Pat Morris 1, Thijs de Graauw 2, Emmanuel Lellouch 3, Therese Encrenaz 3, Helmut Feuchtgruber 4, & Stephane Erard 3
1 SRON, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
2 SRON, Landleven 12, 9700 AV Groningen, the Netherlands
3 DEPSA, Observatoire de Paris, Meudon, France
4 MPE-Garching, D-84748 Garching, Germany
Disk-integrated observations of Mars taken with ISO-SWS at lowest and
highest grating resolutions in July-August 1997 reveal mid-IR spectral
features that may be attributed to mineral signatures of the martian
regolith and atmosphere. Model
atmospheres have been constructed
using wavelength-dependent effective brightness temperatures for the surface
during low atmospheric dust conditions, and an atmospheric thermal profile
fit from the 15
m CO2 absorption profile in each of the three
observations (Lellouch et al., these proceedings). Mineral signatures
are thus obtained by division of the SWS data with model atmospheres.
Concentrating on the 5-15m region, we make use of available laboratory
measurements of silicates, carbonates, sulfates and phosphates to give a
qualitative assay of the minerals globally dominating the surface and/or
atmospheric dust in each pointing. Many factors hinder precise
identifications, the most critical being grain size and surface roughness,
(affecting band widths and depths), the uncertain role of radial
thermal gradients at the martian surface (known to shift the Christensen
frequency in silicates), and the degeneracy of solutions for the
disk-integrated spectrum using linear deconvolution methods. Nonetheless,
we are able to place limits on mass fractions of silicates and carbonates,
with broad-reaching implications for the early martian CO2 atmosphere.