A planetary ring is a ring usually disk-shaped structure around a planet that consists of many billions of dust or ice particles whose size ranges from a grain of sand to that of a residential house. Here, the extent, composition and brightness can be completely different. Several rings around a planet form a concentric ring system.
2014 were in the sky body ( 10199 ) Chariklo first detected also rings around an asteroid or a dwarf planet.
The emergence of a planetary ring is not fully explained until now. One approach is that rings can arise when a small moon comes too close to the planet, that is within the Roche limit, where it is torn apart by the tidal forces of the planets and distributed around the planet. Another approach related to the Roche limit assumes that the rings are remnants of the gas disk from which the planet has formed - within the Roche limit, the remaining gas could form but to no moons.
Another theory says that a planet ring is formed when the planet is hit by another celestial body or two small bodies collide so that they break apart and not put back together due to the high gravity of the planet, but are distributed around the planet.
Known planetary rings
In the solar system, each of the four gas planets has a ring system. Their particles circulate the planet prograde within or very close to its equatorial plane, and still mainly within the Roche limit. Despite the common main features of the structure of the rings in all four cases is very different.
The most famous planetary ring is the ring of Saturn. He is the most extensive, consists of a light material and is therefore already visible with a good amateur telescope. The ring consists of several so-called main rings, which in turn consist of many small rings. The weakest is the ring system of Jupiter. It consists of extremely dark material, moreover, it is vanishingly weak, so that it could only be detected by space probes. It is believed that Jupiter's rings are powered by tiny innermost moons with new material, while the old material trickles steadily on Jupiter. Uranus and Neptune also have extremely dark circles. When Neptune was believed initially that its rings incomplete ring arcs were, would therefore not self-contained.