37th DPS Meeting, 4-9 September 2005
Session 52 TNOs and Centaurs
Oral, Thursday, September 8, 2005, 2:00-3:50pm, Law LG19

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[52.01] Sources of Centaurs and Jupiter-family Comets

M.E. Bailey (Armagh Observatory, Northern Ireland), V.V. Emel'yanenko (South Ural University, Russia), D.J. Asher (Armagh Observatory, Northern Ireland)

Of the various orbital classes of trans-Neptunian objects, the near-Neptune high-eccentricity (NNHE) or `Scattered Disc' region is best able to provide a substantial fraction of Jupiter-family (JF) comets. Using a symplectic integrator, we have carried out a numerical study of the eventual dynamical evolution of NNHE objects, calculating the capture rate to the JF region. As a transition population, the Centaurs (defined here by perihelion distance, 5 < q < 28 AU, irrespective of semimajor axis or inclination) provide important constraints on the transfer of objects from NNHE to JF space. The same numerical study yields an orbital distribution of Centaurs for comparison with observations. We have developed a debiasing procedure to allow the true NNHE and Centaur populations to be estimated from the sample of discovered objects.

Although Centaurs can be produced from the NNHE region, their numbers and orbital distributions are inconsistent with this region being the primary source of all Centaurs. In particular, the majority of Centaurs produced in this way have semimajor axis below about 60 AU, whereas the intrinsic number of observed Centaurs is dominated by longer period objects, the number with a > 60 AU exceeding that for a < 60 AU by roughly an order of magnitude. Therefore another source must exist, especially for the longer period, more populous group. The most likely source for these objects is the Oort cloud. Thus the Centaurs contain two separate but overlapping dynamical classes, one originating from the Oort cloud and the other from the NNHE region. These two source regions produce roughly similar numbers of Centaurs with a < 60 AU and also similar numbers of JF comets.

Research at the Armagh Observatory is funded by the Northern Ireland Department of Culture, Arts and Leisure; VVE thanks RFBR (Grant 04-02-96042) for support.

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