The Dance of Pluto's Moons

The New Horizons mission is shedding new light on Pluto’s fascinating system of moons, and their unusual properties. For example, nearly every other moon in the solar system — including Earth’s moon — is in synchronous rotation, keeping one face toward the planet. This is not the case for Pluto’s small moons.

Pluto’s small lunar satellites are spinning much faster, with Hydra — its most distant moon — rotating an unprecedented 89 times during a single lap around the planet. Scientists believe these spin rates may be variable because Charon exerts a strong torque that prevents each small moon from settling down into synchronous rotation.

Another oddity of Pluto’s moons: scientists expected the satellites would wobble, but not to such a degree.

Pluto’s moons behave like spinning tops,” said co-investigator Mark Showalter of the SETI Institute in Mountain View, California.

Images of Pluto’s four smallest satellites also indicate several of them could be the results of mergers of two or more moons.

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