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M.Ya. Marov (Inst. Appl. Math., Moscow), S.I. Ipatov (NRC/NAS Senior Research Associate, NASA/GSFC; Inst. Appl. Math., Moscow)
Migration processes of planetesimals and trans-Neptunian objects from the outer to inner regions of the solar system are addressed as an important mechanism in the formation and evolution of the inner planets. While the relative contribution of the concurrent processes of endogeneous and exogeneous origins to the volatile reserves is difficult to assess, it is assumed that these objects could be responsible for the delivery of the majority of volatiles. According to our model, icy comets/asteroid chondrites that impacted on the Earth during the formation of the giant planets could have delivered a mass of water comparable to that found in the Earth's oceans. The model further predicts that Mars would have acquired more and Venus slightly less water per unit of planetary mass than the Earth (at least from objects with a>1 AU). This would have resulted in a relatively large ancient Martian ocean. During the following 4 Gyr, the effectiveness of the transport mechanism was much lower and accounted for less than 0.1% of the total mass of volatiles inventory. The above estimates were based on the study of the orbital evolution of trans-Neptunian and Jupiter-crossing objects. Direct numerical integration of the evolution of thousands of Jupiter-crossers under the gravitational influence of the giant planets showed that they could collide with the terrestrial planets mainly from Encke-type or typical near-Earth object orbits. Such collisions played a greater role than direct impacts from the Jupiter-crossing orbits. In our analysis, the high probability of collisions with the terrestrial planets were due to less than 1% of the objects residing in orbits with an aphelion distance Q<4.7 AU during more than 0.5 Myr. All these factors caused a larger amount of cometary material to be delivered to the Earth compared to the estimates of other authors. The relative importance of comets and chondrites in the delivery of volatiles is constrained by the observed fractionation patterns of atmospheric noble gas abundance. 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.