Asteroids,+Comets,+the+Kuiper+belt+and+Ort+cloud

The Asteroid belt


Between Mars and Jupiter lies the Asteroid belt. This consists of more than 100 000 lumps of irregular rock of all sizes, up to several hundred km across, as well as a dwarf planet - Ceres. These rocks are left over from the formation of the solar system and have not managed to clump together to form a planet due to the gravitational disturbance caused by Jupiter.

Comets


Comets are lumps of ice and dust that periodically come into the centre of the solar system from the outer reaches (Kuiper belt or Ort cloud). As comets approach the Sun, the heat makes them start to evaporate. Comets themselves will have a core less than 50 km across, however they have long 'tails' which are made up of jets of gas and dust which can be millions of miles long. These tails point away from the Sun (rather than back along the path of the comet) although the dust tail is deflected less than the ion (gas) tail and so points is a slightly different direction. The dust tail "glows" from the light of the Sun reflecting off the icy material, while the gassy tail glows from ionisation.