Neptune’s Rings
Neither Neptune’s Rings nor the planet itself is visible from Earth with the naked eye, making it the only planet with that distinction. The eighth and most distant Solar System planet is ice giant Neptune.
The planet’s vast distance from the Sun makes it dark and cold. At 30 times as far from the Sun as Earth, Neptune’s noontime looks as dim as our twilight.
Table of Contents
Five relatively young main rings encircle this giant, icy planet. But that’s not all you’ll find. Neptune also has four prominent dust clumps called arcs in its outermost ring. They fascinate scientists because our laws of motion predict the clumps should spread out rather than remain together.
| Planet Type | Ice Giant |
|---|---|
| Radius | 15,299.4 miles (24,622 kilometers) = 4x Earth’s width |
| Moons | 14 |
| Rings | Five main rings, four prominent ring arcs |
| Year Length | 165 Earth years (60,190 Earth days) |
| Day Length | 16 Earth hours |
Neptune Quick View
Voyager 2 is the only spacecraft that flew near the planet, and it photographed Neptune on its way out of the Solar System.
The Voyager 2 ring image below was taken about 683 thousand miles from Neptune in 1989. You can also see the main arc with its three 6-8°-long features.
Let’s take a deep dive into Neptune’s rings.
How Many Rings Does Neptune Have?
Neptune has five dusty rings that range in distance from the planet’s center from approximately 26,000 to 39,100 miles.
Scientists confirmed Neptune’s rings’ presence for the first time during the Voyager flyby. Before that, astronomers thought they existed but couldn’t prove it. William Lassell discovered Neptune’s moon, Titan, and recorded his observation of a ring, but it wasn’t confirmed.
| Name | Distance from Planet’s Center | Observed Width |
|---|---|---|
| Galle | ~26,000 miles (41,900 kilometers) | 1,248 miles (2,000 kilometers) |
| Leverrier | ~33,100 miles (53,200 kilometers) | 68 miles (110 kilometers) |
| Lassell | ~34,400 miles (55,400 kilometers) | 2,485 miles (4,000 kilometers) |
| Arago | ~35,800 miles (57,600 kilometers) | 62 miles (100 kilometers) |
| Adams | ~39,100 miles (62,930 kilometers) | 9 miles (15 kilometers) |
| Arcs: Liberté, Egalité, Fraternité, Courage | ~39,100 miles (62,900 kilometers) | – |
Are Neptune’s Rings Visible?
Yes, the most prominent of Neptune’s rings are visible. The images below come from two 591-second exposures taken with Voyager 2’s wide-angle camera in 1989. The interstellar spacecraft flew about 175,000 miles (280K kilometers) away from Neptune at the time of the pictures.
The two primary rings are backlit by the Sun at a phase angle of 135 degrees and clearly visible. This imaging angle lets you see both rings’ fainter, dusty regions. In addition, the rings around the planet appear complete.
Two NASA photo processing notes:
- The bright center glare comes from over-exposure.
- The two gaps in the outer ring’s upper portion occurred during image processing and didn’t indicate actual gaps.
What Are Neptune’s Rings Made Of?
In 1989, Voyager 2 took an image of Neptune’s rings as it left the planet (top picture above.) The photo is at a 135-degree phase angle, creating ideal conditions for detecting microscopic particles.
Scientists determined that the particles scatter light forward. In addition to their light scattering properties, their brightness indicates that Neptune’s rings consist of dust-sized grains and tiny rocks. They likely formed during the destruction of one of Neptune’s moons and are younger than the planet.
Neptune’s rings differ slightly from those of Saturn, which contains billions of dust-coated ice and rock chunks. Uranus and Jupiter have more similar rings to Neptune with their micrometer-sized dust particles.
The Voyager 2 images below show Neptune’s entire ring system. You can see the thin and bright N53 and N63 rings and the scattered N42 ring. And finally, there’s the plateau outside of N53.
Neptune’s Rings’ Names
In 1846, Johann Galle discovered Neptune using mathematical calculations and predictions from Urbain Le Verrier. As a result, Le Verrier got to suggest the planet’s name after the Roman god of the sea.
Both men were honored by having one of Neptune’s rings named after them. In addition, the remaining rings also received the names of astronomers making important planetary discoveries.
For example, William Lassell discovered the moon Titan. In addition, while Le Verrier used mathematics to predict Neptune’s position, John Couch Adams also made the same calculations.
Adams aimed to explain discrepancies in the laws of Kepler and Newton with Uranus’ orbit. However, neither man knew the other was working towards the same discovery. Le Verrier sent his calculations to Galle at the Berlin Observatory, who confirmed the planet’s existence on September 23, 1846.
Remarkably, Galle found Neptune within one degree of Le Verrier’s calculations. Although Adams did not receive discovery credit for the planet, one of the rings received his name.
And finally, François Arago, a French physicist, played a part in the dispute about Neptune’s discovery. He initially suggested that Le Verrier investigate anomalies in Uranus’ motion. And so, for his contribution, a ring received Arago’s name.
Starting closest to Neptune and moving outward, the planet’s main rings are
- Galle
- Leverrier
- Lassell
- Arago
- Adams
Neptune’s Arcs Names
Neptune has four major arcs within its outermost ring Adams, ~39,000 miles from the planet’s center. The arcs consist of dust clumps and space debris that are likely formed by the nearby moon, Galatea. Scientists think the moon’s gravitational effects help stabilize the arches.
The names of the arcs are
- Liberté (Liberty)
- Egalité (Equality)
- Fraternité (Fraternity)
- Courage
James Webb Neptune Image
The James Webb Space Telescope took the most precise picture of Neptune’s rings since Voyager 2’s flyby. The spectacular September 21, 2022, infrared photograph below came from Webb’s NIRCam (near-infrared camera.)
You can see several narrow and super bright rings. However, Neptune doesn’t appear blue to Webb since it takes photos in the near-infrared range of 0.6 to 5 microns. The planet’s methane gas absorbs red and infrared light, so Neptune looks dark everywhere except in the presence of high-altitude clouds.
You can tell which parts of the picture are methane and ice clouds because they show up as bright spots and streaks. And that’s because they reflect sunlight before the methane gas can absorb it.
What a fascinating view of this ice giant and its rings!
Summary: Neptune’s Rings
While there are no future spacecraft missions to Neptune planned, scientists did risk sending Voyager 2 closer to it than any other planet. And that’s because it was the last stop on the spacecraft’s mission.
Neptune’s rings are dark and likely composed of planetary dust and fine debris, similar to components within the rings of Uranus and Jupiter. Scientists believe Neptune’s rings are much younger than the planet and Solar System. They likely originated when a small inner moon moved close enough to Neptune for its gravity to destroy it.
The planet’s discovery caused an astronomy dispute in 1845. But each scientist, mathematician, and astronomer received the post-humous honor of Neptune’s rings named in honor of their achievements.