Audio Guide：

Astronomers divide the eight planets within our solar system into two groups according to their relative position to the Sun. The four terrestrial planets closer to the Sun include Mercury, Venus, Earth, and Mars. They are smaller in volume and mass, and possess a solid outer crust. Farther away from the Sun, Jupiter, Saturn, Uranus, and Neptune are known as giant planets or Jovian planets. These giant planets are large-mass planets mainly made up of hydrogen and helium and lacking a solid outer shell. Dwarf planets also revolve around the Sun. Their mass fall between planets and asteroids. Excluding planets, satellites, and dwarf planets, all other celestial objects that orbit about the Sun are called small Solar System bodies. Some small Solar System bodies cluster around the asteroid belt between Mars and Jupiter and are the source of meteorites on Earth. Small Solar System bodies can also be found in the Kuiper Belt beyond Neptune’s orbit. Short-period comets we see often come this region. The Oort cloud at the edge of the Solar System is also home to some Small Solar System bodies. The Oort cloud is where long-period comets originate.