Journal Article

Capture of Halley-type comets from the near-parabolic flux

V. V. Emel'yanenko and M. E. Bailey

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 298, issue 1, pages 212-222
Published in print July 1998 | ISSN: 0035-8711
Published online July 1998 | e-ISSN: 1365-2966 | DOI:
Capture of Halley-type comets from the near-parabolic flux

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The dynamical transfer of comets from nearly parabolic to short-period orbits is investigated, considering perturbations by the major planets Jupiter, Saturn, Uranus and Neptune, for 5 Gyr. The combined analytical and numerical scheme includes all the essential features of the dynamical evolution, namely mean-motion resonances, secular oscillations, secular resonances, and close encounters with planets. The orbital evolution of ∼105 randomly oriented near-parabolic orbits is considered, with initial inclinations i and perihelion distances q uniformly distributed respectively in cos i and each of the five ranges 0<q<4 au, 4<q<6 au, 6<q<10.5 au, 10.5<q<18 au and 18<q<31 au. The objects which eventually evolve into Halley-type orbits primarily originate from initial orbits of small perihelion distance, in contrast to those that evolve to Jupiter-family orbits. Most Halley-type comets originate from orbits with q in the range 0<q<4 au, with the majority coming from q<2 au. The inclination-averaged probability for evolution from a nearly parabolic orbit with 0<q<4 au into a Halley-type orbit, assuming an isotropic distribution of initial inclinations, is about 0.01. When we include non-gravitational forces (for example, taking typical values for Halley-type, short-period, and nearly parabolic comets), this figure increases to 0.02, 0.04 and >0.06 respectively. The probability for nearly parabolic orbits with initial perihelia in the range 10.5<q<18 au to evolve into Halley-type orbits is about 0.0002, again assuming an isotropic distribution of inclinations. However, the new-comet flux in the outer planetary region is expected to be much higher than that in the inner Solar system, so the outer Solar system flux may be a significant additional source of Halley-type comets. Our results show that the number of Halley-type objects arising from the observed nearly parabolic cometary flux with absolute magnitudes brighter than H10=7 and q<4 au is hundreds of times greater than the number of known Halley-type comets. The resolution of this discrepancy must lie in more observations and a deeper understanding of the physical evolution of comets, which together become the key issues for understanding the number of Halley-type objects and the terrestrial-planet impact rate due to both active and inactive objects in Halley-type orbits.

Keywords: methods: numerical; celestial mechanics, stellar dynamics; comets: general; Solar system: general.

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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