Mercury: Evidence for Anorthosite and Basalt from Mid-infrared (7.3-13.5 μm) Spectroscopy
✍ Scribed by A.L. Sprague; R.W.H. Kozlowski; F.C. Witteborn; D.P. Cruikshank; D.H. Wooden
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 660 KB
- Volume
- 109
- Category
- Article
- ISSN
- 0019-1035
No coin nor oath required. For personal study only.
✦ Synopsis
Spectroscopic observations (7.3-13.5 (\mu \mathrm{m}) ) of three locations on the surface of Mercury are reported. The observed spectral radiance emanated from equatorial and low latitude regions between 12 and (32^{\circ}) mercurian longitude on 8 December 1990 , from the longitudinal region (22-44^{\circ}) on 10 December 1990, and from the longitudinal region (110-130^{\circ}) on 12 July 1992; all locations are primarily intercrater plains. Spectra indicate compositional differences among these three locations. The emissivity maximum, or Christiansen emission peak, occurs at (8.1 \mu \mathrm{m}) in the 8 December 1990 spectra, but at shorter wavelengths in the data of 10 December 1990 and 12 July 1992. Emission peaks near (8 \mu \mathrm{m}) indicate rocks of intermediate or mafic composition. Spectra from 22 to (44^{\circ}) longitude resemble spectra of terrestrial basalt and diorite with (\mathrm{SiO}_{2}) content between 49 and (55 %). The Christiansen feature in spectra from near (110-130^{\circ}) longitude strongly suggests the presence of plagioclase, in particular labradorite, while the overall spectrum resembles anorthosite. The spectra from all three locations on Mercury show distinct and recognizable features, the principal Christiansen emission peak being the most prominent, but they also contain features that we have not yet identified. The general indication from the spectra is that Mercury's surface consists of minerals more depleted in oxidized iron than those on the Moon. We also explore the theoretical and observational complexities of ground-based mid-infrared spectroscopy of airless bodies in general and Mercury in particular. A spectroscopic study of quartzite in both reflectance and emittance illustrates the practical, spectral validity of Kirchhoff's Law. O 1994 Academic Press, Inc.