A study of the high-inclination population in the Kuiper belt – I. The Plutinos

Abstract

The dynamics of the high-inclination Plutinos is systematically studied. We first present the peculiar features of the 2:3 Neptune mean motion resonance (NMMR) for inclined orbits, especially for the correlation of resonant amplitude Aσ with inclination i. Using the numerical integrations for the age of the Solar system, the dynamical structure of the 2:3 NMMR is mapped out on the plane of semimajor axis versus i for different eccentricities. We have shown that i of stable resonant orbits could be as high as 90°; and the stable region is roughly surrounded by the contours of Aσ = 120°. These new findings allow us to further explore the 2:3 NMMR capture and retention of planetesimals with initial inclinations i0 ≤ 90° in the frame of the planet migration model. We find that the outward transportation of Plutinos is possible for any inclined or even perpendicular orbits. The role of i0 in the formation of Plutinos during Neptune's migration is highlighted and interesting results are obtained: (1) the capture efficiency of the 2:3 NMMR decreases drastically first with the increase of i0, but it then raises instead when i0 exceeds ∼50°; (2) the magnitude of i-variation is limited to less than 5° for any i0, and moreover, for Plutinos with i ≳ 48°, their i are forced to decrease throughout the outward migration; (3) Plutinos with i ≳ 48° are certainly outside the Kozai mechanism, since an inclination increase is prohibited by the migrating 2:3 NMMR; (4) the 7:11 inclination-type NMMR could be responsible for nearly circular Plutinos, and a minimum i0 ∼ 15° is required to intrigue this mechanism.