ICARUS 111, 106-123 (1994)

     Spectroscopy of Mars from 2.04 to 2.44 um during the 1993 Opposition:
              Absolute Calibration and Atmospheric vs Mineralogic
                     Origin of Narrow Absorption Features

                    JAMES F. BELL III AND JAMES B. POLLACK

              NASA Ames Research Center, Space Science Division,
                     Moffett Field, California 94035-1000
                      E-mail: jimbo@anarchy.arc.nasa.gov

                               THOMAS R. GEBALLE

                  Joint Astronomy Center, Hilo, Hawaii 96720

                              DALE P. CRUIKSHANK

              NASA Ames Research Center, Space Science Division,
                     Moffett Field, California 94035-1000

                                      AND

                               RICHARD FREEDMAN

              Sterling Software Inc., Palo Alto, California 94030


                                   ABSTRACT
 
        We present moderate-resolution (lambda/delta(lambda) = 300 to 370)
     reflectance spectra of Mars from 2.04 to 2.44 um that were obtained at
     UKIRT during the 1993 opposition.  Seven narrow absorption features
     were detected and found to have a Mars origin.  By comparison with
     solar and Mars atmospheric spectra, five of these features were
     attributed all or 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 um).  Two of the bands (2.331 +/- 0.001 and 2.357 +/- 0.002
     um) appear to have widths and depths that are consistent with
     additional, nonatmospheric absorptions, although a solar contribution
     cannot be entirely ruled out.  Two other weak bands centered at 2.278
     +/- 0.002 and 2.296 +/- 0.002 um 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 libraries and previous moderate
     spectral resolution mineral studies indicates that the most likely
     origin of these features is either (bi)carbonate 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.