Introduction

Earlier chapters have demonstrated that spectral features of most rock-forming minerals in the visible to near-infrared region originate from the presence of transition elements in their crystal structures. Iron and titanium have higher crustal abundances on terrestrial planets relative to other transition elements and, consequently, are expected to contribute significantly to the reflectance spectra of planetary surfaces. Spectral profiles of sunlight reflected from planetary surfaces, when correlated with measured optical spectra of rock-forming minerals, may be used to detect the presence of individual transition metal ions, to identify constituent minerals, and to determine modal mineralogies of regoliths on terrestrial planets. The origin and applications of such remotesensed reflectance spectra measured through Earth-based telescopes are described in this chapter.

Chemical composition of the terrestrial planets

Properties of the terrestrial planets that are central to this chapter are summarized in table 10.1 and information about element abundances is contained in Appendix 1. The crustal abundance data for the Earth indicate the presence of relatively high concentrations of Fe, and to a lesser extent Ti, compared to other first-series transition elements.