What distinguishes dwarf planets from regular planets?

Dwarf planets are distinguished from regular planets primarily because they are not able to clear their orbits of other debris and celestial objects. This means that while they may be spherical in shape—an important characteristic of both planets and dwarf planets—they still share their orbital zone with other bodies of significant size.

This inability to clear their orbits is one of the defining criteria set by the International Astronomical Union (IAU) in 2006 when classifying celestial bodies. In contrast, regular planets, such as Earth and Jupiter, are capable of dominating their orbits, effectively clearing out smaller objects.

Spherical shape and having a solid surface could apply to both dwarf planets and some regular planets, but it does not distinctly separate them in classification. Additionally, dwarf planets are generally larger than comets, so size comparisons that categorize dwarf planets as smaller than comets do not accurately reflect their classifications. Therefore, the key factor is the capability to clear their orbit, making the second option the correct choice.