Mercury does not have to go so far around the sun because it is so close. Venus is the second planet. It is a rocky planet that is covered by by thick clouds of poisonous gases. The thick clouds act like insulation and keep the surface warm. Venus is the hottest planet in the solar system even though it is not as near to the Sun as Mercury.
Earth is the third planet from the Sun.
The Earth is a small rocky planet with an atmosphere. Most of the surface is covered by water or ice. The temperature on Earth is just right for carbon based life. It takes 365 and a quarter days for the Earth to go around the Sun. Earth has a small grey Moon.