  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 (fractional eccentricity difference
|e-e_p|/e_p<=0.1) can be stable because the longitude difference librates, in a
manner similar to the tadpole and horseshoe libration in coorbital satellites.
Plutinos with |e-e_p|/e_p>=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.
