The inner planets, or terrestrial planets, are the four planets closest to the Sun: Mercury, Venus, Earth, and Mars.The asteroid belt or main belt is a ring of small and large rocks and dust between the orbits of Mars and Jupiter. Planets that are ‘‘inside’’ - or before - the asteroid belt (which means they are closer to the sun) are called inner planets. Planets that are ‘‘outside’’ - that is, after - the asteroid belt are called outer planets: Jupiter, Saturn, Uranus and Neptune.