Before the flying over Neptune by the American probe Voyager-2, in 1989, only two satellites, Triton and Nereid, were known. Since thanks to this flying unless 5000 km of distance to Travel 2, Neptune is much better known. It is surrounded with a thick atmosphere on base of hydrogen, with helium and with methane. The absorption of the red radiations, by the methane is responsible, some blue tint of the planet. As we presumed it since observations made from the Earth in 1984 and 1985, Neptune is surrounded with a system of rings formed by rocks and by dusts. Five different rings were identified, among which very diffuse two, at distances included between 42900 and 62900 km of the planet.
The most outside contain three regions of stronger density which correspond to bows observed since the Earth. In 1989, the images taken by Voyager-2 revealed new satellites which form a regular system turning on circular and little tilted orbits. The probe also showed that the planet was surrounded with a complete system of fine rings crimped by brilliant bows. In 2003 the number of satellites of Neptune was 13.
Moons of Neptune |
diameter (km) |
Semi-major axis (km) |
Triton | ≈2 706 | 354 759 |
Proteus | ≈420 | 117 646 |
Nereid | ≈340 | 5 513 818 |
Larissa | ≈194 | 73 548 |
Galatea | ≈176 | 61 953 |
Despina | ≈150 | 52 526 |
Thalassa | ≈82 | 50 074 |
Naiad | ≈66 | 48 227 |
Halimede | ≈62 | 16 611 000 |
Neso | ≈60 | 49 285 000 |
Sao | ≈44 | 22 228 000 |
Laomedia | ≈42 | 23 567 000 |
Psamathe | ≈40 | 48 096 000 |
S/2004 N1 | ≈18 | 105 283 |
Triton is seventh and bigger of the satellites of Neptune. It carries the name of the god of the Greek mythology. Its orbit is reactionary that is that its sense of rotation is set against that of the rotation of Neptune, it supposes that Triton is an outside body which was captured. The moons which have a reactionary orbit cannot have been formed in the same region of the primitive solar nebula as the planets all around of which they turn: they are thus the captured moons. This scenario because of the mass of Triton, is exceptional in the solar system, the known cases have much smaller sizes.
Triton | Moon of Neptune | |
diameter | 2706,8 km | |
mass | 2,140 ×1019 kg | |
discovered in | October 10th 1846 | |
discovered by | William Lassell |
Proteus of irregular shape, is the second biggest moon of Neptune. Protée is an object very dark, looking like the soot, he reflects only 10 % of the light which strikes it. It was discovered on May 24th, 1981 by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Tholen during an eclipse of star.
Its existence was confirmed in 1989 by Stephen p. Bradford A Synnott and. Smith during the passage of the Voyager probe 2 near Neptune.
Proteus is a celestial body covered with craters of impact. Proteus is the name of a marine god of the Greek mythology who could change at will shape, son of Poseidon.
Proteus | Moon of Neptune | |
diameter | 436×416×402 km | |
mass | 5 ×1019 kg | |
discovered in | may 24th 1981 | |
discovered by | Harold J. Reitsema William B. Hubbard Larry A. Lebofsky David J. Tholen |
Larissa of irregular shape, is the fifth moon of Neptune. It was discovered by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Tholen during an eclipse of star by Neptune May 24th, 1981. Its existence was confirmed by Stephen p. Synnott during the passage of the Voyager probe 2 near Neptune in 1989. The orbit of Larissa, close to the planet, is unstable and declines towards Neptune.
Larissa will form a new ring or will be absorbed by Neptune. In the Greek mythology, Larissa is a girl of Triopas, a king of Argos.
Larissa | Moon of Neptune | |
diameter | 208×178 km | |
mass | 5 ×1018 kg | |
discovered in | may 24th 1981 | |
discovered by | Harold J. Reitsema William B. Hubbard Larry A. Lebofsky David J. Tholen |
Galatea of irregular shape, is the fourth moon of Neptune. It was discovered during the passage of the Voyager probe 2 in 1989.
Its name comes from a Nereid (marine nymph) of the Greek mythology. The orbit of Galatea, close to the planet, is unstable and declines towards Neptune. Galatea will form a new ring or will be absorbed by Neptune.
Galatea | Moon of Neptune | |
diameter | 204×184×144 km | |
mass | 4 ×1018 kg | |
discovered in | 1989 | |
discovered by | Stephen P. Synnott |