The 2.4-45 mu m spectrum of Mars observed with the Infrared Space Observatory

The spectrum of Mars at 2.4-45 mum has been observed on July 31, 1997 (L-s = 157 degrees) by the Short-Wavelength Spectrometer of the Infrared Space O bservatory. The data consist of a high signal to noise, complete grating sp ectrum (resolving power R similar to 1500-2500) and portions of the 20-45 m um spectrum observed in Fabry-Perot mode (R similar to 31000). The data sho w the infrared bands of known martian atmospheric species (CO2, H2O, and CO ) with an unprecedented amount of details. The vertical distribution of H2( O) is determined, showing saturation near 10 km. Evidence for scattering in the saturated CO2 band at 2.7 mum and for fluorescence emission in the CO2 4.3 pm band is obtained. No detection of new atmospheric species is achiev ed, but upper limits are obtained for CH4 and H2CO. In the solar reflected part of the spectrum, which dominates at lambda less than or equal to 4.2 m um, the surface reflectance clearly shows the hydration band with maximum a bsorption at 2.9 mum, from which a 2.0 -2.7% (by weight) water content in t he martian uppermost layer is estimated. A decrease of reflectance from 3.8 to 5 mum is also seen. This behaviour is consistent with basalts and palag onite, but not hematite. Ln the thermal part, mineralogic signatures at 5-1 2 mum are globally consistent with a basaltic composition. Specific minima an also detected at 5.7, 6.3 (tentative), 7.2 and 11.1 mum. Reexamination o f earlier datasets indicates that the latter two have been observed before, although generally not discussed. The presence of additional absorptions a t 26.5, 31 and 33.5 mum is also indirectly suggested. Carbonate minerals ar e tentatively detected from this ensemble of features, though no single car bonate species can be unambiguously identified. (C) 2000 Elsevier Science L td. All rights reserved.