Migrating Moons

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Science  25 Aug 2006:
Vol. 313, Issue 5790, pp. 1016f
DOI: 10.1126/science.313.5790.1016f

Pluto's two recently discovered moons travel in orbits that appear to be influenced by the largest satellite, Charon. The two moons' orbits are circular and coplanar with that of Charon, which suggests that they formed in a common impact as opposed to being captured independently. However, all three moons lie at large distances from Pluto, so if they were formed together in a collision they must have migrated outward. Ward and Canup (p. 1107, published online 6 July; see the Perspective by Lissauer) propose that the two moons were created in the same impact that produced Charon. To avoid the disruption of the system as it expanded, the two small moons remained in corotation resonances with Charon. Corotation type resonances, similar to those that constrain Neptune's ring arcs, would not have altered the eccentricities of the satellites after capture.

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