Which celestial object is primarily composed of a nucleus of ice and dust?

A comet is primarily composed of a nucleus of ice and dust, which distinguishes it from other celestial objects such as asteroids, meteors, and planets. The nucleus of a comet, often referred to as a "dirty snowball," is made up of frozen gases, water ice, and dust particles. When a comet approaches the Sun, the heat causes the ices to sublimate, creating a glowing coma and often a tail that extends away from the Sun due to solar wind and radiation pressure.

This unique composition is what allows comets to display striking features when they are close to the Sun, contrasting with asteroids, which are primarily made of rock and metal, and do not typically exhibit such activity. Similarly, meteors are merely the glowing trails produced when bits of space debris enter the Earth's atmosphere, and planets are large celestial bodies that have cleared their orbits of other debris and are typically composed of various materials, including metals and gases. Thus, the correct identification of a comet lies in its icy, dusty nucleus that creates its distinctive appearance when encountered with solar energy.