What defines a dwarf planet?

The defining characteristic of a dwarf planet is that it orbits a star, maintains a nearly round shape due to its self-gravity, and has not cleared its orbital zone of other debris. This definition highlights the importance of both the celestial body's shape and its orbital dynamics in distinguishing it from full-fledged planets.

To clarify further, while it is true that many dwarf planets, like Pluto, are smaller than Earth, the key aspect of the definition lies in their inability to clear their orbit, which differentiates them from planets. Additionally, the assertion that a dwarf planet does not orbit a star is inaccurate since all dwarf planets must orbit a star, specifically our Sun in the case of those in our solar system. Lastly, the composition of a dwarf planet is not limited to ice; they can be made of various materials, including rock. Thus, the first option encapsulates the core definition of a dwarf planet, making it the correct choice.