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Author Topic: Could a double "polar ring-system" exist around an earth-like planet?  (Read 1618 times)

Offline xaphlactus

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I was trying to come up with a world for a book I'm writing, and I was wondering if it was possible to have a world that has 2 rings, each on one side of the equator (equidistant?), circling close to the poles.

If this is indeed possible, then how would it and what kind of dynamics would/could it add to my planet?


 

Offline evan_au

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If you are considering circular ice/dust rings like those around Saturn, these loose particles are orbiting the planet. Because they are attracted to the center of the planet, the center of the orbit is located at the center of the planet.

A path that follows a line of latitude (apart from the equator) is not centered on the center of the planet, is not an orbit, and will quickly crash onto the planet.

You could, however, have an orbit which is at an angle to the equator, and centered on the planet core. The International Space Station has an orbit like this. A captured asteroid in an inclined orbit could break up, forming a ring angled relative to the planet's equator.

You can also have several orbits which are inclined to the equator, and in a different plane to each other. The GPS satellites are arranged like this. In this case, you could imagine that several moons around a planet were intentionally destroyed, resulting in several rings, at different angles to the equator, and at different distances from the planet.
 

Offline Craig W. Thomson

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I was trying to come up with a world for a book I'm writing, and I was wondering if it was possible to have a world that has 2 rings, each on one side of the equator (equidistant?), circling close to the poles.

If this is indeed possible, then how would it and what kind of dynamics would/could it add to my planet?
Interesting question. To the best of my knowledge, ring systems are formed by a moon of a planet being destroyed. For example, Jupiter's moon Io is presently being warped and stretched by Jupiter's gravity, making it the most geologically active body in the solar system, with volcanoes erupting almost constantly. Eventually, it will get close enough to break apart, which will result in an even more spectacular ring system than Saturn's.

Speculatively, I would argue that ring systems will tend to align with their planet's equators. Most "natural" moons (not captured ones like Phobos and Deimos) tend to be aligned with the equator anyway, so the bits of pieces of them after they are destroyed would stay in that plane. The gravitational field of a planet derives from the shape of the planet, which is in turn determined by its rotation, and orbits aligned with that shape tend to be the most stable. If a planet has any significant amount of equatorial bulge, that would tend to throw a ring system into chaos if it is orbiting at an angle to the equatorial plane. Intuitively, I would say a stable ring system requires "stable gravity," not gravity that changes from pole to equator as the rings circle the planet. That would likely throw components of the ring system out of equilibrium and destroy it.
 

Offline evan_au

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The bright, shiny rings of Saturn are possible because the ring is composed primarily of reflective ice. Saturn is a long way from the Sun, meaning that it is extremely cold, and chunks of ice will stay solidly frozen.

In contrast, an Earthlike planet will be much closer to its star, and any chunks of ice will quickly sublimate (turn into a gas) and be blown away by the Solar wind.

So if you want bright shiny rings, you will need to assume that someone recently moved a comet from the outer solar system into an angled orbit, and broke it up into little pieces.

If these were natural rings, they probably would have evaporated away long ago, leaving only a ring of dust and dirt.
 

Offline Atomic-S

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I think that a planet that contains, just beneath the north pole, a large mass of lead, and also just  beneath the south pole a large mass of lead, all the rest of the planet being composed of Styrofoam, might do what you want: support two "halos" orbiting close to the surface near the poles, the center of each halo being located just a little bit off of the center of mass of its corresponding lead body.  And because Styrofoam might not be strong enough to stop the lead endpieces from gravitating into each other. you might want to add a support column between them in the form of a titanium tube.
 

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