Rings of Neptune - Inner Rings

Inner Rings

The innermost ring of Neptune is called the Galle ring after Johann Gottfried Galle, the first person to see Neptune through a telescope (1846). It is about 2,000 km wide and orbits 41,000–43,000 km from the planet. It is a faint ring with an average normal optical depth of around 10−4, and with an equivalent depth of 0.15 km. The fraction of dust in this ring is estimated from 40% to 70%.

The next ring is named the Le Verrier ring after Urbain Le Verrier, who predicted Neptune's position in 1846. With an orbital radius of about 53,200 km, it is narrow, with a width of about 113 km. Its normal optical depth is 0.0062 ± 0.0015, which corresponds to an equivalent depth of 0.7 ± 0.2 km. The dust fraction in the Le Verrier ring ranges from 40% to 70%. The small moon Despina, which orbits just inside of it at 52,526 km, may play a role in the ring's confinement by acting as a shepherd.

The Lassell ring, also known as the plateau, is the broadest ring in the Neptunian system. It is the namesake of William Lassell, the English astronomer who discovered Neptune's largest moon, Triton. This ring is a faint sheet of material occupying the space between the Le Verrier ring at about 53,200 km and the Arago ring at 57,200 km. Its average normal optical depth is around 10−4, which corresponds to an equivalent depth of 0.4 km. The ring's dust fraction is in the range from 20% to 40%.

There is a small peak of brightness near the outer edge of the Lassell ring, located at 57,200 km from Neptune and less than 100 km wide, which some planetary scientists call the Arago ring after François Arago, a French mathematician, physicist, astronomer and politician. However, many publications do not mention the Arago ring at all.