Largest ring system in the Solar System

The largest ring system in the solar system is found in orbit around the gas giant Saturn. The rings have a combined mass of 1.54 x 10^19 kg (1.69 x 10^16 US tons) and extend from 7,000 km (4,300 mi) above Saturn's equator to around 80,000 km (50,000 mi). The almost imperceptibly fine Phoebe Ring is located even further out, with its outer edge located roughly 15 million km (9.3 million miles) from Saturn.

Saturn's rings are mostly water ice, with dust and fragments of rock mixed in. The most likely origin for the main rings is the destruction of comets and asteroids, which broke up after getting captured by Saturn's gravity. While most of the particles in the rings are dust grains or small gravel-like fragments, some house-sized blocks of ice or rock have been observed. The average thickness of the rings is around 10 m (30 ft).

The main rings of Saturn are assigned a letter by the International Astronomical Union. The original naming scheme designated the outermost visible ring "A" and then the three rings inwards from that B, C and D. Over the years this naming system has become rather confusing as more rings were discovered. A distant ring, located between the orbits of Mimas and Titan, was designated ring E, and then another ring, just beyond the A ring, was named ring F.

As a result, today the list of rings from innermost to outermost goes as follows: D, C, B, A, F, G, E, Pheobe. There are also a few other faint rings whose status is ambiguous, including the Janus/Epimetheus ring, the Pallene Ring and the partial Methone and Anthe ring arcs.

The first person to observe the rings of Saturn was famed Italian astronomer Galileo Galilei in 1610, but the telescopes available at the time were not powerful enough for him to make sense of what he saw. He could make out a central planet and two "lobes" when he first observed Saturn, but his theories didn't stand up to his own subsequent observations. He never went public with his ideas.

The first person to correctly identify Saturn's rings was Dutch astronomer Christian Huygens, who recorded his breakthrough in 1656 by publishing the baffling cipher "aaaaaaacccccdeeeeeghiiiiiiillllmmnnnnnnnnnooooppqrrstttttuuuuu" in a pamphlet entitled De Saturni luna observation nova. This strange statement was an example of what was then a common method of recording preliminary findings or theories, without running the risk of scientific rivals stealing them before they were ready.

In 1659, after confirming his theory, Huygens published Systema Saturnium, sive de causis mirandorum Saturni phaenomenon, et comite ejus planeta novo, in which he explained that his 1656 pronouncement was an anagram of “Annulo cingitur, tenui, plano, nusquam cohaerente, ad eclipticam inclinato." This roughly translates as “It is surrounded by a thin flat ring, nowhere touching, and inclined to the ecliptic.”

The current figures for the mass of Saturn's rings were obtained from measurements taken by the Cassini spacecraft in the final months of its mission in 2017. During this period its orbit was adjusted to bring it between Saturn's cloud-tops and the innermost rings.