Comets

Comets
Beyond Pluto's orbit are the leftovers of the cloud that formed the solar system. It contains billions of icy lumps called comets, and now and then one might be knocked off course and sent in the direction of the Sun. During its journey towards the sun, the ice melts form the giant head of the comet to create an enormous tail. As a comet travels it sheds pieces of itself. From Earth these are seen as showers of light called meteors. If astronomers could get a hold of a comet sample it would be really incredible because it can give them information on the birth of the solar system.
The nucleus of a comet was at first not sure of what it contained until a space probe called Giotto flew past the nucleus of Halley?s Comet in 1986. Giotto sent back pictures showing a nucleus that looks like an icy, rocky potato, and measures 10 x 5 miles (16 x 8 km). This was the first confirmation that comets are giant dirty snowballs.
Comets shed enormous amounts of gas and dust. After about 1,000 years, this dust forms a ring. If the Earth passes through this, the dust burns up in the atmosphere. From Earth, this is seen as a meteor shower or shooting stars.
Comets have been observed and recorded for thousands of years, but they have not always been understood. They were once called "hairy stars," and their sudden appearances made superstitious people regard them as bad omens.