DPS 34th Meeting, October 2002
Session 27. Comet Nuclei
Oral, Chair(s): C. Lisse and Y.R. Fernandez, Thursday, October 10, 2002, 2:00-4:00pm, Ballroom

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[27.10] Migration of comets to near-Earth orbits

S.I. Ipatov (NRC/NAS Senior Research Associate, NASA/GSFC; Inst. Appl. Math., Moscow), J.C. Mather (NASA/GSFC)

The orbital evolution of ~5000 Jupiter-crossing objects rbital evolution of ~5000 Jupiter-crossing objects (JCOs) with initial periods <10 yr under the gravitational influence of the planets (except Mercury and Pluto) was integrated using the Bulirsh-Stoer method. The simulations showed that most of the collisions of former JCOs with the terrestrial planets are due to a small (~0.1-1%) portion of objects that moved for several Myrs in orbits with aphelion distances Q<4.7 AU. Some had typical asteroidal and NEO orbits and could have Q<3 AU for millions of years. Usually ~0.1% of JCOs reached semi-major axes a<2 AU for \ge0.5 Myr, and some moved in such orbits for more than 5 Myr. In our runs one former JCO had Aten-type orbits for >3 Myr, and the probability of its collision with the Earth was greater than that of all other simulated former JCOs. This object also moved for about 10 Myr (before its collision with Venus) in inner-Earth orbits (with Q<0.983AU) and its probability of collision with Venus was even greater than the total probability of collisions of all the other simulated JCOs with Earth. On average, one of 300 JCOs collided with the Sun, and an object spent 0.13 Myr in Jupiter-crossing orbits, and for 1/3 of this time it had a period <20 yr. The above results were obtained using the method of Bulirsh and Stoer, but the evolution of 3100 orbits was also investigated with a symplectic method. For a symplectic method, simulated former JCOs spent more time in orbits with a<2 AU. Results of the orbital evolution of JCOs show that many Earth-crossing objects can move in highly eccentric (e>0.6) orbits and, probably, most of the 1-km objects in such orbits have not yet been discovered. Results of the orbital evolution of trans-Neptunian objects and JCOs showed that a considerable portion of NEOs could have come from the trans-Neptunian belt (so they can be extinct comets). In principle, this belt can provide most of the Earth-crossing objects (especially, those with a>2 AU), but, of course, many NEOs came from the main asteroid belt. This work was supported by NRC (0158730), NASA (NAG5-10776), INTAS (00-240), and RFBR (01-02-17540).

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