The dust that is released from the comet nucleus is pushed behind the comet to form a diffuse tail.
The escaping gas of a comet creates a sort of atmosphere around the nucleus which is picked up by solar radiation to form plasma tail.
The heart of a comet is a solid body, a dirty snowball of ice and rock, which is called the nucleus. Near the Sun ices on its surface begin to evaporate.
Comets, composed of a rocky nucleus, the coma, a dust tail and a plasma tail, can inform us about the early history of the Sun and the planets.