Future measurements and missions

Reflectance spectroscopy has proven to be the most powerful and versatile remote-sensing technique for determining surface mineralogy, chemical compositions and lithologies of planetary objects, as well as constituents of their atmospheres. Table 10.1 summarizes information that has been deduced for the terrestrial planets based on spectral properties of light in the visible and near-infrared regions reflected from their surfaces. 

The planetary reflectance spectral data constituting Table 10.1 traditionally have been obtained with Earth-based telescopes. Such remote-sensed measurements are limited by telescope availability, favourable observational conditions, and optimum viewing alignments of the planetary objects. As a result, 

Future spacecraft missions to solar system objects are primarily being oriented towards remote-sensing experiments, in contrast to the soft-landed in situ experiments and sample-return initiatives during the 1970 s and 1980 s. Because reflectance spectroscopy has become one of the most important investigative techniques in the planetary sciences, current and planned space missions for the 1990 s and 21st century should include visible and near-infrared spectrometers in their instrument payloads. Reflectance spectral measurements from space would provide more favourable viewing geometries, eliminate problems due to telluric water and C02, and improve the resolution of areas scanned on a nearby planetary surface. 

Chapter 10 describes how spectral measurements of sunlight reflected from surfaces of planets, when correlated with experimental visible to near-infrared spectra of rock-forming minerals, have been used to detect transition metal ions, to identify constituent minerals, and to determine modal mineralogies of regoliths on terrestrial planets. 

Compositions of terrestrial planets. Geochemical data derived from lunar samples returned by the Apollo and Luna missions to the Moon, in situ chemical 

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