The Universe and Galaxies: Uranus and Neptune

Discovery Space: Uranus and Neptune

Uranus and Neptune are the two giant outer planets of the solar system. Neptune is further from the sun and is not visible with the naked eye.

Uranus is slightly larger than Neptune, and both planets are about four times larger than the Earth. Their gaseous envelopes resemble Jupiter and Saturn and consist primarily of hydrogen and helium. Their bluish green appearance is caused by methane.

Both planets have rocky cores. High pressure located deep inside the atmospheres of these planets surrounds their cores with liquid mantles of water, ammonia, and methane. Due to the enormous distances to the sun, both planets receive little solar energy. However, the atmosphere of Neptune is penetrated by strong wind currents and cyclonic storms in the form of oval spots, which can be seen in Neptune’s atmosphere.

The rotational axis of Uranus is tilted sideways, so that it appears as if this planet is inclined toward one side. This inclination is the result of a collision with another celestial body.

Rings and moons

Both planets possess dark ring systems, although they are not as well defined as that of Saturn. Moreover, the ring system of Neptune contains unusual ring arcs as well as extremely fine dust. Uranus is encircled by roughly 27 moons. The five largest are composed of ice and rock. One moon, Miranda, has a diameter of only 292 miles (470 km), but it has a unique surface—rock fragments border onto terrace-like plains and canyons up to 12 miles (20 km) deep. The small moons of Uranus seem to be captured asteroids

Neptune has at least 13 moons. Triton, with a diameter of 1,678 miles (2,700 km), is by far the largest. Since its icy surface reflects most of what little sunlight there is, this moon, with a temperature of only -400°F (-240°C), is one of the coldest objects in the solar system. Its icy volcanoes spew liquid nitrogen, methane, and dust. This mixture freezes immediately and precipitates back to the surface as snow.


Neptune was the very first planet to be found mathematically After the discovery of the planet Uranus in 1781, measurements of the expected trajectory revealed deviations. It was presumed that this was due to gravitational interference by another planet.

John Couch Adams and Urbain Jean Joseph Le Verrier each calculated the trajec tory and the mass of the presumed planet, which was confirmed almost 60 years later.


DISTANCE TO THE SUN: Uranus 1.785 million miles (2,872 million km). Neptune 2,793 million miles (4,495 million km)

ORBIT: Uranus 84.0 years, Neptune 164.8 years

ROTATION PERIOD: Uranus 17.2 hours. Neptune 16.1 hours