Which of the following is NOT a component of a planetary system?

A planetary system is primarily composed of a star and various celestial bodies that are gravitationally bound to it, including planets, moons, asteroids, comets, and sometimes other smaller bodies. The defining feature of a planetary system is its organization around a central star, which provides the necessary gravitational pull to keep the other objects in orbit.

In this context, stars, planets, and comets are all integral components of a planetary system. Stars are the central objects around which the entire system is structured, planets are the significant bodies that orbit these stars, and comets can also be part of the system, occasionally entering orbits that bring them near the star.

Clouds, while they can exist in space and may be involved in the formation of stars and planets (such as molecular clouds that collapse to form new stars), are not classified as components of a fully formed planetary system. Instead, clouds can be considered more of a precursor or a part of the interstellar medium rather than a fixed part of the structure and composition of a planetary system. This distinction makes clouds the correct answer to the question of which is NOT a component of a planetary system.