Abstract
Plutinos are Kuiper belt objects that share the 3:2 Neptune resonance with Pluto. The long-term stability of Plutino orbits depends on their eccentricity. Plutinos with eccentricities close to Pluto's (fractional eccentricity difference Δe/eP = |e - eP|/eP ≲ 0.1) can be stable because the longitude difference librates, in a manner similar to the tadpole and horseshoe libration in co-orbital satellites. Plutinos with Δe/eP ≳ 0.3 can also be stable; the longitude difference circulates and close encounters are possible, but the effects of Pluto are weak because the encounter velocity is high. Orbits with intermediate eccentricity differences are likely to be unstable over the age of the solar system, in the sense that encounters with Pluto drive them out of the 3:2 Neptune resonance and thus into close encounters with Neptune. This mechanism may be a source of Jupiter-family comets.
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