WILLIAM & DEBORAH HILLYARD

Solar System -

Neptune

Neptune's Rings

It is not generally known that Neptune has a ring system comprising 5 principle rings called Galle, Le Verrier, Lassell, Arago, and Adams.  There is another very faint, unnamed ring that lies in the orbit of the moon Galatea. 

The Adams ring, unlike any other known in the Solar System, has five distinct arcs that are named Fraternité, Égalité 1 and Égalité 2, Liberté, and Courage. They are quite close together, within less than 50º of longitude, and appear stable.  There have been some changes, however.  The Courage arc moved along its orbit by 8º, and the Fraternité and both Égalité arcs vary in their brightness, amongst other changes.  The reason for their stability was thought to be a  resonance with the moon Galatea that orbits just inside the Adams ring, but observations are casting doubt on this theory, and there is no current alternative.  The arcs occur within a continuous but much fainter ring. 

Astronomers believe that all the rings are relatively young, compared to the age of the Solar System, and are not likely to survive for long.  In fact, since they were first imaged  in 1989, some have visibly deteriorated.  They comprise between 20% and 70% dust particles, which makes them more like Jupiter's ring system than that of Saturn or Uranus.  The general belief is that they are the result of several small moonlets that disintegrated over time. 

Here are some basic statistics about the ring system:
This scematic shows the ring structure together with the moons in their vicinity. 
This is a photograph of the Adams Ring showing three of the arcs; left: Fraternité, center: Égalité, and right: Liberté).  The Le Verrier ring is on the inside.  Credit: NASA/JPL
Ring Name Radius (km) Width (km) Depth (km) Comments
Galle 40,900-42,900 2,000 0.15 A wide, faint ring
Le Verrier 53,200 ± 20 113 0.7 ± 0.2 A narrow, bright ring
Lassell 53,200-57,200 4,000 0.4 A broad, faint ring between the Le Verrier and Arago rings.
Arago 57,200 <100 Unknown
Adams 62,932 ± 2 15 - 50 0.4, (1.25-2.15
within the arcs)
Comprises five bright arcs. 
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