Scientists know it as Oceanus Procellarum, but the rest of us generally refer to it as the "Man on the Moon"—the huge dark splotch on the moon visible from Earth. Either way, how did it get there? One commonly held view is that a massive asteroid slammed into the young moon and left its mark. But researchers at MIT say they've got new evidence showing that the 1,800-mile-wide region came not from beyond but from within, specifically from a volcanic eruption that unleashed a "large plume of magma deep within the moon's interior." As the lava made its way to the surface and cooled, it created the dark spots we see today, reports the Telegraph.
In their study, researchers say one of the giveaways is that new data from NASA shows that the region's border is not actually round, but is instead "rimmed by structures that run in straight lines and intersect at angles, similarly to a rectangle," explains Nature. "Such a shape is hard to attribute to a collision, which would be expected to produce a more circular rim." Definitive proof might not come unless astronauts return to the moon, but in the meantime, astronomy writer Phil Plait at Slate thinks the theory makes sense. "I’ve always had a problem with the impact idea," he writes, adding that the "secondary effects" that would have accompanied such a huge meteor strike don't appear to be evident. (Another recent study found that the moon is shaped like a lemon.)