Dark microbiome and extremely low organics in Atacama fossil delta unveil Mars life detection limits.

Identifying unequivocal signs of life on Mars is one of the most important objectives for sending missions to the red planet. Here we report Red Stone, a 163-100 My alluvial fan-fan delta that formed under arid conditions in the Atacama Desert, rich in hematite and mudstones containing clays such as vermiculite and smectites, and therefore geologically analogous to Mars. We show that Red Stone samples display an important number of microorganisms with an unusual high rate of phylogenetic indeterminacy, what we refer to as "dark microbiome", and a mix of biosignatures from extant and ancient microorganisms that can be barely detected with state-of-the-art laboratory equipment. Our analyses by testbed instruments that are on or will be sent to Mars unveil that although the mineralogy of Red Stone matches that detected by ground-based instruments on the red planet, similarly low levels of organics will be hard, if not impossible to detect in Martian rocks depending on the instrument and technique used. Our results stress the importance in returning samples to Earth for conclusively addressing whether life ever existed on Mars.

Compositionally and density stratified igneous terrain in Jezero crater, Mars.

Before Perseverance, Jezero crater's floor was variably hypothesized to have a lacustrine, lava, volcanic airfall, or aeolian origin. SuperCam observations in the first 286 Mars days on Mars revealed a volcanic and intrusive terrain with compositional and density stratification. The dominant lithology along the traverse is basaltic, with plagioclase enrichment in stratigraphically higher locations. Stratigraphically lower, layered rocks are richer in normative pyroxene. The lowest observed unit has the highest inferred density and is olivine-rich with coarse (1.5 millimeters) euhedral, relatively unweathered grains, suggesting a cumulate origin. This is the first martian cumulate and shows similarities to martian meteorites, which also express olivine disequilibrium. Alteration materials including carbonates, sulfates, perchlorates, hydrated silicates, and iron oxides are pervasive but low in abundance, suggesting relatively brief lacustrine conditions. Orbital observations link the Jezero floor lithology to the broader Nili-Syrtis region, suggesting that density-driven compositional stratification is a regional characteristic.

Optical calibration of the SuperCam instrument body unit spectrometers.

The SuperCam remote sensing instrument on NASA's Perseverance rover is capable of four spectroscopic techniques, remote micro-imaging, and audio recording. These analytical techniques provide details of the chemistry and mineralogy of the rocks and soils probed in the Jezero Crater on Mars. Here we present the methods used for optical calibration of the three spectrometers covering the 243-853 nm range used by three of the four spectroscopic techniques. We derive the instrument optical response, which characterizes the instrument sensitivity to incident radiation as a function of a wavelength. The instrument optical response function derived here is an essential step in the interpretation of the spectra returned by SuperCam as it converts the observed spectra, reported by the instrument as "digital counts" from an analog to digital converter, into physical values of spectral radiance.

Multiplexing of frequency-modulation spectroscopy by spread-spectrum codes, demonstrated in continuous-wave LIDAR.

Frequency-modulation spectroscopy (FMS) is generally suited to code-division multiplexing, and we demonstrate that capacity in a form of continuous-wave LIDAR, utilizing a sharp CO2 absorption transition at 1.6 µm in simple ranging setups. The approach retains the advantages of FMS, including coherent detection and good rejection of broad absorption backgrounds. Extensions of this multiplexed approach to the continuous, simultaneous detection of several transitions would come by transmitting an encoded combination of frequency-modulated carriers, each tuned to detect a unique absorption transition. Signal analysis at the receiver involves a simple process of de-multiplexing that, in a general application, reveals targets at various distances and the absorption-related FMS signals in between.

OrganiCam: a lightweight time-resolved laser-induced luminescence imager and Raman spectrometer for planetary organic material characterization.

OrganiCam is a laser-induced luminescence imager and spectrometer designed for standoff organic and biosignature detection on planetary bodies. OrganiCam uses a diffused laser beam (12° cone) to cover a large area at several meters distance and records luminescence on half of its intensified detector. The diffuser can be removed to record Raman and fluorescence spectra from a small spot from 2 m standoff distance. OrganiCam's small size and light weight makes it ideal for surveying organics on planetary surfaces. We have designed and built a brassboard version of the OrganiCam instrument and performed initial tests of the system.

Mechanistic Study of the Production of NOx Gases from the Reaction of Copper with Nitric Acid.

Copper dissolution in nitric acid is a historic reaction playing a central role in many industrial processes, particularly for metal recovery from the electronics to nuclear industries. The mechanism through which this process occurs is debated. In order to better understand this process, quantum chemical calculations were performed to elucidate the key steps in the mechanism of copper dissolution in nitric acid. We combine both Kohn-Sham density functional theory and ab initio molecular dynamics simulations to understand the mechanism of the formation of the key products: NO2, HNO2, and NO. Our calculations suggest that the mechanisms of formation of NO2, HNO2, and NO are interconnected.

"Standoff Biofinder" for Fast, Noncontact, Nondestructive, Large-Area Detection of Biological Materials for Planetary Exploration.

UNLABELLED: We developed a prototype instrument called the Standoff Biofinder, which can quickly locate biological material in a 500 cm(2) area from a 2 m standoff distance with a detection time of 0.1 s. All biogenic materials give strong fluorescence signals when excited with UV and visible lasers. In addition, the luminescence decay time of biogenic compounds is much shorter (<100 ns) than the micro- to millisecond decay time of transition metal ions and rare-earth ions in minerals and rocks. The Standoff Biofinder takes advantage of the short lifetime of biofluorescent materials to obtain real-time fluorescence images that show the locations of biological materials among luminescent minerals in a geological context. The Standoff Biofinder instrument will be useful for locating biological material during future NASA rover, lander, and crewed missions. Additionally, the instrument can be used for nondestructive detection of biological materials in unique samples, such as those obtained by sample return missions from the outer planets and asteroids. The Standoff Biofinder also has the capacity to detect microbes and bacteria on space instruments for planetary protection purposes. KEY WORDS: Standoff Biofinder-Luminescence-Time-resolved fluorescence-Biofluorescence-Planetary exploration-Planetary protection-Noncontact nondestructive biodetection. Astrobiology 16, 715-729.

Planetary geochemical investigations using Raman and laser-induced breakdown spectroscopy.

An integrated Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) instrument is a valuable geoanalytical tool for future planetary missions to Mars, Venus, and elsewhere. The ChemCam instrument operating on the Mars Curiosity rover includes a remote LIBS instrument. An integrated Raman-LIBS spectrometer (RLS) based on the ChemCam architecture could be used as a reconnaissance tool for other contact instruments as well as a primary science instrument capable of quantitative mineralogical and geochemical analyses. Replacing one of the ChemCam spectrometers with a miniature transmission spectrometer enables a Raman spectroscopy mineralogical analysis to be performed, complementing the LIBS chemical analysis while retaining an overall architecture resembling ChemCam. A prototype transmission spectrometer was used to record Raman spectra under both Martian and Venus conditions. Two different high-pressure and high-temperature cells were used to collect the Raman and LIBS spectra to simulate surface conditions on Venus. The resulting LIBS spectra were used to generate a limited partial least squares Venus calibration model for the major elements. These experiments demonstrate the utility and feasibility of a combined RLS instrument.

Comparison of two partial least squares-discriminant analysis algorithms for identifying geological samples with the ChemCam laser-induced breakdown spectroscopy instrument.

ChemCam, a laser-induced breakdown spectroscopy (LIBS) instrument on the Mars Science Laboratory rover, will analyze the chemistry of the martian surface beginning in 2012. Prior to integration on the rover, the ChemCam instrument collected data on a variety of rock types to provide a training set for analysis of data from Mars. Models based on calibration data can be used to classify rocks via multivariate statistical techniques such as partial least squares-discriminant analysis (PLS-DA). In this study, we employ a version of PLS-DA in which modeling is applied in a defined classification flow to a variety of geological materials and compare the results with the traditional PLS-DA technique. Results show that the modified algorithm is more effective at classifying samples.

Examining natural rock varnish and weathering rinds with laser-induced breakdown spectroscopy for application to ChemCam on Mars.

A laser-induced breakdown spectroscopy (LIBS) instrument is traveling to Mars as part of ChemCam on the Mars Science Laboratory rover. Martian rocks have weathered exteriors that obscure their bulk compositions. We examine weathered rocks with LIBS in a martian atmosphere to improve interpretations of ChemCam rock analyses on Mars. Profile data are analyzed using principal component analysis, and coatings and rinds are examined using scanning electron microscopy and electron probe microanalysis. Our results show that LIBS is sensitive to minor compositional changes with depth and correctly identifies rock type even if the series of laser pulses does not penetrate to unweathered material.

Remote-Raman spectroscopic study of minerals under supercritical CO2 relevant to Venus exploration.

The authors have utilized a recently developed compact Raman spectrometer equipped with an 85 mm focal length (f/1.8) Nikon camera lens and a custom mini-ICCD detector at the University of Hawaii for measuring remote Raman spectra of minerals under supercritical CO(2) (Venus chamber, ∼102 atm pressure and 423 K) excited with a pulsed 532 nm laser beam of 6 mJ/pulse and 10 Hz. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10× beam expander to a 1mm spot on minerals located at 2m inside a Venus chamber, it is possible to measure the remote Raman spectra of anhydrous sulfates, carbonates, and silicate minerals relevant to Venus exploration during daytime or nighttime with 10s integration time. The remote Raman spectra of gypsum, anhydrite, barite, dolomite and siderite contain fingerprint Raman lines along with the Fermi resonance doublet of CO(2). Raman spectra of gypsum revealed dehydration of the mineral with time under supercritical CO(2) at 423 K. Fingerprint Raman lines of olivine, diopside, wollastonite and α-quartz can easily be identified in the spectra of these respective minerals under supercritical CO(2). The results of the present study show that time-resolved remote Raman spectroscopy with a compact Raman spectrometer of moderate resolution equipped with a gated intensified CCD detector and low power laser source could be a potential tool for exploring Venus surface mineralogy both during daytime and nighttime from a lander.

Time-resolved remote Raman study of minerals under supercritical CO2 and high temperatures relevant to Venus exploration.

We report time-resolved (TR) remote Raman spectra of minerals under supercritical CO(2) (approx. 95 atm pressure and 423 K) and under atmospheric pressure and high temperature up to 1003 K at distances of 1.5 and 9 m, respectively. The TR Raman spectra of hydrous and anhydrous sulphates, carbonate and silicate minerals (e.g. talc, olivine, pyroxenes and feldspars) under supercritical CO(2) (approx. 95 atm pressure and 423 K) clearly show the well-defined Raman fingerprints of each mineral along with the Fermi resonance doublet of CO(2). Besides the CO(2) doublet and the effect of the viewing window, the main differences in the Raman spectra under Venus conditions are the phase transitions, the dehydration and decarbonation of various minerals, along with a slight shift in the peak positions and an increase in line-widths. The dehydration of melanterite (FeSO(4).7H(2)O) at 423 K under approximately 95 atm CO(2) is detected by the presence of the Raman fingerprints of rozenite (FeSO(4).4H(2)O) in the spectrum. Similarly, the high-temperature Raman spectra under ambient pressure of gypsum (CaSO(4).2H(2)O) and talc (Mg(3)Si(4)O(10)(OH)(2)) indicate that gypsum dehydrates at 518 K, but talc remains stable up to 1003 K. Partial dissociation of dolomite (CaMg(CO(3))(2)) is observed at 973 K. The TR remote Raman spectra of olivine, alpha-spodumene (LiAlSi(2)O(6)) and clino-enstatite (MgSiO(3)) pyroxenes and of albite (NaAlSi(3)O(8)) and microcline (KAlSi(3)O(8)) feldspars at high temperatures also show that the Raman lines remain sharp and well defined in the high-temperature spectra. The results of this study show that TR remote Raman spectroscopy could be a potential tool for exploring the surface mineralogy of Venus during both daytime and nighttime at short and long distances.

Inelastic scattering from glyoxal: collision kinematics rather than the interaction potential dominates rotational channel selection.

Relative cross sections have been obtained for the rotationally and rovibrationally inelastic scattering of S1 trans-glyoxal (CHO-CHO) in its zero point level with K' = 0 from the target gases H2, D2, and He. Emphasis is placed on using crossed molecular beam conditions that provide several choices of collision kinematics (center-of-mass collision energy, relative velocity, center-of-mass collision momentum) for each collision pair. The cross sections define the state-to-state competition among numerous rotational channels involving destination states with DeltaK' ranging from 1 to >15 for collisions with each target gas and under every kinematic condition. They also resolve a similar rotational competition among rovibrational channels where the torsion nu7' is collisionally excited. The cross section sets also allow the relative overall magnitudes of the two types of scattering to be compared. The primary motivation of these experiments concerns the rotationally inelastic scattering. Earlier studies with rare gases and fixed kinematics demonstrated that the distribution of rotational cross sections is remarkably similar from one collision pair to another. The new data show that the competition among rotational channels actually has a small but distinct dependence on kinematic conditions. Data analysis shows that the dependence is a systematic function of the available collision momentum and entirely unrelated to the identity of the target gases, including the heavier rare gases used in earlier studies. The competition among the rotational energy transfer channels and its kinematic heritage is discussed in the context of a classical hard ellipse model of linear momentum to angular momentum conversion much used with room temperature systems. When adapted to our beam conditions, the resulting account of the rotational scattering is accurate and provides insight into the collisional details.

Time-dependent infrared emission following photodissociation of nitromethane and chloropicrin.

Nitromethane (CH(3)NO(2)) and its chlorinated analogue, chloropicrin (CCl(3)NO(2)), were photolyzed at 193, 248, and 266 nm, and the products were observed by time-dependent Fourier transform infrared emission spectroscopy. At 193 and 248 nm, the primary photodissociation pathway for nitromethane was cleavage of the C-N bond to produce CH(3) + NO(2)(A (2)B(2)). At 266 nm, weak emission was observed following photodissociation of nitromethane, but an infrared spectrum could not be obtained. The photodissociation of chloropicrin at 193 nm produced the analogous product channel CCl(3) + NO(2)(A (2)B(2)) in addition to several other product channels. At 248 and 266 nm, only CCl(3) + NO(2)(A (2)B(2)) was observed. The production of phosgene (CCl(2)O) from chloropicrin photodissociation was not observed in this study.

Treatment of compounds and alloys in radiation hydrodynamics simulations of ablative laser loading.

Different methods were compared for constructing models of the behavior of a prototype intermetallic compound, nickel aluminide, for use in radiation hydrodynamics simulations of shock wave generation by ablation induced by laser energy. The models included the equation of state, ionization, and radiation opacity. The methods of construction were evaluated by comparing the results of simulations of an ablatively generated shock wave in a sample of the alloy. The most accurate simulations were obtained using the "constant number density" mixture model to calculate the equation of state and opacity, and Thomas-Fermi ionization. This model is consistent with that found to be most accurate for simulations of ablatively shocked elements.