What type of celestial body is primarily composed of ice and dust and forms a tail when near the Sun?

A celestial body that is primarily composed of ice and dust, forming a tail when it approaches the Sun, is classified as a comet. Comets originate from areas in the solar system such as the Kuiper Belt and the Oort Cloud, where they reside in relatively stable orbits far from the Sun.

When a comet nears the Sun, the heat causes the ice within it to vaporize, creating a glowing coma and often forming a tail that points away from the Sun due to the solar wind and radiation pressure. This tail can be quite spectacular and is one of the defining characteristics of comets, differentiating them from other celestial objects like asteroids, which are mainly composed of rock and metal and do not develop tails.

The icy composition is significant, as it facilitates the comet's transformation and the development of its tail, which occurs due to the interaction between the Sun's energy and the comet's materials. Understanding this distinction is crucial for identifying the unique behaviors of comets within our solar system.