An interesting characteristic that all the jovian planets possess is their rings. The most remarkable and noticeable of these are Saturn’s, which extend hundreds of thousands of kilometers wide. However, Jupiter, Uranus, and Neptune all have rings as well, on a much smaller scale. Although the rings are rather wide, they are only 1-1000 m thick at most, proving to be extremely thin.
The rings are not physically part of the planets themselves, but are really a disk-shaped group of moonlets, dust, or other small planetary objects orbiting the planet. It is believed that this material came together in one of three ways: from material that was within the Roche limit and therefore could not condense into a moon, from debris of a moon that was hit by a large impactor, or from debris of a moon interrupted by tidal stresses when passing within the Roche limit. A small amount of material could have been ejected from the planets themselves as well. The rings are generally composed of ice, dust, and various rocky materials. The particles have a wide range of sizes, from very small rocks to large boulders.
The rings are not just one piece – there are several gaps between each “ring” where there are no materials orbiting. Specifically within Saturn, some of these gaps are due to the presence of tiny moons orbiting around within it; they have cleared a path for which to orbit and that prevents any material to occupy that space. Ring spacing is also maintained by the gravitational effects of small shepherd moons such as Saturn’s Prometheus and Pandora. The orbits of these moons regulate the orbit of certain rings, drawing them away from the planet and pulling it back in so it maintains its relative position.
Although rings are currently a jovian quality, it is believed that Mars’s moon, Phobos, will soon break up due to its low orbit and create a ring around the planet. It is unclear, but perhaps rings will become a more common planetary characteristic as many years go by.
