Mars, the “red planet”, is easily observed in the sky with the naked eye. It is the only planet in the solar system other than Mercury whose solid surface is visible from Earth. The rich red color makes it one of the most fascinating celestial bodies, around which numerous stories have been set. Since ancient times, people have fantasized that it was the home of various gods. For example, the ancient Egyptians named the planet “Horus on the Horizon” (after the Egyptian god of the sky), the Greeks called it “Ares” (after the Greek god of war), and the name “Mars” (after the Roman god of war) was given by the Romans. The ancient Chinese observed that the color of Mars was like fire and that it sometimes moved across the sky from west to east, but sometimes from east to west. This confusing phenomenon led to the name “Yinghuo”, which means “gleaming flame that confounds our expectations”.