The nine planets in our solar system vary greatly in size. If you think of them as objects you know,you can understand the sizes. Think of the earth as a small pea. Mercury and Pluto would be pinheads. Mars would be a large pinhead. Venus would be a small pea. Neptune and Uranus would be marbles. Saturn would be a ping-pong ball. Jupiter would be a golf ball. The sun would be a large.