The asteroid belt divides planets into two groups-inner planets and outer planets. They are rocky and small. They are gaseous and larger. Some astronomers do not consider Pluto as the ninth planet. Instead, they think it is a large asteroid.
Planets travel in orbits around the Sun.
If you look from above, they all move in counter-clockwise direction, but with different speed . The orbits of Mercury and Pluto are elongated and make a slightly tilted plane. The length of time that the earth takes to complete one circle around the Sun is called a year. This time varies for different planets depending on their distance from the Sun. Mercury takes about 88 days to complete one circle.