Bright and dark regions on Mars: Particle size and mineralogical characteristics based on Thermal Emission Spectrometer data

Abstract

[1] Emissivity spectra (1670-200 cm À1 ) from the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) show significant differences between bright and dark surfaces, allowing further investigation of their physical and mineralogical character. TES spectra from bright surfaces (albedo !0.2) typically show lower emissivity at high wavenumbers (>1300 cm À1 ) than that of dark surfaces (albedo <0.2). The opposite behavior is evident in the low wavenumbers (<560 cm À1 ), where bright surfaces have higher emissivity than dark ones. These trends are consistent with the spectral behavior of silicate materials of varying particle size. The short wavelength feature displayed by TES spectra of bright surfaces is a relatively strong absorption that likely is the result of particle size effects of surface silicate particles (100 mm in size. A dust cover index (DCI) is developed that exploits this short wavelength feature, serving to identify surfaces that range from dust-covered to dust-free. As a gauge of surface-obscuring silicate dust that can impact spectral measurements, the DCI is more direct than thermal inertia or albedo measurements. Spectral ratio analysis using emissivity spectra from adjacent bright and dark surfaces is explored as a means of deriving the mineralogy of surface dust. The result shows that the dust is dominated by silicate minerals with indication of a significant plagioclase feldspar component.

Simulating the interannual variability of major dust storms on Mars using variable lifting thresholds

“…1 have not translated into widespread dust loss, as most of the dust lifted at these latitudes is advected primarily by the circumpolar flow and is deposited again at a similar latitude. The source regions seen here correlate well with those suggested in the Dust Cover Index (DCI) of Ruff and Christensen (2002) (see their Fig. 14).…”

“…The qualitative spatial distribution of surface dust (particles smaller than ∼ 100 µm) was derived from Thermal Emission Spectrometer (TES) albedo measurements by Ruff and Christensen (2002), who found the southern hemisphere overall to be more sparsely covered by dust grains than the northern hemisphere. Periodic changes in surface albedo, notably in the wake of major dust storms, were detected by Szwast et al (2006), indicating the redistribution of significant portions of this surface dust.…”

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

“…3 and 4), Hesperian carbonate outcrops of any size have not been detected thus far. Of course it is possible that these Hesperian carbonates are simply hidden from view since much of the martian surface is obscured by dust (Ruff and Christensen 2002) that can't be penetrated by the NIR or TIR spectrometers although that has not posed a problem for detections of other alteration minerals such as sulfates, phyllosilicates and clays.…”

Eolian dunes and deposits in the western United States as analogs to wind-related features on Mars

“…TES spectra have revealed two distinct volcanic compositions abundant on the Martian surface: a typical basaltic composition and a slightly more chemically evolved basaltic andésite composition (Bandfield el al., 2000) that is comparable to several rocks at the Mars Pathfinder landing site (Golombek et al, 1999). The TES basalt component has a high concentration in Syrtis Major (Bandfield el al., 2000;Ruff and Christensen, 2002), a classic lowalbedo feature that includes large barchan dunes (Figure 9.8). The presence of basaltic dunes on Mars increases the importance of studies of basaltic sand dunes on Earth, like those at Moses Lake (#22) (e.g., Bandfield ei al.. 2002).…”