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Neptune: Rings
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This Voyager image, FDS 11412.51, shows the three main arcs in Neptune's Adams Ring. The Liberty arc is near the lower edge of the image, followed by Equality and Fraternity above it. A fourth, fainter arc, called Courage, would be just ahead of Liberty.
This Voyager image, FDS 11412.51, shows the three main arcs in Neptune's Adams Ring. The Liberty arc is near the lower edge of the image, followed by Equality and Fraternity above it. A fourth, fainter arc, called Courage, would be just ahead of Liberty.

Evidence for incomplete arcs around Neptune first arose in the mid-1980s, when stellar occultation experiments were found to occasionally show an extra "blink" just before or after the planet occulted the star. Images by Voyager 2 in 1989 settled the issue, when the ring system was found to contain several faint rings, the outermost of which, named Adams, contains three prominent arcs now named Liberty, Equality and Fraternity. The existence of arcs is very difficult to understand because the laws of motion would predict that arcs spread out into a uniform ring over very short timescales. The gravitational effects of Galatea, a moon just inward from the ring, are now believed to confine the arcs.

Several other rings were detected by the Voyager cameras. In addition to the narrow Adams Ring 63,000 km from the center of Neptune, the Leverrier Ring is at 53,000 km and the broader, fainter Galle Ring is at 42,000 km. A faint outward extension to the Leverrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km.

References:
Murray, C. D., and S. F. Dermott 1999. Solar System Dynamics, Cambridge University Press.

USGS Astrogeology: Gazetteer of Planetary Nomenclature -- Ring Nomenclature

Neptune's Rings
Ring Name: 1989 N3R Galle
Distance*: 41,900 km
Width: 15 km
Albedo: Low

Ring Name: 1989 N2R Leverrier
Distance*: 53,200 km
Width: 15 km
Albedo: Low

Ring Name: Lassell
Distance*: 55,400 km
Width: - km
Albedo: Low

Ring Name: Arago
Distance*: 57,600 km
Width: - km
Albedo: Low

Ring Name: 1989 N1R Adams
Distance*: 57,600 km
Width: - km

Ring Name: Liberte ("Leading" Adams arc)
Distance*: 62,930 km
Width: < 50 km
Albedo: Low

Ring Name: Egalite ("Equidistant" Adams arc)
Distance*: 62,900 km
Width: - km

Ring Name: Fraternite ("Following" Adams arc)
Distance*: 62,900 km

Ring Name: Courage (arc)
Distance*: 62,900 km
Width: - km

* The distance is measured from the planet center to the start of the ring.
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Last Updated: 2 Apr 2014