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L.M. Ozernoy (GMU), S.I. Ipatov (IAM, Moscow)
The goal of this project is to determine which particular kinds of ice sources in the outer Solar system could have provided the largest contribution of water onto the planets of the Earth group. As is known, the contemporary influx of comets and asteroids is just a tiny fraction of impact delivery occuring at the epoch of the planet formation. Our approach has demonstrated that the amount of water delivered to the Earth during this epoch has been substantially underestimated. The following factors neglected in the previous work turn out to be very important: 1)~Previous studies were based on symplectic integration and ignored the influence of terrestrial planets. In our direct numerical integrations, which take into account the terrestrial planets, the fraction of Jupiter-crossers that reached the orbit of the Earth is greater by a factor of 2 than that obtained by the symplectic method with the integration step of 30\rm d. 2)~While considering collisions of planetesimals with the planets, we need to take into account that the bodies move non-uniformly in their orbits. As a result, the mean time between the collisions with Earth from Jupiter-crossing orbits increases by a factor of 2. 3)~Finally, a large factor that can considerably (up to an order of magnitude) increase the amount of water delivered to the Earth is the collisions of planetesimals with the Earth from the orbits, which entirely located inside Jupiter's orbit. Although the fraction of these orbits is relatively small (\le 0.01), such bodies spend in Earth-crossing orbits much longer time (perhaps, by two orders of magnitude) and collide with the Earth from orbits of smaller eccentricities than Jupiter-crossing objects. To sum up, the total amount of water delivered to the Earth during the formation of the giant planets could be comparable to that in the Earth oceans. The amount of water delivered to Venus is less by a factor of 3, and that delivered to Mars is less by a factor of 2 for Jupiter-family comets and by a factor of 30 for near-Earth objects. We acknowledge support of this work by NASA grant NAG5-10776, the RFP ``Astronomy", RFBR, and INTAS~(00-240).
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