4.7  Densities of Solar System planets

The planets in the Solar System all have different compositions, and this affects their densities.

In general, terrestrial (rocky) planets are denser than the gas and ice giants. Earth has a density of around 5.5 g/cm³ compared with Jupiter’s density of 1.3 g/cm³.

Mercury and Earth are the densest planets in the Solar System (Figure 13) with densities similar to the iron-rich mineral haematite. Saturn, the least dense planet in the Solar System on the other hand, has a density lower than that of water. It may sound strange, but this means that Saturn would actually be able to float in a container of water if you could find one large enough.

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Figure 13  Solar System planet densities compared with the density of iron, rock and water. Densities of some moons and one asteroid are also shown.

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This is a graph with density (g/cm³) on the y-axis. On the x-axis there are the planets Mercury, Venus, Earth and Mars (grouped as terrestrial planets), Jupiter, Saturn, Uranus and Neptune (grouped as giant planets), Moon, Triton, Enceladus and Hyperion (grouped as moons), and Vesta, grouped as an asteroid. There are red lines running horizontally across the graph, the top one being iron, the middle one being rocks, and the bottom one water.

Figure 13  Solar System planet densities compared with the density of iron, rock and water. Densities of some moons and one asteroid are ...