Mastcam-Z is a multispectral, stereoscopic imaging investigation on the Mars 2020 mission’s
Perseverance
rover. Mastcam-Z consists of a pair of focusable, 4:1 zoomable cameras that provide broadband ...red/green/blue and narrowband 400-1000 nm color imaging with fields of view from 25.6° × 19.2° (26 mm focal length at 283 μrad/pixel) to 6.2° × 4.6° (110 mm focal length at 67.4 μrad/pixel). The cameras can resolve (≥ 5 pixels) ∼0.7 mm features at 2 m and ∼3.3 cm features at 100 m distance. Mastcam-Z shares significant heritage with the Mastcam instruments on the Mars Science Laboratory
Curiosity
rover. Each Mastcam-Z camera consists of zoom, focus, and filter wheel mechanisms and a 1648 × 1214 pixel charge-coupled device detector and electronics. The two Mastcam-Z cameras are mounted with a 24.4 cm stereo baseline and 2.3° total toe-in on a camera plate ∼2 m above the surface on the rover’s Remote Sensing Mast, which provides azimuth and elevation actuation. A separate digital electronics assembly inside the rover provides power, data processing and storage, and the interface to the rover computer. Primary and secondary Mastcam-Z calibration targets mounted on the rover top deck enable tactical reflectance calibration. Mastcam-Z multispectral, stereo, and panoramic images will be used to provide detailed morphology, topography, and geologic context along the rover’s traverse; constrain mineralogic, photometric, and physical properties of surface materials; monitor and characterize atmospheric and astronomical phenomena; and document the rover’s sample extraction and caching locations. Mastcam-Z images will also provide key engineering information to support sample selection and other rover driving and tool/instrument operations decisions.
The presence of hydrated phases in the soil and near‐surface bedrock of Gale Crater is thought to be direct evidence for water‐rock interaction in the crater in the ancient past. Layered sediments ...over the Gale Crater floor are thought to have formed in past epochs due to sediment transport, accumulation, and cementation through interaction with fluids, and the observed strata of water‐bearing minerals record the history of these episodes. The first data analysis of the Dynamic Albedo of Neutrons (DAN) investigation on board the Curiosity rover is presented for 154 individual points of active mode measurements along 1900 m of the traverse over the first 361 Martian solar days in Gale crater. It is found that a model of constant water content within subsurface should be rejected for practically all tested points, whereas a two‐layer model with different water contents in each layer is supported by the data. A so‐called direct two‐layer model (water content increasing with depth) yields acceptable fits for odometry ranges between 0 and 455 m and beyond 638 m. The mean water (H2O) abundances of the top and bottom layers vary from 1.5 to 1.7 wt % and from 2.2 to 3.3 wt %, respectively, while at some tested spots the water content is estimated to be as high as ~5 wt %. The data for odometry range 455–638 m support an inverse two‐layer model (water content decreasing with depth), with an estimated mean water abundance of 2.1 ± 0.1 wt % and 1.4 ± 0.04 wt % in the top and bottom layers, respectively.
Key Points
First analysis of active neutron data from DAN instrument on board MSL roverEstimations of water distribution along MSL rover traverse by DAN instrumentEstimations of chlorine abundance along MSL rover traverse by DAN instrument
We report the water abundance of Bagnold Dune sand in Gale crater, Mars by analyzing active neutron experiments using the Dynamic Albedo of Neutrons instrument. We report a bulk ...water‐equivalent‐hydrogen abundance of 0.68 ± 0.15 wt%, which is similar to measurements several kilometers away and from those taken of the dune surface. Thus, the dune is likely dehydrated throughout. Furthermore, we use geochemical constraints, including bulk water content, to develop compositional models of the amorphous fraction for which little information is known. We find the amorphous fraction contains ∼26‐ to 64‐wt% basaltic glass and up to ∼24‐wt% rhyolitic glass, suggesting at least one volcanic source for the dune material. We also find a range of hydrated phases may be present in appreciable abundances, either from the incorporation of eroded aqueously altered sediments or the direct alteration of the dune sand.
Plain Language Summary
Dune sands in Gale crater are analagous to the globally distributed sands on Mars; however, their source and history, which is intimately related to their composition, is not well constrained. The minerals that compose the dune sands are determined and constrained from in situ analysis of samples, but much less has been determined for the amorphous (noncrystalline) component. These materials compose a sizable fraction of the dune material (40%) and can provide insight into the history of the dune material, including its interactions with water. We combine the analysis of several instruments onboard the Mars Science Laboratory Curiosity rover to constrain the noncrystalline component of Bagnold Dune sands in Gale crater. Particularly, we find the low water content of the dunes constrains the abundance of several amorphous materials and indicates that at least one, but potentially multiple, volcanic sources contributed to the dune. These results help provide a more holistic compositional description of the Bagnold Dune sands and potentially can be used to help determine the likely source regions in future studies.
Key Points
Active neutron experiments show active dunes are the driest material in Gale crater
Bagnold Dunes are dehydrated throughout; however, the presence of aqueously altered phases could not be ruled out
Modeling of amorphous compositions shows the origin to be predominantly volcanic, potentially involving multiple or evolving sources
Data gathered with the Dynamic Albedo of Neutron (DAN) instrument onboard rover Curiosity were analyzed for variations in subsurface neutron flux and tested for possible correlation with local ...geological context. A special DAN observation campaign was executed, in which 18 adjacent DAN active measurements were acquired every 0.75–1.0 m to search for the variations of subsurface hydrogen content along a 15 m traverse across geologic contacts between the Sheepbed and Gillespie Lake members of the Yellowknife Bay formation. It was found that several subunits in Sheepbed and Gillespie Lake could be characterized with different depth distributions of water‐equivalent hydrogen (WEH) and different chlorine‐equivalent abundance responsible for the distribution of neutron absorption elements. The variations of the average WEH at the top 60 cm of the subsurface are estimated at up to 2–3%. Chlorine‐equivalent neutron absorption abundances ranged within 0.8–1.5%. The largest difference in WEH and chlorine‐equivalent neutron absorption distribution is found between Sheepbed and Gillespie Lake.
Key Points
DAN special campaign in Yellowknife Bay
DAN local measurements of water and chlorine abundance
Correlation of DAN measurements and geological context
The NASA Curiosity rover Mast Camera (Mastcam) system is a pair of fixed-focal length, multispectral, color CCD imagers mounted approximately 2 m above the surface on the rover's remote sensing mast, ...along with associated electronics and an onboard calibration target. The left Mastcam (M-34) has a 34 mm focal length, an instantaneous field of view (IFOV) of 0.22 mrad, and a FOV of 20 deg × 15 deg over the full 1648 × 1200 pixel span of its Kodak KAI-2020 CCD. The right Mastcam (M-100) has a 100 mm focal length, an IFOV of 0.074 mrad, and a FOV of 6.8 deg × 5.1 deg using the same detector. The cameras are separated by 24.2 cm on the mast, allowing stereo images to be obtained at the resolution of the M-34 camera. Each camera has an eight-position filter wheel, enabling it to take Bayer pattern red, green, and blue (RGB) 'true color' images, multispectral images in nine additional bands spanning approximately 400-1100 nm, and images of the Sun in two colors through neutral density-coated filters. An associated Digital Electronics Assembly provides command and data interfaces to the rover, 8 Gb of image storage per camera, 11 bit to 8 bit companding, JPEG compression, and acquisition of high-definition video. Here we describe the preflight and in-flight calibration of Mastcam images, the ways that they are being archived in the NASA Planetary Data System, and the ways that calibration refinements are being developed as the investigation progresses on Mars. We also provide some examples of data sets and analyses that help to validate the accuracy and precision of the calibration.
The Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, has been used to map a stratigraphically conformable layer of high‐SiO
2 material in Gale crater. ...Previous work has shown that this material contains tridymite, a high‐temperature/low‐pressure felsic mineral, interpreted to have a volcanic source rock. We describe several characteristics including orientation, extent, hydration, and geochemistry, consistent with a volcaniclastic material conformably deposited within a lacustrine mudstone succession. Relationships with widely dispersed alteration features and orbital detections of hydrated SiO
2 suggest that this high‐SiO
2 layer extends at least 17 km laterally. Mineralogical abundances previously reported for this high‐SiO
2 material indicated that hydrous species were restricted to the amorphous (non‐crystalline) fraction, which is dominated by SiO
2. The low mean bulk hydration of this high‐SiO
2 layer (1.85
± 0.13 wt.% water‐equivalent hydrogen) is consistent with silicic glass in addition to opal‐A and opal‐CT. Persistent volcanic glass and tridymite in addition to opal in an ancient sedimentary unit indicates that the conversion to more ordered forms of crystalline SiO
2 has not proceeded to completion and that this material has had only limited exposure to water since it originally erupted, despite having been transported in a fluviolacustrine system. Our results, including the conformable nature, large areal extent, and presence of volcanic glass, indicate that this high‐SiO
2 material is derived from the product of evolved magma on Mars. This is the first identification of a silicic volcaniclastic layer on another planet and has important implications for magma evolution mechanisms on single‐plate planets.
Plain Language Summary
Using the Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, we mapped a silica‐rich layer throughout a small region in Gale crater known as Marias Pass. Previous work has shown that some rocks in Marias Pass contain minerals formed in explosive volcanic eruptions. We determined several key characteristics including orientation, extent, hydration, and elemental composition, which are consistent with material derived from a volcanic deposit. This layer is likely related to nearby silica‐rich material deposited by groundwater along subsurface fractures, and geometric relationships to hydrated silica identified from orbit suggest that this high‐silica layer extends over at least 17 km. Mineralogical data from previous work indicates the crystalline fraction is anhydrous. As such, we interpret the low hydration of this material, attributable to the amorphous (non‐crystalline) fraction, as being consistent with a significant abundance of volcanic glass in addition to other hydrated phases. The presence of volcanic glass indicates that this material has had limited exposure to water since its formation, because glasses tend to preferentially weather. Our results show that this layer is parallel to surrounding rocks, covers a large area, and contains volcanic glass, indicating that it derived from an explosive volcanic product.
Key Points
A >1 m thick SiO
2‐ and tridymite‐rich layer in Gale crater likely extends over several kilometers
This layer is stratigraphically conformable, with low water content consistent with significant volcanic glass
This material is consistent with an evolved igneous material deposited in a lacustrine environment
The Dynamic Albedo of Neutrons (DAN) experiment, part of the scientific payload of the Mars Science Laboratory (MSL) rover mission, will have the ability to assess both the abundance and the burial ...depth of subsurface hydrogen as the rover traverses the Martian surface. DAN will employ a method of measuring neutron fluxes called “neutron die-away” that has not been used in previous planetary exploration missions. This method requires the use of a pulsed neutron generator that supplements neutrons produced via spallation in the subsurface by the cosmic ray background. It is well established in neutron remote sensing that low-energy (thermal) neutrons are sensitive not only to hydrogen content, but also to the macroscopic absorption cross-section of near-surface materials. To better understand the results that will be forthcoming from DAN, we model the effects of varying abundances of high absorption cross-section elements that are likely to be found on the Martian surface (Cl, Fe) on neutron die-away measurements made from a rover platform. Previously, the Mars Exploration Rovers (MER) Spirit and Opportunity found that elevated abundances of these two elements are commonly associated with locales that have experienced some form of aqueous activity in the past, even though hydrogen-rich materials are not necessarily still present. By modeling a suite of H and Cl compositions, we demonstrate that (for abundance ranges reasonable for Mars) both the elements will significantly affect DAN thermal neutron count rates. Additionally, we show that the timing of thermal neutron arrivals at the detector can be used together with the thermal neutron count rates to independently determine the abundances of hydrogen and high neutron absorption cross-section elements (the most important being Cl). Epithermal neutron die-away curves may also be used to separate these two components. We model neutron scattering in actual Martian compositions that were determined by the MER Alpha Proton X-Ray Spectrometer (APXS), as examples of local geochemical anomalies that DAN would be sensitive to if they were present at the MSL landing site. These MER targets, named “Eileen Dean,” “Jack Russell,” and “Kenosha Comets,” all have unusually high or low Cl or Fe abundances as a result of geochemical interactions involving water. Using these examples we demonstrate that DAN can be used not only to assess the amount of present-day hydrogen in the near-surface but also to identify locations that may preserve a geochemical record of past aqueous processes.
In Situ Analysis of Opal in Gale Crater, Mars Rapin, W.; Chauviré, B.; Gabriel, T. S. J. ...
Journal of geophysical research. Planets,
August 2018, Letnik:
123, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Silica enrichments resulting in up to ~90 wt% SiO2 have been observed by the Curiosity rover's instruments in Gale crater, Mars, within the Murray and Stimson formations. Samples acquired by the ...rover drill revealed a significant abundance of an X‐ray amorphous silica phase. Laser‐induced breakdown spectroscopy (LIBS) highlights an overall correlation of the hydrogen signal with silica content for these Si‐enriched targets. The increased hydration of the high‐silica rocks compared to the surrounding bedrock is also confirmed by active neutron spectroscopy. Laboratory LIBS experiments have been performed to calibrate the hydrogen signal and show that the correlation observed on Mars is consistent with a silica phase containing on average 6.3 ± 1.4 wt% water. X‐ray diffraction and LIBS measurements indicate that opal‐A, amorphous hydrated silica, is the most likely phase containing this water in the rocks. Pyrolysis experiments were also performed on drilled samples by the Sample Analysis at Mars (SAM) instrument to measure volatile content, but the data suggests that most of the water was released during handling prior to pyrolysis. The inferred low‐temperature release of water helps constrain the nature of the opal. Given the geological context and the spatial association with other phases such as calcium sulfates, the opal was likely formed from multiple diagenetic fluid events and possibly represents the latest significant water‐rock interaction in these sedimentary rocks.
Key Points
Sedimentary rocks with high amorphous silica content were analyzed at Gale crater on Mars
Calibration of the LIBS hydrogen signal reveals >4 wt% water content associated with silica
The stability of opal‐A over several billion years is an anomaly relative to terrestrial mineralogy
Glen Torridon (GT) is a geomorphic feature of Aeolis Mons (informally Mt. Sharp) in Gale crater, Mars, variably covered by local regolith and wind‐blown basaltic sands. The Mars Reconnaissance ...Orbiter's Compact Imaging Spectrometer for Mars (CRISM) detected clay minerals in GT, making GT a target of investigation by the Mars Science Laboratory (MSL) rover, Curiosity, which confirmed a large abundance of clays. The MSL Dynamic Albedo of Neutrons (DAN) instrument observed enrichments in bulk subsurface (<50 cm) hydration along the rover traverse compared to lower stratigraphic sections of Mt. Sharp. Here, we investigate the relationship between the CRISM 3 µm hydration index and DAN results, taking into consideration the different spatial scales and effective depths of these two instruments. We show that the elevated hydration observed by CRISM in one area of GT corresponds to elevated DAN‐derived hydration, while the lower CRISM hydration in another area of GT does not correspond to a significantly lower DAN‐derived hydration. We find that CRISM measured lower hydration in areas with good bedrock exposure or sand cover, while DAN bulk hydration is relatively insensitive to these characteristics. DAN active neutron results also show that the stratigraphically higher section of GT has significantly higher neutron absorption, which could be due to Fe‐ and Mn‐rich diagenetic features. Additionally, DAN results show that GT is enriched in hydrogen with respect to other, less clay‐rich units observed throughout the traverse, suggesting that subsurface clay minerals could be a significant reservoir for the hydration measured by DAN in GT.
Plain Language Summary
Glen Torridon (GT) is a region of Mt. Sharp in Gale crater, Mars. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), an orbital instrument, detected abundant clay minerals in GT, which the NASA rover, Curiosity, later confirmed. Both CRISM and the DAN instrument on Curiosity (used to measure subsurface water) detected greater hydration in GT than in other rock layers investigated by the rover. CRISM measures hydration of the uppermost surface layer, while DAN measures the subsurface hydration to a depth of ∼50 cm. CRISM detected greater surface hydration in northern GT than in southern GT, but DAN sees little difference in the hydration of these two areas. Northern GT has a rougher surface (the bedrock is covered by small rocks and pebbles) than southern GT, which is mostly exposed bedrock. Although northern GT appears to be more hydrated to CRISM, it is probably an effect of the loose surface material boosting the signal. Because DAN is not affected by surface roughness, DAN does not see this enhancement. Instead, DAN sees elevated hydration throughout GT, suggesting that subsurface clays may be more hydrated than previously thought.
Key Points
The bulk hydration of a clay‐rich unit in Gale crater is greater than that of clay‐poor units, suggesting hydrated clays are present
The bulk hydration of this clay unit corresponds to enhanced spectral features in some, but not all, areas measured from orbit
Hydration features in orbital spectra are enhanced for areas with a surface cover of regolith characterized by loose pebbles
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