The Moon's lopsided appearance may finally be explained by a cosmic collision between the Earth's satellite and an errant dwarf planet.
For years, scientists have tried to find an explanation as to why the Moon looks asymmetrical compared to other natural satellites in space.
Several theories have come up, including one where the Earth once had two moons that collided with each other, and another where a tiny planet or asteroid smashed into the surface of the satellite.
This second theory is what an international team of scientists focused on its search for a plausible answer.
The Moon's Lopsidedness Explained
Meng Hua Zhu, an astrophysicist from Macau University of Science and Technology in China, led a team in studying measurements of the Moon taken during NASA's Gravity Recovery and Interior Laboratory mission in 2012.
Data from GRAIL has revealed that the far side of the moon has an additional layer of material on its crust and is filled with craters. Meanwhile, the satellite's nearside is littered with open basins.
Meng and his team used the measurements from the mission to run 360 computer simulations of various cosmic collisions that may have caused the damage on the moon. They tried hitting the Earth's satellite with a number of space objects of different sizes and at different speeds.
Lunar Black Eye Caused By Asteroid Or Dwarf Planet
For an object to produce such damaging to the moon, the researchers found that it should be at least 480 miles in diameter. This places it slightly smaller compared to the Ceres dwarf planet, according to the team.
In this scenario, the space object would have smashed into the Moon's near side at speeds of about 14,000 miles per hour. This would have caused lunar material to rise and fall back into the satellite's far side.
The researchers believe this additional layer of debris would have been between 3 and 6 miles (5-10 km) thick. This is consistent with the layer of lunar material the GRAIL mission found on the m's far side.
Another plausible scenario is a 450-mile in diameter object colliding with the moon at about 15,000 mph.
Meng said the culprit in both scenarios would likely have been either an asteroid or a dwarf planet, not a second Earth moon.
These theories might also help explain why the Earth has different isotopes compared to the moon. The natural satellite has vastly different isotopes of potassium, phosphorus, and other rare elements compared to its host planet.
This last point has been a major question in the scientific world, given that the Moon most likely would have been an offshoot of the Earth.
While the new study offers a viable explanation for the moon's lopsidedness, some scientists remain skeptical of such scenarios.
Steve Hauck, a researcher from Case Western Reserve University and editor-in-chief of the journal that features the study, called the findings "very provocative."
"Understanding the origin of the differences between the nearside and the far side of the Moon is a fundamental issue in lunar science," Hauck said.
"Indeed, several planets have hemispherical dichotomies, yet for the Moon we have a lot of data to be able to test models and hypotheses with, so the implications of the work could likely be broader than just the Moon."
The findings of the international study are featured in the Journal of Geophysical Research: Planets.