.
There's also tidal friction, which causes the material in the rings to either spiral outwards(like our Moon does) or inwards, depending on the orbital velocity.
 
  • #3
Thanks Bandersnatch. And what factors affect the Roche limit? Like if a planet is extraordinarily huge but has weak gravitational field, the limit may lie within the planet's surface..etc. I found this formula on wiki but it does not include the rigidity factor of the orbiting body
##d=1.26R_m{\Big({\frac{M}{m}}\Big)}^{1/3}##
 
  • #4
and why one side of the moon always faces away from Saturn.

Like almost all the other moons in the solar system. (Hyperion is an exception, as may be Jupiter's Himalia group). I'm not sure I would take this as a good source.
 
  • #5
Vanadium 50 said:
Like almost all the other moons in the solar system. (Hyperion is an exception, as may be Jupiter's Himalia group). I'm not sure I would take this as a good source.

Hmm..Yes.. like all other moons.. you are right. But because Iapetus is further away from saturn than other moons, they might be thinking of low tidal forces incapable of reducing the rapid spinning(?) and the large impact craters like Turgis and Engelier, which might be signs of devastating collisions that slowed the moon down. The source actually says that the findings were published in arXiv:http://arxiv.org/abs/1404.2337
 
  • #6
PhysicoRaj said:
Thanks Bandersnatch. And what factors affect the Roche limit? Like if a planet is extraordinarily huge but has weak gravitational field, the limit may lie within the planet's surface..etc. I found this formula on wiki but it does not include the rigidity factor of the orbiting body
##d=1.26R_m{\Big({\frac{M}{m}}\Big)}^{1/3}##

In the idealised scenario, as can be glanced from the equation, the limit depends only on radius and the ratio of masses, or equivalently, on the ratio of denisties(with radius changing to that of the primary rather than of the satellite). As you say, for a high denisty satellite and low density planet, the limit may lie under the planet's surface.

On the wiki page, you can find the derivations for two extreme cases of an ideal rigid and fluid body. The two differ by the numerical factor in the equation - 1.26 and 2.44. The actual non-ideal bodies will lie somewhere in-between.

Additionally, the Roche limit as expressed by the above equation concerns only bodies held together solely by their gravity. It does not take into account any other forces that may affect cohesion, so, for example, a human being within Roche limit of Earth(~27 000 km for a ~1g/cm^3 dense human body) does not disintegrate, as other forces than gravity hold his body together.

I've never seen the actual calculations for real-world cases, but I hear they're not trivial.
 
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  • #7
Bandersnatch said:
Additionally, the Roche limit as expressed by the above equation concerns only bodies held together solely by their gravity. It does not take into account any other forces that may affect cohesion, so, for example, a human being within Roche limit of Earth(~27 000 km for a ~1g/cm^3 dense human body) does not disintegrate, as other forces than gravity hold his body together.

That really convinced me. So there is room for speculation that Iapetus ridge may have been formed by gravitational influence of Saturn or other moons. It orbits beyond Titan but it might have once orbited much close, so tides pulled down its spin, then something might have ejected it out.

Are the rings of saturn (or any other planet with ring system for that matter) present inside the Roche limit of the planet?
 
  • #8
For Saturn, some of the rings are inside and some are outside. I didn't check the other planets.
 
  • #9
mfb said:
For Saturn, some of the rings are inside and some are outside. I didn't check the other planets.

Ty. But why are equatorial ridges unique to the Saturnian system? (http://en.wikipedia.org/wiki/Equatorial_ridge)
 

1. How did the Iapetus equatorial ridge form?

The Iapetus equatorial ridge is believed to have formed through a process called "accretion." This occurs when smaller particles and debris in the surrounding space collide and stick together, gradually forming larger and larger objects. In the case of Iapetus, it is believed that the ridge was formed when small pieces of debris from the surrounding space collided and stuck to the moon's surface, eventually forming the long, ridge-like structure.

2. Did the Iapetus equatorial ridge fall from the skies?

The exact origin of the Iapetus equatorial ridge is still a topic of debate among scientists. While some theories suggest that it may have been formed through accretion, others suggest that it may have originated from within the moon itself. There is currently no evidence to suggest that the ridge literally "fell from the skies," but further research is needed to fully understand its formation.

3. How long is the Iapetus equatorial ridge?

The Iapetus equatorial ridge is approximately 1,300 kilometers long, which is about 80% of the circumference of the moon. It is also quite narrow, with a width of only 20 kilometers on average. This makes it one of the longest and most prominent features on Iapetus.

4. What is the composition of the Iapetus equatorial ridge?

The composition of the Iapetus equatorial ridge is still not fully understood. Studies have suggested that it may be made up of a mix of different materials, including water ice, rock, and organic compounds. However, more research is needed to determine the exact composition of the ridge.

5. Could the Iapetus equatorial ridge have been formed by a collision?

Some theories propose that the Iapetus equatorial ridge may have been formed by a major collision with another object in space. However, this idea is still debated and there is currently no conclusive evidence to support it. Other theories, such as accretion, seem to better explain the formation of the ridge, but more research is needed to fully understand its origin.

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