Surveyor Thermal Emission Spectrometer Data Research Articles

Thermal infrared spectral characteristics of martian dust deposits and evidence for atmosphere-regolith interactions

It has been hypothesized that the dust component of the Martian surface is globally homogeneous, based on chemical similarity between landing sites and spectral similarity from select areas within bright regions. We tested that hypothesis by producing the first near-global data set of surface spectral emissivity (excluding polar regions) across the ∼233–508 and 825–1650 cm−1 (∼20–50 and 6–12 μm) spectral ranges from Mars Global Surveyor Thermal Emission Spectrometer data and using various data reduction techniques to search for any spectral heterogeneity in bright regions that might be present. We found no unequivocal evidence for spectral heterogeneity, supporting the hypothesis that dust is globally homogenized. The global emissivity product permits new spectral parameter maps and preliminary assessments of atmosphere-regolith interactions. We produced the first map of the Christiansen feature (CF) and show that, unlike on the Moon, where CF is a proxy for bulk silica content, CF position on Mars is primarily associated with dust cover. We produced an updated map of the 1630 cm−1 emissivity peak that arises from bound H2O in fine-particulate material and show that the peak is nearly ubiquitous across the Martian surface, including in dark regions with relatively low dust cover. This is attributed to minor amounts of dust disproportionally contributing to the spectral signal in the ∼1630 cm−1 region. We show that regions within the equatorial dust deposits with higher annual modeled frequency of nighttime CO2 frosts are more likely to have lower emissivity in the ∼1350-1400 cm−1 region, consistent with a higher fraction of unconsolidated dust. This provides the first spectral evidence for a previously hypothesized regolith gardening process via a diurnal CO2 cycle, representing an important surface-atmosphere interaction that may contribute to near-surface porosity and affect diffusive exchange of H2O between atmosphere and hydrated solids (ice, minerals) in the regolith.

Retrieval algorithm for atmospheric dust properties from Mars Global Surveyor Thermal Emission Spectrometer data during global dust storm 2001A

We present a new parameter retrieval algorithm for Mars Global Surveyor Thermal Emission Spectrometer data. The algorithm uses Newtonian first-order sensitivity functions of the infrared spectrum in response to variations in physical parameters to fit a model spectrum to the data at 499, 1099, and 1301 cm −1. The algorithm iteratively fits the model spectrum to data to simultaneously retrieve dust extinction optical depth, effective radius, and surface temperature. There are several sources of uncertainty in the results. The assumed dust vertical distribution can introduce errors in retrieved optical depth of a few tens of percent. The assumed dust optical constants can introduce errors in both optical depth and effective radius, although the systematic nature of these errors will not affect retrieval of trends in these parameters. The algorithm does not include the spectral signature of water ice, and hence data needs to be filtered against this parameter before the algorithm is applied. The algorithm also needs sufficient dust spectral signature, and hence surface-to-atmosphere temperature contrast, to successfully retrieve the parameters. After the application of data filters the algorithm is both relatively accurate and very fast, successfully retrieving parameters, as well as meaningful parameter variability and trends from tens of thousands of individual spectra on a global scale (Elteto, A., Toon, O.B. [2010]. Icarus, this issue). Our results for optical depth compare well with TES archive values when corrected by the single scattering albedo. Our results are on average 1–4 K higher in surface temperatures from the TES archive values, with greater differences at higher optical depths. Our retrieval of dust effective radii compare well with the retrievals of Wolff and Clancy (Wolff, M.J., Clancy, R.T. [2003]. J. Geophys. Res. 108 (E9), 5097) for the corresponding data selections from the same orbits.

Principal components analysis of Mars in the near-infrared

Principal components analysis and target transformation are applied to near-infrared image cubes of Mars in a study to disentangle the spectra into a small number of spectral endmembers and characterize the spectral information. The image cubes are ground-based telescopic data from the NASA Infrared Telescope Facility during the 1995 and 1999 near-aphelion oppositions when ice clouds were plentiful [ Clancy, R.T., Grossman, A.W., Wolff, M.J., James, P.B., Rudy, D.J., Billawala, Y.N., Sandor, B.J., Lee, S.W., Muhleman, D.O., 1996. Icarus 122, 36–62; Wolff, M.J., Clancy, R.T., Whitney, B.A., Christensen, P.R., Pearl, J.C., 1999b. In: The Fifth International Conference on Mars, July 19–24, 1999, Pasadena, CA, pp. 6173], and the 2003 near-perihelion opposition when ice clouds are generally limited to topographically high regions (volcano cap clouds) but airborne dust is more common [ Martin, L.J., Zurek, R.W., 1993. J. Geophys. Res. 98 (E2), 3221–3246]. The heart of the technique is to transform the data into a vector space along the dimensions of greatest spectral variance and then choose endmembers based on these new “trait” dimensions. This is done through a target transformation technique, comparing linear combinations of the principal components to a mineral spectral library. In general Mars can be modeled, on the whole, with only three spectral endmembers which account for almost 99% of the data variance. This is similar to results in the thermal infrared with Mars Global Surveyor Thermal Emission Spectrometer data [Bandfield, J.L., Hamilton, V.E., Christensen, P.R., 2000. Science 287, 1626–1630]. The globally recovered surface endmembers can be used as inputs to radiative transfer modeling in order to measure ice abundance in martian clouds [Klassen, D.R., Bell III, J.F., 2002. Bull. Am. Astron. Soc. 34, 865] and a preliminary test of this technique is also presented.

Spatial and temporal distributions of Martian north polar cold spots before, during, and after the global dust storm of 2001

In the 1970s, Mariner and Viking observed features in the Mars northern polar region that were a few hundred kilometers in diameter with 20 μm brightness temperatures as low as 130 K (considerably below CO2 ice sublimation temperatures). Over the past decade, studies have shown that these areas (commonly called “cold spots”) are usually due to emissivity effects of frost deposits and occasionally to active CO2 snowstorms. Three Mars years of Mars Global Surveyor Thermal Emission Spectrometer data were used to observe autumn and wintertime cold spot activity within the polar regions. Many cold spots formed on or near scarps of the perennial cap, probably induced by adiabatic cooling due to orographic lifting. These topographically associated cold spots were often smaller than those that were not associated with topography. We determined that initial grain sizes within the cold spots were on the order of a few millimeters, assuming the snow was uncontaminated by dust or water ice. On average, the half‐life of the cold spots was 5 Julian days. The Mars global dust storm in 2001 significantly affected cold spot activity in the north polar region. Though overall perennial cap cold spot activity seemed unaffected, the distribution of cold spots did change by a decrease in the number of topographically associated cold spots and an increase in those not associated with topography. We propose that the global dust storm affected the processes that form cold spots and discuss how the global dust storm may have affected these processes.

Evidence for extensive, olivine-rich bedrock on Mars

Color infrared observations of an area around the Nili Fossae acquired by the Mars Odyssey thermal emission imaging system have been used to map the regional distribution and geologic context of olivine-rich materials that first were identified from Mars Global Surveyor thermal emission spectrometer data. Spectral, thermal, geomorphic, and topographic data demonstrate that the majority of olivine-rich material is in the form of inplace layered rock covering an area roughly four times larger than previously recognized. Some high olivine concentrations are associated with spatially small areas dominated by sediments. We favor olivine-rich basalts as the origin of the observed olivine enrichment, although several hypotheses are viable.

Spectral evidence for zeolite in the dust on Mars

Spectral features observed in Mars Global Surveyor Thermal Emission Spectrometer data ( ∼ 1670 –220 cm −1) of martian surface dust provide clues to its mineralogy. An emissivity peak at ∼ 1630 cm −1 is consistent with the presence of an H 2O-bearing mineral. This spectral feature can be mapped globally and shows a distribution related to the classical bright regions on Mars that are known to be dust covered. An important spectral feature at ∼ 830 cm −1 present in a newly derived average spectrum of surface dust likely is a transparency feature arising from the fine particulate nature of the dust. Its shape and location are consistent with plagioclase feldspars and also zeolites, which essentially are the hydrous form of feldspar. The generally favored visible/near-infrared spectral analog for martian dust, JSC Mars-1 altered tephra, does not display the ∼ 830 cm −1 feature. Zeolites commonly form from the interaction of low temperature aqueous fluids and volcanic glass in a variety of geologic settings. The combination of spectral features that are consistent with zeolites and the likelihood that Mars has (or had) geologic conditions necessary to produce them makes a strong case for recognizing zeolite minerals as likely components of the martian regolith.

Eos Chasma, Mars: Regional setting for a potential landing site for astrobiology

The floor of Eos Chasma, centered at about 13.4°S and 41.5°W at an elevation of −3.5 km, is proposed as a future landing site on Mars. Deposits in this area were derived from a variety of sources, including chaotic terrain (interpreted to reflect the release of subsurface water) and possible paleolake materials, which could shed light on the astrobiological potential of Mars, climate history, and the evolution of the surface. Analyses of the physical properties of the proposed site suggest a rock abundance of 10–18% (based on Viking Orbiter Infrared Thermal Mapper data), set in a matrix of medium to coarse sands (based on Mars Global Surveyor Thermal Emission Spectrometer data), sparse covering by dust (based on albedo measurements), and a surface roughness of <1 to 1.7 m (derived from the Mars Orbiter Laser Altimeter). Although these attributes are within the engineering constraints for current lander designs, models of the atmosphere suggest that wind shear (generated primarily by the proximity to local topography, i.e., the Chasma canyon wall) might preclude the site with current landing systems.

Traveling waves in the Northern Hemisphere of Mars

Analysis of temperature retrievals from Mars Global Surveyor Thermal Emission Spectrometer data has revealed the presence of regular, eastward propagating waves in the Northern Hemisphere. A large amplitude, zonal wave 1 with a long (∼20 sol) period is particularly prominent during early winter (Ls = 220–270°). After Ls = 270°, a weaker and more rapidly propagating (6.5 sol period) zonal wave 1 is dominant. These waves have a deep vertical structure (>40 km) correlated with the axis of the winter hemisphere westerly jet. Simulations with a Mars general circulation model suggest that the fast wave is associated with baroclinic instability due to the strong meridional temperature gradient at the surface and is consistent with surface pressure oscillations seen in Viking Lander data. By contrast, the slow wave has the appearance of a large‐amplitude Rossby wave that is coupled with an inertially unstable region in the subtropics.