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Phyllosilicates on Mars and implications for early martian climate


The recent identification of large deposits of sulphates by remote sensing and in situ observations has been considered evidence of the past presence of liquid water on Mars. Here we report the unambiguous detection of diverse phyllosilicates, a family of aqueous alteration products, on the basis of observations by the OMEGA imaging spectrometer on board the Mars Express spacecraft. These minerals are mainly associated with Noachian outcrops, which is consistent with an early active hydrological system, sustaining the long-term contact of igneous minerals with liquid water. We infer that the two main families of hydrated alteration products detected—phyllosilicates and sulphates—result from different formation processes. These occurred during two distinct climatic episodes: an early Noachian Mars, resulting in the formation of hydrated silicates, followed by a more acidic environment, in which sulphates formed.

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Figure 1: Phyllosilicate spectra as identified in the OMEGA observations.
Figure 2: Variation of the position and shape of the absorption feature in the 2.30-µm region, attributed to varying Fe/Mg abundance.
Figure 3: Dark deposit in a depression in Ismenius Lacus.
Figure 4: Detection of Fe-rich clays over Noachian outcrop in Syrtis Major.
Figure 5: Spatial distributions of minerals in the Nili Fossae region.
Figure 6: Identification of clays in Mawrth Vallis.


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Mars Express is operated by ESA/ESOC. Laboratory reflectance data used in this paper are provided through cooperation between the OMEGA team and NASA and the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) team. Reflectance measurements were acquired at the NASA Reflectance Experiment Laboratory (RELAB) at Brown University.

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Poulet, F., Bibring, JP., Mustard, J. et al. Phyllosilicates on Mars and implications for early martian climate. Nature 438, 623–627 (2005).

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