Saturn Could Float in Water. And There's a Hexagon on Top.
Saturn weighs ninety-five times what Earth weighs, but its density is less than water. If there were a bathtub big enough, Saturn would bob. And at its north pole there is a six-sided storm thirty thousand kilometres across that nobody fully explains.
Saturn has more strange facts per square kilometre than any other planet. Two of them stop people mid-sentence the first time they hear them.
A planet that would float
Saturn weighs 95 times what Earth weighs. It is also nearly ten times the diameter. The mass divided by the volume comes out to 0.69 grams per cubic centimetre, which is less than water. If there were a bathtub the size of the solar system, Saturn would bob.
This is not a joke. Most of Saturn is hydrogen and helium, the lightest two elements that exist. There is a small rocky core somewhere deep inside, surrounded by metallic hydrogen, surrounded by liquid hydrogen, surrounded by the gas atmosphere we see. The whole structure averages out to slightly less dense than tap water.
It is the only planet in the solar system that does this. Jupiter, Neptune, and Uranus are all denser than water despite being mostly gas, because their gravity squeezes them harder. Neptune compresses methane into diamond at depth. Saturn, somehow, does not squeeze hard enough to do anything similar. The leading theory is that Saturn's interior layers mix less than Jupiter's, but the full picture is still being worked out. The Saturn planet guide covers what else is going on under the rings.
A six-sided storm
Bolted to the top of all that hydrogen is a cloud pattern shaped like a hexagon.
Voyager 2 saw it in 1981. Cassini confirmed it was still there in 2006, and again throughout its mission until 2017. The sides are remarkably straight. The whole hexagon is roughly 30,000 km across, which means you could fit four Earths inside it. At each corner, the jet stream changes direction by exactly 60 degrees, every time.
Lab experiments with rotating fluids have produced six-sided patterns under specific conditions. The leading theory is that Saturn's polar jet stream is doing something similar at planetary scale: a fluid rotating at one speed inside a fluid rotating at another, with the boundary between them folding into a polygon. Why six sides and not five or seven, nobody is entirely sure. Nature is allowed to be specific without explaining itself. Venus rotates in a way nobody fully explains either, and it has done so for billions of years.
Inside the hexagon is a swirling vortex, also rotating. The whole structure has been observed continuously for over forty years and shows no sign of breaking down.
It is the kind of thing that, if you painted it on a postcard, people would assume the artist had taken liberties.