DPS Meeting, Madison, October 1998
Session 22P. Mars Surface I, II
Contributed Poster Session, Monday, October 12, 1998, 3:15-4:15pm, Hall of Ideas

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[22P.08] Mariner 7 IRS Revisited: Evidence for Goethite on Mars

L. E. Kirkland (Lunar and Planetary Inst. / Rice U), K. C. Herr (Aerospace Corp.)

Spectra acquired by the 1969 Mariner Mars 7 Infrared Spectrometer (IRS), spanning the wavelength region 1.8-14.4Ám, have recently been recovered and calibrated (Kirkland {\it et al}. LPSC XXIX abs. 1516, 1998). Absorptions detected at 2.4, 3, 11.25, and 12.5Ám provide strong spectral evidence for the presence of a hydrous weathering product on the martian surface, interpreted to be goethite. The 11.25 and 12.5Ám bands do not correlate with atmospheric path length, neither do they correlate with 12.6Ám atmospheric CO2 band depth, or the 9Ám atmospheric dust band depth. Thus we ascribe the 11.25 and 12.5Ám bands to the surface. An in-depth examination of the 2.4 and 3Ám band strengths must await completion of the more comprehensive calibration that is currently in progress. The presence of a hydrous weathering product is geologically significant and has important implications for the present and past climate on Mars. These spectral features are consistent with spectra recently returned by the Mars Global Surveyor Thermal Emission Spectrometer (TES), covering 6-50Ám. IRS and TES have similar spectral resolution in the ~10 to 13Ám region. The 11.25 and 12.5Ám bands may be examined in IRS spectra directly, but the lower spectral sampling of TES precludes a direct examination of the 12.5Ám band without an atmospheric removal. However, TES spectra exhibit a band at 11.25Ám that matches very well the feature in IRS spectra. Furthermore, TES spectra show a 23Ám band, and this is consistent with the goethite interpretation.

The author(s) of this abstract have provided an email address for comments about the abstract: kirkland@lpi.jsc.nasa.gov

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