Evolution of the seasonal polar caps of Mars over more than one martian year

The Vis/NIR OMEGA imaging spectrometer on-board Mars Express has been operating in Mars orbit since January 2004. Its spectral range makes it possible to identify H2 O and CO2 ices and frosts from their characteristic signatures in the near IR. The dominant icy component (either H2 O ice or CO2 ice) can be determined, as well as constraints on grain sizes and inclusions (dust and the other type of ice). The available OMEGA data now covers more than one full martian year of the climatic cycle. The similarities and differences between the two M-years will be discussed. It is interesting to note that the type of ices which dominates the perennial cap (H2 O ice in the North, CO2 ice in the South) also dominates the seasonal cap after mid local spring. The other type of ices is present in isolated patches, which are stable in position in the South (H2 O ice) with much stronger variations in position in the North (CO2 ice). These results have interesting implications for surface atmosphere interactions