Disk‐resolved observations of Phobos acquired by OMEGA at a range of lighting and viewing geometries were fit with the Hapke photometric function to solve for the single particle phase function and ...single scattering albedos from 0.4 to 2.5 μm. Single scattering albedos were recovered from CRISM observations of Phobos using the OMEGA derived single particle phase function and are similar to those from OMEGA data. Both the ubiquitous red unit and the blue unit around the crater Stickney exhibit a smooth red‐sloped spectrum, with a steeper continuum in the redder unit. Single scattering albedos retrieved from CRISM measurements of Deimos are similar to those for the red unit on Phobos. Retrieval of single scattering albedos from OMEGA data at 2.8 to 5.0 μm has greater uncertainty, but results in this wavelength range are also consistent with a smooth, red‐sloped spectrum. Phobos' and Deimos' low reflectances, lack of mafic absorption features, and red spectral slopes are incompatible with even highly space weathered chondritic or basaltic compositions. These results, coupled with similarities to laboratory spectra of Tagish Lake (possible D‐type asteroid analog) and CM carbonaceous chondrite meteorites, show that Phobos and Deimos have primitive compositions. If the moons formed in situ rather than by capture of primitive bodies, primitive materials must have been added to the Martian system during accretion or a late stage impact.
Key Points
Modeled 0.4‐2.5 um spectra of Phobos and Deimos using Hapke equation
Recast Phobos & Deimos spectra to lab viewing conditions & compared with analogs
Phobos & Deimos have primitive, undifferentiated compositions
The Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) hyperspectral image data covering eastern Terra Meridiani indicate the ubiquitous presence of molecular ...water in etched terrain materials that disconformably overlie heavily cratered terrains and underlie the hematite-bearing plains explored by the Opportunity rover. Identification of crystalline water in kieserite (MgSO₄·H₂O) is linked to materials exposed in a valley and plateau to the north of hematite-bearing plains. The mineralogical similarities between the etched terrain deposits examined with OMEGA data and the layered rocks examined by Opportunity imply that the ancient aqueous environments inferred from analyses of the rover data extend over regional scales.
The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline ...hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (~20 to 30%), and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.
Water played a major role in the formation and alteration of rocks and soils in the Columbia Hills. The extent of alteration ranges from moderate to extensive. Five distinct rock compositional ...classes were identified; the order for degree of alteration is Watchtower ≅ Clovis > Wishstone ≅ Peace > Backstay. The rover's wheels uncovered one unusual soil (Paso Robles) that is the most S‐rich material encountered. Clovis class rocks have compositions similar to Gusev plains soil but with higher Mg, Cl, and Br and lower Ca and Zn; Watchtower and Wishstone classes have high Al, Ti, and P and low Cr and Ni; Peace has high Mg and S and low Al, Na, and K; Backstay basalts have high Na and K compared to plains Adirondack basalts; and Paso Robles soil has high S and P. Some rocks are corundum‐normative, indicating that their primary compositions were changed by loss and/or gain of rock‐forming elements. Clovis materials consist of magnetite, nanophase ferric‐oxides (npOx), hematite, goethite, Ca‐phosphates, Ca‐ and Mg‐sulfates, pyroxene, and secondary aluminosilicates. Wishstone and Watchtower rocks consist of Fe‐oxides/oxyhydroxides, ilmenite, Ca‐phosphate, pyroxene, feldspar, Mg‐sulfates, and secondary aluminosilicates. Peace consists of magnetite, npOx, Mg‐ and Ca‐sulfates, pyroxene, olivine, feldspar, apatite, halides, and secondary aluminosilicates. Paso Robles consists of Fe3+‐, Mg‐, Ca‐, and other sulfates, Ca‐phosphates, hematite, halite, allophane, and amorphous silica. Columbia Hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks, volcaniclastic materials, and/or impact ejecta by solutions that were rich in acid‐volatile elements.
Visible/short‐wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic ...feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late‐stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.
Plain Language Summary
Satellites orbiting Mars map the composition of the planet's surface, tell us about past environments, and guide rovers to interesting locations on the surface. The Curiosity rover investigated a ridge named Vera Rubin ridge where indications of the mineral hematite (Fe2O3) was suggested from orbital data. In this paper, we investigate why the hematite detection on the ridge was so clear from orbit and what the implications are for how the hematite formed. We found several factors influence the orbital data, but the biggest reason hematite at Vera Rubin ridge was so easily detected from orbit was because the bedrock there was unique. Water had interacted with rocks at the ridge sometime after they were deposited, and this interaction affected the properties of the hematite and made it more visible from orbit. Curiosity's data help us reinterpret the orbital data over Mt. Sharp and reveal hematite is probably present in most of the bedrock there. Furthermore, there are other areas with particularly clear hematite detections that likely formed in a similar manner as Vera Rubin ridge. We end this paper with a discussion of lessons learned from this experience for using orbital data to guide rovers in the future.
Key Points
Areas on Vera Rubin ridge with deep ferric absorptions from orbit also have deep ferric absorptions in Curiosity spectral data sets
Ferric phases are more widespread on Mt. Sharp than originally reported. Diagenesis deepened ferric absorptions in several locations
Combining orbital and in situ observations enhances planetary exploration
The ~100 m wide Marathon Valley crosscuts the Cape Tribulation rim segment of the 22 km diameter, Noachian‐age Endeavour impact crater on Mars. Single‐scattering albedo spectra retrieved from three ...Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) Full‐Resolution Targeted (FRT, regularized to 18 m/pixel) and two Along Track Oversampled (ATO, regularized to 12 m/pixel) observations indicate the presence of Fe3+‐Mg2+ smectite exposures located in Marathon Valley with combination vibration metal‐OH absorption strength comparable to smectite spectral signatures in Mawrth Vallis. The Opportunity rover was directed to the exposures and documented the presence of Shoemaker formation impact breccias that have been isochemically altered, likely by fracture‐controlled aqueous fluids.
Key Points
Fe3+‐Mg2+ smectites detected in Marathon Valley using five CRISM observations
Opportunity found that Shoemaker formation breccias dominate Marathon Valley
Breccias were isochemically altered to generate Fe3+‐Mg2+ smectites
Ancient Aqueous Environments at Endeavour Crater, Mars Arvidson, R. E.; Squyres, S. W.; Bell, J. F. ...
Science (American Association for the Advancement of Science),
01/2014, Letnik:
343, Številka:
6169
Journal Article
Recenzirano
Odprti dostop
Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe(+3)-rich smectites. The ...signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.
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. Nevertheless, 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 visible/near‐infrared spectra that suggest enrichment of olivine. Collectively, 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 H2O‐ or OH‐bearing 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.
Plain Language Summary
The Bagnold dune field is an active sand field with moving dunes and sits between the landing site of the Curiosity rover and rocks of interest higher up on Mount Sharp. When passing through the dune field, we used all of Curiosity's instruments to measure the chemistry, mineralogy, and grain size of sands in the Bagnold dune field in order to figure out where they came from, how the sands are transported, and what volatile materials (like water) lie within Martian soils. We found that the Bagnold sand dunes are very well sorted; no dusty materials are found within them, in stark contrast to soils seen previously with Curiosity and with rovers at other landing sites. We found that the coarser sand grains are enriched in the volcanic minerals olivine and pyroxene, confirming a prediction from orbit that wind‐related activity seems to concentrate these phases. We also found that the dunes were much lower in water and other volatile elements like sulfur and chlorine versus all previous Mars soils. Using a combination of the rover's sieving system and chemical measurement tools, we figured out that two types of materials host water. In the first type of material, common in these sands, water is low in abundance (≤~1%), very tightly bound to the grains, and is not released until temperatures >200°C. In the second type of material, water is higher in abundance (2%) and more easily released by heating. Sieved water‐bearing fine materials may be a useful resource for human explorers.
Key Points
Because of ongoing aeolian activity, the Bagnold dunes consist of well‐sorted sands and lack the finer grains typical of Martian soils
Dune sands are chemically distinct with elevated Si, Mg, and Ni and lower H2O, S, and Cl relative to all previously measured Martian fines
Two distinct, water‐/OH‐bearing amorphous components are identified: Fe‐, S‐, and Cl‐rich material in dust and Si‐rich material in the sands
The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling ~8 kilometers and detecting features that reveal ancient environmental conditions. These ...include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict "hopper crystals" that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition. Observations from microscopic to orbital scales indicate that ancient Meridiani once had abundant acidic groundwater, arid and oxidizing surface conditions, and occasional liquid flow on the surface.
Geochemical diversity of rocks and soils has been discovered by the Alpha Particle X‐Ray Spectrometer (APXS) during Spirit's journey over Husband Hill and down into the Inner Basin from sol 470 to ...1368. The APXS continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission. Germanium has been added to the Spirit APXS data set with the confirmation that it occurs at elevated levels in many rocks and soils around Home Plate. Twelve new rock classes and two new soil classes have been identified at the Spirit landing site since sol 470 on the basis of the diversity in APXS geochemistry. The new rock classes are Irvine (alkaline basalt), Independence (low Fe outcrop), Descartes (outcrop similar to Independence with higher Fe and Mn), Algonquin (mafic‐ultramafic igneous sequence), Barnhill (volcaniclastic sediments enriched in Zn, Cl, and Ge), Fuzzy Smith (high Si and Ti rock), Elizabeth Mahon (high Si, Ni, and Zn outcrop and rock), Halley (hematite‐rich outcrop and rock), Montalva (high K, hematite‐rich rock), Everett (high Mg, magnetite‐rich rock), Good Question (high Si, low Mn rock), and Torquas (high K, Zn, and Ni magnetite‐rich rock). New soil classes are Gertrude Weise (very high Si soil) and Eileen Dean (high Mg, magnetite‐rich soil). Aqueous processes have played a major role in the formation and alteration of rocks and soils on Husband Hill and in the Inner Basin.
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