Out Near Pluto: A 'Grateful Dead' Dance

A chaotic dance is taking place at the far end of our solar system, involving Pluto and five of its closest friends, a new study finds. Hubble Space Telescope images of Pluto, its largest moon Charon, and tinier moons Styx, Nix, Hydra, and Kerberos show the odd rhythmic gyrations of the six distant objects in a dance unlike anything in our solar system. "It's kind of like you'd see at a Grateful Dead concert," says one planetary scientist. What makes it so odd is that there's a double set of dances going on. First, Pluto and Charon are locked together in their own waltz "as if they are a dumbbell" with a rod connecting them, says study author Mark Showalter of the SETI Institute in California.

"It's pretty darn weird," Showalter says. But Pluto and Charon aren't alone, and that's where it gets more complicated. The four little moons circle the Pluto-Charon combo, wobbling a bit when they go closer to either Pluto or Charon, being pushed and pulled by the two bigger objects. Those four moons orbit Pluto-Charon in a precise rhythmic way, but with a twist: They also interact when they near each other. So it seems like they all dance to one overarching beat but not quite in the same way, just doing their own thing, says Heidi Hammel of the Association of Universities for Research in Astronomy. She's the scientist who made the Grateful Dead comparison. (More Pluto stories.)