Britannica
Sources used in this answer
- Uranus - The interior
- meteorite - Meteorites and the formation of the early solar system
- astronomy - Study of the solar system
- solar system - Planets and their moons
- sizes of the planets
- Jupiter: Top Questions
- atmosphere - The atmospheres of other planets
- extraterrestrial life - Jovian planets
- Neptune - Interior structure and composition
Why are Jupiter, Saturn, Uranus, and Neptune much less dense than Earth?
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Solar system
The planets (in comparative size) in order of distance from the Sun.
The significant difference in density between the terrestrial planets (like Earth) and the outer giant planets (Jupiter, Saturn, Uranus, and Neptune) is primarily due to their vastly different compositions, which resulted from conditions during the early formation of the solar system.12
- Terrestrial Planets: These inner planets are composed primarily of rock and metals, resulting in high average densities ranging from 3.9 to 5.5 grams per cubic centimeter.12
- Giant Planets: In contrast, the outer planets have densities close to 1 gram per cubic centimeter. Jupiter and Saturn are composed primarily of hydrogen and helium, the lightest elements in the universe. While Uranus and Neptune also contain hydrogen and helium, they possess a higher proportion of "ices" (water, methane, and ammonia) and rock compared to the gas giants, though they remain far less dense than Earth.12345
This compositional split is attributed to temperature gradients in the early solar nebula, which dictated where different materials could condense and accumulate during planetary growth.61