Planetary scientists have identified a massive rectangular shape that appears to be just below the surface of the moon.

According to BBC News, authors of a study published in the journal Nature used data from NASA's GRAIL mission to detect a system of large hidden valleys. After only be able to spot it via gravity maps, scientists can now see it on ordinary photos when knowing where to look.

"Instead of a central circular gravity anomaly like all other impact basins, at Procellarum we see these linear features forming this huge rectangle," study co-author Jim Head, a professor of geological sciences at Brown University, said in a press release. "This shape argues strongly for an internal origin and suggests internal forces."