On Mars, Laser-Induced Breakdown Spectroscopy (LIBS) as performed by the ChemCam instrument can be used to measure the hydrogen content of targets in situ, under a low pressure CO2 atmosphere. ...However, unexpected variations observed in the Martian dataset suggest an effect related to target roughness. Here, we present a series of laboratory experiments that reproduce the effect observed on Mars and explore possible causes. We show that the hydrogen peak intensity increases significantly with increasing exposure of the target surface to the LIBS plasma, and that these variations are specific to hydrogen, as other emission lines in the spectra are not affected. The increase of the signal could be related to an addition of hydrogen to the plasma due to interaction with the surrounding target surface, yet the exact physical process to explain such effect remains to be identified. More generally, this effect should be taken into account for the quantification of hydrogen in any LIBS applications where the roughness of the target is significant.
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•The LIBS hydrogen signal specifically varies near protrusions or cavities in Mars targets.•Experiments confirm variations of the LIBS hydrogen signal due to millimeter-scale surface roughness.•Careful target selection is necessary for the quantification of hydrogen by LIBS on Mars.
SuperCam is a highly integrated remote-sensing instrumental suite for NASA’s Mars 2020 mission. It consists of a co-aligned combination of Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved ...Raman and Luminescence (TRR/L), Visible and Infrared Spectroscopy (VISIR), together with sound recording (MIC) and high-magnification imaging techniques (RMI). They provide information on the mineralogy, geochemistry and mineral context around the Perseverance Rover.
The calibration of this complex suite is a major challenge. Not only does each technique require its own standards or references, their combination also introduces new requirements to obtain optimal scientific output. Elemental composition, molecular vibrational features, fluorescence, morphology and texture provide a full picture of the sample with spectral information that needs to be co-aligned, correlated, and individually calibrated.
The resulting hardware includes different kinds of targets, each one covering different needs of the instrument. Standards for imaging calibration, geological samples for mineral identification and chemometric calculations or spectral references to calibrate and evaluate the health of the instrument, are all included in the SuperCam Calibration Target (SCCT). The system also includes a specifically designed assembly in which the samples are mounted. This hardware allows the targets to survive the harsh environmental conditions of the launch, cruise, landing and operation on Mars during the whole mission. Here we summarize the design, development, integration, verification and functional testing of the SCCT. This work includes some key results obtained to verify the scientific outcome of the SuperCam system.
We have assessed the characteristics of clasts along Curiosity's traverse to shed light on the processes important in the genesis, modification, and transportation of surface materials. Pebble‐ to ...cobble‐sized clasts at Bradbury Landing, and subsequently along Curiosity's traverse to Yellowknife Bay, reflect a mixing of two end‐member transport mechanisms. The general clast population likely represents material deposited via impact processes, including meteorite fragments, ejecta from distant craters, and impactites consisting of shocked and shock‐melted materials from within Gale Crater, which resulted predominantly in larger, angular clasts. A subset of rounded pebble‐sized clasts has likely been modified by intermittent alluvial or fluvial processes. The morphology of this rounded clast population indicates that water was a more important transporting agent here than at other Mars sites that have been studied in situ. Finally, we identified populations of basalt clasts and porphyritic clasts of undetermined composition by their morphologic and textural characteristics; basalts are confirmed by geochemical data provided by ChemCam.
Key Points
We examined Curiosity clasts to assess modification and transport processes
Pebble‐ to cobble‐sized clasts reflect a mix of two transport mechanisms
Water was an important transporting agent at the Curiosity landing site
Continuous seismic observations across the Ross Ice Shelf reveal ubiquitous ambient resonances at frequencies >5 Hz. These firn‐trapped surface wave signals arise through wind and snow bedform ...interactions coupled with very low velocity structures. Progressive and long‐term spectral changes are associated with surface snow redistribution by wind and with a January 2016 regional melt event. Modeling demonstrates high spectral sensitivity to near‐surface (top several meters) elastic parameters. We propose that spectral peak changes arise from surface snow redistribution in wind events and to velocity drops reflecting snow lattice weakening near 0°C for the melt event. Percolation‐related refrozen layers and layer thinning may also contribute to long‐term spectral changes after the melt event. Single‐station observations are inverted for elastic structure for multiple stations across the ice shelf. High‐frequency ambient noise seismology presents opportunities for continuous assessment of near‐surface ice shelf or other firn environments.
Plain Language Summary
Ice shelves are the floating buttresses of large glaciers that extend over the oceans and play a key role in restraining inland glaciers as they flow to the sea. Deploying sensitive seismographs across Earth's largest ice shelf (the Ross Ice Shelf) for 2 years, we discovered that the shelf nearly continuously sings at frequencies of five or more cycles per second, excited by local and regional winds blowing across its snow dune‐like topography. We find that the frequencies and other features of this singing change, both as storms alter the snow dunes and during a (January 2016) warming event that resulted in melting in the ice shelf's near surface. These observations demonstrate that seismological monitoring can be used to continually monitor the near‐surface conditions of an ice shelf and other icy bodies to depths of several meters.
Key Points
High‐frequency (>5 Hz), narrow‐band signals observed on an ice shelf are sensitive to changes in the near‐surface firn layer
Spectral peak frequency changes coincide with melt/freeze events on the ice shelf as well as with storm‐driven redistribution snow
Melt events have a unique spectral signature and can be modeled in terms of the penetration depth to which these thermal anomalies diffuse
Although prior work suggests that a mantle plume is associated with Cenozoic rifting and volcanism in West Antarctica, the existence of a plume remains conjectural. Here we use P wave receiver ...functions (PRFs) from the Antarctic POLENET array to estimate mantle transition zone thickness, which is sensitive to temperature perturbations, throughout previously unstudied parts of West Antarctica. We obtain over 8000 high‐quality PRFs using an iterative, time domain deconvolution method filtered with a Gaussian width of 0.5 and 1.0, corresponding to frequencies less than ∼0.24 and ∼0.48 Hz, respectively. Single‐station and common conversion point stacks, migrated to depth using the AK135 velocity model, indicate that mantle transition zone thickness throughout most of West Antarctica does not differ significantly from the global average, except in two locations; one small region exhibits a vertically thinned (210 ± 15 km) transition zone beneath the Ruppert Coast of Marie Byrd Land and another laterally broader region shows slight, vertical thinning (225 ± 25 km) beneath the Bentley Subglacial Trench. We also observe the 520 discontinuity and a prominent negative peak above the mantle transition zone throughout much of West Antarctica. These results suggest that the mantle transition zone may be hotter than average in two places, possibly due to upwelling from the lower mantle, but not broadly across West Antarctica. Furthermore, we propose that the transition zone may be hydrated due to >100 million years of subduction beneath the region during the early Mesozoic.
Key Points:
Two thermal anomalies may exist within the West Antarctic mantle transition zone
The West Antarctic mantle transition zone is likely hydrated
Laser-induced breakdown spectroscopy (LIBS) is demonstrated as a quantitative technique for geochemical analysis. This study demonstrates the applicability of LIBS to bulk elemental analysis of ...igneous rock powders. LIBS spectra of 100 igneous rocks with highly varying compositions were acquired at 9
m standoff distance under Mars atmospheric conditions. LIBS spectra were modeled using partial least squares regressions to predict major element compositions. A series of comparative tests determined the most effective methodologies for pre-processing of spectral and compositional data, and choice of calibration set. In the best cases, calculated 1−
σ errors are 1.6
wt.% SiO
2, 1.5
wt.% Al
2O
3, 0.4
wt.% TiO
2, 1.2
wt.% Fe
2O
3T, 1.6
wt.% MgO, 0.02
wt.% MnO, 1.1
wt.% CaO, 0.5
wt.% Na
2O, 0.2
wt.% P
2O
5, and 0.4
wt.% K
2O, with totals near 100%. The largest improvement came as a result of scaling the elemental distributions to equalize the ranges of variability. Optimal predictions for this data set were produced with calibration set compositions input as weight % oxides and not atomic fractions. Predictions were also improved when calibration sets represented the smallest range of compositional variability possible, and completely encompassed the compositional range encountered. Multiple calibration sets relevant to different rock types are preferred over a single all-encompassing calibration set. Baseline removal and transforming spectral data by their first derivative do not improve predictions and can even have negative effects. These results are directly applicable to spectra that will be acquired by the ChemCam experiment on Mars Science Laboratory, but also apply more broadly to terrestrial LIBS applications.
► LIBS analysis of geologic materials can provide quantitative geochemical information. ► PLS regressions yield predictions better than 1.5
wt.% oxide for major elements. ► Use of wt.% oxide is favored of atomic fractions. ► Weighting input compositions equally improves predictions. ► Carefully selected calibration sets improve predictions over random sets.
The NASA Mars Science Laboratory rover will carry the first Laser Induced Breakdown Spectroscopy experiment in space: ChemCam. We have developed a laboratory model which mimics ChemCam's main ...characteristics. We used a set of target samples relevant to Mars geochemistry, and we recorded individual spectra. We propose a data reduction scheme for Laser Induced Breakdown Spectroscopy data incorporating de-noising, continuum removal, and peak fitting. Known effects of the Martian atmosphere are confirmed with our experiment: better Signal-to-Noise Ratio on Mars compared to Earth, narrower peak width, and essentially no self-absorption. The wavelength shift of emission lines from air to Mars pressure is discussed. The National Institute of Standards and Technology vacuum database is used for wavelength calibration and to identify the elemental lines. Our Martian database contains 1336 lines for 32 elements: H, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ar, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Cs, Ba, and Pb. It is a subset of the National Institute of Standards and Technology database to be used for Martian geochemistry. Finally, synthetic spectra can be built from the Martian database. Correlation calculations help to distinguish between elements in case of uncertainty. This work is used to create tools and support data for the interpretation of ChemCam results.
► Chemcam: first Laser Induced Breakdown Spectroscopy technique on Mars. ► Creation of a LIBS specific database to ChemCam on Mars. ► Data reduction scheme is proposed. ► Best signal under Martian conditions. ► LIBS emission lines database: subset of NIST database for Martian geochemistry.
NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived ...solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are “ground truth” for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in the DLC. The resulting SW Mg fractionation relative to the DSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (total) error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. (2011).
Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made ...possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}624,9/2^{-}734) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}624,9/2^{-}734)⊗8^{-}π^{2}(7/2^{-}514,9/2^{+}624) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.
The ChemCam instrument suite on the Mars Science Laboratory rover Curiosity provides standoff compositional information using the first Laser‐Induced Breakdown Spectroscopy (LIBS) on a planetary ...mission and provides visual data on sample texture using a remote microimager. The LIBS technique is normally used to provide both qualitative (PCA, ICA) and quantitative (PLS) measurements. In this study we test its ability to evaluate variations in the proportion of different mineral phases, the distribution of mineral grains and the relative proportions of pyroxene and plagioclase in five basaltic rocks: (1) three picritic samples: Martian shergottite Dar al Gani 476 with olivine phenocrysts in a coarse‐grained pyroxene‐rich matrix; a terrestrial analog of Gusev basalt with a fine‐grained matrix and equal amounts of pyroxene and plagioclase; a synthetic microlitic glass and (2) two basaltic terrestrial rocks. LIBS measurements were acquired at a 3‐m standoff distance using a constant 400 μm beam size. The number of analysis locations per sample was fixed to five regardless of the rock texture. Results show that olivine phenocrysts can be easily distinguished from groundmass. The standard deviation of Ca/Al emission line ratios correlates with the grain size of the analyzed rocks and corresponds to the amount of plagioclase and pyroxene in the sample, even when the grain size is smaller than the laser spot size.
Key Points
LIBS analyses on picritic basalts
Textural and modal interpretation from the LIBS spectra
Comparison of groundmasses
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