Very few images taken by satellites can match the serene tranquility of the Saturnian system. The planet itself is fairly unremarkable to look at on most occasions, and were it not for the beautiful set of rings around it, the planet would just be a duller version of Jupiter. Rings are a fine addition to any planet. They are truly surreal – a thin sheet of rock and ice arrayed beautifully away from their parent body. So why is it, given all of their grandeur, that so few people try to understand these features? One will see when you dive into them that they have an intricate relationship to their planet as well as the other satellites that orbit.
To understand how rings form, you first must understand the relationship between a planet and objects in orbit around it. For an understandable analogue, we will use the Earth-Moon system. As the moon rotates around the earth, its gravitational pull on us can be felt in the form of tides. It is not just the moon that affects the Earth, the Earth pulls tremendously on the moon, causing fairly regular moonquakes. Were the moon closer to the Earth, the intensity of these moonquakes would increase to the point where at some given distance, the moon would no longer be able to hold itself together and would slowly to fall apart. This imaginary line in space surrounding each body is termed the Roche limit. Any object within its Roche limit will fall apart due to tidal forces. Any object outside should be able to hold itself together.
For the rings of Saturn, dust and particles that were within the Roche limit when the planet formed made the magnificent ring system and any moon that fell too close joined the rings. In the case of Jupiter, there are currently two moons within the Roche limit that are apparently feeding some of the inner rings. As these moons crumble, the rings will become more visible and while they will not be able to match the beauty of Saturn, it may be an interesting feature for future generations to observe. While Mars does not currently have rings, as Phobos approaches the planet’s surface over the next few million years, it will pass through the Roche limit and will begin to form a ring system of its own.
In the case of our own planet, it could be possible that at one point the Earth had rings of its own as the moon formed. The moon had to have precipitated outside the Roche limit, but the material within has long since either been lost due to gravitational effects from the moon or crashed down in the form of meteor showers. One could say that our planet has its own ring system, though it is made of synthetic telecommunications satellites. If any of these were to break up, it could pose disastrous threats to other satellites. This could cause a chain reaction, but of course, in the spirit of cliff-hangers that will have to be saved for next time!
May the stars sine brightly in your skies.