\n<\/p>\n
This could be true, but simpler explanations exist \u2014 specifically, that Saturn\u2019s rings could have been\u00a0formed more recently by smaller objects like comets, asteroids, or small moons. Simulations suggest that objects like these could have collided near the planet, their debris spreading into the rings. Alternatively, small bodies could have been\u00a0sucked in and then torn apart by the planet\u2019s powerful gravity. These explanations would also explain the near purity of the rings\u2019 icy composition better than the primordial ring theory: If the rings were 4.5 billion years old, they would have gotten \u201cdirty\u201d by now, by accumulating dark material from meteorites and interplanetary dust. It is still possible, however, that the rings could be ancient but continuously “cleaned” by new icy material, keeping them bright despite their age.\u00a0<\/p>\n
One thing we do know for certain is that some of Saturn\u2019s rings are fed by its moons. Cassini confirmed that a lot of the material for the E-ring \u2014 a diffuse ring outside the bright, main rings \u2014 comes from icy particles venting from the moon\u00a0Enceladus. Cassini also found that many of Saturn\u2019s inner rings are made of particles from the moons that orbit within them, likely blasted off by micrometeoroid impacts.<\/p>\n
This is similar to how Jupiter\u2019s rings are formed. Scientists think that the thin\u00a0Jovian rings are in a constant state of decay and replenishment. While material is constantly falling into Jupiter\u2019s atmosphere, new material is steadily added to the rings from meteoroid impacts on the small inner moons Metis, Adrastea, Thebe, and Amalthea.\u00a0<\/p>\n
Uranus and Neptune\u2019s rings are less well understood, but the leading idea is that they formed from the debris of small moons that were shattered by collisions or gravitational disruption.\u00a0<\/p>\n
A major factor in how planets form rings is called the\u00a0Roche limit.\u00a0<\/p>\n
When an object orbits a planet, there are two gravitational forces at work: the pull of the planet, and the satellite object\u2019s own gravity that holds its matter together. When a satellite orbits close enough, the gravitational pull of the planet can compromise that self-gravity. This can lead to the smaller object being ripped apart as the side of it nearer to the planet gets pulled on more than the far side.\u00a0<\/p>\n
The conditions in which an orbiting object will be ripped apart is called the Roche limit, and it mainly depends on distance from a planet. Within that limit, loose material also doesn\u2019t coalesce into a solid object like a moon. The Roche limit of a planet (or dwarf planet, or smaller body) depends primarily on its size and density. However, the size, density, and material composition of an orbiting object are also all factors in whether it will be torn up within the Roche limit. Saturn, for example, has \u201cring moons\u201d \u2014 tiny moons that orbit within its rings. These likely have enough material strength to withstand Saturn\u2019s gravitational effects, at least temporarily.\u00a0<\/p>\n<\/div>\n