The "Man in the Moon" illusion, familiar to various cultures around the world,
was created by powerful asteroid impacts that rocked the satellite billions of
years ago, a new study suggests.
The study,
performed by Laramie Potts and Ralph von Frese of Ohio State University, reveals that ancient lunar impacts
played a much larger role in shaping the Moon's surface than scientists had
previously thought. It may also help explain the origins of two mysterious
bulges on the Moon's surface.
The new
analysis reveal that shock waves from some of the Moon's early asteroid impacts
traveled through the lunar interior, triggering volcanic eruptions on the
Moon's opposite side. Molten magma spewed out from the deep interior and
flooded the lunar landscape.
When the magma
cooled, it created dark patches on the Moon called "lunar maria" or "lunar
seas."
During a
full Moon, some of these patches combine to form what looks like a grinning
human face, commonly known as the "Man
in the Moon." The man's eyes are the Mare Imbrium and Mare Serenitatis, its
nose is the Sinus Aestuum and its grinning mouth is the Mare Nubium and Mare Cognitum.
The effects
of some of those traveling shock waves are still visible in the Moon's interior
today. Cross-sectional
images of the insides reveal that a part of the mantle, the section between
the Moon's core and crust, still juts into its core today, 700 miles below the
point of one of the impacts. The images were created from data collected by
NASA's Clementine
and Lunar
Prospector satellites.
Mysterious
bulges
Early
surveys by the Apollo missions revealed that the moon isn't a perfect sphere.
There is a bulge on the Earth-facing side, called the near side, and another
bulge on the far side.
According
to one hypothesis, these bulges are the result of Earth's gravity tugging on
the Moon during the early years following its cataclysmic
formation, when its surface was still molten and malleable.
The current
study suggests that this scenario is only partly correct. The researchers think
the Moon was struck by at least two very powerful asteroid impacts in its past
(in addition to countless smaller impacts that left smaller craters easily
identifiable still today). One of the major impacts struck the near side,
sending shock waves that traveled through the lunar interior to create the
bulge on the far side; the other impact struck the far side and created the
bulge on the side.
The researchers think the
impacts happened about four billion years ago. At that time, roughly half a
billion years after the birth of the solar system, the Moon was still
geologically active and its core and mantle were still molten and malleable.
Back then, the Moon was much
closer to the Earth than it is today and the gravitational interactions
between the two were much stronger. The researchers think that when magma
spilled out of the Moon's interior, Earth's gravity immediately grabbed hold
and hasn't let go since.
"This research shows that
even after the collisions happened, the Earth had a profound effect on the
Moon," Potts said.
The
findings were detailed in a recent issue of the journal Physics of the Earth
and Planetary Interiors.
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