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How does a 3:2 resonance with Neptune keep Pluto’s orbit stable?
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Kuiper belt
An artist's rendition of a binary object in the Kuiper belt. The two objects depicted orbit each other at the edge of the solar system.
Pluto’s orbit is kept stable through a 3:2 mean motion resonance with Neptune. In this configuration, Pluto completes exactly two orbits around the Sun in the same amount of time it takes Neptune to complete three.12
This gravitational interaction ensures that the two bodies never collide, even though Pluto’s highly eccentric orbit brings it closer to the Sun than Neptune for part of its revolution. The resonance locks their relative positions such that they can never pass closer than approximately 17 astronomical units to each other. This relationship is a defining characteristic of the Plutinos, a group of Kuiper belt objects that share this stable orbital resonance with Neptune.21