Neptune

Neptune showing it's storms, the great spot and scooter

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 sun8th planet
Diameter 50,600 km
Distance from sun4,500,000,000 km
Day length 16.1 hours
Year length 164 years
Number of moons14
Surface temperature-230 °C
Gravity11.2 m/s2
AtmosphereHydrogen, helium, methane
FUN FACT: Neptune was discovered in 1846 by Johann Gottfried Galle.
neptune seen from Triton
Image Credit: NASA/JPL/USGS

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.

Voyager 2 photo of Neptune's moon Triton.
Image Credit: NASA/JPL/USGS
Do you think Triton looks like a melon?

Activity The solar system

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.

PlanetDistance from Sun (cm)
Mercury6
Venus11
Earth15
Mars23
Jupiter78
Saturn143
Uranus278
Neptune450
These numbers will let you set out a solar system so the planets are all the correct distances from the Sun, at a scale of 10 million kilometres in space to one centimetre on your model.

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.

PlanetSize (mm)
Mercury4.6
Venus12
Earth13
Mars6.3
Jupiter130
Saturn110
Uranus45
Neptune46
These numbers will let you set out a solar system so the planets are all the correct sizes compared to each other, at a scale of 1000 kilometres in space to one millimetre on your model.

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.

The MoonVenusMercury
Moon landing sites for Apollo missions
The SunMarsAsteroids
An image of the Sun in 2018 when it had no sunspots.
JupiterSaturnUranus
Hubble Views of JupiterQuadruple Saturn moon transit snapped by HubbleThis is an image of the planet Uranus taken by the spacecraft Voyager 2 in 1986.