Busy Little Iceball

Galileo's Pendulum

So Pluto has a fifth moon in orbit, temporarily designated P5, to accompany Charon, Nix, Hydra, and um…P4. (I guess someone will get around to naming P4 and P5 one day. I nominated “Fred” and “George”.) P5 is so tiny and faint that even our best instruments can only give it a maximum size: it’s no bigger than 25 kilometers across, and likely smaller. All five moons appear to be regular satellites, orbiting Pluto in the same direction as Pluto’s rotation, and in the same plane. That indicates they formed together, possibly when a rogue object slammed into Pluto in the early Wild-West days of the Solar System.

Obviously we don’t know a lot about P5, or for that matter P4, Nix, or Hydra—they’re too small and faint. The New Horizons spacecraft, when it arrives in 2015, will provide a wealth of information about this miniature…

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2 comments on “Busy Little Iceball

  1. Pluto is not an “iceball,” as it is estimated at 70 percent rock. Eris, being marginally smaller but 27 percent more massive, is likely even more rocky. Calling Pluto an “iceball” is therefore misleading. Also, Eris was discovered by a team of three, not by Brown alone. Please credit Dr. Chad Trujillo and Dr. David Rabinowitz who co-discovered Eris with Brown. Interestingly, Rabinowitz signed the petition of 300 professional astronomers rejecting the IAU definition of planet.

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