太陽系：惑星 - Map Quiz Game

There are eight planets in the solar system – Pluto was the ninth until being changed to the status of a “dwarf planet”. Planets are masses of rock, liquid, or gas held together by gravity and orbiting the sun as a result of the sun’s gravitational pull. The more massive the planet, the stronger the gravity at the surface. Most planets (except Venus and Mercury) have at least one moon, and some have many.