The dynamics of Plutinos

Plutinos are Kuiper belt objects that share the 3:2 Neptune resonance with Pluto. The long-term stability of Plutino orbits depends on their eccentric ity. Plutinos with eccentricities close to Pluto's (fractional eccentricity difference Delta e/e(P) = \ e - e(P)\/e(P) less than or similar to 0.1) ca n be stable because the longitude difference librates, in a manner similar to the tadpole and horseshoe libration in co-orbital satellites. Plutinos w ith Delta e/e(P) greater than or similar to 0.3 can also be stable; the lon gitude difference circulates and close encounters are possible, but the eff ects of Pluto are weak because the encounter velocity is high. Orbits with intermediate eccentricity differences are likely to be unstable over the ag e of the solar system, in the sense that encounters with Pluto drive them o ut of the 3:2 Neptune resonance and thus into close encounters with Neptune . This mechanism may be a source of Jupiter-family comets.