Small Satellites Near The Rings

Four known satellites orbit near or within the Neptune ring system (see Table 8.1). These include Naiad, Thalassa, Despina, and Galatea. Naiad, Thalassa, and Despina are all between the Galle and Le Verrier rings. Galatea seems to circle Neptune precisely 43 times for every 42 circuits of particles in the Adams ring. In scientific terms, that means that the Adams ring and its ring arcs are located at a 42: 43 outer Lindblad resonance [17] of Galatea. Galatea may therefore be partly responsible for the narrowness of the Adams ring. It may also play a role in the azimuthal confinement of the ring arcs. Over time, its gravitational influence will create 42 nodes in the Adams ring which may inhibit the azimuthal motion of ring particles past those nodes, which would be separated by 8.57° of ring longitude. Six nodes would span a longitudinal range of about 42.85°, very nearly the same as the longitude span covered by the five known arcs.

Table 8.1. Neptune ring dimensions (1RN = 24,674 km, 1MN = 10.246 x 1025 kg).

Ring region

Boundary

Boundary

Velocity,

Period

Mass

(km)

(RN)

(km/s)

(hr)

(Mn)

Galle ring

~40,900

1.66

12.94

5.518

??

~42,900

1.74

12.63

5.927

(Naiad

48,227

1.95

11.914

7.065

2 x 10-9)

(Thalassa

50,075

2.02

11.690

7.476

4 x 10-9)

(Despina

52,526

2.12

11.414

8.032

20 x 10-9)

Le Verrier ring

53,200 ± 20

2.15

11.35

8.187

??

Lassell ring

53,200

2.15

11.35

8.187

??

57,200

2.31

10.92

9.129

Arago ring

57,200

2.31

10.92

9.129

??

Unnamed ring

~61,950

2.50

10.50

10.290

??

(Galatea

61,953

2.50

10.508

10.290

37 x 10-9)

Adams ring

62,932 ± 2

2.54

10.42

10.535

??

(Larissa

73,548

2.97

9.643

13.312

48 x 10-9)

Note: Widths of the narrow rings (in km) are: Le Verrier ~110; Arago and Unnamed <100; Adams 15-50.

Note: Widths of the narrow rings (in km) are: Le Verrier ~110; Arago and Unnamed <100; Adams 15-50.

Despina is relatively close to the Le Verrier ring, but its gravitational force seems to have no effect on that ring. The center of the ring is only a few kilometers from the position of a potential 53: 52 outer Lindblad resonance, but the 54: 53 resonance is only 13.1 km closer to the planet, and the Le Verrier ring has a width of about 110 km. Furthermore, the absence of azimuthal inhomogeneity or internal radial structure would seem to rule out substantial gravitational effects from Despina. If the Le Verrier ring's width is affected by a Lindblad resonance, it does not appear to be that of Despina.

Galatea seems also to be subject to bombardment by meteoroids that have blasted material from its surface. That is probably the source of the tenuous and possibly intermittent ring that shares its orbit. Little more is known about this tenuous ring that has yet to garner an official name from the International Astronomical Union's Nomenclature Commission.

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