10 Facts About the Outer Planets

There are 4 outer planets in the outer region of our Solar System. These are, from largest to smallest, Jupiter, Saturn, Uranus and Neptune. All 4 are gas giants and have ring systems. What follows are 10 facts about the outer planets.

1. The Great Red Spot on Jupiter is a storm

Jupiter red spot.

The area of the storm is bigger than the Earth and it has been raging for hundreds of years.

2. Jupiter is two and a half times more massive than all of the other planets put together

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The above image shows the size comparison between the Earth and Jupiter. Jupiter’s composition is more like that of a star but it is too small to have ignited. If it had, there would have been two ‘suns’ in our Solar System.

3. Europa, one of Jupiter’s moons, has the smoothest surface in the Solar system

Europa, moon of Jupiter.

This suggests that the surface is very young and that there could be an ocean of liquid water beneath the icy crust.

4. The clouds at the north pole of Saturn form a hexagonal shape

Hexagonal cloud formation on Saturn.

This was first seen during the Voyager mission and photographed more clearly by the spacecraft Cassini.

5. Water geysers have been seen on one of Saturn’s moons, Enceladus

Water geysers, Enceladus.

These were first observed in 2005 and are the source of material for one of Saturn’s rings.

6. Galileo Galilei was the first human to see the rings of Saturn through a telescope — he described them as looking like ears!

Voyager image of Saturn.

7. Uranus was discovered in 1781 by William Herschel

Herschel.

It is just about bright enough to be seen by the naked eye under clear, dark skies, but it moves very slowly and was not recognised as a planet until well into the age of astronomy with telescopes.

8. Uranus’s axis of rotation is tilted at 98 degrees to the orbit so it appears to rotate on its side

Uranus from the Hubble Space Telescope.

It is thought that a collision with a planet the size of Earth could have caused this to happen. The above photo was taken by the Hubble Space Telescope and is a false-colour infra-red image.

9. Neptune has some of the strongest winds of all the planets

Neptune.

Winds of almost supersonic speeds sweep through the atmosphere, which is coloured blue because the high methane content absorbs the red light.

10. Between 1846 and 1930, Neptune was regarded as the outermost planet

Le Verrier.

Pluto was discovered in 1930 and became the 9th and outermost planet. But in 2006, the International Astronomical Union (IAU) decided that it was to be called a dwarf planet and so Neptune once again became the outermost of the planets. The picture above shows Urbain Le Verrier, the French astronomer who used mathematics to predict where Neptune should be found.

Taught science for 16 years at a secondary school in the East Midlands.