Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.u51a..04m&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #U51A-04
Physics
4271 Physical And Chemical Properties Of Seawater, 5455 Origin And Evolution, 6040 Origin And Evolution
Scientific paper
It is now generally accepted that in the inner solar system the process of runaway growth ended with the formation of many ``planetary embryos'' of lunar to martian mass (1,2). The terrestrial planets then formed on a longer time-scale (from several tens to a hundred million years), by the high-velocity mutual collisions of these embryos (3,4,5). The radial extent of the primordial population of planetary embryos is not known. In principle, a system of embryos originally within 2 AU from the Sun could form terrestrial planets on time-scales compatible with geochemical constraints (4). However, an even better agreement with the geochemical time-scales is achieved if one postulates that the formation of the embryos occurred also in the asteroid belt (5). This scenario has also additional advantages: (i) the original presence of planetary embryos explains the presently observed properties of the asteroid belt (6); (ii) in 3/4 of the cases a terrestrial planet accreted at least one embryo coming from the outer asteroid belt, which was presumably heavily hydrated, on the basis of meteorite analyses and modeling of the solar nebula. This could have brought to the Earth up to 10 times the present amount of water in the crust, with the correct hisotopic composition (7). The amount of water carried to the Earth by small asteroids and comets is negligible with respect to that acquired through the accretion of an hydrated embryo, and it would not be enough to explain the current budget of water on Earth. Nevertheless this contribution may be important, because it occurred since the very beginning of the planet's formation. selected references: (1) Wetherill and Stewart, 1989, Icarus, 106, 190 (2) Weidenschilling et al., 1997, Icarus, 128, 429 (3) Wetherill, 1992, Icarus, 100, 307 (4) Chambers and Wetherill, 1998, Icarus 136, 304 (5) Agnor et al., 1999, Icarus, 142, 219 (6) Petit et al., 2001, Icarus, in press (7) Morbidelli et al., 2000, Meteoritics, 35, 1309
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