The theory

Neptune was discovered as a theory, before it was officially discovered and viewed.

Uranus had already been discovered in 1781, and the years following had scientists noticing it was being pulled out of its orbit. Using math, John Couch Adams and Urbain Le Verrier "discovered" Uranus in 1845.

It was finally viewed for the first time in 1846. Neptune has been visited by only one spacecraft, the Voyager 2, in 1989. The spacecraft sent many pictures back to NASA that helped discover more about Neptune.



Neptune, named for the Roman God of the sea because its blue color, is the 4th largest planet in the solar system.

The methane in the atmosphere absorbs all red light, so any sunlight reflected back to us from the atmosphere is blue.

Composed of 85% hydrogen, 13% helium, and 2% methane, the planet Neptune is a mostly gas and it would be impossible to land on the surface, let alone walk around.


Neptune compared to Earth


The smallest planet of the four Gas Giants, Neptune is also the farthest planet from the sun.

While Neptune may be a small planet in comparison to Jupiter, Saturn, and Uranus, it is still almost 4 times wider, and 57 times the volume, of Earth.



Neptune's gravity is 14% stronger than Earth's.

Example: A person weighing 45 kilograms (100 pounds) would weigh about 51 kilograms (114 pounds) at the equator of Neptune, that is if you could get there, or even stand on the planet, which you can't, as we will see.


Neptune is 4.5 billion km (almost 3 billion miles) from the sun, which is almost 6 times farther away than Jupiter.

Being this far away from the sun means amazingly cold temperatures that are cold enough to turn nitrogen into a liquid. Neptune's average temperature is -214° C (-353° F) but can go as low as -220°C (-364°F).

Neptune is unique in that its poles are around 10 degree warmer than the rest of the planet when exposed to the sun. This is due to the odd orbit of Neptune which is tilted at a 30 degree angle. The North and South Pole take turns being exposed to the sun.

Rotation and Revolution

It takes Neptune about 165 years to revolve around the sun. But it only takes 16 hours to rotate once on its own axis.

Not all of the the planet rotates at the same speed, however. Because Neptune is not solid, it takes about 18 hours for the middle to rotate, while the poles rotate in 12 hours.



The core of the planet is made up of rock, metal, and ice, and it heats up to 7000°C (12,632°F), which is hotter than the surface of the Sun at 5500°C (10,000° F).

Due to the heat of the core, the cold of the planet, the tilt, and its distance from the sun, Neptune has intense seasons that each last 41 years. The weather on Neptune has been noted as having the most violent weather of any planet in the Solar System.

Neptune has a group of storms that revolve around the planet, which have been clocked up to 2,100 km (1,305 miles) per hour, the fastest on any planet.

The fastest wind speed ever recorded on Earth is small in comparison at 407 km (253 miles) per hour.


Triton in front, Neptune in the distance


Neptune has 13 moons, the largest called "Triton", named after the son of Neptune in Roman mythology.

It has been surmised that Triton was caught up in Neptune's gravitational pull at one time, as its rotation goes in the opposite direction of Neptune's own rotation.



Neptune also has five rings made of dust and rocks. Scientists over the years speculated there may be rings, but it was not until 1968 one was actually discovered. Even then, it was not positive to be a complete ring.

When Voyager 2's went by the planet in 1989, it was finally proven to have the 5 rings.

They are named after the scientists who had the most to do with discovering the planet: Adams, Arago, Galle, Lassell, and Le Verrier.


Mercury, Venus, Earth, Mars, the Gas Giants Jupiter, Saturn, Uranus and (lastly) Neptune

(Images courtesy NASA.)