On the Plutinos and Twotinos of the Kuiper Belt

We illuminate dynamical properties of Kuiper Belt Objects (KBOs) in the 3:2(``Plutino'') and 2:1 (``Twotino'') Neptunian resonances within the model ofresonant capture and migration. We analyze a series of numerical integrations,each involving the 4 migratory giant planets and 400 test particles distributedthroughout trans-Neptunian space, to measure efficiencies of capture asfunctions of migration speed. Snapshots of the spatial distribution of resonantKBOs reveal that Twotinos cluster +/- 75 degrees away from Neptune's longitude,while Plutinos cluster +/- 90 degrees away. Longitudinal clustering persistseven for surveys that are not volume-limited in their ability to detectresonant KBOs. Remarkably, between -90 degrees and -60 degrees of Neptune'slongitude, we find the sky density of Twotinos to nearly equal that ofPlutinos, despite the greater average distance of Twotinos. We couple ourfindings to observations to crudely estimate that the intrinsic Twotinopopulation is within a factor of 3 of the Plutino population. Most strikingly,the migration model predicts that more Twotinos may lie at longitudes behindthat of Neptune than ahead of it. The magnitude of the asymmetry amplifiesdramatically with faster rates of migration and can be as large as 300%. Adifferential measurement of the sky density of 2:1 resonant objects behind ofand in front of Neptune's longitude would powerfully constrain the migrationhistory of that planet.