Yearly and seasonal variations of low albedo surfaces on Mars in the OMEGA/MEx dataset: Constraints on aerosols properties and dust deposits

The time variations of spectral properties of dark martian surface features are investigated using the OMEGA near-IR dataset. The analyzed period covers two Mars years, spanning from early 2004 to early 2008 (includes the 2007 global dust event). Radiative transfer modeling indicates that the apparent albedo variations of low to mid-latitude dark regions are consistent with those produced by the varying optical depth of atmospheric dust as measured simultaneously from the ground by the Mars Exploration Rovers. We observe only a few significant albedo changes that can be attributed to surface phenomena. They are small-scaled and located at the boundaries between bright and dark regions. We then investigate the variations of the mean particle size of aerosols using the evolution of the observed dark region spectra between 1 and 2.5 {\mu}m. Overall, we find that the observed changes in the spectral slope are consistent with a mean particle size of aerosols varying with time between 1 and 2 {\mu}m. Observations with different solar zenith angles make it possible to characterize the aerosol layer at different altitudes, revealing a decrease of the particle size of aerosols as altitude increases

Iron mineralogy and aqueous alteration from Husband Hill through Home Plate at Gusev Crater, Mars: Results from the Mössbauer instrument on the Spirit Mars Exploration Rover

Spirit’s Mössbauer (MB) instrument determined the Fe mineralogy and oxidation state of 71 rocks and 43 soils during its exploration of the Gusev plains and the Columbia Hills (West Spur, Husband Hill, Haskin Ridge, northern Inner Basin, and Home Plate) on Mars. The plains are predominantly float rocks and soil derived from olivine basalts. Outcrops at West Spur and on Husband Hill have experienced pervasive aqueous alteration as indicated by the presence of goethite. Olivine-rich outcrops in a possible mafic/ultramafic horizon are present on Haskin Ridge. Relatively unaltered basalt and olivine basalt float rocks occur at isolated locations throughout the Columbia Hills. Basalt and olivine basalt outcrops are found at and near Home Plate, a putative hydrovolcanic structure. At least three pyroxene compositions are indicated by MB data. MB spectra of outcrops Barnhill and Torquas resemble palagonitic material and thus possible supergene aqueous alteration. Deposits of Fe3+-sulfate soil, located at Paso Robles, Arad, and Tyrone, are likely products of acid sulfate fumarolic and/or hydrothermal activity, possibly in connection with Home Plate volcanism. Hematite-rich outcrops between Home Plate and Tyrone (e.g., Montalva) may also be products of this aqueous activity. Low water-to-rock ratios (isochemical alteration) are implied during palagonite, goethite, and hematite formation because bulk chemical compositions are basaltic (SO3-free basis). High water-to-rock ratios (leaching) under acid sulfate conditions are implied for the high-SiO2 rock and soil in Eastern Valley and the float rock FuzzySmith, which has possible pyrite/marcasite as a hydrothermal alteration product

Results from the Mars Phoenix Lander Robotic Arm experiment

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95618/1/jgre2693.pd

The Vertical Structure of Martian Aerosols Explored Using a 3D Spherical Monte-Carlo Model and Observations at the Terminator by OMEGA

International audienc

The Vertical Structure of Martian Aerosols Explored Using a 3D Spherical Monte-Carlo Model and Observations at the Terminator by OMEGA

International audienc

The Vertical Structure of Martian Aerosols Explored Using a 3D Spherical Monte-Carlo Model and Observations at the Terminator by OMEGA

International audienc

The Vertical Structure of Martian Aerosols Explored Using a 3D Spherical Monte-Carlo Model and Observations at the Terminator by OMEGA

International audienc

The Vertical Structure of Martian Aerosols Explored Using a 3D Spherical Monte-Carlo Model and Observations at the Terminator by OMEGA

International audienc

The Vertical Structure of Martian Aerosols Explored Using a 3D Spherical Monte-Carlo Model and Observations at the Terminator by OMEGA

International audienc

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

International audienceGlobal mapping by the visible/near‐infrared OMEGA spectrometer gives the first opportunity to study in detail the characteristics of the 3 μ m 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 μ m 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 μ m. 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