![]() One possibility, he noted, is that the gravitational tides of Pluto and Charon may work against each other, leaving the moons free to maintain a high spin. Instead, “it’s just as if the moons picked some random rate of rotation and Pluto and Charon have no role with any of that,” said Showalter. The fast spin rates are so surprising, said Showalter, because even if the moons formed as rapid rotators, the push and pull of the gravitational tides of Pluto and Charon ought to have slowed down that motion. The push and pull of the gravitational tides of Pluto and Charon ought to have slowed down that motion. Analyses of images recorded by the mission’s spacecraft in the weeks leading up to the flyby led to the discovery of the moon’s surprising speeds, unveiled Monday at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences in National Harbor, Md. Last July, the New Horizons mission carried out the first ever flyby of Pluto. “No one has ever seen a moon that rotates 89 times during a single orbit.” “This is unlike anything we’ve seen elsewhere in the solar system,” he added. ![]() “These Pluto moons are essentially spinning tops, and that radically changes the way we understand the dynamics of how they operate,” planetary scientist Mark Showalter of NASA’s New Horizons mission and of the SETI Institute in Mountain View, Calif., told Eos. Among Pluto’s moons, Charon plays by the usual rules, rotating once per orbit of Pluto, but the other, smaller moons don’t. ![]() Earth’s Moon, for instance, rotates once each 27 days 8 hours, the time it takes to orbit our planet once. These are fast rotation rates for moons, which usually keep one face pointed at their central planet, rotating just once per orbit of that planet. Kerberos spins the slowest, once every 5.33 Earth days, whereas Hydra is the whirling dervish of the quartet, rotating once every 10 hours 19 minutes. The small moons-Styx, Nix, Kerberos, and Hydra, in order of proximity to Pluto-all rotate much faster than the 20 to 38 Earth days the moons take to orbit the Pluto-Charon system, scientists reported Monday. Hydra is the whirling dervish of the quartet, rotating once every 26 minutes. Like disobedient children, Pluto’s four small outer moons are spinning at inexplicably high rates, apparently defying the steadying influence expected from Pluto and its large partner moon, Charon.
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