Danika Wellington

Calcium sulfate veins characterized by ChemCam/Curiosity at Gale crater, Mars

The Curiosity rover has analyzed abundant light-toned fracture-fill material within the Yellowknife Bay sedimentary deposits. The ChemCam instrument, coupled with Mastcam and ChemCam/Remote Micro Imager images, was able to demonstrate that these fracture fills consist of calcium sulfate veins, many of which appear to be hydrated at a level expected for gypsum and bassanite. Anhydrite is locally present and is found in a location characterized by a nodular texture. An intricate assemblage of veins crosses the sediments, which were likely formed by precipitation from fluids circulating through fractures. The presence of veins throughout the entire similar to 5 m thick Yellowknife Bay sediments suggests that this process occurred well after sedimentation and cementation/lithification of those sediments. The sulfur-rich fluids may have originated in previously precipitated sulfate-rich layers, either before the deposition of the Sheepbed mudstones or from unrelated units such as the sulfates at the base of Mount Sharp. The occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions.

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

Abstract 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.

Visible/near-infrared spectral diversity from in situ observations of the Bagnold Dune Field sands in Gale Crater, Mars

As part of the Bagnold Dune campaign conducted by Mars Science Laboratory rover Curiosity, visible/near-infrared reflectance spectra of dune sands were acquired using Mast Camera (Mastcam) multispectral imaging (445–1013 nm) and Chemistry and Camera (ChemCam) passive point spectroscopy (400–840 nm). By comparing spectra from pristine and rover-disturbed ripple crests and troughs within the dune field, and through analysis of sieved grain size fractions, constraints on mineral segregation from grain sorting could be determined. In general, the dune areas exhibited low relative reflectance, a weak ~530 nm absorption band, an absorption band near 620 nm, and a spectral downturn after ~685 nm consistent with olivine-bearing sands. The finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest ~530 nm bands, highest relative reflectances, and weakest red/near-infrared ratios, consistent with a combination of crystalline and amorphous ferric materials. Coarser-grained samples were the darkest and bluest and exhibited weaker ~530 nm bands, lower relative reflectances, and stronger downturns in the near-infrared, consistent with greater proportions of mafic minerals such as olivine and pyroxene. These grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands. Sieved dune sands exhibited progressive decreases in reflectance with increasing grain size, as observed in laboratory spectra of olivine size separates. The continuum of spectral features observed between the coarse- and fine-grained dune sands suggests that mafic grains, ferric materials, and air fall dust mix in variable proportions depending on aeolian activity and grain sorting.

The Mars Science Laboratory Curiosity rover Mastcam instruments: Preflight and in-flight calibration, validation, and data archiving

The NASA Curiosity rover Mast Camera (Mastcam) system is a pair of fixed-focal length, multispectral, color CCD imagers mounted ~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° × 15° 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° × 5.1° 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 ~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. Plain Language Summary We describe the calibration and archiving of the images being obtained from the Mastcam multispectral, stereoscopic imaging system on board the NASA Curiosity Mars rover. Calibration is critical to detailed scientific analysis of instrumental data, and in this paper we not only describe the details of the calibration process and the steps in our resulting data calibration pipeline but also present some examples of the kinds of scientific analyses and discoveries that this calibration has enabled.

Visible to near-infrared MSL/Mastcam multispectral imaging: Initial results from select high-interest science targets within Gale Crater, Mars

Abstract The Mastcam CCD cameras on the Mars Science Laboratory Curiosity Rover each use an 8-position filter wheel in acquiring up to 1600 × 1200 pixel images. The filter set includes a broadband near-infrared cutoff filter for RGB Bayer imaging on each camera and 12 narrow-band geology filters distributed between the two cameras, spanning the wavelength range 445–1013 nm. This wavelength region includes the relatively broad charge-transfer and crystal-field absorption bands that are most commonly due to the presence of iron-bearing minerals. To identify such spectral features, sequences of images taken with identical pointings through different filters have been calibrated to relative reflectance using pre-flight calibration coefficients and in-flight measurements of an onboard calibration target. Within the first 1000 sols of the mission, Mastcam observed a spectrally diverse set of materials displaying absorption features consistent with the presence of iron-bearing silicate, iron oxide, and iron sulfate minerals. Dust-coated surfaces as well as soils possess a strong positive reflectance slope in the visible, consistent with the presence of nanophase iron oxides, which have long been considered the dominant visible-wavelength pigmenting agent in weathered martian surface materials. Fresh surfaces, such as tailings produced by the drill tool and the interiors of rocks broken by the rover wheels, are grayer in visible wavelengths than their reddish, dust-coated surfaces but possess reflectance spectra that vary considerably between sites. To understand the mineralogical basis of observed Mastcam reflectance spectra, we focus on a subset of the multispectral data set for which additional constraints on the composition of surface materials are available from other rover instruments, with an emphasis on sample sites for which detailed mineralogy is provided by the results of CheMin X-ray diffraction analyses. We also discuss the results of coordinated observations with the ChemCam instrument, whose passive mode of operation is capable of acquiring reflectance spectra over wavelengths that considerably overlap the range spanned by the Mastcam filter set (Johnson et al. 2016). Materials that show a distinct 430 nm band in ChemCam data also are observed to have a strong near-infrared absorption band in Mastcam spectral data, consistent with the presence of a ferric sulfate mineral. Long-distance Mastcam observations targeted toward the flanks of the Gale crater central mound are in agreement with both ChemCam spectra and orbital results, and in particular exhibit the spectral features of a crystalline hematite layer identified in MRO/CRISM data. Variations observed in Mastcam multi-filter images acquired to date have shown that multispectral observations can discriminate between compositionally different materials within Gale Crater and are in qualitative agreement with mineralogies from measured samples and orbital data.