Neptune, the eighth planet in the solar system, was the first planet whose existence was predicted more mathematical than through normal observations of the sky.
When Uranus did not move as expected by the astronomers, two independently working mathematicians speculated that the position and mass of another, previously unknown planet influences Uranus orbit. Although “the establishment” ignored this prediction, a young astronomer decided to search after this putative planet.
This planet, Neptune, was discovered in 1846. 17 days later his biggest moon, Triton, was discovered.
Neptune is the last planet in our solar system and nearly 4.5 billion kilometers away from the sun, its orbit around the sun lasts about 165 years.
Neptune has the smallest diameter of all large gas giant planets (Jupiter, Saturn, Uranus and Neptune) occurring in our solar system. This definition refers to the circumstances, that they all don´t have a solid surface. Nevertheless Neptune´s volume corresponds 60 times of the earth´s volume.
Neptune’s axis is inclined 30° to its orbit around the sun. Its seasons last incredible 41 years. During the southern summer the sun appears at the South Pole for 41 years, and for 41 years in the northern summer at the North Pole. Neptune’s atmosphere is composed of hydrogen, helium and methane. The methane gas gives the atmosphere its blue color (because methane absorbs red light). Despite its great distance from the Sun and the low solar energy Neptune storms are three times stronger than Jupiter´s, and nine times stronger than that on Earth.
In 1989, Voyager 2 discovered a large oval dark storm in Neptune’s southern hemisphere. This hurricane-like “Great dark spot” would be large enough to devour the whole earth; it rotates counterclockwise and moves westward with about 1200 km/h.
In recent images from the Hubble Space Telescope the “Large dark spot” was no longer visible, although a comparable spot appeared in Neptune’s northern hemisphere in 1997.
The planet has several rings of different width, which were confirmed by Voyager 2 in 1989. The outermost ring, Adams, contains of 5 different arcs (incomplete rings) named Liberté, Equalité 1, Equalité 2, Fraternité and Courage. The next is an unnamed ring with the same orbit as the moon Galatea, followed by Le Verrier, Lassell, Arago and Galle. It is believed that Neptune’s rings are relatively young and short-lived.
Neptune has 14 known moons, 6 of these were discovered by Voyager 2. The largest moon, Triton, orbits Neptune in a rotation of the planet opposite orbit. He gets more and more closer to the planet and will probably collide in 10 to 100 million years with Neptune, which will constitute enormous rings around Neptune, similar to the rings around the planet Saturn. Triton is the coldest object that has ever been visited in our solar system: its surface temperature is about -235 °C. Despite these extreme cold Voyager discovered 2 great geysers of gaseous nitrogen on Triton.
| Discovery date | 1846 (Johann Galle) |
| Semi-major axis | 4 494 967 199 km = 4.494 x 109 km (30.047 AU) Comparison: 30.047 x Earth |
| Perihelion | 4 444 403 119 km = 4.444 x 109 km (29.709 AU) Comparison: 29.709 x Earth |
| Aphelion | 4 545 531 279 km = 4.545 x 109 km (30.385 AU) Comparison: 30.385 x Earth |
| Diameter | 49 528 km = 4.9528 x 104 km Comparison: 3.883 x Earth |
| Circumference | 155 597 km = 1.55597 x 105 km |
| Volume | 62 526 000 000 000 km3 = 6.2526 x 1013 km3 Comparison: 57.7 x Earth |
| Mass | 102 440 000 000 000 000 000 000 000 kg = 1.0244 x 1026 kg Comparison: 17.147 x Earth |
| Density | 1.76 g/cm3 Comparison: 0.317 x Earth |
| Surface area | 7 640 800 000 km2 = 7.6408 x 109 km2 Comparison: 14.980 x Earth |
| Surface gravity | 10.71 m/s2 Comparison: Someone with 100 kg on Earth, would weigh 110 kg on Neptune. |
| Escape velocity | 85 356 km/h = 23 710 m/s Comparison: 2.12 x Earth |
| Sidereal rotation period | 0.67125 Earth days 16.11 hours |
| Orbital period (Length of a year) |
164.79 Earth years 60 190 Earth days |
| Average orbital speed | 19 720 km/h = 5477.8 m/s Comparison: 0.490 x Earth |
| Eccentricity | 0.00859 Comparison: 0.514 x Earth |
| Inclination | 1.769° |
| Axial tilt | 29.58° Comparison: 1.261 x Earth |
| Peripheral orbit | 28 142 000 000 km = 2,8142 x 1010 km Comparison: 30.44 x Earth |
| Minimum/Maximum surface temperature |
-214 °C = 59 K Comparison: The temperature of the Earth is ~ 185/331 K |
| Composition of the atmosphere |
Hydrogen (H2), Helium (He), Methane (CH4) Comparison: The atmosphere of the Earth is mainly composed of N2 and O2. |
Moons:
Neptune has 14 known moons which are named after sea gods and nymphs in Greek mythology.