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  • Writer's pictureJames Paulson

Planetary Ring Structures in the Solar System

The rings around Saturn are an item of incredible beauty. For as long as the hobby of amateur astronomy has existed, these rings have been a major feature visible to backyard astronomers. When Saturn is visible, it is the crown jewel of many public observation nights.

What most people may not realize is that Saturn is not the only planet with rings, but rather is the single planet we can see with highly visible rings. The other 3 gas giants, Jupiter, Uranus and Neptune all have complex ring systems that were visible to the Voyager spacecraft after the discovery of the rings around Uranus using airborne photometers on the Kuiper Airborne Observatory in March of 1977 as SAO158687 underwent occultation by Uranus and dips in the readings were observed pre and post occultation. Jupiter and Neptune had their ring systems uncovered from Voyager missions.

All of this leaves us with more questions than it does answers, because now we have to offer up an explanation for why planets develop ring systems and just how that process takes place. In order to do this, we have to come up with some theories as to why matter is dispersed in the plane of an orbit around the planet as well as an explanation for how the matter came to this place and found its way in this configuration.

One theory states that these were once moons that got too close, and gravitational tidal action ripped apart these moons and with time, this debris was scattered all though the orbit of the moon, spread by physics and organized by gravity. Scientists have arrived at what is known as the Roche limit – that unique radius at which the main bodies tidal forces are stronger than the secondary bodies gravitational force to keep it together. In fact, no planets ring radius exceeds this limit except for Saturn’s E-ring, which could actually be made up of the remnants of the protoplanets planetary accretion disc, or the debris field that coalesced to make the planet itself. Gravity alone may not be all that creates this split as it could also be supplemented by internal forces such as thermal stress, gas pressures, and even rotational breakage, some of the same forces responsible for things like earthquakes and mountain formation on planets themselves.

Another theory is that these rings were made up from the particles that bombarded the moons and planet and left considerable debris in space as a result, and that gravity and time sorted into a planar ring system. One thing is certain, without proper data collection, that is, sampling, all we can do is design models to help explain the formation of these beautiful features.

I have seen an analogy that compares the thickness of Saturn’s rings to a sheet of paper in thickness going around a basketball, just to give you an idea of how fragile these rings actually are

The key to ring formation lies in what they are actually made up of. Saturn’s rings are made up of water ice and dust, where Jupiter’s are primarily just dust. The rings of both Neptune and Uranus are primarily water ice with some dark-radiation-processed organics. This suggests the formation of the rings themselves has more to do with physics and mechanics and less to do with chemistry, but the chemistry also provides clues. If the surface conditions do not reflect the ring conditions, we can rule out any surface impacts as being the precursor to the formation of rings. The rings themselves represent a resonance with the rotation of the planet, and in the case of Saturn, what would one expect from a planet where it literally rains diamonds?

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