DPS 2001 meeting, November 2001
Session 25. Solar System Origins II
Oral, Chairs: M. Drake, H. Levison, Wednesday, November 28, 2001, 5:00-6:30pm, Regency GH

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[25.08] Landau Damping of Apsidal Spiral Density Waves in the Kuiper Belt

G.R. Stewart (Univ. of Colorado)

Ward and Hahn (1998) have suggested that Neptune launched apsidal spiral density waves into the primordial Kuiper belt at the secular resonance located near 40 AU. Ward and Hahn concluded that these waves could have damped Neptune's orbital eccentricity to its current value of 0.009 if the Kuiper Belt contains slightly more than a earth mass of material out to 75 AU. However, their analysis was based upon a fluid model of the disk and therefore omitted the possibility of Landau damping instabilities. Landau wave damping can occur when the local asymmetric drift of Kuiper belt objects (KBOs) is equal to the difference in precession frequencies of the longitudes of perihelia of Neptune and the KBOs. The asymmetric drift is proportional to the square of the orbital eccentricities of the KBOs and the shear rate of their mean orbital motion. For KBO eccentricities less than 0.001, the asymmetric drift produces a minor shift in the secular resonance location. More importantly, the asymmetric drift can lead to Landau damping of the apsidal density wave and strong excitation of orbital eccentricities at the resonance location. Since growing KBO eccentricities shift the resonance location inward toward Neptune, it may be impossible for Neptune to launch a coherent apsidal density wave into the Kuiper belt unless sufficient nebular gas was still present to damp the orbital eccentricities.

This work was supported by NASA's Origins of Solar Systems Program.

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