The Satellites of Neptune

By Daniel Zimmermann

This e-book treats the satellites of Neptune. Considerable space is devoted to the physical features on Triton and the meaning of their names. Treated are its craters, its catenae, its cavi, its dorsa, its fossae, its regiones, its sulci, its planitia, its plana, its paterae, its maculae, and its plumes. An article is devoted to its rings.

• Language: English
• Publisher: Lulu.com
• Release date: Mar 3, 2019
• ISBN: 9780359478187

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The Satellites of Neptune

The Satellites of Neptune

By Daniel Zimmermann

The Dark Rings of Neptune

Names

If you are acquainted with the rings of Saturn and the rings of Uranus, the rings of Neptune may surprise you. Ordinary capital letters supply names for the principal rings of Saturn. They are called the A Ring, B Ring, C Ring, etc. Similarly, most of the rings of Uranus are named after Greek letters. So we would naturally expect the rings of Neptune to bear the names of Arabic or Russian letters, or perhaps Chinese characters.

The scientists who named Neptune's rings had a different idea. They named the rings after people who were somehow associated with the planet Neptune. The innermost ring is called Galle. His name commemorates the discovery of the planet Neptune by the German astronomer Johann Gottfried Galle in 1846. The next closest ring is called LeVerrier after Urbain Jean Joseph LeVerrier, who calculated the position of Neptune from its gravitational effect on Uranus and told Galle where he could find this new planet. The next closest ring is a faint outward extension of the LeVerrier Ring, according to NASA. It is called the Lassell Ring in honor of William Lassell, who discovered Triton, the largest moon of Neptune. Next comes the Arago Ring, named after the French astronomer Dominique François Jean Arago, who invented the polariscope. The outermost ring is the Adams Ring. Like Leverrier, John Couch Adams calculated the position of Neptune before the planet was actually discovered. He told an astronomer named Airy where he could find it, but the Airy did not act on the information. Consequently, Neptune does not have any Airy Ring.

Discovery of the Rings

In 1977, Elliot, Dunham and Fink discovered rings of Uranus when they observed a star as the planet was moving in front of it. Whenever the star was directly behind a ring, the starlight temporarily appeared dimmer; so the three astronomers correctly concluded that rings were obstructing the passage of light.

This inspired Edward Guinan and others to look for Neptunian rings when the planet moved in front of a star. However, the results were perplexing. Sometimes the starlight dimmed when ring material passed in front of it, but sometimes it did not.

When Voyager 2 finally reached Neptune in 1989, it was discovered that Neptune had rings that were not uniform in composition. The rings did not always dim the starlight because some parts of the rings contained fewer particles.

In case of the Adams Ring, some of the more opaque parts were given names. From pictures taken by Voyager 2, it was learned that the Adams Ring contained several ring arcs, which were called Liberté, Egalité, and Fraternité, which is French for Liberty, Equality, and Fraternity.

Dark Albedo of the Rings

The rings of Neptune do not reflect much light. They are much darker than the principal rings of Saturn.

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