Asteroids are thousands of little space rocks that circle round the Sun in a big band from an asteroid belt between Mars and Jupiter. The biggest asteriod is Ceres which is 1000 km across. However, most asteriods are smaller. Till today, over 3200 asteriods have been identified!

As asteriods are too small to be considered as planets, they are known as minor planets. Some of them have orbits that cross Earth's path and some have even hit the Earth in the past! One of the best preserved examples is Barringer Meteor Crater near Winslow, Arizona!

Asteroids are actually material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago. Asteroids may also be material that never coalesced into a planet. If the estimated total mass of all known asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across -- less than half the diameter of our Moon. However, there may have been more material originally.

Spectacular comets are just dirty iceballs a few kilometres across. Normally, they circle the outer reaches of the solar system. But occasionally, one of them is drawn in towards the Sun. As it hurtles towards the Sun, it melts and a vast tail of gas is blown behind by the solar wind. We may see this spectacular tail in the night sky shining in the sunlight for a few weeks unti it swings rond the Sun and out of sight. The most recent comet was Hale-Bopp in 1997.

When comets are near the Sun and active, they have several distinct parts: