How do Saturn's rings stay distinct?
December 7, 2006 1:31 PM
How do Saturn's rings stay distinct?
I realize that shepherd moons are responsible for keeping some rings from spreading out, but does that hold true for the dozens (hundreds?) of distinct rings you see in photos? That seems unlikely, since these objects would be large enough to observe. I must be missing something--with my admittedly dim recollection of physics--since otherwise, wouldn't the ring system become one undifferentiated disc without some external influence?
I realize that shepherd moons are responsible for keeping some rings from spreading out, but does that hold true for the dozens (hundreds?) of distinct rings you see in photos? That seems unlikely, since these objects would be large enough to observe. I must be missing something--with my admittedly dim recollection of physics--since otherwise, wouldn't the ring system become one undifferentiated disc without some external influence?
Grab a copy of this month's National Geographic, there's a great article that covers your exact question.
To summarize, there are a few small moons within the rings whose gravity very subtly affects the rings. They create the gaps and keep the rings tidy.
posted by backseatpilot at 1:48 PM on December 7, 2006
To summarize, there are a few small moons within the rings whose gravity very subtly affects the rings. They create the gaps and keep the rings tidy.
posted by backseatpilot at 1:48 PM on December 7, 2006
Nobody knows what causes the fine-grain rings or what causes the spokes. The best guess right now is gravitational resonance from the outer moons, but that's mostly by default. (The only other thing they even possibly could be is a consequence of Saturn's magnetic field, and that seems unlikely.)
posted by Steven C. Den Beste at 2:07 PM on December 7, 2006
posted by Steven C. Den Beste at 2:07 PM on December 7, 2006
Current thinking is that the fine structure in Saturn's rings is due largely to the interplay between shepherd moons and Saturn's own gravity. Shepherd moons sweep up material (like in the Encke Gap), influence the rings by causing density waves, and can act in concert to keep a ring in place. Saturn's magnetosphere is thought to interact with the rings as well, creating radial features called "spokes".
Saturn's ring system is quite a robust gravitational phenomenon - the influences of shepherd moons account for most of the phenomena observed in them, including the fine structures you are referring to.
posted by the painkiller at 2:07 PM on December 7, 2006
Saturn's ring system is quite a robust gravitational phenomenon - the influences of shepherd moons account for most of the phenomena observed in them, including the fine structures you are referring to.
posted by the painkiller at 2:07 PM on December 7, 2006
Related question, as the OP's question seems to be answered:
The accretion disc around the sun eventually coalesced into the planets/asteroid belt. Is this broadly the same mechanism as the rings? Would the rings coalesce into moons if they weren't being perturbed by the existing moons?
posted by Leon at 3:00 PM on December 7, 2006
The accretion disc around the sun eventually coalesced into the planets/asteroid belt. Is this broadly the same mechanism as the rings? Would the rings coalesce into moons if they weren't being perturbed by the existing moons?
posted by Leon at 3:00 PM on December 7, 2006
Leon, the opposite is the case here: the reason the rings never coalesced was that they were prevented from doing so by the gravitational influence of Saturn and the larger outer moons.
The equivalent in the Solar System is the asteroid belt. A planet should have formed there, but could not because the gravitational influence of Jupiter prevented it.
posted by Steven C. Den Beste at 3:26 PM on December 7, 2006
The equivalent in the Solar System is the asteroid belt. A planet should have formed there, but could not because the gravitational influence of Jupiter prevented it.
posted by Steven C. Den Beste at 3:26 PM on December 7, 2006
Leon, the opposite is the case here: the reason the rings never coalesced was that they were prevented from doing so by the gravitational influence of Saturn and the larger outer moons.
This is pure speculation. I think you should be honest here. There is no generally accepted theory of how Saturn's rings even came to be...or what they will look like in the future.
posted by vacapinta at 4:30 PM on December 7, 2006
This is pure speculation. I think you should be honest here. There is no generally accepted theory of how Saturn's rings even came to be...or what they will look like in the future.
posted by vacapinta at 4:30 PM on December 7, 2006
This thread is closed to new comments.
The rings can be viewed using a quite modest modern telescope or with a good pair of binoculars. They extend from 6,630 km to 120,700 km above Saturn's equator, average close to one kilometer in thickness and are composed of silica rock, iron oxide, and ice particles ranging in size from specks of dust to the size of a small automobile. There are two main theories regarding the origin of Saturn's rings. One theory, originally proposed by Édouard Roche in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by tidal forces (see Roche limit). A variation of this theory is that the moon disintegrated after being struck by a large comet or asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material that Saturn formed out of. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin. (emphasis mine)
So yes, apparently, the ring system will become one undifferentiated disc, but this process will take quite a long time.
posted by SBMike at 1:43 PM on December 7, 2006