Moon Density Comparison: Earth vs. Moon

Density is defined as mass per unit volume. The Moon's average density ($\approx 3.34 \, \text{g/cm}^3$) is significantly lower than Earth's ($\approx 5.51 \, \text{g/cm}^3$). This difference is primarily due to variations in their internal composition and structure, specifically their cores.

Core Composition Differences

Planetary bodies with larger, denser cores tend to have higher average densities. Key differences between Earth and the Moon include:

• Earth's Core: Earth possesses a substantial metallic (iron-nickel) core, which includes a solid inner core and a liquid outer core. This dense core constitutes a significant portion of Earth's total mass and volume.
• Moon's Core: In contrast, the Moon has a much smaller core relative to its overall size. Seismic data suggests it's likely composed mainly of lighter elements or has a smaller proportion of iron compared to Earth's core. It might be mostly molten or semi-molten.

Impact on Average Density

Because the Moon has a relatively thinner core (making up a smaller fraction of its total mass and volume) compared to Earth, the Moon's overall average density is lower. The higher proportion of less dense silicate mantle and crustal materials in the Moon significantly outweighs the contribution of its smaller core to the overall density calculation.

Therefore, the primary reason for the Moon's lower average density compared to Earth is its thinner core.