Scientists classify objects based upon various...

Scientists classify objects based upon various characteristics. If we rank the terrestrial planets according to their densities (mass divided by volume), we will get one relationship. If we then rank the terrestrial planets according to their uncompressed densities, we will get a slightly different relationship. Compare the rankings. What do the differences in the rankings tell us about the planets themselves?

Key Concepts

Density

Density is a measure of how much mass is contained within a given volume of a planetary body. It is calculated by dividing mass by volume and offers insights into the overall concentration of material, which can be influenced by both the planet's composition and the effects of gravitational self-compression.

Uncompressed Density

Uncompressed density refers to the intrinsic density of a planet's materials without the effects of gravitational compression. This measure helps to isolate the contribution of the planet’s composition, allowing scientists to compare the 'true' material densities between different planetary bodies.

Gravitational Self-Compression

Gravitational self-compression is the process by which a planet’s own gravity compresses its interior, leading to higher observed densities than would be seen if the material were uncompressed. This phenomenon means that larger or more massive planets might appear denser due to the significant pressure effects acting on their internal materials.

Planetary Internal Structure

The differences in rankings between density and uncompressed density reveal variations in the internal structure and composition of planets. They indicate how much of a planet’s measured density is due to material properties versus compression effects, which in turn provides clues about the size and composition of the core and mantle, and the overall differentiation within the planet.

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