The moon’s largest dark spot—known as the Ocean of Storms—may have been caused by a massive cosmic impact that created it as many as 4 billion years ago.
The giant magma sea posited by Japanese researchers would have been 1,000 feet wide and several hundred miles deep, exponentially deeper than any ocean on Earth. A lunar orbiter provided the data, which identified deposits consistent with melted mantle material.
The team behind the study on the 1,800-mile spot said its findings might help explain why the near and far sides of the moon are so different. The near side, for example, is packed with volcanic rock, but the far side has barely any.
The new theory joins several others proposed in the past, including the possibility that a baby second moon orbiting the Earth collided with the one we have today.