All about comets in brief; what you always wanted to know, but did not ask, NASA explains

Comets are leftovers from the formation of our solar system. Comets can tell us what the early solar system was like, says NASA.

Scientists believe many of these small worlds have changed very little since they first formed as there is no weathering on them unlike the Earth with its volcanoes and earthquakes.

What is a comet? It is a small body made of dust, ice and rocks left over after the Sun, the planets, and the moon formed.

Comets orbit the sun similar to the way the earth does. Comets reside mostly in the Kuiper belt beyond the orbit of Neptune and the Oort cloud in the outer solar system.

They are probably formed in the outer solar system, their diameters range between  6 and 25 miles. They contain a lot of ice along with rock and hydrocarbons

Their surface is very unstable and changeable, as ice boils off when the comet approaches the sun. They develop comas and tails as they approach the sun.

They may even have contributed a large part of the earth's water.

Comets are different from asteroids. While Comets are mostly made of ice, asteroids are mostly made of rock.