Different molecules reflect sunlight at different characteristic wavelengths and the OMEGA imaging spectrometer analyses reflected radiation in the near-infrared part of the spectrum to identify and map the distribution of various molecules and minerals on the surface of the planet.

Jean-Pierre Bibring and colleagues at the Institut d’Astrophysique Spatiale (IAS) near Paris and colleagues identified dark-coloured iron-bearing silicates in both the northern and southern Martian crust, and localised concentrations of hydrated "phyllosilicates" and sulphates. These minerals may have formed during the early evolution of Mars. They also found frozen water mixed with dust at both poles, covered by a thin veneer of carbon dioxide ice (Sciencexpress 1108806).

In a related study, led by Yves Langevin of the IAS, the OMEGA team found hydrated gypsum - sulphates that are rich in calcium - in the north polar region. This implies that water played an important role in the formation of these minerals. According to Langevin and co-workers the gypsum may have formed when acidic frozen ice reacted with calcium-rich minerals during periods of extensive volcanic activity in the past, or when salt-rich water evaporated from massive outflows of liquid water (Sciencexpress 1109091).

Another team led by Aline Gendrin, also of the IAS, identified hydrated sulphates at much lower latitudes: outcrops in Valles Marineris, Magaritifer Sinus and Terra Meridiani contain kieserite (hydrated magnesium sulphate), gypsum and polyhydrated sulphates. Again, the presence of these minerals is a direct record of the planet’s watery past (Sciencexpress 1109087).

The OMEGA team also reported on how bright, small-grained frost with grain sizes of less than 100 microns at the north pole gradually disappears during the Martian summer to reveal larger-grained permanent ice, with a grain size of about 1 millimetre, lying below (Sciencexpress 1109438). However, the team has not been able to explain why there is so little dust in this ice.

The two remaining papers report evidence for the presence of rock-forming minerals such as olivine and pyroxene, and the presence of water in surface materials such as kieserite. This last result confirms similar findings made by NASA’s Opportunity rover elsewhere on Mars last year.