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What are Neptune’s rings mostly made of?
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Neptune
A photograph of clouds in Neptune's atmosphere, taken by Voyager 2 in August 1989. The view is from below the planet's equator, and north is up. The Great Dark Spot (center left) is 13,000 km (8,100 miles)—about the diameter of Earth—in its longer dimension. Accompanying it are bright, wispy clouds thought to comprise methane ice crystals. At higher southern latitudes lies a smaller, eye-shaped dark spot with a light core (bottom left). Just above that spot is a bright cloud dubbed Scooter. Each of these cloud features was seen to travel eastward but at a different rate, the Great Dark Spot moving the slowest.
The exact chemical composition of Neptune’s rings is not definitively known. However, observations indicate that the rings are largely populated by dust-sized particles, as they are most visible when backlit by sunlight, which causes these small particles to scatter light forward.1
While their precise makeup remains uncertain, it is hypothesized that the surfaces of the ring particles—and potentially the particles in their entirety—may be composed of radiation-darkened methane ices, similar to the rings of Uranus. Additionally, studies of the rings' interaction with light suggest they are nearly devoid of larger particles, specifically those in the centimeter-size range or greater.1