Mathematics – Logic
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dps....31.6007l&link_type=abstract
American Astronomical Society, DPS meeting #31, #60.07
Mathematics
Logic
Scientific paper
In July--August 1997, the Infrared Space Observatory (ISO) acquired three 2.4--45 mu m spectra of Mars at R = 1500--2500 resolution. The spectra clearly show the resolved CO_2, H_2O and CO which can be modelled and divided out. This makes appear spectral mineralogic features in the 5--12 mu m range, originating either in the suspended dust or at the surface. Besides the prominent broad silicate absorption at 8--12 mu m, the spectra show weaker absorptions around 5.7, 6.3 (tentative), 7.2, and 11.2 mu m. Reassessment of earlier observations suggests that these bands, and in particular those at 7 and 11 mu m, have actually been detected before, although not much attention has given to them. A 7 mu m feature was reported by Pollack et al (JGR 1990) from KAO observations, correctly identified as partly gaseous and partly mineralogic, and tentatively assigned to carbonate / bicarbonate ions. A non--gaseous band at 7.2 mu m is also clearly present in a large average of Mariner 9 /IRIS data (see Maguire, Icarus 1977), in some Mariner 6/7 IRS spectra (see Kirkland et al. LPSC 1998), and in MGS/TES observations (see Christensen et al. Science 1998). After elimination of the gas contribution, the Mariner 9 spectrum exhibits a subtle absorption at 11.0--11.5 mu m, though not as narrow as in the ISO data. A 11.2 mu m shoulder is also present is ground-based spectra of Acidalia (Moersch et al. Icarus, 1997). Association of bands near 7 and 11 mu m may be a hint for the presence of carbonates (see companion talk by Morris et al.). We will investigate the variation of these features in the Mariner 9 spectra. Finally, we will present an analysis of the ISO spectrum longward of 18 mu m. Although the ISO spectra are affected by non--linear photometric response there, an indirect method based on the water vapor rotational features allows us to infer the surface/aerosol emissivity, and a 31 mu m absorption feature is tentatively suggested.
de Graauw Th.
Encrenaz Th.
Erard Stephane
Lellouch Emmanuel
Morris Pat
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