The planet known for having the highest mountain, Olympus Mons, is Mars. Olympus Mons is a shield volcano and stands approximately 13.6 miles (22 kilometers) high, making it nearly three times the height of Mount Everest, the tallest mountain on Earth. The volcano spans about 370 miles (600 kilometers) in diameter, which is roughly equivalent to the size of the state of Arizona. Its enormous size is attributed to Mars’ lower gravity and geological activity, allowing volcanic structures to grow larger over time. Olympus Mons is a key feature in the study of Martian geology and climate.