A few comets draw nearer to the Sun and accordingly lose mass all the more rapidly. Â
Long-period comets (those which take over 200 years to orbit around the Sun) start from the Oort Cloud. Â Danish space expert Jan Oort suggested that comets live in an immense cloud at the external scopes of the close planetary system, a long ways past the orbit of Pluto. This came to be called as the Oort Cloud. Â
The major constituents of a comet are ice, dust and water.
Comets don't generally have tails. They build up a fluffy, shell-like cloud known as a coma, and one, two, or three tails when close to the Sun.