The Moon, which is an astronomical body that orbits around the earth is a differentiated world; it comprises of different layers that differ from one another in composition. The heaviest materials are found in the center of the Moon, and the lightest materials are found on the surface or outermost layer. Studies on rotational, seismic and gravity measurement have provided us with information about different layers within the Moon.
The Moon’s dense, metallic core is found at the center. Iron and nickel make up a significant portion of the core. The inner core, which is a solid mass has a diameter of about 480km. The inner core is surrounded with a fluid outer core; thus, increasing the overall diameter of the core to about 660 km. The Moon has a small core which is about 20% of the Moon’s diameter, unlike other terrestrial world like planet Earth with cores nearly 50% of their diameter.
The Mantle and crust are above the Moon’s core. The difference in compositions between these layers illustrates that the moon is completely composed of a large ocean of magma. Crystal formation begins within the magma as it cools off. Lighter minerals, especially anorthositic plagioclase feldspar, crystalized and migrated to the surface forming the Moon’s crust. While crystals of denser minerals, such as pyroxene and olivine moved down to the bottom of the ocean. The mantle is more extensive than the crust; it has a thickness of about 1350km while the crust has an average thickness of about 50 km. Another interesting fact is that the Moon’s crust appears thinner on the side of the Moon facing Earth, and the side of the Moon not facing Earth is thicker. Many researchers are still investigating why this is so.
The seismometers left by the Apollo astronauts on the Moon’s surface have shown that four types of moonquakes happen on the Moon. Deep moonquakes that occur about 700 km beneath the lunar surface are tidal activities; this occurs when the Earth’s gravity tug and stretch the Moon’s internal structures. Moonquakes that happen on or close to the surface happen when meteoroid comes in contact with the Moon. Thermal expansion and contraction of rock on the surface or close to the surface can cause another type of extremely shallow moonquake; this goes from the extremely frigid lunar night to the extremely hot lunar daytime. The fourth type of moonquake which can last for over 10 minutes originates at the moderately shallow depths of 20-30 km; this quake can register about 5.5 on the Richter scale. Researchers are still trying to unveil the cause of this fourth type of moonquake.