The NASA Visualization Explorer Moons In Chaos says Hydra and Nix, two of the moons of Pluto, show chaotic movement due to the shifting gravitational field.

How long a day lasts and where the sun rises and sets are impossible to forecast on one of Pluto’s five moons, Nix. When NASA’s Hubble Space Telescope observed odd changes in the sunlight Nix was reflecting, researchers realized that Nix does not rotate predictably like Earth’s moon. Instead, it tumbles chaotically as it revolves around Pluto. Nix’s erratic nature comes from orbiting a double planet: Pluto and its largest moon, Charon, which is about half Pluto’s size. The two swing around each other like a dumbbell with unequal weights, shifting the gravity field that Nix experiences and tugging the potato-shaped moon in different directions about its axis. The same chaos afflicts Hydra, another tiny Pluto moon. Watch the video to see an animation showing Nix’s wobbles as it orbits Pluto.

I was wondering if knowing more about their chaotic behaviour can help us advance Astronomy?

Personally, I believe we wouldn’t gain much from knowing more about their movement since chaotic movements become very different even for minute changes in the parameters.

If there are any applications or conclusions from this though, I’d like to know what they are.

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    $\begingroup$ There is a good question here, you can make it better in a few ways: First "sources" What is the source of your claim about chaotic movement. Secondly "Assumptions" Why do you suppose it will affect space exploration? (you could explain you thinking or tell us the source of this idea. Finally, are you aware or Space Exploration? $\endgroup$
    – James K
    Commented Jun 16, 2021 at 5:32
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    $\begingroup$ Thank you, I’ve made an edit adding information…I wasn’t sure about tagging this with space exploration since it’s specifically about the chaotic movement $\endgroup$ Commented Jun 16, 2021 at 5:39
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    $\begingroup$ Other example include Saturn's moon, Hyperion and asteroid 4179 Toutatis and possibly Styx and Kerberos, and also Neptune's Nereid. $\endgroup$ Commented Jun 16, 2021 at 7:26
  • $\begingroup$ I don't think closing this question and blocking answers serves the site in this case; there are now two answers (one is mine) and I've edited the question to help a new user get used to question-writing. Voting to keep open! $\endgroup$
    – uhoh
    Commented Jun 25, 2021 at 4:39

2 Answers 2


Understanding what is out there in the universe, where it is, how it is moving and why is what space exploration is about.

Chaotic orbits and trajectories are very important for trajectory planning of spacecraft since one can use them for low-energy transfers. If one wanted to go to an object in a chaotic orbit it is also valuable to know that it is in fact chaotic and with what characteristics, so that one can plan an appropriate trajectory. Often the time until predictability is lost for planetary bodies is fairly long on a human or project timescale. For the moons in question the timescale looks like it is many years for their orbits, and weeks for their rotation.


I agree with your thinking as far as it goes; it is probably not possible to learn about chaos theory nor celestial mechanics by observing these moons, because:

  1. We (believe we) know the underlying laws and mathematics that govern motion (in general at least)
  2. We won't be able to study such objects long enough and careful enough to make any tests that haven't been done more carefully elsewhere.

However, we may be able to learn something about the internal structure of these moons or perhaps Pluto itself. The quoted passage mentions "potato-shaped moon" and that's a hint. I went to Wikipedia's Pluto and searched for "chao.." and at the bottom found three interesting links.

While none of these references point to a single sure thing we can learn by studying them, there is discussion of how the system evolved; how pluto came to be in the orbit it's in at the moment, and how it captured and held on to these moons. Since they are profoundly non-spherical, the evolution of their orbits will be different than for spherical moons.

For more on that see answer(s) to Which mass distributions guarantee two bodies have non-Keplerian orbits? Which non-spherical distributions still allow noncircular Keplerian orbits? in Physics SE.

This illustration shows the scale and comparative brightness of Pluto’s small satellites. The surface craters are for illustration only and do not represent real imaging data. Credits: NASA/ESA/A. Feild (STScI)

Source (primary)

This illustration shows the scale and comparative brightness of Pluto’s small satellites. The surface craters are for illustration only and do not represent real imaging data. Credits: NASA/ESA/A. Feild (STScI)


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