The image was captured on May 7 by the Curiosity rover’s Mastcam while it ascended Mount Sharp. While the grainy black-and-white image may have conspiracy theorists over the moon, it almost definitely doesn’t show the entrance to an underground alien society.

“It’s just the space between two fractures in a rock,” Ashwin Vasavada told Gizmodo in a phone call today. Vasavada is a project scientist in the Mars Science Laboratory, and he said the formation is definitely not the entrance to a video game’s dungeon level. “We’ve been traversing through an area that has formed from ancient sand dunes,” he said. These sand dunes were cemented together over time, creating the sandstone outcrops Curiosity is passing by.

Vasavada told us that the fracture is only about a foot tall and that, once these sand dunes were compacted together, they were buried and unburied over time as the sand on Mars’ surface shifted. During this process, the sandstone was under varying pressure, causing it to buckle and fracture in different places. “The fractures we see in this area are generally vertical,” he explained. This particular doorway-shaped fracture likely formed in one of two ways.