Hydration state of the Martian surface as seen by Mars Express OMEGA: 1. Analysis of the 3 μm hydration feature

Abstract

[1] Global mapping by the visible/near-infrared OMEGA spectrometer gives the first opportunity to study in detail the characteristics of the 3 mm hydration absorption on the surface of Mars. This feature is caused by bending and stretching vibrations of adsorbed or structural H 2 O and/or OH-bound to minerals. A specific data reduction scheme has been developed to remove the contribution of thermally emitted radiance from OMEGA spectra. With the derived albedo spectra, variations in strength and shape of the 3 mm feature can be accurately assessed. Calibration issues are discussed and data only within the nominal calibration level of the instrument are analyzed, which corresponds to a surface coverage of $30%. All OMEGA spectra exhibit the presence of this absorption feature, which can be explained by the presence of adsorbed water as well as by alteration rinds or coatings resulting from weathering. Strong variations of the band strength are observed. Correlations between hydration, albedo, and elevation are examined. Terrains enriched in phyllosilicates, sulfates, or hydroxides exhibit an increased hydration signature as well as a weaker combination overtone H 2 O absorption at $1.9 mm. Careful analysis also reveals seasonal variations in surface hydration, with soils in the northern midlatitudes decreasing in hydration between northern spring and summer. This hydration change is best explained by the presence of winter frost followed by equilibration of frost-free soil with the atmosphere and by increased surface temperatures reducing the adsorptive capacity of the regolith.

Spectral properties of simulated impact glasses produced from martian soil analogue JSC Mars-1

“…These authors also demonstrated that only the 3-µm absorption band may be used for this purpose, unless it is saturated. Surface water content on Mars shows significant variations across the planet Jouglet et al, 2007;Milliken et al, 2007). Milliken et al (2007) demonstrate that equatorial regions are the driest ones with ~2-5 wt.% H 2 O, while hydration increases with latitude and may be as high as 15 wt.%.…”

“…Nevertheless, some influence cannot be ruled out. For example, non-altered impact melt fragments may mask the weak metal-OH feature near 2.2 μm observed in many spectra of bright areas (e.g., Murchie et al, 1993, Beinroth andArnold, 1996) and may contribute to the decrease in depth of the bound water band at 3 μm, which also shows significant spatial variations (Bibring et al, 1989Murchie et al, 1993;Calvin, 1997;Jouglet et al, 2007;Milliken et al, 2007). Recent analysis showed that a broad weak absorption band centered near 1.8 μm is present in most OMEGA spectra of bright regions (Le Mouélic et al, 2006;Combe et al 2008).…”

Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars

“…Thermodynamic models of ice stability [e.g., (7)] and equilibration models of various hydrous minerals [e.g., (8,9)] have ruled out some simple explanations for the origin of this water reservoir. Although hydrated sulfates and clay minerals have been detected from orbit, they cover only a small fraction of the entire surface (10)(11)(12) and, to the extent of what can be observed by remote sensing, are limited to bedrock outcrops (13,14), whereas the hydration of the topmost microns of the regolith probed by the Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA) aboard the European Space Agency's Mars Express orbiter is global and usually unrelated to bedrock exposures (6,15). Therefore, the nature and origin of this global hydration remain largely unknown.…”

Quantitative compositional analysis of martian mafic regions using the MEx/OMEGA reflectance data 1. Methodology, uncertainties and examples of application

“…Hematite-bearing plains (Ph unit) are at the top of a section of layered material (referred as etched terrains E unit) that is hundreds of meters thick and extends beneath the Opportunity landing site; these etched terrain materials sit unconformably on the late Noachian dissected cratered terrain materials (Hynek et al, 2002;Arvidson et al, 2003;Edgett, 2005). OMEGA data covering the etched terrains show enhanced water bands at 1.9 and 3.0 µm (Jouglet et al, 2007;Poulet et al, 2008) and, in some where discrete stratigraphic horizons are exposed Griffes et al, 2007).…”