What do you think of this fact?
A planet 95 times heavier than Earth that floats in the bath? Sounds like nonsense, but it’s physics. According to NASA, Saturn is the only planet in our solar system with an average density lower than water’s.
Huge, but fluffy
The numbers: BBC Sky at Night Magazine puts Saturn’s average density at just 0.687 grams per cubic centimeter. Water comes in at 1 gram per cubic centimeter. So Saturn is about 30 percent less dense than water. For comparison, NASA’s Saturn fact sheet lists Earth’s density as 5,513 kilograms per cubic meter. Saturn’s is just 687.
And Saturn is anything but a lightweight. It has 95 times the mass of Earth and, according to NASA, is about 9 times wider than Earth. According to NASA’s fact sheet, Earth would fit into Saturn’s volume about 764 times.
The trick: all that mass is spread over an even more enormous volume. Saturn is made mostly of hydrogen and helium, the two lightest elements in the universe. Lots of volume, comparatively little mass, and the average density hits rock bottom.
About that bathtub
NASA puts it like this: the gas giant could float in a bathtub “if such a colossal thing existed”. That’s the catch. According to BBC Sky at Night Magazine, the tub would have to be about 120,000 kilometers wide. Nothing like that exists anywhere, so the whole thing is a thought experiment.
Saturn isn’t evenly fluffy all the way through, either. Beneath its thick cloud layers, BBC Sky at Night Magazine says, lies a core of heavier elements surrounded by metallic hydrogen. So the 0.687 is an average across the whole planet.
According to NASA, Saturn’s main rings are typically only about 10 meters thick. They’re made of billions of small chunks of ice and rock.
On top of that, the giant spins fast: a day on Saturn lasts only 10.7 hours, NASA says. A Saturn year, on the other hand, takes about 29.4 Earth years.
So the lord of the rings is basically a gigantic beach ball, just without the beach.