Mars is the second smallest planet in the solar system and is often called the red planet due to its reddish appearance. It is made up of rocks. Christian Huygens first discovered Mars in the 1600s, though he was not certain. Giovanni Schiaparelli later observed water canals on Mars that he believed were made by an intelligent creature. A diagram shows key features of Mars including its north and south poles, water ice clouds, dust storms, and the Viking Lander site where NASA landers touched down.