Mars has no little green men, but it's a fascinating place. It has a mountain three times the height of Everest and a deep valley that dwarfs the Grand Canyon. Although Mars has no liquid water on the surface, if the southern polar icecap melted, it could cover the planet 36 feet deep in water.

Mars - Facts for Kids

Valles Marineris is the biggest known canyon system in the Solar System. Here is a picture of Valles Marineris with the outline of the USA drawn on it. The USA's Grand Canyon in tiny in comparison.