In 2012, led by the Massachusetts Institute of Technology, NASA launched the Grail mission, which involved two very similar satellites chasing each other around the moon while mapping it in multiple ways. Now, scientists have identified the remains of old rift valleys, once filled with lava, just beneath the moon’s surface.

Huge Rectangle Found Just Below Moon's Surface

Moon’s bizarre feature

The feature is centered on the moon’s Procellarum region and was undetectable before the Grail mission’s gravity mapping efforts. Now that gravity mapping has brought it to light, scientists are now seeing that it can be identified in standard photography.

“It’s really amazing how big this feature is,” says Professor Jeffery Andrews-Hanna of the Colorado School of Mines. “It covers about 17% of the surface of the Moon. And if you think about that in terms relative to the size of the Earth, it covers an area equivalent to North America, Europe and Asia combined,” he recently told BBC News.

“When we first saw it in the Grail data, we were struck by how big it was, how clear it was, but also by how unexpected it was,” said Andrews-Hanna

“No-one ever thought you’d see a square or a rectangle on this scale on any planet,” he continued.

Similar to Earth? Not quite

The scientist and his compatriots point out that the region is comprised of numerous native radioactive elements including uranium, potassium, and thorium which in the past would have heated the lunar crust and contracted upon cooling. That contraction tore into the moon’s surface and formed massively deep valleys.

A smaller scale example here on Earth is the Giant’s Causeway in Northern Ireland, where cooling and contraction produced hexagons with 120 degree angles.

“What we’re seeing is a clever trick of spherical geometry. For structures on this scale, a polygon with 120-degree angles at the corners actually has four sides instead of six,” explained Andrews-Hanna when explaining the lunar feature compared to similar valley’s here on our planet.

While scientists are unsure when this occurred but thanks to the Apollo missions they are estimating that the rifts were made around 3.5 billion years ago.