Saturn Is the Solar System’s Only Planet Less Dense Than Water

Saturn is the only planet with an average density lower than water, so a gigantic enough water tank could theoretically let it float.

Astronomy

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Saturn is the only planet in our solar system whose average density is lower than water. Its mean density is about 0.687 grams per cubic centimeter, compared with roughly 1 gram per cubic centimeter for water. That unusual number comes largely from Saturn being a huge gas giant made mostly of hydrogen and helium. The familiar idea that Saturn could float in water is therefore based on a real density comparison, not on Saturn having a solid surface that could literally be placed in an ordinary bathtub. Saturn is enormous, and a container capable of holding it would introduce overwhelming gravitational and structural effects of its own. In other words, the floating bathtub is a useful way to picture the density difference, but not a practical experiment. Saturn has no solid surface like Earth, and pressure increases dramatically as you descend through its atmosphere. The planet’s low average density remains one of the most striking examples of how enormous size does not necessarily mean high density.

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