Neptune
Neptune is the furthest planet from the Sun, more than 30 times further away than the Earth.
This photograph of Neptune was made from two images taken by the space probe Voyager 2. You can see the Great Dark Spot, accompanied by bright, white clouds. Below the Great Dark Spot is a bright feature that scientists have called “Scooter” because it whizzes round the planet at crazy speeds. Farther south is “Dark Spot 2,” which has a bright core.
Image Credit: NASA/JPL
| Neptune factfile | |
|---|---|
| Position from the sun | 8th planet |
| Diameter | 50,600 km |
| Distance from sun | 4,500,000,000 km |
| Day length | 16.1 hours |
| Year length | 164 years |
| Number of moons | 14 |
| Surface temperature | -230 °C |
| Gravity | 11.2 m/s2 |
| Atmosphere | Hydrogen, helium, methane |
Tanno and Iguda visited Neptune’s largest moon, Triton. It’s 2,700 kilometres across, so about 22% smaller than Earth’s moon. Triton has the coldest surface anywhere in the Solar System. Like Earth, it has a mostly nitrogen atmosphere, and that’s really unusual. Saturn’s moon Titan is the only other place in the solar system with a mostly nitrogen atmosphere.
This picture shows the view of Neptune on Triton’s horizon. Because of their orbits, Neptune won’t rise but will appear to roll along the horizon from left to right.
When Voyager 2 flew past in 1989, it found geysers blowing darker material up onto the surface making dark streaks. The pinkish deposits form a big south polar cap, probably made of methane ice. A bluish-green band goes all the way around Triton near its equator. This may be new nitrogen frost deposits. The greenish areas includes what is called the ‘cantaloupe terrain’ or ‘melon skin surface’. Astronomers aren’t sure what causes these, but it could be more piles of material from the geyser plumes.
Activity 
By reaching Neptune, Tanno and Iguda got to the furthest planet from our Sun. You can make (or maybe just mark out) a scale model of the solar system to give you an idea of how crazy big it is!
There are two possible models you could make: the sizes of the planets, or the distance to the planets.
| Planet | Distance from Sun (cm) |
|---|---|
| Mercury | 6 |
| Venus | 11 |
| Earth | 15 |
| Mars | 23 |
| Jupiter | 78 |
| Saturn | 143 |
| Uranus | 278 |
| Neptune | 450 |
For the next model, the sizes of the planets, you could draw out circles and colour them in, or maybe you could find objects at home that are about the right size.
| Planet | Size (mm) |
|---|---|
| Mercury | 4.6 |
| Venus | 12 |
| Earth | 13 |
| Mars | 6.3 |
| Jupiter | 130 |
| Saturn | 110 |
| Uranus | 45 |
| Neptune | 46 |
Don’t try building both models in one – at the scale in the bottom table, your Mercury will need to be 58 metres from your Sun! Or, at the scale of the top table, your Mercury will need to be smaller than the size of a red blood cell!
You can go to the previous secret pages by clicking the planets below.
