The formation of the Moon is intimately tied to the formation of the Earth, and therefore the material of which the Moon is made is very similar to that of Earth. Between 1969 and 1972, astronauts visiting the Moon conducted many geophysical surveys and brought back to Earth 842 pounds of rocks, drill cores, and loose surface material samples.
The Formation of the Moon
From the geological and geophysical studies conducted, planetary geologists have been able to piece together the formation and evolution of the Moon, and how it played a part in the formation and evolution of Earth. Several hypothesis have emerged regarding the formation of the Moon, which was about 4.5 billion years ago. These hypothesis include:
- The Moon is a chunk of the Earth that was torn away due to great centrifugal forces; however, this would have required greater centrifugal forces than may have existed on Earth
- The Moon was already formed and later captured by Earth's gravity as it was flying by; however, it is unlikely that Earth has ever had this much gravitational force.
- During the accretionary stage of the Earth's formation, some material separated and accreted into the Moon; however, the absence of an iron core on the Moon makes this scenario unlikely as some iron would have accreted into a core for the Moon as it did with Earth.
- The Moon formed as a result of a Mars-sized object crashing into Earth, where the Earth's early crust and magma oceans were blown away and eventually accreted to form the Moon; given the Moon's geological composition, this seems the most likely candidate. This is called the giant impact hypothesis.
The Geology and Geomorphology of the Moon
The giant impact hypothesis requires that the Moon is made out of the same material as the early Earth. Sure enough, geochemical analysis of the many Moon rocks and drill cores that the Apollo missions returned do show that the Moon is covered with ancient basaltic lava flows. These lava flow fields look to the naked eye like dark, lowland oceans, and early astronomers called them maria. These maria are visible on the side of the moon that is facing the Earth. On the other side of the Moon that is not visible to Earth, there are highlands, called terrae. These terrae, or highlands, also formed as a result of solidifying magma oceans that erupted out of ancient Moon volcanoes.
Other fun facts about the Moon are that it is the largest moon in the Solar System relative to its planet. The Moon is about one quarter the diameter of Earth and 1/81 Earth's mass. It also is the only other body in the Solar System where man has walked. Scientists are currently studying the possiblity and requirements for eventually building a manned research outpost on the Moon to act as a waypoint in manned missions to Mars.
Source:
Spudis, Paul D. "Moon", nasa.gov
Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
