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Juventae Chasma is a depression north of Valles Marineris on Mars, approximately 185 km wide and 270 km long. It
contains several mounds of light-toned, layered deposits several tens of kilometers of maximum extension and up to
3300 m in elevation. Near infrared spectral data from the Observatoire pour l'Eau, des Glaces et l'Activité onboard ESA's
Mars Express indicated mono- and polyhydrated sulfates as main constituents of these deposits, including gypsum in one
of the mounds (Gendrin et al., 2005, Science). We analyze the light-toned outcrops based on data from NASA's Compact
Reconnaissance Imaging Spectrometer for Mars (CRISM), featuring an increased spatial resolution of up to 18m/pixel
and increased spectral resolution of 7 nm. We perform Spectral Mixture Analysis (SMA) in order to introduce physical
modeling and to enhance some surface units. We use one type of SMA, the Multiple-Endmember Linear Unmixing
Model MELSUM (Combe et al., 2008, PSS), which guarantees positive mixing coefficients and allows us to limit the
number of spectral components used at a time. We use linear unmixing both as a similarity measure using spectra from
the image itself as endmembers to assess the internal variability of the data, and to detect mineral spectra within the
observations. We successfully confirm the presence of the monohydrated sulfate szomolnokite (previously detected by
Kuzmin et al., 2008, and Rossi et al., 2008) in all of the four light-toned deposits observed. Based on our analysis, we
reject the presence of gypsum on mound B (previously detected by Gendrin et al., 2005). A possible match for the
polyhydrated sulfate present here could be rozenite, but other sulfate minerals also have to be considered. The
implications of the possible presence of iron bearing polyhydrated sulfates such as rozenite and the absence of calcium -
bearing gypsum for the geological history of the outcrops are not yet fully understood. Our next step is the geochemical
modeling of the weathering of Martian basaltic rocks, dominated by iron and magnesium silicates, to iron bearing
sulfates, under acidic conditions.
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