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Encyclopedia > Numbers about the solar system XII
Orbital elements of satellites: NEPTUNE
The planet Neptune has rings and three families of satellites, orbiting around it (15 satellites of which 14 numbered on December 3, 2022):
- the rings were discovered in 1989 by Voyager but have been suspected during the Earth-based observation of an occultation of a star by the planet Neptune.
- the inner satellites: these satellites are orbiting inside the orbit of Triton, the main satellite. Because of the closeness of the planet, they are very difficult to observe. Infrared observations are necessary in order to decrease the contrast brightness between the planet and the satellites.
- the main large inner satellite : Neptune has a big satellite Triton, similar to a small planet, which is bright and easily observable. However, it is close to the planet.
- the main outer satellite : Neptune has a faint satellite Nereide orbiting outside the orbit of Triton. It is observable as an asteroid, independantly of the planet Neptune far from it. Only its faintness is a difficulty for its observation.
- the outer satellites: these satellites are orbiting outside the orbit of Nereide, the farthest main satellite. They are very faint due to their small sizes and their orbits are neither circular, nor in the equatorial plane of Neptune as the inner and the main satellites. They are observable as asteroids, independently of the planet Neptune far from them. Only their faintness is a difficulty for their observation.
The tables below provide the main characteristics (size, magnitude) of these satellites togther with the orbital elements. These data may change either because new data are more precise, or because some parameters are evoluting year after year. The year of the discovery is provided by the provisional name of the satellite. For some satellites, specific descriptive pages are available.
The rings
| Rings and inner satellites |
Distance to the center of Neptune |
Size of the ring | Albedo |
|---|---|---|---|
| 1989 N3R (Galle) | 41 900 km | 15 km | very faint |
| satellite Naiade (N-3) | 48 227 km | - | - |
| satellite Thalassa (N-4) | 50 075 km | - | - |
| satellite Despina (N-6) | 52 526 km | - | - |
| 1989 N2R (Le Verrier) | 53 200 km | 15 km | very faint |
| 1989 N4R (Lassell, Arago) | 53 200 km | 5 800 km | very faint |
| satellite Galatea (N-6) | 61 953 km | - | - |
| 1989 N1R (Adams) | 62 930 km | less than 50 km | very faint |
The inner satellites
| satellites |
a in km | P in days | eccentricity | inclination on the equator of Neptune | d in km | mv | ap in arcsec | discovery |
|---|---|---|---|---|---|---|---|---|
| Naiade - N 3 | 48 227 | 0.294 40 | 0.000 33 | 4.74° | 58 | 24.7 | 2.3 | 1989 N6 |
| Thalassa - N 4 | 50 075 | 0.311 48 | 0.000 16 | 0.21° | 80 | 23.8 | 2.4 | 1989 N5 |
| Despina - N 5 | 52 526 | 0.334 66 | 0.000 139 | 0.07° | 148 | 22.6 | 2.5 | 1989 N3 |
| Galatea - N 6 | 61 953 | 0.428 75 | 0.000 12 | 0.05° | 158 | 22.3 | 3.0 | 1989 N4 |
| Larissa - N 7 | 73 548 | 0.554 65 | 0.001 39 | 0.20° | 208 x 192 x 178 | 22.0 | 3.5 | 1989 N2 |
| Proteus - N 8 | 117 647 | 1.122 32 | 0.000 44 | 0.04° | 436 x 416 x 402 | 20.3 | 5.6 | 1989 N1 |
The size d provided corresponds to : sub-planetary equatorial diameter, equatorial diameter along the orbit and polar diameter of the triaxial ellipsoide
The main satellite
| Triton - N 1 | |
|---|---|
| semi-major axis in km | 354 759 |
| period of revolution | 5.876 85 d |
| eccentricity | 0.000 02 |
| inclination on the equator of Neptune | 156.3 ° |
| size in km | 2705.2 |
| magnitude at opposition | 13.7 |
| apparent distance to Neptune at opposition | 17 arcsec |
The main outer satellite
| Nereide - N 2 | |
|---|---|
| semi-major axis in km | 5 513 410 |
| period of revolution | 360.135 d |
| eccentricity | 0.751 |
| inclination on the equator of Neptune | 6.68 ° |
| size in km | 340 |
| magnitude at opposition | 18.7 |
| apparent distance to Neptune at opposition | 4 min 24 arcsec |
The outer satellites
| satellites: |
a in km | a in AU | P in years | eccentricity | inclination on the ecliptic | d in km | mv | ap |
|---|---|---|---|---|---|---|---|---|
| Halimede - N 9 (S/2002 N1) | 15 728 000 | 0.1051 | 5.15 | 0.571 | 134°.1 | 61 | 24.5 | 19 min |
| Sao - N 11 (S/2002 N2) | 22 422 000 | 0.1499 | 7.98 | 0.293 | 48.5° | 40 | 25.4 | 27 min |
| Laomedeia - N 12 (S/2002 N3) | 23 571 000 | 0.1576 | 8.67 | 0.424 | 138° | 40 | 25.4 | 28 min |
| Psamathe - N 10 (S/2003 N1) | 46 695 000 | 0.3121 | 24.96 | 0.450 | 137°.4 | 38 | 25.6 | 56 min |
| Neso - N 13 (S/2002 N4) | 48 387 000 | 0.3234 | 26.66 | 0.495 | 132°.6 | 60 | 24.6 | 58 min |