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An introduction to exoplanets
An introduction to exoplanets

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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.

Activity _unit3.4.2 Activity 4  Densities of Solar System planets

Timing: Allow about 5 minutes

You’ll be shown a density value and you need to decide which of two planets it belongs to, based on the information provided above.

Density: 1.6 g/cm3

a. 

Neptune


b. 

Mars


The correct answer is a.

Density: 0.69 g/cm3

a. 

Mercury


b. 

Saturn


The correct answer is b.

Density: 5.2 g/cm3

a. 

Venus


b. 

Uranus


The correct answer is a.

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.

Described image
Figure _unit3.4.8 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.