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S.I. Ipatov (George Mason U. and Keldysh Inst. of Applied Mathematics, Russia), J.C. Mather (NASA/GSFC)
Migration of Jupiter-family comets (JFCs) to near-Earth object (NEO) orbits under the gravitational influence of planets was investigated. The orbital evolution of about 9000 and 7000 JFCs was integrated with the use of the method by Bulirsh-Stoer and a symplectic method (RMVS3 code), respectively. The main results obtained were close for these methods. For initial orbital elements close to those of Comets 2P, 10P, 44P, and 113P, a few objects (<0.1%) got Earth-crossing orbits with semi-major axes a<2 AU and aphelion distances Q<4.2 AU and moved in such orbits for more than 1 Myr (up to tens or even hundreds of Myrs). Three of them (from 2P and 10P runs) even got inner-Earth orbits (Q<0.983 AU) and Aten orbits for millions of years. Based on orbital elements sampled with a step of 500 yr, we calculated collision probabilities with the terrestrial planets. A collision probability with the Earth for one JFC that moved in typical NEO orbit for millions of years can be much greater than that for thousands of other JFCs. For orbits close to that of Comet 2P the mean collision probabilities of JFCs with the terrestrial planets were greater by more than two orders of magnitude than for most other JFCs. Even if we do not consider a few objects with the largest probabilities with the Earth, the mean collision probabilities are enough to conclude that the amount of water delivered to the Earth during the formation of the giant planets could be about the mass of the Earth oceans. Our runs showed that if a former JFC is observed moving in a typical near-Earth object orbit, it usually has already moved in such orbit for millions of years so during most of this time it was an extinct comet. We suppose that during such long lifetimes some extinct comets can change their albedo or can be destructed into mini-comets. From the dynamical point of view, there could be many extinct comets among the NEOs, or the number of trans-Neptunian objects migrating inside solar system could be smaller than it was earlier considered. Several our papers on this problem were put in http://arXiv.org/format/astro-ph/: 0108187, 0205250, 0210131, 0211618, 0212177, 0303219, 0305519. This work was supported by NASA (NAG5-10776), RFBR (01-02-17540), and INTAS (00-240).
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.