The Mars Science Laboratory Curiosity rover carries a basalt calibration target for monitoring the performance of the alpha particle X-ray spectrometer. The spectrum acquired on Sol 34 shows ...increased contributions from Mg, S, Cl and Fe relative to laboratory spectra recorded before launch. Mars Hand Lens Imager images confirm changes in the appearance of the surface. Spectra taken on Sols 179 and 411 indicate some loss of the deposited material. The observations suggest deposition of a surface film likely consisting of dust mobilized by impingement of the sky crane’s terminal descent engine plumes with surface fines during Curiosity’s landing. New APXS software has been used to model the thin film that coated the calibration target on landing. The results suggest that a film of about 100nm thickness, and containing predominantly MgO, Fe2O3, SO3, Cl and Na2O could give rise to the observed spectral changes. If this film is also present on the alpha particle sources within the APXS, then its effect is negligible and the terrestrial calibration remains appropriate.
The Mars Hand Lens Imager (MAHLI) is a 2-megapixel, color camera with resolution as high as 13.9 µm pixel-1. MAHLI has operated successfully on the Martian surface for over 1150 Martian days (sols) ...aboard the Mars Science Laboratory (MSL) rover, Curiosity. During that time MAHLI acquired images to support science and science-enabling activities, including rock and outcrop textural analysis; sand characterization to further the understanding of global sand properties and processes; support of other instrument observations; sample extraction site documentation; range-finding for arm and instrument placement; rover hardware and instrument monitoring and safety; terrain assessment; landscape geomorphology; and support of rover robotic arm commissioning. Operation of the instrument has demonstrated that imaging fully illuminated, dust-free targets yields the best results, with complementary information obtained from shadowed images. The light-emitting diodes (LEDs) allow satisfactory night imaging but do not improve daytime shadowed imaging. MAHLI's combination of fine-scale, science-driven resolution, RGB color, the ability to focus over a large range of distances, and relatively large field of view (FOV), have maximized the return of science and science-enabling observations given the MSL mission architecture and constraints.
The Mars Global Surveyor Mars Orbiter Camera (MGS MOC) has observed several atmospheric events repeat within a few degrees of Ls from one year to the next over 3 Mars years during a portion of the ...northern summer, southern winter seasons (Ls = 124°–140°). The repeatability suggests a previously unobserved lack of significant variation in the present Martian northern summer seasonal climate. Nonetheless, interannual variations in the seasonal south polar cap and in the residual north polar cap were observed. These appear to have had a negligible effect in perturbing Mars' weather during the northern summer season.
The particle size of Martian aeolian dunes Edgett, Kenneth S.; Christensen, Philip R.
Journal of Geophysical Research,
25 December 1991, Letnik:
96, Številka:
E5
Journal Article
Recenzirano
The effective particle size of unconsolidated materials on the Martian surface can be determined from thermal inertia, due to a pore size dependence of thermal conductivity at Martian atmospheric ...pressures. Because dunes consist of a narrow range of well-sorted, unconsolidated particles, they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the Martian surface. Two independent approaches are used. First, thermal inertia data indicate that Martian dunes have an average particle size of about 500 +/-100 microns, or medium to coarse sand. Second, expected dune particle sizes are determined from grain trajectory calculations and the particle size transition from suspension to saltation. On earth, the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed, u*(t) is near unity; for grains at u*(t) this occurs at about 52 microns. Terrrestrial dune sands have a mean of 250 microns and are composed entirely of grains greater than 52 microns. The corresponding Martian transition grain size is about 210 microns, suggesting that Martian dunes should be significantly coarser than terrestrial dunes. Grain saltation path length as a function of particle size also shows that, under Martian conditions, larger grains than on earth will become suspended. Both approaches indicate that Martian dune sand should be coarser than terrestrial dune sand. These results closely match the grain sizes determined from thermal inertia models, providing the first direct test of the validity of these models for actual Martian surface materials.
The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are ...rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nonetheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Together, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H2O.
The Optical Microscope (OM) on the Phoenix Mars lander (operated from May through October 2008) was used to search for visible-wavelength luminescence of soil particles excited by ultraviolet (UV) ...illumination (λ=360–390nm). No luminescent particles were found, with the possible exception of a few potentially luminescent features comprising about 0.02% of the total soil volume. The luminescence quantum efficiency of bulk soil as well as individual soil particles at the Phoenix site is constrained to less than 0.04%. A similar UV experiment will be performed by the Mars Hand Lens Imager (MAHLI) on the upcoming Mars Science Laboratory (MSL) mission. We compare OM and MAHLI UV experiments to each other and suggest a strategy to search for UV-excited luminescence with MAHLI.
► Microscopic images of Martian soil particles under UV illumination are analyzed. ► The UV luminescence quantum efficiency (QE) of soil particles is less than 0.04%. ► Expected luminescent materials are listed and luminescence search algorithms are presented. ► These studies prepare UV luminescence experiments onboard MSL (landing 6-Aug-2012).
“Stealth” is a region on Mars that has no distinguishable radar return. Stealth was discovered in 1988 by Muhleman et al. 1991 in 3.5 cm Earth‐based radar images, and it was found to extend ∼2000 km ...along the Martian equator west of Arsia and Pavonis Montes. Stealth was proposed to be a deposit of unconsolidated, granular material with a minimum thickness of several meters, with the most likely explanation being that Stealth is a volcanic tephra deposit Muhleman et al., 1991, 1995. Stealth overlies some of the youngest geologic units on Mars, including lava flows and a giant, curvilinear‐ridged lobate unit on the west flank of Arsia Mons. Stealth also overlies part of a region of smooth and wind‐scoured materials called the Medusae Fossae Formation. Examination of high‐resolution Viking orbiter images suggests that Stealth is the youngest of several discontinuous, wind‐worked mantles of fine‐grained (≪1 cm) sediment. Older deposits of fine sediment appear to be interbedded with lava flows and show evidence of aeolian deposition (dunes and deposits in the lee of topographic obstacles) and erosion (yardangs and pedestal craters). The geologic context supports a volcanic ash origin for Stealth. If Stealth is composed of tephra, then its extent and the nature of landforms in the region indicate that it resulted from multiple eruptions that occurred relatively late in Martian history. Possible source vents include linear depressions (flanked by constructive volcanic landforms) that are located on the lower western slopes of Arsia and Pavonis Montes.
Lithology and physical properties of strata exposed at the Earth's surface have direct influence on the erosion and geomorphic expression of landforms. While this is well known on our planet, ...examples on Mars are just coming to light among the tens of thousands of airphoto-quality images (resolutions 1.5–12 m/pixel) acquired since 1997 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC). Specific examples occur among martian north polar layered materials, which MOC images reveal are divided into two distinct stratigraphic units: a lower, dark-toned layered unit and a younger, upper, lighter-toned layered unit. The lower unit is less resistant to wind erosion than the upper unit. The upper unit most likely consists of stratified dust and ice, while the lower unit contains abundant, poorly cemented sand. Sand is more easily mobilized by wind than dust; the lower resistance to erosion of the lower unit results from the presence of sand. Where wind erosion in polar troughs has penetrated to the lower unit, geomorphic change has proceeded more rapidly: sand has been liberated from the lower unit, and arcuate scarps have formed as the upper unit has been undermined. Wind erosion of the lower unit thus influences the geomorphology of the north polar region; this result likely explains the genesis of the large polar trough, Chasma Boreale, and the relations between dunes and arcuate scarps that have puzzled investigators for nearly three decades. The properties of the stratigraphic units suggest that the upper limit for the amount of water contained in the north polar layered materials may be 30–50% less than previously estimated.
High spatial resolution (1.5 to 6 m/pixel) Mars Global Surveyor Mars Orbiter Camera images obtained September 1997 to June 2001 show that each of the large, dark wind streaks of western Arabia Terra ...originate at a barchan dune field on a crater floor. The streaks consist of a relatively thin ( < 1 m) coating of sediment deflated from the dune fields and their vicinity. In most cases, this sediment drapes over a previous mantle that more thickly covers nearly all of western Arabia Terra. No concurrent eolian bedforms are found within the dark streaks, nor do any dunes climb up crater walls to deliver sand via saltation to the streaks. The relations between dunes, wind streak, and subjacent terrain imply that dark-toned grains finer than those that comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain. Previous eolian physics and thermal inertia studies suggest that, under modern Martian conditions, such grains likely include silt (3.9-62.5 microns), very fine sand (62.5-125 microns), and possibly fine sand (to about 210 microns). The streaks change in terms of extent, relative albedo, and surface pattern over periods measured in years; however, through June 2001, very little evidence for recent eolian activity (dust plumes, storms, dune movement) was observed. (Author)
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