Evolution of asteroids

Kleine, T., Touboul, M., Bourdon, B. et al. (2009) Hf-W chronology of the accretion and early evolution of asteroids and terrestrial planets. Geochimica et Cosmochimica Acta,... 

Gaffey M. J., Kelley M. S., and Hardersen P. S. (2002b) Meteoritic and asteroidal constraints on the identification and colhsional evolution of asteroid famihes. Lunar Planet. Sci. XXXIII, 1506. The Lunar and Planetary Institute, Houston (CD-ROM). 

Bottke W. F., Vokrouhlicky D., Rubincam D., and Broz M. (2002) The effect of Yarkovsky thermal forces on the dynamical evolution of asteroids and meteoroids. In Asteroids III (eds. W. F. Bottke, A. Cellino, P. Paolicchi, and R. Binzel). University of Arizona Press, Tucson, pp. 395 -408. 

Nagasawa M., Tanaka M., and Ida S. (2000) Orbital evolution of asteroids due to sweeping secular resonances. Astron. J. 119, 1480-1497. 

Evolution of Asteroids Chondritic Miner alogic Properties... 

Chabot, N.L. and Haack, H. (2006) Evolution of asteroidal cores, in Meteorites and the Early Solar System II (eds. D.S. Lauretta, and H.Y. McSween Jr), University of Arizona Press,... 

Extraterrestrial materials consist of samples from the Moon, Mars, and a variety of smaller bodies such as asteroids and comets. These planetary samples have been used to deduce the evolution of our solar system. A major difference between extraterrestrial and terrestrial materials is the existence of primordial isotopic heterogeneities in the early solar system. These heterogeneities are not observed on the Earth or on the Moon, because they have become obliterated during high-temperature processes over geologic time. In primitive meteorites, however, components that acquired their isotopic compositions through interaction with constituents of the solar nebula have remained unchanged since that time. 

Clark, B.E., Hapke, B., Pieters, C. and Britt, D. (2002) Asteroid space weathering and regolith evolution. In Asteroids HI, eds. Bottke, W. E, Cellino, A., Paolicchi, P. and Binzel, R. P. Tucson University of Arizona Press, pp. 585-602. 

The astrophysical models of protoplanetary disks based on optical observations and laboratory experiments and meteoritic measurements provide the basis for theories of nebular evolution. The best and most precise relevant measurements are from meteoritic analysis. Meteorites from the Asteroid Belt of our Solar System are the best record of the evolution of the solar nebula from a gas-dust mixture to an organized planetary system. The addition of cometary and solar-wind sample analysis complement these data. Combination of fundamental laboratory-based experiments and modeling efforts has led to a highly resolved understanding of the chemical conditions and processes in the primordial solar nebula (see Chapter 6). In this chapter an overview of recent advances in our understanding of the chemical and isotopic evolution of the early Solar System and protoplanetary disks is presented. 

Several types of the early Solar System materials are available for laboratory analysis (see Chapter 1 and Table 1.1 and Fig. 1.1). Each material has unique characteristics and provides specific constraints on the chemistry of the solar nebula. Major components of this sample are meteorites, fragments of asteroids, that serve as an excellent archive of the early Solar System conditions. Primitive chondritic meteorites contain glassy spherical inclusions termed chondrules, some of the oldest solids in the Solar System. Most chondrites were modified by aqueous alteration or metamorphic processes in parent bodies but there are some chondrites that are minimally altered (un-equilibrated chondrites, UCs). They have yielded a wealth of information on the chemistry, physics, and evolution of the young Solar System. 

In this chapter we compare the evolution of protoplanetary disks to that of the proto-solar nebula. We start by summarizing the observational constraints on the lifetime of protoplanetary disks and discuss four major disk-dispersal mechanisms. Then, we seek constraints on the clearing of gas and dust in the proto-solar nebula from the properties of meteorites, asteroids, and planets. Finally, we try to anchor the evolution of protoplanetary disks to the Solar System chronology and discuss what observations and experiments are needed to understand how common is the history of the Solar System. 

Meteorites provide perhaps the best record of the chemical evolution of small bodies in the Solar System, and this record is supplemented by asteroidal spectroscopy. Meteorites show progressive degrees of thermal processing on their parent asteroids, from primitive carbonaceous chondrites that contain percent-level quantities of water, through ordinary chondrites that show a wide range of degree of thermal metamorphism, to the achondrites that have been melted and differentiated. 

Earth and Mars clearly contain H2O. Venus s atmosphere is very dry, and composed mainly of CO2, but the high D/H ratio of the small amount of water present suggests Venus was once much wetter than today (Zahnle 1998). Mercury is perhaps too small and too close to the Sun to have acquired and retained water. Water may have been present in much of the material that accreted to form the Earth. Small amounts of water may have been adsorbed onto dust grains at 1 AU by physisorp-tion or chemisorption (Drake 2005). Once Jupiter formed, substantial amounts of water could have been delivered to the growing Earth in the form of planetesimals and planetary embryos from the Asteroid Belt (Morbidelli et al. 2000). It is also possible that Earth lay beyond the snowline at some point during the evolution of the solar nebula (Chiang et al. 2001) so that local planetesimals contained ice. 

The giant planets, especially Jupiter and Saturn, significantly influenced accretion in the inner Solar System, with important consequences for the properties of the terrestrial planets, described in Section 10.4.1. The influence of the giant planets is especially strong in the Asteroid Belt. Given that meteorites are our primary samples of primitive Solar System material, understanding the role of dynamical and collisional processes in the formation and evolution of the Asteroid Belt is of fundamental importance for theories of planet formation (Section 10.4.2). 

Bottke et al (2005a,b) found that the current asteroid size distribution arose early in its history, when the total mass and collision rate were much higher than today. Once the Asteroid Belt was dynamically depleted and reached roughly its current mass (via the processes described above), there was little further evolution of the size distribution, and hence it has been referred to as a fossil size distribution. Collisions still occur, albeit at a reduced rate, and large collisions lead to the formation of asteroid families, which are groups of asteroids that are clustered in orbital-element (a, e, i) space. Numerous asteroid families can be seen in Fig. 10.6. 

Safronov, V. S. 1969, Evolution of the Protoplanetary Cloud and Formation of the Earth and Planets, Nauka Press, Moscow (English Translation NASA TIE-677). Safronov, V. S. 1979, in Asteroids, ed. T. Gehrels, University of Arizona Press, 975-991. Sakamoto, N., Seto, Y., Itoh, S et al. 2007, Science, 317, 231. 

Chondritic meteorites contain a complex record of processes that occurred during the earliest stages of solar system evolution, from the formation of the earliest solids by condensation in the solar nebula to the accretion of asteroidal... 

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