Saturn is the sixth planet out from the sun and is the second of the gas giants, it is also the second largest planet after Jupiter. It has been a popular target for observation for many centuries, and it formed the outer limit of the early solar system as it is the last planet clearly visible to the naked eye.
Saturn has many interesting features: – Despite it being the second largest planet in solar system it is also the least dense. It is so diffuse that if Saturn was placed in a trough of water (it would have to be impossibly large of course! ) it would float, this means that Saturn’s average density is less than 1gcm3.
Saturn also possesses the most spectacular ring system in the solar system. Ten complete ring have been discovered with another two discovered incomplete rings or ring arcs. The most recent ring to be discovered is the Phoebe Ring, this is a massive ring on the exterior of the ring system. It is a tenuous collection of dust particles and is believed to extend from around 59 Saturn radii out to around 300 Saturn radii. It is nearly invisible and is undetectable by the human eye and amateur telescopes. Despite being difficult to detect the ring has been shown to be around 20 times the thickness of the planet itself.Its creation is believed to be a result of micrometeorid and larger impacts on the moon Phoebe (from which the ring gets its name). The moon Phoebe has an average orbital distance Saturn radii which puts well within the ring itself. Material from the ring slowly moves inwards towards the planet due to a process called infalling – this in itself is caused by incoming solar radiation destabilising the ring’s components orbits. This added to Saturn’s gravity is slowly causing the breakup of all the rings as they slowly migrate towards the planet’s upper atmosphere where they are absorbed. Don’t worry though the rings will remain a prominent feature for millions of years yet! If the Phoebe was visible to the naked eye it would make Saturn appear larger in the sky than the full moon!
A graphic showing Saturn and two of its moon's in relation to the Phoebe ring Image credit: NASA/JPL-Caltech
The other main rings in the Saturnine system are (travelling from the outer atmosphere) D, C, B, A, F – All of these are found in the main ring system – G, E – these are found outside the main ring ‘belt’. There are numerous divisions or gaps in the rings, small separations are called gaps with larger ones called divisions. Some of the main divisions are: – The Cassini division between rings A & B and the Roche division between rings A & F. Some of the gaps include the Encke and Keeler gaps both are found within A ring.
This an image was created from a number of Cassini images and shows Saturn's main ring system Credit: NASA
This image is only here to demonstrate the diversity of the rings. For a detailed look at them I advise you to open the image in another tab of your browser, unfortunately site limitations prevent me from doing it full justice directly in the post.
The rings are held in place and maintained by some of Saturn’s 63 moons – these are fittingly called shepherd moons. Each of the shepherd moon’s gravity helps keep the rings orbit stable and helps to maintain its structure. In some cases particular orbital resonances - orbital distance ratios – have created the many gaps in the ring and it is also this phenomenon that prevents these gaps from ‘closing’. Sometimes shepherd moon work in pairs, an example Pandora and Prometheus - This pair is responsible for maintaining the G ring.
