Dwarf planets differ from the other planets in that they a. have no atmosphere. b. have no moons. c. are all very far from the Sun. d. have lower mass. e. are covered in ice.

The International Astronomical Union (IAU) is the authority responsible for naming celestial bodies and defining astronomical terms. Established in 1919, the IAU brings together astronomers from all over the globe to promote and safeguard the science of astronomy. They have the final say in the classification of objects in space.

In 2006, the IAU introduced the term 'dwarf planet'. This designation filled a gap between what was considered a planet and smaller objects like asteroids. The IAU set specific criteria to differentiate these celestial bodies from regular planets. This was essential in establishing a clear understanding and uniformity in what defines various objects in our solar system.

To classify an object as a dwarf planet, several criteria must be met:

• It must orbit the Sun.
• It must not be a satellite (meaning it does not orbit another planet).
• It must have not cleared its orbital path of other debris.
• It must have enough mass for its gravity to shape it into a nearly round form.

The most critical criterion distinguishing dwarf planets from regular planets is their inability to clear their orbital path. Regular planets exert enough gravitational force to clear the neighborhood around their orbit, pushing or pulling smaller objects away. Dwarf planets, however, lack the necessary mass and, hence, gravitational force to achieve this. This inability leads to a more cluttered orbital path, filled with other small bodies like asteroids.

Mass is a crucial element in the classification of celestial bodies. The mass of a dwarf planet is significantly smaller than that of a regular planet. This difference in mass has several implications:

• Lower mass means less gravitational pull, making it harder for dwarf planets to clear their orbits.
• The smaller mass affects the shape, though they are typically rounded due to their gravity.

For example, Pluto, a well-known dwarf planet, does not have enough mass to clear its orbital zone of other objects. Instead, it shares its orbit with a multitude of other bodies in the Kuiper Belt. This inability to clear its orbit is a direct result of its lower mass compared to the eight main planets in our solar system. Understanding these distinctions helps clarify the unique characteristics that separate dwarf planets from their larger counterparts.