In the early years of the 21st century, several objects were discovered orbiting the Sun at vast distances. These objects appeared to be similar to large asteroids. Surprisingly, one of them was larger than Pluto.

This now raised an interesting question: are these objects planets?

The Sky Chart shows the orbits of the outer planets (nearly edge-on) and several of the newly discovered objects. Some of these objects orbit the Sun in a region called the Kuiper Belt, and are therefore called Kuiper Belt objects.

Question 2a: How do the distances (from the Sun) of these objects compare to the distances of the outer planets?

Question 2b: How do the orientations of the orbits of the Kuiper Belt objects compare to the gas giants?

Question 2c: What evidence suggests that these objects are not major planets?

Eris, which is larger than Pluto, is also called a dwarf planet. It is the largest dwarf planet discovered so far. As more information becomes available, some of the other objects may also become dwarf planets. For now, these asteroids are called small solar system bodies.

Question 2d: Why is it so difficult to get accurate data for these objects?