Pluto with its five moons. Image taken with WFC3, the new wide field camera on the Hubble Space Telescope.

The Many Moons of Pluto

TITLE: The Formation of Pluto’s Low Mass Satellites
AUTHORS: Scott Kenyon and Benjamin Bromley
FIRST AUTHOR’S INSTITUTION: Smithsonian Astrophysical Observatory, Cambridge, MA

Oh, Pluto. You’re one of our most intriguing and mysterious planets dwarf planets. You were found by accident, because you happened to be in the right place at the right time. None of the inner planets or Ceres have more than two moons, but you have five! The largest, Charon, is about half your diameter but only ten percent of your mass. The other four moons, Nix, Hydra, P4, and P5 (the last two will be getting new names soon) are much smaller, perhaps as small as tens of kilometers across. These small moons, all found in the past decade by the Hubble Space Telescope, are intriguingly near a 1:3:4:5:6 resonance, meaning the innermost moon (Charon) orbits 3 times for every orbit of P5, 4 times for every orbit of Nix, and so on. The orbits of small bodies (which would form these moons) are often destabilized near resonances. We observe this in the inner solar system by detecting gaps in the asteroid belt caused by resonances with Jupiter. The existence of this near-resonant configuration tells us these moons likely formed somewhere other than their present locations, and then migrated into resonance. Pluto and its moons will receive very close study over the next few years as the New Horizons probe approaches the planet in 2015. This mission will provide fantastic information about the properties of Pluto’s companions, as well as the existence (or nonexistence) of other companions, which will inform theories of moon formation. The authors of this paper, studying possible formation scenarios of these planets, create numerical simulations to study how these moons might have formed and what New Horizons might uncover.

Read more: The Many Moons of Pluto | astrobites.

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