SPECTROSCOPY OF MARS FROM 2.04 TO 2.44 MU-M DURING THE 1993 OPPOSITION - ABSOLUTE CALIBRATION AND ATMOSPHERIC VS MINERALOGIC ORIGIN OF NARROW ABSORPTION FEATURES

We present moderate-resolution (lambda/DELTAlambda = 300 to 370) refle ctance spectra of Mars from 2.04 to 2.44 mum that were obtained at UKI RT during the 1993 opposition. Seven narrow absorption features were d etected and found to have a Mars origin. By comparison with solar and Mars atmospheric spectra, five of these features were attributed all o r in part to Mars atmospheric CO2 or CO (2.052 +/- 0.003, 2.114 +/- 0. 002, 2.150 +/- 0.003, 2.331 +/- 0.001, and 2.357 +/- 0.002 mum). Two o f the bands (2.331 +/- 0.001 and 2.357 +/- 0.002 mum) appear to have w idths and depths that are consistent with additional, nonatmospheric a bsorptions, although a solar contribution cannot be entirely ruled out . Two other weak bands centered at 2.278 +/- 0.002 and 2.296 +/- 0.002 mum may be at least partially mineralogic in origin. The data provide no conclusive identification of the mineralogy responsible for these absorption features. However, examination of terrestrial spectral libr aries and previous moderate spectral resolution mineral studies indica tes that the most likely origin of these features is either (bi)carbon ate or (bi)sulfate anions in framework silicates or (Fe, Mg)-OH bonds in sheet silicates. If the bands are caused by phyllosilicate minerals , then an explanation must be found for the extremely narrow widths of the cation-OH features in the Mars spectra as compared to terrestrial minerals. (C) 1994 Academic Press, Inc.