Computer Science
Scientific paper
Oct 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996icar..123..256w&link_type=abstract
Icarus, Volume 123, Issue 2, pp. 256-268.
Computer Science
24
Scientific paper
Theoretical considerations of Mars' climate evolution and conceptions about the weathering processes of martian crustal rocks suggest that carbonate minerals might be present as likely secondary minerals in the soil and dust on Mars. However, only limited evidence for the existence of carbonates on the surface of Mars has been found. We investigate the spectral contrast (or band intensity) of diagnostic features as a function of varying carbonate content in Mars soil analogues. Specifically, we mixed siderite and dolomite/ankerite in samples of palagonite and tholeiite. From measurements of spectral reflectance the carbonate band at ~4 μm is chosen as the best feature for carbonate detection. At this wavelength, however, Mars' thermal emission must be taken into account. Thermal emission increases the total radiance in the considered wavelength region. Moreover, the shapes of spectral features are opposites in the reflectance and emittance spectra; i.e., a reflectance trough becomes an emittance peak. This results in partial compensation of the diagnostic spectral features and should be considered in addition to the increased flux. Unfortunately, this reduces the possibility for spectroscopic carbonate detection. Furthermore, for increasing particle size the diagnostic spectral features are weaker. Using our results from reflectance and emissivity measurements for Mars soil analogues mixed with various percentages of carbonates, the contributions of both reflected and emitted radiation can be examined. The spectra for the various mixtures show a drastic weakening of the 4-μm carbonate feature with increasing temperature. From these spectra, obtained for several surface temperatures and grain size ranges, we estimate carbonate detection limits which suggest that possibly more than 7 wt% (at 275 K) or ~20 wt% (at 300 K) carbonate can be included in the surface but not observed spectroscopically.
Schade Ulrich
Wagner Clemens
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