Chemistry of anhydrous planetesimals

Many asteroids are dry, as evidenced by meteorites in which water is virtually absent. These samples include many classes of chondrites, as well as melted chunks of the crusts, mantles, and cores of differentiated objects. Anhydrous bodies were important building blocks of the rocky terrestrial planets, and their chemical compositions reveal details of processes that occurred within our own planet on a larger scale. The distributions of these asteroids within the solar system also provide insights into their formation and evolution. 

Anhydrous planetesimals formed within the inner solar system, unlike the ice-bearing bodies discussed in the next chapter. These objects, composed of rock and metal, were the primary building blocks of the terrestrial planets. Relics of that population may survive today as asteroids that dominate the inner portions of the main belt. 

Asteroids have been a focus of spectroscopic studies for decades. Spectra obtained from telescopes on the Earth can identify some of the minerals that make up asteroids, but do not measure asteroid chemistry. Nevertheless, spectroscopic matches can be used to link some meteorite classes to then probable parent bodies, and thus allow indirect assessments of then chemical compositions. A few asteroids have been visited and analyzed by spacecraft. Chemical analyses require long data integrations from orbit or actually landing on the surface, and analyses of only two small near-Earth asteroids have been reported. 

Most of the thousands of meteorites in our collections are bits and pieces of rocky or metallic asteroids. Because we can analyze these meteorites in the laboratory, they play a pivotal role in cosmochemistry. In this chapter we will focus on the compositions of meteorites that were anhydrous, or nearly so. The hydrated carbonaceous chondrites, in particular the Cl and CM chondrites, which sample bodies that once contained ices and fluids, will be considered in Chapter 12. 

Meteoritics involves the laboratory study of rocks without geologic context. Asteroid spectra provide a means to link some asteroid types to specific meteorite classes. Scientists can use the detailed information obtained from meteorites to reconstruct the chemical 

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A survey of the chemistry of anhydrous planetesimals and the samples we have of them... 

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