Why is lunar material "lighter" than Earth material?
The mass of the Moon is only 1/80 of that of the Earth, but the radius of the Moon is about 1/4 of that of the Earth. Therefore, the density of the Moon (about 3.3 g/cm^3) is less than that of the Earth (about 5.6 g/cm^3), or to put it another way, lunar material is "lighter" than Earth material. Why is lunar material lighter? This mainly depends on the differences in the internal structures of the Earth and the Moon.
From the outside to the inside, the Moon is roughly divided into three regions. From the lunar surface inward for 60-65 kilometers, there is the lunar crust, which is mainly composed of oxygen, silicon, magnesium, iron, calcium, and aluminum. However, important trace and micro-trace elements such as titanium, potassium, and hydrogen are also present. Then, the range from about 1,600 to 500 kilometers inward from the center of the Moon belongs to the lunar mantle, which is mainly composed of olivine, orthopyroxene, and clinopyroxene, and contains more iron than the Earth. The innermost region with a diameter of about 300-500 kilometers is the lunar core. The lunar core is divided into an inner core and an outer core: the inner core is a solid, iron-rich sphere with a diameter of about 240 kilometers, and outside the inner core, there is a liquid outer core mainly composed of iron.
Comparison of density and volume between the Earth and the Moon The core of the Moon accounts for less than 1% of the Moon's size, while the cores of most other terrestrial-type celestial bodies account for nearly 10%. As can be seen from the table below: the densities of the lunar crust and lunar mantle are similar to those of the Earth's crust and mantle, respectively. However, the density of the iron core is lower than that of the Earth, and the volume proportion of the iron core is also lower. Therefore, compared with the Earth, the average density of the Moon is smaller.