The solar system’s smallest planet may look like Earth’s moon, but don’t mistake Mercury for another familiar face. Before 2008, fewer than half of the planet’s surface features had ever been seen by humans. Now, NASA’s MESSENGER spacecraft has imaged over 90 percent of the planet to help paint a complete picture of its geologic past. Like the moon, scores of craters pock Mercury’s exterior. But unlike the moon, gigantic scarps, or cliffs, climb thousands of feet above its terrain. Such features are the result of the planet’s crust shrinking during a period of cooling after its formation. As scientists piece together its history, they hope to ultimately learn about the processes that forged Mercury over four billion years ago. Watch the video to see close-up views of the surface taken from orbit.