Asteroid Belt formation

These models provide an explanation for the thermal structure of the asteroid belt that is probably correct in principle but not in its details. The recognition that differentiated asteroids formed earlier than chondrites, perhaps within the terrestrial planet region, requires models in which asteroid accretion was initiated earlier than 2 Myr after CAI formation. 

In this model, large gravitationally bound clumps form only occasionally, which would explain why planetesimal formation in the Asteroid Belt continued for several million years. This mechanism also reproduces the narrow size distribution of chondrules seen in chondritic meteorites (Cuzzi et al. 2001). While the mean chon-drule size differs from one meteorite type to another, the size distributions closely... 

The effect of the giant planets and the formation of the Asteroid Belt... 

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. 

Energy released during impacts causes large embryos and planets to melt and differentiate, forming iron-rich cores and silicate mantles. Earth acquired most of its water before its core finished forming, possibly from the Asteroid Belt. It gained the last 1 % of its mass in the form of non-fractionated material after core formation was complete. 

Two features in this table deserve comments 1. - There is no planet corresponding to n == 5, that is, to = 2.8 AU. However, there is a belt made up of several asteroid rings approximately at this distance from the Sun. This suggests that the asteroid belt might be the embryo of a planet in formation, or the remnants of a planet that was hit... 

Stellar dynamics and may have analogs in the formation of orbits in planetary ring systems and the asteroid belt. 

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