Rings of Neptune facts for kids

The planet Neptune has a faint ring system made of several separate rings and some special "ring arcs". These ring arcs are only found in the outermost ring, called the Adams ring. The tiny pieces that make up the rings are unusually dark and have a lot of microscopic dust. Neptune has 13 known moons. Four of these moons orbit the planet inside its outermost rings.

How Neptune's Rings Were Found

Scientists first found clues about Neptune's rings by watching the planet pass in front of a star. This event is called a "stellar occultation." When Neptune passed in front of a star, the star's light would briefly dim or "blink" just before or after the planet covered it. This showed that something around Neptune was blocking the light, but it wasn't a complete ring. This happened five times in the early 1980s.

In 1989, the robotic spacecraft Voyager 2 flew past Neptune. Voyager 2 sent back amazing pictures that gave scientists most of what they know about Neptune's rings today. The pictures also helped explain why the rings looked incomplete from Earth.

Voyager 2 could take pictures with the Sun shining behind the rings. This made tiny dust particles glow brightly, helping scientists see what the rings were made of and how the particles were arranged. From Earth, we always see the rings with the Sun shining towards them, which makes them very hard to spot.

Today, with better telescopes, scientists can see some of Neptune's rings from Earth. However, Neptune itself is very bright, which makes its much dimmer rings hard to see. The very faintest rings still can't be seen, even with powerful telescopes.

The Adams Ring and Its Special Arcs

The most famous of Neptune's rings is the thin outer Adams ring. It's much harder to see than the rings of planets like Saturn or Uranus. The Adams ring is special because it has features called "arcs," which haven't been seen on any other planetary rings. These are three long, narrow parts that are much brighter and look more solid than the rest of the ring.

Each arc stretches for about 4 to 10 degrees of the whole ring. All the arcs are close together, covering less than 40 degrees of the ring's edge. Scientists used to wonder why the material in these arcs didn't spread out evenly around the whole ring.

The three main arcs are named Liberté, Égalité, and Fraternité. These names come from a famous saying of the French Revolution: "Liberty, Equality, and Brotherhood!" Scientists who discovered them during stellar occultations in 1984 and 1985 suggested these names.

How Moons Affect the Arcs

Four of Neptune's 13 moons orbit inside its ring system. The moon closest to the Adams ring is called Galatea. It's a lumpy rock that orbits Neptune at about the same speed as the planet spins. Galatea is about 1,000 kilometers inside the ring.

Many scientists now believe that the moon Galatea helps keep the three arcs in the Adams ring from spreading out. The ring also has 42 small "wiggles," which are like waves about 30 kilometers high. Scientists use these wiggles to figure out how much Galatea weighs.

The best photos from Voyager 2 showed that there are clumps of particles in the rings. It's not clear if these clumps are just fine dust or if they also contain bigger pieces. All of Neptune's rings have a lot of tiny "microscopic dust," especially the arcs of the Adams ring. Scientists know this because these arcs looked very bright in the photos Voyager 2 took with the Sun shining behind them. Neptune's rings have much more dust than the rings of Saturn.

The Adams ring looks very red. The background particles that make up the ring appear twice as bright near the three arcs compared to the opposite side of the ring.

Changes in the Ring Arcs

Scientists have looked at the ring arcs many times since 1998, using powerful telescopes like the Hubble Space Telescope. They've found that the arcs are surprisingly active and change a lot over just a few years.

For example, the Fraternité and Égalité arcs have been swapping material and changing their lengths. Even more dramatically, the Liberté arc seems to be fading away. By 2003, it was only 30% as bright as it was in 1989, and it was barely visible in 2005. It also seemed to split into two parts and moved closer to the Égalité arc.

Another small arc, Courage, was very dim during the Voyager flyby. But in 1998, it suddenly got brighter. More recently, it's back to being dim but has moved ahead of the other arcs. This suggests it might have jumped to a new stable position. Scientists are still trying to understand why the ring arcs are so active and change so much.

Neptune's Inner Rings

Besides the outer Adams Ring, Neptune has other rings closer to its surface:

• An unnamed ring: This is a faint, clumpy ring of dust that follows the orbit of the moon Galatea.

• The large Lassell Ring (1989 N4R): This is a thin sheet of material that stretches for 4,000 kilometers. It's dusty, but less so than some other rings. There's a brighter part on its outer edge called the Arago Ring (1989 N5R). The Lassell Ring touches the LeVerrier Ring on its inner edge.

• The narrow LeVerrier ring (1989 N2R): This is the second most famous of Neptune's rings. It's just outside the orbit of the moon Despina by about 700 kilometers. It's very dusty and similar to the ring arcs.

• The innermost Galle Ring (1989 N3R): This ring is very small and not well known. It's deep inside the orbit of Neptune's innermost moon, Naiad. The Galle Ring is also very dusty, like the ring arcs.

Pictures from Voyager also hint at a wide, spread-out disk of material surrounding the Galle ring. However, it's hard to tell it apart from Neptune's own brightness, so scientists aren't completely sure if it exists.

List of Neptune's Rings

The rings are named after astronomers who made important discoveries about Neptune.

Four of Neptune's moons—Naiad, Thalassa, Despina, and Galatea—orbit inside the ring system.

Images for kids

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  A Voyager ring image shown at increased brightness to bring out fainter features

See also

In Spanish: Anillos de Neptuno para niños