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Mars Express Providing Evidence For Large Aquifers On Early Mars
Paris (ESA) Dec 01, 2005 The findings from the OMEGA instrument on board ESA's Mars Express are strongly indicating that liquid water must have been present, in a stable form, in Mars' early history, having implications for the planets climatic history, and questions of life in the past. These conclusions were drawn thanks to data on Martian surface minerals obtained by OMEGA (Observatoire pour la Mineralogy, l'Eau, les Glaces et l'Activite), the visible and infrared mapping spectrometer on board ESA's Mars Express. From previous observations, Mars must have undergone water-driven processes, which left their signature in surface structures such as channel systems and signs of extensive aqueous erosion. However, such observations do not necessarily imply the stable presence of liquid water on the surface over extended periods of time during the Martian history. The data collected by OMEGA unambiguously reveal the presence of specific surface minerals which imply the long-term presence of large amounts of liquid water on the planet. These 'hydrated' minerals, so called because they contain water in their crystalline structure, provide a clear 'mineralogical' record of water-related processes on Mars. During 18 months of observations OMEGA has mapped almost the entire surface of the planet, generally at a resolution between one and five kilometres, with some areas at sub-kilometre resolution. The instrument detected the presence of two different classes of hydrated minerals, 'phyllosilicates' and 'hydrated sulphates', over isolated but large areas on the surface. Both minerals are the result of a chemical alteration of rocks. However, their formation processes are very different and point to periods of different environmental conditions in the history of the planet. Phyllosilicates, so-called because of their characteristic structure in thin layers ('phyllo' = thin layer), are the alteration products of igneous minerals (minerals of magmatic origin) sustaining a long-term contact with water. An example of phyllosilicate is clay. Phyllosilicates were detected by OMEGA mainly in the Arabia Terra, Terra Meridiani, Syrtis Major, Nili Fossae and Mawrth Vallis regions, in the form of dark deposits or eroded outcrops. Hydrated sulphates, the second major class of hydrated minerals detected by OMEGA, are also minerals of aqueous origin. Unlike phyllosilicates, which form by an alteration of igneous rocks, hydrated sulphates are formed as deposits from salted water; most sulphates need an acid water environment to form. They were spotted in layered deposits in Valles Marineris, extended exposed deposits in Terra Meridiani, and within dark dunes in the northern polar cap. When did the chemical alteration of the surface that led to the formation of hydrated minerals occur? At what point of Mars's history was water standing in large quantities on the surface? OMEGA's scientists combined their data with those from other instruments and suggest a likely scenario of what may have happened.
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