Would Saturn float in water? Yes, it is the only planet in the solar system less dense than water.

• ✓NASA planetary fact sheet — Saturn mean density 0.687 g/cm³
• ✓Water density 1.0 g/cm³

What if I told you one of the biggest planets in our solar system would float in water like a rubber duck? Saturn is the only planet in the solar system less dense than water: its average density is about 0.69 grams per cubic centimetre, so given a big enough ocean, Saturn would float. For comparison, water sits at exactly 1.0 grams per cubic centimetre — Saturn clocks in well below that, lighter than most hardwoods you could hold in your hand. That seems impossible for a world almost ten times wider than Earth, but Saturn is overwhelmingly made of hydrogen and helium gas — the two lightest elements in the universe. Pack a vast sphere of gas loosely enough, and the whole thing weighs almost nothing per unit of space it fills. Every other planet in our solar system sinks. Saturn alone defies that. A planet the size of a small star, and it would bob at the surface.