Quick guide to the planets

There are officially eight planets in the Solar System. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Here is a quick guide to the planets.

A representation of the Solar System by an artist. Distances are not to scale. Image credit: NASA

Until 2006, Pluto was considered the ninth planet, but its status was altered to a new one of dwarf planet. A number of planetary scientists are campaigning to have Pluto classified as a planet once again.


Mercury is the innermost planet in the Solar System, and is a rocky world, 4,880 km in diameter. It has a very eccentric orbit and it is covered with craters. Mercury is bright enough to be seen with the unaided eye, but only when it is far enough away from the Sun in the sky to be glimpsed in morning or evening twilight. Read more about Mercury.


Venus is the second planet from the Sun, and only slightly smaller than the Earth. It is a rocky world shrouded completely by cloud. Its surface has been shown to be covered in volcanoes and completely inhospitable, with poisonous air, crushing atmospheric pressure and searing temperatures. Read more about Venus.


Mars is the next planet out from the Sun after Earth. Smaller than our own planet, with a diameter of 6,795 km, it is similarly rocky. Visiting space probes and landers have shown that it was once covered with seas, though the water has long been lost underground or into space. Scientists are keen to discover if Mars was ever home to life. Read more about Mars.


Jupiter is by far the biggest of the planets, and larger than all the others combined. Its diameter at the equator is a mighty 142,984 km. Unlike the inner planets, it is a fast-spinning ball of gases, but with a solid core deep within. Jupiter has many natural satellites including four large moons. These moons, along with belts and bands in Jupiter’s cloud tops and a Great Red Spot, can be seen with small telescopes. Read more about Jupiter.


Saturn is a smaller gas giant than Jupiter, and 120,540 km wide at the equator. Its yellowish cloud tops are more bland than Jupiter’s, but the planet is encircled by bright rings which make it a spectacular sight through a telescope. These rings are made up of countless icy and rocky particles. Saturn also has multiple moons, the largest of which is Titan, which has a dense atmosphere. Read more about Saturn.


Uranus is the first of the planets to be discovered, in 1781 by Sir William Herschel, because it was too faint to be noticed by ancient people. In fact it is just bright enough to see with the unaided eye if you have perfectly dark skies. Through a telescope it has a bluish hue. Uranus is the first of two planets termed ice giants. Its diameter is 50,724 km and it has 27 known moons. Read more about Uranus.


Neptune is the outermost planet in the Solar System, following the reclassification of Pluto.  It was discovered in 1846 by Urbain Le Verrier. Neptune’s equatorial diameter is 49,244 km and it has 13 known moons. Neptune is another ice giant. Its atmosphere is bluer than Uranus, and it occasionally shows dark spots and other features in its cloud tops. Read more about Neptune.