Newbie question...what about the rings ?

[Mike Godfrey]

Hi Stargazing Dudes,

I ve been thinking about the Saturn rings and in fact any ring system and I have what feels like a newbie question in 3 parts .....can you enlighten moi?

1.Why is it that ring material rotates around the equator of a planet?

I guess it has something to do with the speed of rotation being greatest at the equator ?

2.Why is it that the material doesn't fall into the planet due to gravitational force? ,considering that other planetary bodies do not have ring systems.I can only think that they are replenished by other material being vacuumed in?

3.Assuming the rings are very old ( I have no evidence for that assumption)why doesn't the ring material coalesce -here I'm thinking of the idea of solar evolution ?Or do they coalesce and thats where the Shepard moons come from ? whoops a 4 question.sorry for all the questions maybe I should just . :walk:

Ta dudes

[Ant]

1. I would agree that it may well be something to do with the speed of rotation but I'm not sure.

2 & 3 I think are covered by the moons... I've heard them described and "shepherds of the rings" So (and I'm guessing a little here) i would imagine that the moons gravitational forces keep the materials in the correct orbit - thus not needing replenishment and also stopping he material coalescing...

Hopefully someone will be along soon that will know for certain.

Ant

[Jamie]

Here is some info on Saturn that might help.

FACTS ABOUT SATURN

(Bevan M. French and Stephen P. Maran, eds., "A Meeting with the Universe," NASA EP-177, U.S. Government Printing Office, 1981.)

About the Planet Saturn

* Among important recent findings from Earth-based observations of the Saturn system have been the detection of a deuterium compound in the atmosphere of Saturn, indications that the small ring particles are composed of or covered by ice, the detection of ice on the moons Rhea, Iapetus, and Dione, and the discovery of methane in the atmosphere of Titan.

* The first spacecraft flyby was accomplished by Pioneer Saturn in 1979. Among the findings were

* Confirming ground-based studies, Saturn has an internal heat source like Jupiter and radiates about twice as much energy as it receives from the Sun.

* As suspected, Saturn must have internal shells of liquid and metallic hydrogen, small amounts of helium, ammonia, and water, and perhaps a small rocky core.

* A magnetic field was discovered around Saturn, larger than the Earth's, but smaller than that of Jupiter. It is five times as weak as predicted by theory.

* The axis of Saturn's magnetic field is aligned parallel to the planet's rotation axis, contrary to the circumstances in both the Earth and Jupiter.

* The boundary of the magnetic field varies due to changes in the pressure of the solar wind on the sunward side, as was found in the case of Jupiter.

* The atmosphere of Saturn has weak bands, rather than the conspicuous belts and zones seen on Jupiter.

* There is a high haze, perhaps composed of crystals of ammonia ice, above the clouds.

* Apparent high-speed jet streams were detected in the atmosphere.

* Confirming ground-based measurements, the cloud-top temperatures were measured at about‹ 200° C (-330° F), only about 73° C (130° F) above absolute zero.

* Radiation belts were discovered that are weaker than those of Jupiter. The radiation is absorbed (cut off) by the rings and moons of Saturn. Cutoffs in the radiation data were used to infer the presence of additional rings and moons beyond those already known from visual observations.

* The Voyager 1 encounter (November, 1980) provided a closer look at Saturn and its surroundings. Some of the new discoveries were

* The details of Saturn's atmosphere appear similar to Jupiter's, with alternating light and dark bands and circulating storm systems.

* Wind speeds up to 1,500 kilometers per hour (930 miles per hour) were measured near Saturn's equator; these winds are four to five times as fast as those measured on Jupiter.

* Unusual atmospheric features include a ribbon- like wave feature, large and small clouds, and a red oval similar to, but smaller than, Jupiter's Great Red Spot.

* Aurorae were observed in the atmosphere above Saturn's poles.

* Although lightning bolts were not observed on Saturn, radio signals typical of lightning flashes were recorded. The signals may be produced by electrical discharges in the rings rather than in Saturn's atmosphere.

The Rings

* The Pioneer Saturn flyby in 1979 made several new discoveries about the rings:

* The rings consist largely of particles several centimeters in diameter. They are extremely cold and possibly composed of frozen water and other ices.

* An extensive cloud of hydrogen was discovered around the rings.

* Two new rings (called F and G) were discovered, and a gap between rings was confirmed.

* Voyager 1 provided much more detail on the beauty, complexity, and sometimes baffling nature of the rings. Among the discoveries were

* The six known rings are actually composed of hundreds of tiny, thin ringlets with intervening spaces, so that the whole ring system looks something like the grooves in a phonograph record. Even the Cassini division, once thought to be empty space between the A and B rings, contains several dozen ringlets. There are far too many rings to be explained by our present theories of how planetary rings form and remain stable.

* Elongated radial features that last from hours to days were observed in the Bring. These "spokes" may be clouds of electrified dust rotating around Saturn above the plane of the rings.

* The thin outer F-ring, discovered by Pioneer Saturn, was resolved into three distinct but intertwined ringlets. This braided ring structure is very difficult to explain; it seems likely that both electrical and gravitational forces are at work.

* Two small moons, one on each side of the F-ring, may act as "shepherds," their gravitational attraction keeping the ring particles on track between the orbits of the two moons.

The Moons

* Nine (possibly ten) moons had been detected from Earth. The encounter of Pioneer Saturn (September, 1979) provided several new discoveries:

* At least two new moons were discovered by Pioneer and ground-based observations.

* Accurate masses were determined for the moons Rhea and Iapetus.

* The cloud-top temperature of Titan was found to be very low, about -200°C (-330°F), and a hydrogen cloud was discovered around Titan.

* A much closer look at several of Saturn's moons was provided by Voyager 1. The new results included:

* Six tiny, unnamed moons were photographed, some of them for the first time. Satellites 10 and 11 share the same orbit and must frequently undergo some orbital "evasive actions" to avoid colliding. Satellite 12 shares the orbit of the larger moon Dione. The shepherd Satellites 13 and 14, on either side of the thin F-ring, may exert gravitational forces to keep the ring in place, while Satellite 15, located just outside the large A-ring, likewise may help keep that ring in place.

* The inner moons Mimas, Tethys, Dione, and Rhea all have heavily cratered surfaces like those of the Moon and Mercury, although Saturn's moons are composed largely of water ice. This shows that meteorite bombardment, even as far out as Saturn, has been a major process in shaping the solar system. Mimas is marked by a huge impact crater that is fully one-fourth the diameter of Mimas itself. This crater makes Mimas look like a staring eyeball, and the impact that formed it was almost intense enough to blast Mimas into fragments.

* The inner moons also show traces of internal geological activity. Tethys has a rift-like valley that stretches 800 kilometers (500 miles) across its surface. Dione shows several sinuous, branching valleys. Both Dione and Rhea have bright, wispy streaks on their surfaces.

* Although Enceladus orbits between two heavily cratered moons, Mimas and Dione, it seems smooth and entirely uncratered, as viewed from Voyager 1.

* Titan, Saturn's largest moon, has a diameter of 5,120 kilometers (3,180 miles), which makes it smaller than Jupiter's moon Ganymede.

* Titan's dense, hazy atmosphere is at least 400 kilometers (250 miles) thick and completely shrouds the surface from view. Titan's atmosphere was found to be mostly nitrogen (like the Earth's), with minor methane and other hydrocarbons. At the surface, the pressure of Titan's atmosphere is at least twice that on the Earth. The surface temperature, about 175° C ( 280° F), is low enough to permit lakes and streams of liquid nitrogen to form on its surface.

* Long-range Voyager 1 photographs of Iapetus, an outer satellite, confirmed Earth-based observations by showing that the satellite has light and dark faces, but no explanation for this puzzling difference was found.

[Mike Godfrey]

Thanks guys for your replies,it looks like perhaps the Shepard moons have a bigger role than I thought -maybe they are examples of coalescence but I wonder if they are responsible for the rings remaining in orbit rather than all that ice and dust making a head long dash for the gas giant?

How many Shepard moons would you need to keep the ring system going ?

Interesting stuff.

cheers

Mike :saturn:

[The Warthog]

I've read recently that ring systems are evanescent phenomena, lasting millions of years, but far from forever. Both Jupiter and Uranus have faint rings, I don't know about Neptune, but why should he be left out? Maybe 30 million years ago the gas planets were a real feast for astronomers.

[GordonCopestake]

On a recent Discovery Science program (i forget the title) it mentioned that recent evidence shows that saturns rings are infact fairly new, only 10,000's of years old. The rings are slowly moving away from the planet and that the rings nearer the planet are more recent than the rings on the outer edge. This can be proved because the ring particles, mostly ice, blacken in the sunlight (im unsure of the mechanism) and if they were millions of years old the entire ring system would be black. This is not the case.

There remains mysteries in our solar system and saturns rings havn't given us all their answers yet! We just dont know!