Final answer:
Saturn is an outer planet because it is located beyond the main asteroid belt, which lies between Mars and Jupiter.
Step-by-step explanation:
Saturn is considered to be an outer planet because it is located after the main asteroid belt. The major planets in our solar system, in order of distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
The asteroid belt is the region between Mars and Jupiter, containing most asteroids, which extends from 2.2 to 3.3 AU (Astronomical Units) from the Sun. This places Saturn, with its orbit at almost 10 AU from the Sun, well beyond the main asteroid belt, making it one of the four giant planets in the outer solar system along with Jupiter, Uranus, and Neptune. These giant planets are characterized by their large sizes, long orbital periods, and systems of rings and moons.