Mars is home to Olympus Mons, a volcano so gigantic that Mount Everest would stand less than halfway up its slopes.
Olympus Mons is the largest known volcano in the Solar System, rising about 21.9 kilometers (13.6 miles) above the Martian surface. At more than twice the height of Mount Everest, which stands 8,849 meters (29,032 feet) above sea level, it is the tallest volcano ever discovered.
Its immense size extends beyond its height. Olympus Mons stretches roughly 600 kilometers (370 miles) across, and its slopes are so gradual—averaging only about a 5% incline—that someone standing nearby on Mars might not even realize they were looking at a mountain. Scientists believe it reached these extraordinary dimensions because Mars lacks active plate tectonics, allowing lava to erupt from the same hotspot for millions of years. At its peak lies a vast caldera complex nearly 80 kilometers (50 miles) wide, large enough to encompass many major cities on Earth.