The geologic feature that causes the “man in the moon” phenomenon is called the Oceanus Procellarum, and is a gigantic crater with a diameter of 1,800 miles. The general scientific consensus was that the Oceanus Procellarum was formed by a gigantic asteroid impact millions of years ago. New research using gravity data from NASA’s twin GRAIL spacecraft has, however, found convincing evidence that the crater was formed in the aftermath of a huge volcanic eruption rather than by a major asteroid strike.
Details on the new man in the moon study
Researchers from MIT, the Colorado School of Mines, and others created a high-resolution map of the Procellarum using the GRAIL data, and discovered that its border is not circular, but polygonal. Moreover, the edges of the bowl are sharp angular formations that could not have been created by a massive asteroid. The researchers believe that the angular formations are tension cracks in the moon’s crust after it cooled following the breakthrough of a plume of hot material from the interior of the moon.
Maria Zuber, the E.A. Griswold Professor of Geophysics and MIT’s vice president for research, says that the cracks in effect formed a “plumbing system” in the crust through which magma could flow to the surface. Over time, magma filled the smaller basins, creating the dark spots on the near side of the moon that many poets and dreamers have called the “man in the moon.”
Statement from principal investigator
“A lot of things in science are really complicated, but I’ve always loved to answer simple questions,” explained Zuber, the principal investigator for the Gravity Recovery and Interior Laboratory — GRAIL — 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!”
“How such a plume arose remains a mystery,” Zuber noted. “It could be due to radioactive decay of heat-producing elements in the deep interior. Or, conceivably, a very early large impact triggered the plume. But in the latter case, all evidence for such an impact has been completely erased. People who thought that all this volcanism was related to a gigantic impact need to go back and think some more about that.”