Astronomy Practice Exam

What distinguishes a dwarf planet like Pluto from traditional planets?

1. Its size and orbital characteristics

2. Its composition of rock and ice

3. Its distance from the Sun

4. Its lack of moons

The correct answer is: Its size and orbital characteristics

A dwarf planet, such as Pluto, is primarily distinguished from traditional planets by its size and orbital characteristics. While traditional planets are classified as bodies that have cleared their orbital paths of other debris, dwarf planets share orbits with other objects of similar size and have not cleared their orbital zones. This means that they do not dominate their orbits like the eight recognized planets do. In the case of size, dwarf planets are generally smaller than the major planets, which contributes to the enhanced distinction between the two categories. While other factors, such as composition and distance from the Sun, may play a role in the characteristics of dwarf planets, these elements do not intrinsically define the classification. For example, both dwarf planets and traditional planets can be made of rock and ice (as in the case of many celestial bodies in the outer solar system), and their distances from the Sun do not serve as a defining characteristic for their classification. Additionally, many dwarf planets possess moons, making the lack of moons less relevant as a discriminatory factor. Therefore, it is primarily the combined aspects of size and the ability to clear their orbit that set dwarf planets apart from traditional planets.