Scientists have found that the 'Man in the Moon' image on the lunar surface was created by a large plume of magma deep within the Moon's interior.
New data obtained by NASA's GRAIL mission showed 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 2,896 km in diameter.
Researchers from Massachusetts Institute of Technology, the Colorado School of Mines, and other institutions have created a high-resolution map of the Procellarum, 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, MIT's vice president for research, said 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."
The team mapped the Procellarum region using data obtained by GRAIL - twin probes that orbited the Moon from January to December 2012.
From this mapping, the researchers observed that the rim of the Procellarum region is composed of edges that abut at 120-degree angles.
As asteroid impacts tend to produce circular or elliptical craters, Zuber said the Procellarum's angular shape could not have been caused by an impact.
Instead, the team explored an alternative scenario: Some time after the Moon formed and cooled, a large plume of molten material rose from the lunar interior, around where the Procellarum region is today.
The steep difference in temperature between the magma plume and the surrounding crust caused the surface to contract over time, creating a pattern of fractures that provided a conduit for molten material to rise to the surface.
To test the hypothesis, the researchers modelled the region's gravitational signal if it were to contain volcanic intrusions - magma that seeped up to just beneath the Moon's surface and, over time, cooled and crystallised.
The resulting simulation matched the gravity signal recorded by GRAIL, supporting the idea that the Procellarum was caused by a magma plume, and not an asteroid.
The study was published in the journal Nature.
