# Unraveling the Moon's Mysterious Geology and History
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Chapter 1: The Moon's Surface Secrets
The Moon, our familiar celestial neighbor, is dominated by expansive regions known as maria—smooth basins formed from ancient lava flows. These dark areas are prominent on the side of the Moon that faces Earth. In contrast, the Moon's far side presents a puzzling landscape, lacking these vast basins, a phenomenon that has intrigued astronomers for years. An international research team now believes they have uncovered the reason behind this difference. It appears that a dwarf planet may have collided with the Moon billions of years ago, significantly altering its geological makeup.
The Moon is thought to have originated from a cataclysmic event when a semi-molten Earth collided with a Mars-sized body in the early solar system. This hypothesis, however, raises questions regarding the Moon's chemistry, which differs from Earth's as evidenced by lunar samples returned by Apollo astronauts. The collision with a body akin to Ceres, the largest asteroid in our inner solar system, might explain these chemical disparities.
An artistic depiction illustrating the Moon's collision with a dwarf planet, leading to its current state. Image credit: NASA/JPL-Caltech
"The giant impact theory provides a plausible explanation for the observed differences in isotopes of potassium, phosphorus, and rare-earth elements, such as tungsten-182, between the Earth and Moon's surfaces," researchers from the American Geophysical Union state. "These elements might have been incorporated into the Moon as a result of the colossal impact."
Section 1.1: Theories of Lunar Formation
Various theories have emerged to elucidate the discrepancies between the Moon's two hemispheres. One hypothesis suggests that the Earth once had two moons that merged when the Moon was still largely molten, resulting in the single satellite we recognize today.
Another significant theory posits that a dwarf planet, orbiting the Sun, collided with the Moon during the solar system's formative years. Evidence supporting this notion was gathered from the Gravity Recovery and Interior Laboratory (GRAIL) mission, which launched in 2012.
The GRAIL mission revealed that the Moon's far side has a thicker crust compared to the Earth-facing side. Additionally, the far side features an extra layer of material absent on the near side, as indicated by GRAIL data.
A computer simulation illustrating how a dwarf planet's collision with the Moon might have shaped its unusual geological features. Image credit: JGR: Planets/Zhu et al. 2019/AGU
Section 1.2: Simulating the Impact
Researchers conducted 360 computer simulations to analyze potential impacts between the Moon and various celestial bodies, seeking conditions that could result in the geological characteristics observed today. The simulations indicated that an object with a diameter of 780 kilometers (480 miles) colliding with the Moon at a speed of 22,500 kilometers per hour (14,000 MPH) could produce the geological features seen on the far side. This scenario would resemble a collision with a body slightly smaller than Ceres, striking the Moon at approximately one-quarter the speed of meteors entering Earth's atmosphere. Simulations also suggested that a smaller object, measuring 720 kilometers (450 miles) in diameter, could create similar geological features at a slightly higher velocity of 24,500 kilometers per hour (15,000 MPH).
Such a catastrophic event would have ejected enough material on the Moon's far side to blanket it with a layer of rock five to ten kilometers (three to six miles) thick, forming the additional material identified by GRAIL.
The simulations indicated that the impacting object was likely a solar-orbiting body rather than a second moon prior to the event. "Understanding the origin of the differences between the near side and far side of the Moon is a fundamental issue in lunar science," stated Steve Hauck, a professor of planetary geodynamics at Case Western Reserve University.
Chapter 2: Exploration of the Far Side
"When I gaze at the moon, I do not perceive a barren, desolate world. Instead, I see a luminous entity where humanity has embarked on an endless frontier."
- David Scott, Commander of Apollo 15
In October 1959, the Soviet Union's Luna 3 spacecraft became the first vessel to capture images of the Moon's far side.
The initial glimpse of the Moon's far side, captured by Luna 3 in 1959. Image credit: NASA
"The spacecraft returned blurry images, but with the aid of computer enhancement, an initial atlas of the lunar far side was created. These first glimpses revealed a rugged terrain, distinctly different from the near side, featuring only two dark areas named Mare Moscovrae (Sea of Moscow) and Mare Desiderii (Sea of Dreams)," NASA explains.
The Lunar Reconnaissance Orbiter (LRO), launched in June 2009, produced comprehensive elevation maps and photographic mosaics of the Moon, achieving unprecedented detail previously unattainable.
China's Chang’e-4 lander made history as the first spacecraft to softly land on the Moon's far side, deploying the Yutu-2 rover to explore this enigmatic region.
As our understanding of the Moon expands, we are entering a new era of lunar exploration. Once thought to be dry and lifeless, the Moon is now recognized as a location with water ice—some of which may even be present on its surface—and an active interior, leading to moonquakes. NASA plans to return humans to the lunar surface by 2024, with several other nations and organizations also gearing up for their lunar missions.