Mathematics – Logic
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..378d&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Mathematics
Logic
Scientific paper
Introduction The discovery of phyllosilicates on Mars [1] has had major implications on the perceived geologic and climatologic evolution of Mars [2]. Not only do phyllosilicates represent a `wet' period on Mars, they might also represent a potentially favorable environment for life. The phyllosilicates have so far exclusively been found in or close to ancient Noachian highland terrain. Those phyllosilicate deposits studied (e.g. [3]) show a clear association between hydrated mineralogy and heavily eroded and crater-saturated outcrops. Phyllosilicates on Earth are associated with a wide variety of geological processes (volcanism, metamorphism, hydrothermal alteration, sedimentation). The occurrence of phyllosilicates on Mars may be equally diverse in nature. To be able to place constraints on the early Martian environment, the processes by which these phyllosilicates formed need to be reconstructed. To derive this information from individual phyllosilicate deposits, it is necessary to interpret their composition in relation to their geological context and relative time relationships. We conducted such an integrated hyperspectral and geological study of the Tyrrhena Terra region. Data products ad methods HRSC data products (both image at 12 m/pixel and stereo-derived DTMs) are used for examining geologic cross-cutting relationships, geomorphologic landforms and visual determination of unit boundaries. Odyssey THEMIS nighttime TIR images are analyzed for spatial variations in thermal inertia. Where available, HRSC is supplemented by higher-resolution visible observations of CTX or MOC. Hyperspectral analysis is conducted using data from the OMEGA hyperspectral instrument. In order to batch-process large amounts of OMEGA data, an IDL/ENVI tool was developed on top of the existing SOFT04, distributed by PSA. The applied atmospheric correction assumes that atmospheric contributions are multiplicative, and follow a power-law distribution with altitude [4]. The ratio of two spectra taken at base and summit of Olympus Mons provides the atmospheric spectrum. To quickly assess the mineralogy of a large region, CRISM multispectral summary products [5] are applied to OMEGA datasets. Hydrated mineral deposits are located on the basis of the absorption feature centered at ~1.9um. This feature is the result of a combination of v2 bend and v3 (asymmetrical) stretch mode overtones. Noise reduction is performed by applying a principal component transform to the OMEGA data. Principal components which are dominated by noise are manually selected and discarded, after which the data are transformed back to the wavelength domain. Using this approach, a large degree of system noise can be effectively eliminated without significantly affecting signal quality [6]. Results The methods described have led to positive identification of large deposits of hydrated mineralogy in Tyrrhena Terra. Whilst several deposits are evidently associated with cratering processes (e.g. [7]), one major deposit in particular draws attention (figure 1). In this deposit, the light-colored hydrated minerals are generally associated with very rough morphology. In addition, they seem to be located underneath a dark, crater-saturated unit. Given the limited quality of local OMEGA-derived spectra, it is impossible to unambiguously determine the exact mineralogy of the deposit. The hydrated signature is correlated with high night-time temperatures as observed in THEMIS IRnight observations (figure 2). This indicates the hydrated material is present as a solid bedrock mass (e.g. mudstone) instead of a loose concretion. The deposit is situated in a topographic low, bounded by a channel-rich unit in the north and a sharp unit contact in the south. Discussion The sharp unit contact south of the hydrated deposit coincides with a sharp contrast in topographic elevation. It strikes parallel to the contours of Isidis Planitia, a trend which is continued on larger scale. Given the strike and morphological characteristics, this contact is likely a normal fault, which was created as a direct result of the Isidis impact event. To accommodate the extensional regime associated with the late stage of such a major impact, the footwall block may have tilted to form a topographic depression. The observed deposit would then be a sedimentary basin infill, supplied by a topographically higher channel-rich unit north. Many channels seem to converge towards the depression, which supports this notion. As an important implication, this places the Isidis impact event before the hydrous activity. OMEGA data are subject to significant levels of noise. This introduces a probability for false-positives in the case of spectral parameters (see [4]). This probability can be minimized by taking into account a minimum detection threshold and performing crossobservation validation. Although part of this noise can be countered using principal component analysis, care must be taken not to overdo, as the method has the potential to erase fine signal elements. The BD530-parameter will be used to quickly assess dust cover and thus spectral quality of the scene [8]. Future work will first focus on integrating various datasets to provide unambiguous identification of hydrated mineralogy and their geological setting. References [1] Bibring, J-P., et al. (2005), Science 307 [2] Poulet, F., et al. (2005), Nature 438 [3] Loizeau, D., et al. (2007), JGR 112 [4] Bibring, J.P., et al. (1989), Nature 341 [5] Pelkey, S.M., et al. (2007), JGR 112 [6] Antonelli, P. et al. (2004), JGR 109 [7] Pelkey, S.M., et al. (2007), in LPSC 2007, # 1994 [8] Poulet, F., et al. (2007), JGR 112
den Haan J.
Rossi Alessandro
van der Werff M. A. H.
van Ruitenbeek J. A. F.
Zegers Tanja E.
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