The rings

Astronomers on Earth thought Neptune might have some incomplete rings or arcs when they observed an occultation of a star by Neptune in

Figure 12.7 Neptune's two main rings as seen by Voyager 2. The image of the planet is over-exposed to capture detail in the rings. (Photo: NASA)

1984. However, pictures taken by Voyager 2 revealed that these arcs were part of a narrow ring that contains three particularly bright areas. A second narrow ring was identified, as well as two other rings that were more spread out. The ring closest to Neptune is about 42 000 km above the cloud tops. The outer ring, which contains the arcs, is about 63 000 km from Neptune.

Neptune's rings are hard to see because they consist of small particles that reflect little light. Their exact composition is unknown but, because the temperature is so low, they probably contain frozen methane. Some of this methane has been changed by radiation into other carbon compounds, thus making the rings appear dark.

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