NEPTUNE - NEPTUNE'S MOONS

SATELLITES:
Neptune has eight moons. Triton is Neptune's largest satellite. It is the only moon that 
makes an orbit in the opposite direction than it's planet.

TRITON:
       Neptune has eight moons. The largest of these, is Triton with a radius of 1350 km. 
This is three fourth the size of our Earth's moon. Discovered by Lassell in 1846, Triton has
an unusual type of orbit around Neptune. It orbits its planet in the opposite direction of 
the way the planet spins, which leads scientists to believe that Triton formed independently
of Neptune in the outer solar system and was later "captured" by the planet's gravity. 
Scientific evidence shows that the surface of Triton has a thin methane atmosphere. There 
is also a layer of ice covering the surface which may be frozen nitrogen. Another unusual 
characteristic of this moon is its appearance. There are large crater like features. 
However, these craters, instead of being formed by outside material hitting the planet at 
random, are all the same size and shape. This leads scientists to believe that these craters
are evidence of something going on inside the moon itself. In addition to these craters, 
there are dark plumes or geysers, which are formed when sunlight warms the material beneath 
the frozen nitrogen, causing it to vaporize and burst out through the ice. Triton has the 
coldest temperatures in the solar system (it is currently farther out from the sun than 
Pluto), with a surface temperature of -235° C (-391° F). The atmospheric pressure at 
Triton's surface is about 15 microbars.

NEREID:
       Nereid, with a radius of 170 km, was discovered by Kuiper in 1949. Although it 
encircles Nepune in a prograde orbit, it is very eccentric and inclined. In addition, 
Nereid also has a strange shape as well as surface in comparison to other satellites. 
Scientists have tried to determine the spin rate of this moon but have reached several 
contradictory results. It seems that either this moon has a dark spot on its surface or that
it is irregularly shaped and is tumbling chaotically similar to Hyperion, Saturn's moon.

NAIAD:
       Naiad was the last of Neptune's satellites to be discovered. It's diameter is 54 km 
and it's orbital period is 7 hours and 6 minutes at a distance of 23,200 km from Neptune. 
Naiad is oddly shaped and circles Neptune in the same direction as the planet rotates. Naiad
was discovered by Voyager 2 in 1989. It's mass is unknown but it's equatorial radius is 
29 km. The average distance from Neptune is 48,000 km long. Naiad's orbital period is only 
0.294396 days. The magnitude is 24.7 Vo.

THALASSA:
       Another of Neptune's moons is Thalassa. Thalassa is about 80 km in diameter. It's 
orbital period is 7 hours, 30 minutes and is at a distance of 25,200 km from Neptune. This 
satellite is irregularly shaped. Thalassa circles the planet in the same direction as 
Neptune rotates. Thalassa was discovered by Voyager 2 in 1989. It's mass remains unknown, 
but its equatorial radius is 40 km. Its average distance from Neptune is 50,000 km. The 
orbital period for Thalassa is only 0.311485 days. Thalassa has a magnitude of 23.8 Vo.

DESPINA:
       Despina is 27,700 km from Neptune, and makes it's orbit every 8 hours. This moon's 
diameter is about 150 km. It is irregularly shaped and it circles the planet in the same 
direction as Neptune rotates. Despina was discovered by Voyager 2 in 1989. Its mass remains 
unknown, but it has an equatorial radius of 74 km. The average distance of Despina from 
Neptune is 52,500 km. Despina's orbital period is about 0.33 days. Its diameter is about 
150 kilometers (90 miles). It is irregularly shaped and shows no sign of any geological 
modification. Despina circles the planet in the same direction as Neptune rotates, and 
remains close to Neptune's equatorial plane.

GALATEA:
       Galatea is 37,200 km from Neptune. It has a diameter of 180 km with an orbital period
of 10 hours, 18 minutes. It is irregularly shaped and circles the planet in the same 
direction as Neptune rotates.
       Galatea was discovered by Voyager 2 in 1989. The mass remains unknown but it's 
equatorial radius is 79 km. The average distance from Neptune is 62,000 km. Galatea has an 
orbital period of 0.428745 days. Galatea has a magnitude of 22.3 Vo.

LARISSA:
       Larissa is about 48,800 km from Neptune and circles the planet in 13 hours, 18 
minutes. Larissa's diameter is about 190 km. It is irregularly shaped and circles the planet
in the same direction as Neptune rotates. Larissa was discovered by Stephen Synnott in 1989.
It's mass remains unknown and has a radius of 104x89 km. The average distance from Neptune 
is 73,600 km. It has an orbital period of 0.554654 days. The magnitude is 22.0 Vo.

PROTEUS:
       Proteus, the sixth moon of Neptune, is one of the darkest moons in the solar system. 
It reflects only 6 percent of the sunlight that strikes it. Proteus is 400 km in diameter, 
It orbits Neptune from 92,800 km away, making one revolution every 26 hours, 54 minutes. 
Scientists say Proteus is almost as large as a moon can be without its shape being altered 
by its own gravity. It circles Neptune in the same direction as the planet rotates. Proteus 
was discovered by Stephen Synnott in 1989. Proteus' magnitude is 20.3 Vo. The abundance of 
craters points to a history of repeated battering by planetesimals.
       Proteus is irregularly shaped and shows no sign of any geological modification. It 
circles the planet in the same direction as Neptune rotates, and remains close to Neptune's 
equatorial plane.