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Why do the arcs in Neptune’s Adams ring look brighter than other parts of the ring?

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Clouds in Neptune's atmosphere — 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 arcs in Neptune’s Adams ring appear brighter than other parts of the ring because they are regions where the density of ring particles is particularly high.1

While the moon Galatea, which orbits just planetward of the ring, may gravitationally interact with the material to trap particles in these arclike regions, collisions between particles should theoretically cause the material to spread uniformly over time. Consequently, scientists suspect that the event that supplied the material for these enigmatic arcs—possibly the breakup of a small moon—occurred relatively recently, within the past few thousand years.1