Аннотация:As analytical modeling shows (e. g., [1]), extensive internal water oceans could form due to 26Al decay and exist for a considerable time (~5 Myr or even more) at ~4 °C on large (R>100 km) rock-ice bodies in the early Solar system (ESS). After the early water differentiation, Edgeworth-Kuiper objects (EKOs) and pre-planetary bodies in the formation zones of giant planets were probably sources of icy and rock-organic matter after their breaking up at collisions. Intensive fluxes of the materials could considerably change surface mineralogy of asteroid parent bodies (APBs) in the main asteroid belt (MAB) shortly after their accretion.
There is no doubt that a high surface density of matter in the formation zones of giant planets (especially, in Jupiter’s one) [2] led to runaway accretion of the planets themselves and smaller bodies. This ensured a short time of growth of large Jupiter zone bodies (JZBs) and enough 26Al in their interiors for complete melting water-ice except for the ~10-km crust and origin of a global water ocean [1]. If primordial JZBs similarly to comet nuclei consisted of “dirty” ice, sedimentation of solid particles with a density >1 g cm-3 (silicates and heavy organics) in the water ocean was accompanied by the phyllosilicate formation (mainly serpentinization). Thus, a result of water differentiation of JZBs could be accumulation of a considerable silicate-organic core with a size of ~0,7R [1]. This is confirmed by numerical modeling showed also a possibility of higher temperatures (up to several hundred degrees) into silicate-organic cores of similar bodies (e. g., [3]). Mutual collisions could lead to resurfacing crust and supporting a warm state of the bodies. An intense release of H2 and CH4 gases and additional heat at exogenous reaction of serpentinization of silicates [4, 5] in the water oceans of JZBs might have had a similar effect. It is important to note that the factors created probably a heterogeneous and porous structure of JZBs. Then, a lifetime of an internal water ocean on large JZBs could be estimated ~10 Myr. When proto-Jupiter reached a few masses of the Earth, these bodies started to be ejected out of the zone (to the MAB as well) at velocities 1-3 to 10-15 km s-1 [2, 6]. JZBs-APBs' collisions could have different consequences depending on relative velocity and sizes of the bodies. When large relative velocities and/or sizes of JZBs (surpassing considerably these of APBs), they sweep out APBs from the MAB at collisions [6, 7]. On the contrary, when relative velocities of JZBs penetrating the MAB near the lowest boundary (1-3 km s-1) corresponding to eccentricity of their orbits within 0,3-0,4 [6, 7], JZBs-APBs’ collisions end with fragmentation of the former for their weak mechanical strength. It is necessary to emphasize that the collisions were more likely at lower relative velocities of JZBs, if they had been orbiting in less elongated orbits and could penetrate into the MAB at a higher rate and for a longer time. Consequences of this would be delivery of a large amount of grinded icy and hydrosilicate-organic matter (resembling CI-meteorites) of JZBs to the MAB and the survival of the bulk of the primitive compounds at collisions.
Re-accretion of thick layers of JZBs' matter dispersed at collisions on the surfaces of several existed APBs could lead to formation of the largest C-type asteroids (as well as 1 Ceres and 2 Pallas). Considerable fragments of JZBs could become smaller members of the family or replenish close ones. Different groups of carbonaceous chondrites (CM2, CO, CV, etc.) would be formed in the same or other multiple processes of JZBs-APBs' and/or mutual APBs’ collisions depending on the number and intensity of the events. Supporting facts are: 1) a comprehensive heliocentric distribution of C-type asteroids in the MAB [8], 2) a growth of their relative number to the outer edge of the MAB [9], 3) discoveries of atypical hydrated silicates on the surface of high-temperature asteroids (of M-, S-, E- and V-types) [10-13], 4) internal structure of carbonaceous chondrites (i. e., the absolute predominance of phyllosilicates in their matrix, etc.) [14, 15]. The hypothesis is in accordance with a mechanism of origin of chondrules in carbonaceous chondrites at collisions of asteroid-size bodies [16, 17].
References: [1] Busarev et al. (2003), Earth, Moon & Planets, 92, 345. [2] Safronov V. S. (1972) Evolution of the protoplanetary cloud and the formation of the Earth and the planets / TTF-667, Washington, 206 p. [3] McKinnon W. B. et al. (2008), in The Solar System Beyond Neptune / Eds Barucci M. A. et al., Tucson: Univ. Arizona Press, 213. [4] Wilson L. et al. (1999), Met. Planet. Sci., 34, 541. [5] Rosenberg N. D. et al. (2001), Met. Planet. Sci., 36, 239. [6] Safronov V. S., Ziglina I. N. (1991), Sol. Sys. Res., 25, 139. [7] Ruskol E. L. Safronov V. S. (1998), Sol. Sys. Res., 32, 255. [8] Bell J. F., et al. (1989), in Asteroids II (Binzel R. P. et al., eds), Tucson: Univ. Arizona Press, 921. [9] Bus S. J., Binzel R. P. (2002), Icarus, 158, p. 146. [10] Rivkin A. S. et al., (2000), Icarus, 145, 351. [11] Busarev V. V. (2002), Sol. Syst. Res., 36, 35. [12] Busarev V. V. (2010), Sol. Syst. Res., 44, 507. [13] Busarev V.V. (2011) Spectrophotometry of asteroids and its application / LAP LAMBERT Acad. Pablish. GmbH & Co. KG, Saarbrücken, 250 p. [in Russian] [14] Dodd R. T. (1981) Meteorites - A petrologic-chemical synthesis / Cambridge Univ. Press, 368 p. [15] Rubin A. E. (1997), Meteorit. Planet. Sci., 32, 231. [16] Urey H. C. (1952), Geochim. Cosmochim. Acta, 2, 269. [17] Hutchison R. et al. (2005), in Chondrites and the protoplanetary disk / Eds Krot A. N. et al., ASP Conf. Series, v. 341, p. 933.
Ссылка на статью: https://arxiv.org/ftp/arxiv/papers/1211/1211.3042.pdf