This color view shows all of Saturn with its vast rings extending far into space. The view is from above and the shadow of the planet is visible across the rings.

This view shows Saturn's northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Saturn's year is nearly 30 Earth years long, and during its long time there, Cassini has observed winter and spring in the north, and summer and fall in the south.

First discovered by Galileo in 1610, Saturn’s rings have long fascinated scientists. Ring formation and evolution offer tantalizing clues to planetary formation processes.

The first few million years after the formation of our solar system 4.57 billion years ago were tumultuous, with collisions between planetesimals being common. Astronomers previously assumed that Saturn’s rings came from this early period, which was supported by their orbits and predominantly water-ice compositions. However, understanding of orbital mechanics and particle collisions showed that the ring material should be constantly showering the planet, undermining the idea of ancient saturnian rings.

Are the saturnian rings a new feature or an artifact of the ancient solar system? The answer was unclear for many years.

Recently, Sascha Kempf from the University of Colorado Boulder and colleagues addressed this question using data from the Cassini mission, which orbited Saturn for 13 years. For the first time, the infall rate of ring material was directly measured, and the masses of infalling ring material were found to be inconsistent with the ancient ring origin hypothesis.

The team using Cassini data made a further observation: Saturn’s rings are bright and shiny. In the solar system, there is a constant flux of cosmic dust (tiny silicate particles); over time, water-ice accumulates dust and darkens. The team found that the saturnian rings have little dust accumulation, indicating ages of at most 100-400 Myr.

The young ages for the saturnian rings present a dilemma. The mass contained in the rings is consistent with a Mimas-sized (200-kilometer-radius) body being ripped apart. The destruction of a satellite would have proved cataclysmic for the saturnian system, potentially disrupting the orbits of neighboring icy satellites and providing ample material to impact their surfaces, potentially altering their cratering records. The question of how Saturn developed its brilliant rings is still very much an engaging and open question.

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