Mineralogy of the High Latitudes of Mars including the Phoenix Landing Site

Introduction: The record of variations in the climate of Mars is imprinted in the spatial distribution of a variety of structures and features of the high latitude surfaces. Here, we report the surface distribution of some minerals in the high latitude (>50° North and South) regions of Mars (including the Phoenix landing site) from the OMEGA/MEx observations in the visible and near-infrared wavelength domains (0.4-4 µm). Observations: The analyzed data were acquired during the northern and southern springs and summers of 3 Martian years (01/2004, 11-12/2005, 09-10/2007). The corresponding values of the solar longitude Ls are in the range of 45°-160° for the north and 220°-330° for the south. During this time, the seasonal frost is partly or totally sublimated over the study areas. Data were limited to spectra that do not exhibit water ice or CO 2 ice absorption bands. In addition, quality criteria where applied to the OMEGA database so as to eliminate anomalous data, including non nadir-pointing observations, saturated data, and spectra containing spurious values. A series of spectral criteria were developed in [1] for mapping a broad range of minerals of interest. Here, we use the following representative spectral parameters: band depth of the 2 µm pyroxene feature, olivine index based on the 1 µm band, and band depth at 1.9 µm indicative of the presence of H 2 O-bearing minerals. Results: The pyroxene signatures seen at high latitudes mainly correspond to low albedo terrains (Figures 1A and 1B). Some low albedo terrains also exhibit positive detection for olivine [2]. The mafic material could result from aeolian transport of fine-grained debris eroded from mafic-rich units located in numerous mid-latitude regions. However, their origin could be also found in local volcanic processes. It has been proposed that the Vastitas Borealis formation is underlain by a volcanic unit that flooded and smoothed the northern lowlands in the Early Hesperian [3]. The major units of the southern circumpolar terrains are part of the Plateau Sequence and are interpreted to consist of heavily crated flows, impact breccias, eolian deposits, and pyroclastic material [4,5]. Figures 1C and 1D show the depth of the absorption band at 1.93 µm due to the presence of H 2 O (either adsorbed or structurally bound). We note that the 1.9 µm band increases with latitude larger than 60°, but heterogeneities in longitude are observed, especially in the north circumpolar terrains. The hydrated surface material of …