DPS 34th Meeting, October 2002
Session 9. Centaurs and Kuiper Belt Objects II
Oral, Chair(s): D. Jewitt and R. Millis, Monday, October 7, 2002, 4:30-6:00pm, Ballroom

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[9.01] On the Plutinos and Twotinos of the Kuiper Belt

E. Chiang, A. Jordan (UC Berkeley)

We illuminate dynamical properties of Kuiper Belt Objects (KBOs) in the 3:2 (``Plutino'') and 2:1 (``Twotino'') Neptunian resonances within the model of resonant capture and migration. We analyze a series of numerical integrations to measure the efficiencies of capture into the 3:2 and 2:1 resonances, the efficiencies of capture into Kozai-type secular resonances, and the libration centers and amplitudes of resonant particles, all as functions of the migration speed. We synthesize instantaneous snapshots of the spatial distribution of resonant KBOs, from which we derive the longitudinal variation of the sky density of each resonant family. Twotinos cluster ±75 degrees away from Neptune's longitude, while Plutinos cluster ±90 degrees away. Such longitudinal clustering persists even for surveys that are not volume-limited in their ability to detect resonant KBOs. Remarkably, between -90 degrees and -60 degrees of Neptune's longitude, we find the ratio of sky densities of Twotinos to Plutinos to be nearly unity despite the greater average distance of Twotinos. We couple our findings to observations to crudely estimate that Plutinos intrinsically outnumber Twotinos by a factor not exceeding ~3. Most strikingly, the migration model predicts an asymmetry in the spatial distribution of Twotinos: more Twotinos are expected to lie at longitudes behind that of Neptune than ahead of it. The magnitude of the asymmetry amplifies dramatically with faster rates of migration and can be as large as 300%. By stark contrast, all observed Twotino candidates have been discovered in the forward, not backward, lobe. Whether the actual Kuiper Belt defies the predicted sign of the asymmetry, only future observations will tell.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.