In the 1993 film, Jurassic Park, Ian Malcolm, upon being introduced as a mathematician, says, “Chaotician, actually. Chaotician.”

He tries to explain his field of study and in doing so, flirts with Ellie Sattler.

“You’ve never heard of chaos theory?” he asks. “Non-linear equations? Strange attractions. Dr. Sattler, I refuse to believe you’re not familiar with the concept of attraction.”

Malcolm tries to illustrate chaos theory by dripping water, one drop at a time, onto the back of Sattler’s hand and having her guess which direction each drop will travel, toward the thumb side or the finger side. This, of course, requires him to hold her hand to steady it.

Water drips make a cute movie scene, but an unsatisfactory example of chaos theory. Where can we find a more suitable illustration of chaos? Well, we could fly to Saturn, then look up at Hyperion [high-PEER-ee-un], one of that planet’s moons.

Most moons in our solar system are roundish and tidally locked to their planet. That is, their rotation and orbit take the same amount of time, and so — like our own beloved moon — they always show the same face to their planet. This happens because rotational forces cause a bulge in a moon, and every time that bulge passes in front of a planet during a moon’s rotation, the planet’s gravity pulls on the bulge. Eventually, this slows the rotation of a moon until the bulge is permanently facing the planet.

The moon is still rotating, but its rotation takes the same amount of time as its orbit.

Not so with Hyperion, which is shaped like a potato and rotates roughly every 13 days during its 21-day orbit. Looking up from Saturn at this oddly-shaped moon, we’d never know which surface will be facing the planet as it tumbles by.

From Hyperion’s point of view, things are even weirder. From there, the sun might come up in the east and set in the north. We’d never know till it happened.

To add to the confusion, Hyperion’s orbit is not circular. Sometimes it gets as close as 911,000 miles from Saturn and sometimes it gets as far away as 954,275 miles. This is because Saturn’s largest moon, Titan, tugs at its little neighbor whenever that little neighbor is in the neighborhood, temporarily elongating its orbit. Once Titan has moved further on, its little buddy slowly shifts back to the original orbit.

Because Hyperion is so unpredictable in its behavior, articles about chaos theory often mention Saturn’s potato-shaped moon. (To be fair, two of Pluto’s moons, Nix and Hydra, and one of Neptune’s, Nereid, are also chaotic.)

It hurts our brains a little that we can’t figure out Hyperion’s rotation. We can’t look at all the factors and forces involved, dump them into a computer, and predict which side of the wibbly-wobbly little moon will be facing Saturn at any particular moment. Despite our best efforts to pin it down, Hyperion rotates merrily and chaotically along.

Ian Malcolm would be so proud.


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