Some Planets

The four planets closest to the Sun. Mercury, Venus, Earth and Mars are the four inner planets of the solar system.

After Mars, there are some very large planets. They are called "gas giants" because they do not have a surface you can walk on. The largest planet in the solar system is Jupiter, the fifth planet. Jupiter has many volcanoes and a big red spot. That is a big storm. Spacecraft have been to Jupiter. It has a lot of interesting moons in all. Two of them, Europa and Callisto, may have icy seas. We haven't explored them yet.

Small spacecraft have already explored the sixth planet, Saturn, with its many beautiful rings. We do not yet know what causes the rings. Saturn is very cold and not a good place for humans or for life. One of its moons, called Titan, looks more suitable.

The seventh planet is Uranus. We have not yet learnt much about it. It is blue-green in colour and takes 84 Earth years to travel in orbit around the Sun.

The eighth planet is Neptune, 4.5 billion km from the Sun. Scientists discovered it in 1824. They watched the orbit of Uranus and made use of mathematics to find Neptune. A spacecraft has passed and taken photos, but no spacecraft has studied it carefully.

Pluto lies past the gas giants, very far away. A scientist discovered it in 1930. We have many questions to ask about Pluto, but no spacecraft has gone near it. Pluto is very far from the Sun and very little light or heat reaches it. It is not alone though;there are quite a lot of icy objects out there with it. Scientists have discovered 500 of them, and one, Quaoar, has been "named" the 10th planet by a couple of scientists.