NASA GRAIL: Procellarum region on the Moon

The Moon, as observed in; GRAIL gravity gradients (top), topography (center, where red is high and blue is low), and in visible light (bottom). 

The Procellarum region is a broad region of low topography covered in dark mare basalt. 

The GRAIL gravity gradients reveal a giant rectangular pattern of structures surrounding the region. 

Credit: NASA /Colorado School of Mines /MIT /JPL /Goddard Space Flight Center

New data obtained by NASA's GRAIL mission reveals that the Procellarum region on the near side of the moon, a giant basin often referred to as the "man in the moon," likely arose not from a massive asteroid strike, but from a large plume of magma deep within the moon's interior.

The Procellarum region is a roughly circular, volcanic terrain some 1,800 miles in diameter, nearly as wide as the United States.

One hypothesis suggested that it was formed by a massive impact, in which case it would have been the largest impact basin on the moon.

Subsequent asteroid collisions overprinted the region with smaller, although still large, basins.

Now researchers from MIT, the Colorado School of Mines, and other institutions have created a high-resolution map of the Procellarum region, and found that its border is not circular, but polygonal, composed of sharp angles that could not have been created by a massive asteroid.

Instead, researchers believe that the angular outline was produced by giant tension cracks in the moon's crust as it cooled around an upwelling plume of hot material from the deep interior.

Maria Zuber, the E.A. Griswold Professor of Geophysics and also MIT's vice president for research, says that as cracks occurred, they formed a "plumbing system" in the moon's crust through which magma could meander to the surface.

Magma eventually filled the region's smaller basins, creating what we see today as dark spots on the near side of the moon, features that have inspired the popular notion of a "man in the moon."

"A lot of things in science are really complicated, but I've always loved to answer simple questions," says Zuber, who is principal investigator for the GRAIL (Gravity Recovery and Interior Laboratory) mission.

"How many people have looked up at the moon and wondered what produced the pattern we see, let me tell you, I've wanted to solve that one!"