The Manga Guide to the Universe

How Big Is the Solar System? 127

How Big Is the Solar System?

Although Pluto was removed from the category of planet in 2006, this did not change the

fact that it is one of the heavenly bodies that form the solar system. So what indicates the

extent of the solar system, and how large is it?

First, the distance (semimajor axis) to the outermost planet Neptune in terms of astro-

nomical units is approximately 30 AU. Beyond that, in the range from 30 to 100 AU, is the

Kuiper Belt, where many comets orbit the Sun. Unlike asteroids, these Kuiper Belt objects

(KBOs) consist mainly of different types of ices like water, methane, and ammonia. The Kui- ...