Tayro E. Acosta-Maeda

The pressures and temperatures of meteorite impact: Evidence from micro-Raman mapping of mineral phases in the strongly shocked Taiban ordinary chondrite

Abstract Taiban is a heavily shocked L6 chondrite showing opaque melt veins. Raman spectroscopy was used to characterize the high-pressure silicate assemblages in a thin section crossed by a shock-created 4 mm wide melt vein. Raman spectra using different excitation wavelengths allowed identification of mineral phases such as olivine, wadsleyite, ringwoodite, high-Ca clinopyroxene, majorite-pyrope, jadeite, maskelynite, and lingunite. Olivine is Fe depleted in contact with the ringwoodite, which suggests chemical fractionation during a solid-state olivine-ringwoodite transformation. Raman imaging revealed a close correlation between the blue ringwoodite color and the peak observed at 877 cm-1; this signal shows strong near-resonance Raman enhancement when measured with near-IR excitation lines (785 and 830 nm) close to the optical absorption bands of the ringwoodite. We propose that the blue color of the ringwoodite is due to a small amount of iron in fourfold coordination inside the spinel structure, and that yields the observed spectral features in differently colored ringwoodite. Under the formation conditions of the studied silicate pocket, all enstatite transformed to a majorite-pyrope solid solution, whereas the high-Ca clinopyroxene likely remained unchanged. Maskelynite grains in the margins of the pocket often contain lingunite or are totally transformed to jadeite. Based on static high-pressure results, the mineral assemblages in the pocket suggest peak pressure in the 17-20 GPa range with maximum temperature (Tmax) in the range 1850-1900 K as the formation conditions for this Taiban chondrite during shock.

Next Generation Laser-Based Standoff Spectroscopy Techniques for Mars Exploration

In the recent Mars 2020 Rover Science Definition Team Report, the National Aeronautics and Space Administration (NASA) has sought the capability to detect and identify elements, minerals, and most importantly, biosignatures, at fine scales for the preparation of a retrievable cache of samples. The current Mars rover, the Mars Science Laboratory Curiosity, has a remote laser-induced breakdown spectroscopy (LIBS) instrument, a type of quantitative elemental analysis, called the Chemistry Camera (ChemCam) that has shown that laser-induced spectroscopy instruments are not only feasible for space exploration, but are reliable and complementary to traditional elemental analysis instruments such as the Alpha Particle X-Ray Spectrometer. The superb track record of ChemCam has paved the way for other laser-induced spectroscopy instruments, such as Raman and fluorescence spectroscopy. We have developed a prototype remote LIBS-Raman-fluorescence instrument, Q-switched laser-induced time-resolved spectroscopy (QuaLITy), which is approximately 70 000 times more efficient at recording signals than a commercially available LIBS instrument. The increase in detection limits and sensitivity is due to our development of a directly coupled system, the use of an intensified charge-coupled device image detector, and a pulsed laser that allows for time-resolved measurements. We compare the LIBS capabilities of our system with an Ocean Optics spectrometer instrument at 7 m and 5 m distance. An increase in signal-to-noise ratio of at least an order of magnitude allows for greater quantitative analysis of the elements in a LIBS spectrum with 200-300 μmm spatial resolution at 7 m, a Raman instrument capable of 1 mm spatial resolution at 3 m, and bioorganic fluorescence detection at longer distances. Thus, the new QuaLITy instrument fulfills all of the NASA expectations for proposed instruments.

Cryogenic minerals in Hawaiian lava tubes: A geochemical and microbiological exploration

ABSTRACT The Mauna Loa volcano, on the Island of Hawaii, has numerous young lava tubes. Among them, two at high altitudes are known to contain ice year-round: Mauna Loa Icecave (MLIC) and the Arsia Cave. These unusual caves harbor cold, humid, dark, and biologically restricted environments. Secondary minerals and ice were sampled from both caves to explore their geochemical and microbiological characteristics. The minerals sampled from the deep parts of the caves, where near freezing temperatures prevail, are all multi-phase and consist mainly of secondary amorphous silica SiO2, cryptocrystalline calcite CaCO3, and gypsum CaSO4·2H2O. Based on carbon and oxygen stable isotope ratios, all sampled calcite is cryogenic. The isotopic composition of falls on the global meteoric line, indicating that little evaporation has occurred. The microbial diversity of a silica and calcite deposit in the MLIC and from ice pond water in the Arsia Cave was explored by analysis of ∼50,000 small subunit ribosomal RNA gene fragments via amplicon sequencing. Analyses reveal that the Hawaiian ice caves harbor unique microbial diversity distinct from other environments, including cave environments, in Hawaii and worldwide. Actinobacteria and Proteobacteria were the most abundant microbial phyla detected, which is largely consistent with studies of other oligotrophic cave environments. The cold, isolated, oligotrophic basaltic lava cave environment in Hawaii provides a unique opportunity to understand microbial biogeography not only on Earth but also on other planets.

Multiwavelength scanning standoff time-resolved Raman system for planetary exploration and environmental monitoring

We have developed a multiwavelength Scanning Standoff Time-Resolved Raman spectroscopy (S2TR2S) system to detect minerals and chemicals from a long distance (10-100 m) over a large area. The multiwavelength SSTRRS system uses 532 and 785 nm pulsed lasers and two separate 5x beam expanders to excite spontaneous Raman spectra of the chemicals with 10 mm diameter laser beams. The VIS-NIR system employs a common Meade telescope (F/10, aperture 20.3 cm). In order to improve detection efficiency, the light collected by the telescope is directly coupled into two f/1.8 transmission spectrograph covering the VIS and NIR spectral regions by changing the volume Holographic Raman gratings for 532 and 785 nm laser lines, respectively. The spectrograph is equipped with a gated intensified CCD camera and edge filters are used to reject the reflected and Rayleigh scattered laser light. The S2TR2S system is operated using pan-tilt pointing capability for precise measurements of selected distant points (under computer control). By making standoff Raman measurements over a predefined grid array, a large area can be sampled and Raman composition maps are constructed off the distant target area. This mapping capability of the instruments has been used to identify a wide variety of minerals and hazardous chemicals from their Raman fingerprints and Raman images. The use of pulsed laser and gated detection allow the measurement of the Raman spectra of minerals with minimum interference from photoluminescence from transition metal ions and rare-earths ions, and ambient light.

Standoff Biofinder: powerful search for life instrument for planetary exploration

The “Standoff Biofinder” is a powerful “search for life” instrument that is able to detect biomolecules from a collection of rocks and minerals in a large area with detection time less than a second using a non-contact, non-destructive approach. Biological materials show strong, short-lived fluorescence signals when excited with ultraviolet-visible (UVVis) wavelengths. The Standoff Biofinder takes advantage of the short lifetimes of bio-fluorescent materials to obtain real-time images showing the locations of biological materials among luminescent minerals in a geological context. The Standoff Biofinder uses an expanded and diffused nanosecond pulsed laser to illuminate a large geological region and a gated detector to record time-resolved fluorescence images. The instrument works in daylight as well as nighttime conditions and bio-detection capability is not affected by the background light. The instrument is able to detect both live and dead biological materials, and is a useful tool for detecting the presence of both extant and extinct life on a planetary surface. The Standoff Biofinder instrument will be suitable for locating fluorescent polyaromatic hydrocarbons, amino acids, proteins, bacteria, biominerals, photosynthetic pigments, and diagenetic products of microbial life on dry landscapes and Ocean Worlds of the outer Solar System (e.g., Enceladus, Europa, and Titan). An important feature of the Standoff Biofinder instrument is its capability to detect biomolecules which are inside ice, without sample collection.

Stand-off detection of amino acids and nucleic bases using a compact instrument as a tool for search for life

Amino acids and nucleobases are of particular interest to NASA’s science goal of “Search for life” because they are essential for life as the basic constituents of proteins and deoxyribonucleic acids (DNA). Their detection would point to possible biosignatures and potential life bearing processes and thus there is a need for technologies capable of identifying them. Raman spectroscopy provides univocal and accurate chemical characterization of organic and inorganic compounds and can be used to detect biological materials and biomarkers in the context of planetary exploration. While micro-Raman systems are useful, a remote Raman instrument can increase the analysis area around a rover or lander. At the University of Hawai‘i we developed a portable, compact time-resolved remote-Raman instrument using a small 3” diameter mirror lens telescope, and used it to demonstrate daytime detection of amino acids and nucleobases from a distance of 8 m. The measured spectra allowed us to univocally identify 20 proteinogenic amino acids, four nucleobases, and some non-proteinogenic amino acids, despite the presence of native fluorescence, especially in aromatic compounds. We were also able to distinguish between α and β amino acids, as well as between different polymorphs. We found the remote Raman system is well suited for planetary exploration applications, with no requirement for sample preparation or collection, and rapid measurement times.

Modified spatial heterodyne Raman spectrometer for remote-sensing analysis of organics

A spatial heterodyne Raman spectrometer (SHRS) is a variant of a Michelson interferometer where the mirrors in a Michelson are replaced with stationary diffraction gratings. Instead of generating an interferogram in the time domain, as in the case of a Michelson interferometer, the SHRS interferogram is generated in the spatial domain as a superposition of two-dimensional cosinusoidal spatial fringes. The spatial interferogram is recorded by an intensified charge-coupled device (ICCD) camera, and the Raman spectrum is recovered by taking the Fourier transform of the spatial interferogram. In the modified SHRS utilized in the present work, a λ/10 mirror has replaced one of the diffraction gratings. This alteration has a few effects. First, the ICCD records a greater number of photons because photons are not lost into unused diffraction orders. Second, the spectral bandpass of the modified SHRS has been doubled allowing the measurement of Raman spectra from 100-4000 cm-1. In this work, the authors present Raman spectra of organic compounds taken at remote distances of 19 meters with this modified SHRS.

EXPRESS: A Two-Component Approach for Long Range Remote Raman and Laser-Induced Breakdown (LIBS) Spectroscopy Using Low Laser Pulse Energy

The remote detection of chemicals using remote Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) is highly desirable for homeland security and NASA planetary exploration programs. We recently demonstrated Raman spectra with high signal-to-noise ratio of various materials from a 430 m distance during daylight with detection times of 1–10 s, utilizing a 203 mm diameter telescopic remote Raman system and 100 mJ/pulse laser energy at 532 nm for excitation. In this research effort, we describe a simple two-components approach that helps to obtain remote Raman and LIBS spectra of targets at distance of 246 m with 3 mJ/pulse in daytime. The two components of the method are: (1) a small spectroscopy system utilizing 76 mm diameter collection optics; and (2) a small remote lens near the target. Remote Raman spectra of various chemicals are presented here with detection time of 1 s. Remote LIBS spectra of minerals using single laser pulse of 3 mJ/pulse energy from a distance of 246 m are also presented. This research work demonstrates a simple approach that significantly improves remote Raman and LIBS capabilities for long range chemical detection with compact low laser power Raman and LIBS systems.