Die Kosmochemie des Mars: Mit Raumsonden und Meteoriten

The chemical composition of Martian surface material is deduced using two different approaches: Direct measurements by the Alpha‐Proton‐X‐Ray Spectrometer (APXS) flown to Mars by the Pathfinder mission, and by analyses of SNC meteorites, which are believed to be rocks from Mars. Several surface rocks of Mars measured by the APXS have different chemical compositions than those of SNC meteorites. Both compositions are also different from the Martian soil found at the Pathfinder landing site. However, this soil, which covers the surface of Mars, seems to be a mixture of local rocks, SNC meteoritic material, and an iron‐rich component. From selected element correlations found in SNC meteorites and Martian surface samples, the bulk chemical composition of the planet is obtained. According to this model, Mars has an iron rich core of about 22 wt.%, which is relatively smaller than the Earth's core of about 33.5 %.     

质谱检测技术在火星探测中的应用

火星探测对人类寻找地外生命、探索行星产生和演化机制具有重要的科学意义.质谱技术已经在火星探测方面得到了实际应用,获得的数据正在改写着人类对火星的基本认识.本文综述了国内外质谱技术在火星探测任务中的应用现状,特别是我国学者的研究进展、存在问题和应对策略.     

Spectroscopic and photometric evaluation of images from the Mars Pathfinder camera

The images taken by the Mars Pathfinder camera are used to obtain information about the chemical and mineralogical properties of the Martian stones and soil at the landing site. These tasks are fulfilled by spectroscopic and photometric techniques. A number of scientific groups are engaged in this work. Three aspects of this work, which was done in the DLR Institute of Planetary Exploration, will be shown. A method for measuring the reflectance characteristics of the calibration targets is demonstrated. The determination of the angles of incidence, emergence, and phase for a point in the images is explained. Finally, two different methods of spectral classification of image points are shown.     

Raman Spectroscopic Study of the Phase Transition of Amorphous to Crystalline β‐Carbonic Acid

What's the matter? The laboratory Raman spectra for carbonic acid (H₂CO₃), both for the β‐polymorph and its amorphous state, are required to detect carbonic acid on the surface of the pole caps of Mars in 2009, when the Mars Microbeam Raman Spectrometer lands on the planet. The picture shows a martian crater with ice of unknown composition, possibly containing carbonic acid (image adapted from DLR, with permission from ESA, DLR, and FU Berlin –‐G. Neukum).

     

Life in the sabkha: Raman spectroscopy of halotrophic extremophiles of relevance to planetary exploration

The Raman spectroscopic biosignatures of halotrophic cyanobacterial extremophiles from sabkha evaporitic saltpans are reported for the first time and ideas about the possible survival strategies in operation have been forthcoming. The biochemicals produced by the cyanobacteria which colonise the interfaces between large plates of clear selenitic gypsum, halite, and dolomitized calcium carbonates in the centre of the salt pans are identifiably different from those which are produced by benthic cyanobacterial mats colonising the surface of the salt pan edges in the intertidal zone. The prediction that similar geological formations would have been present on early Mars and which could now be underlying the highly peroxidised regolith on the surface of the planet has been confirmed by recent satellite observations from Mars orbit and by localised traverses by robotic surface rovers. The successful adoption of miniaturised Raman spectroscopic instrumentation as part of a scientific package for detection of extant life or biomolecular traces of extinct life on proposed future Mars missions will depend critically on interpretation of data from terrestrial Mars analogues such as sabkhas, of which the current study is an example.     

Phoenix mars mission—The thermal evolved gas analyzer

The Phoenix spacecraft that was launched to Mars in August 2007 landed safely on the Martian northern arctic region on May 25, 2008. It carried six experiments to study the history of water on the planet and search for organic molecules in the icy subsurface Martian soil. The spacecraft is a lander with an arm and scoop designed to dig a trench though the top soil to reach an expected ice layer near the surface. One of the instruments on board is the thermal evolved gas analyzer (TEGA), which consists of two components, a set of eight very small ovens that will heat samples of the ice soil mixtures from the trench to release imbedded gases and mineral decomposition products, and a mass spectrometer that serves as the analysis tool for the evolved gases, and also for measurements of the composition and isotopic ratios of the gases that comprise the atmosphere of Mars. The mass spectrometer is a miniature magnetic sector instrument controlled by microprocessor-driven power supplies. One feature is the gas enrichment cell that will increase the partial pressures of the noble gases in an atmosphere sample by removing all the active gases, carbon dioxide, and nitrogen, to improve the accuracy of their isotopic ratio measurements.     

Laser induced breakdown spectroscopy on soils and rocks: Influence of the sample temperature,moisture and roughness

ExoMars, ESA's next mission to Mars, will include a combined Raman/LIBS instrument for the comprehensive in-situ mineralogical and elemental analyses of Martian rocks and soils. It is inferred that water exists in the upper Martian surface as ice layers, “crystal” water or adsorbed pore water. Thus, we studied Laser Induced Breakdown Spectroscopy (LIBS) on wet and dry rocks under Martian environmental conditions in the temperature range − 60 °C to + 20 °C and in two pressure regimes, above and below the water triple point. Above this point, the LIBS signals from the rock forming elements have local minima that are accompanied by hydrogen (water) emission maxima at certain temperatures that we associate with phase transitions of free or confined water/ice. At these sample temperatures, the plasma electron density and its temperature are slightly lowered. In contrast to powder samples, a general increase of the electron density upon cooling was observed on rock samples. By comparing the LIBS signal behavior from the same rock with different grades of polishing, and different rocks with the same surface treatment, it was possible to distinguish between the influence of surface roughness and the bulk material structure (pores and grains). Below the triple point of water, the LIBS signal from the major sample elements is almost independent of the sample temperature. However, at both considered pressures we observed a hydrogen emission peak close to − 50 °C, which is attributed to a phase transition of supercooled water trapped inside bulk pores.     

Identification of β-carotene in an evaporitic matrix—evaluation of Raman spectroscopic analysis for astrobiological research on Mars

Since evaporitic rocks on the Martian surface could (or still can) serve as potential habitats for microbial life on Mars, there is a reasonable possibility that these rocks may sustain molecular remnants as evidence for the presence of extinct or extant living organisms on Mars and that β-carotene could be a suitable biomarker. In this paper, Raman microspectrometry was tested as a nondestructive method of determining the lowest detectable β-carotene content in experimentally prepared evaporitic matrices—namely, gypsum, halite and epsomite. Two excitation wavelengths were compared—514.5 nm, because of the resonance Raman enhancement in the carotenoid analysis, and 785 nm, as a more universal wavelength now much used in the detection of biomolecules terrestrially. Mixtures were measured directly as well as with a laser beam penetrating the crystals of gypsum and epsomite. We have obtained β-carotene signals at the 0.1 to 10 mg kg⁻¹ level—the number of registered β-carotene Raman bands differed depending on the particular mineral matrix and the excitation wavelength. Concentrations of β-carotene of about one order of magnitude higher were identified when analysed through single crystals of gypsum and epsomite, respectively.     

Study of sub-mJ-excited laser-induced plasma combined with Raman spectroscopy under Mars atmosphere-simulated conditions

Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are complimentary techniques. LIBS yields elemental information while Raman spectroscopy yields molecular information about a sample, and both share similar instrumentation configurations. The combination of LIBS and Raman spectroscopy in a single instrument for planetary surface exploration has been proposed, however challenges exist for developing a combined instrument. We present LIBS and Raman spectroscopy results obtained using a diode pumped, intracavity doubled, Q-switched, Nd:YLF laser operating at 523 nm, which overcomes some of the difficulties associated with a combined instrument. LIBS spectra were obtained with 170 μJ per pulse at 4 Hz repetition rate in a low pressure Mars-simulated atmosphere and Raman spectra produced with 200 mW at 100 kHz. The Nd:YLF laser is switchable between LIBS and Raman spectroscopy modes only by a change in Q-switch repetition rate. Emissions from Ca, Ca II, Fe, Fe II, Mg, Na, and O atom were identified in the μ-LIBS spectrum of oolithic hematite. Evidence was found for a change in plasma dynamics between 7 and 5 Torr that could be explained as a decrease in plasma temperature and electron density below 5 Torr. This is relevant to future Mars exploration using LIBS as the mean surface pressure on Mars varies from 3.75 to 6 Torr. LIBS plasma dynamics should be carefully evaluated at the pressures that will be encountered at the specific Mars landing site.     

Laser induced breakdown spectroscopy on meteorites

The classification of meteorites when geological analysis is unfeasible is generally made by the spectral line emission ratio of some characteristic elements. Indeed when a meteorite impacts Earth's atmosphere, hot plasma is generated, as a consequence of the braking effect of air, with the consequent ablation of the falling body. Usually, by the plasma emission spectrum, the meteorite composition is determined, assuming the Boltzmann equilibrium. The plasma generated during Laser Induced Breakdown Spectroscopy (LIBS) experiment shows similar characteristics and allows one to verify the mentioned method with higher accuracy. On the other hand the study of Laser Induced Breakdown Spectroscopy on meteorite can be useful for both improving meteorite classification methods and developing on-flight techniques for asteroid investigation.

In this paper certified meteorites belonging to different typologies have been investigated by LIBS: Dofhar 461 (lunar meteorite), Chondrite L6 (stony meteorite), Dofhar 019 (Mars meteorite) and Sikhote Alin (irony meteorite).     

Considerations on the planned use of a scientific balance on Mars

Future European and American Missions to Mars will be focussed on the search for life, and of water, as a precondition for the existence of complex organisms. Besides the polar ice caps of carbon dioxide and water, in the upper few meters of the Martian surface, water and ice bound to the soil surface, is expected. Therefore we propose to investigate the storing capability of Martian soil in situ. This planned quite new type of investigation makes use for the first time of a balance at a celestial body outside Earth.     

Single-particle characterization of soil samples collected at various arid areas of China,using low-Z particle electron probe X-ray microanalysis☆

Individual soil particles collected at arid areas of China are analyzed using a single particle analytical technique, named low-Z particle electron probe X-ray microanalysis (EPMA). The major chemical species encountered in soil samples are SiO₂, aluminosilicates, CaCO₃, Fe-containing particles, and carbonaceous particles. Aluminosilicate particles are the most abundant in soil samples, followed by SiO₂ particles. For soil samples collected at Loess plateau nearby the Yellow river, aluminosilicate and CaCO₃ species are more abundantly observed than for soil samples collected at the Tengger and the Hungshandake deserts. Whereas, sand desert soils have higher content of SiO₂ than loess soils.In this work, using the low-Z particle EPMA, it is clearly demonstrated that the relative abundances of each chemical species significantly vary among soil samples. The frequencies to encounter aluminosilicates and the contents of minor elements in aluminosilicate-containing particles are different between soil samples. Also, the contents of calcite, dolomite, and Fe-containing particles vary from sample to sample. This kind of detailed information on chemical composition of source soils could be useful for the identification of the source region of mineral particles in aerosol samples and in the research of chemical modification of Asian Dust particles during long-range transport.     

Laser-Induced Breakdown Spectroscopy for Mars surface analysis: capabilities at stand-off distances and detection of chlorine and sulfur elements

An international consortium is studying the feasibility of performing in situ geochemical analysis of Mars soils and rocks at stand-off distances up to several meters using the Laser-Induced Breakdown Spectroscopy (LIBS) technique. Stand-off analysis for Martian exploration imposes particular requirements on instrumentation, and it is necessary to first test the performance of such a system in the laboratory. In this paper, we test the capabilities of two different experimental setups. The first one is dedicated to the qualitative analysis of metals and rocks at distances between 3 and 12 m. With the second one, we have obtained quantitative results for aluminum alloys and developed a spectral database under Martian conditions for sulfur and chlorine, two elements that are geologically interesting but generally difficult to detect by LIBS under standard conditions (atmospheric pressure, close distance). These studies were carried out to determine an optimal instrumental design for in situ Mars analysis. The quality of analytical results affected by the optical elements and spectrometer has been particularly highlighted.     

Elemental analysis of fertilizers using X-ray fluorescence and their impact on alpha radioactivity of plants

The fertilizers used for plantation contain different elements including some natural radionuclides with their daughter decay products. The radiological impact of the use of fertilizers may be due to internal irradiation of the lung by the alpha particles, short lived radon-thoron progeny and the external irradiation of the body by gamma ray emitted from the radionuclides. The aim of this study was to estimate the enhanced alpha radioactivity in different parts of plants due to fertilizers and to measure the concentration of different elements present in the fertilizers. A control study was carried out on round gourd plants using different fertilizers. Fertilizers were added to the soil just before the plantation of seeds in the pots. For the measurement of alpha track densities in different parts of plants we used α-sensitive LR-115 type II plastic track detectors. The alpha-track density (T cm^?2 days^?1) was measured in leaves of plants at different interval of time. The variation in alpha track densities was also observed in root, stem leaf and grain parts of the plants. In case of the plants grown using some phosphate fertilizers the alpha radioactivity was found to be more compared with others. A positive correlation between alpha track densities and mass exhalation rates of radon from different fertilizers has been observed. The concentration of major elements (Al, Si, P, S, Cl, K) along with other elements present in fertilizer samples was measured by X-ray fluorescence analysis.     

Enrichment adsorption of a labile substance to the surface of particular mineral particles in river water as investigated by SEM-EDX and dilute-acid extraction/ICP-MS.

The selective enrichment behavior of a labile substance, such as hydroxides, to the surface of particular mineral particles in river water was clarified by scanning electron microscopy/energy dispersive X-ray microanalysis (SEM-EDX). Individual particles other than diatom collected on a 0.45 microm filter from the Fuji and Sagami rivers, central Japan, were analyzed by SEM-EDX and classified into seventeen groups according to the chemical composition and shape. Phosphorus, sulfur, chlorine, manganese and copper detected in each particle collected on the 0.45 microm filter could be successfully used as effective indicators of labile substance secondarily formed and adsorbed afresh in river water, because the detection frequencies of such elements are quite low, or negligible, in fresh mineral particles derived from igneous rocks. The labile substance adsorbed on mineral particles collected on the 0.45 microm filter was also evaluated by dilute-acid leaching, followed by inductively coupled plasma mass spectrometry (ICP-MS). Almost all parts of the manganese detected in individual particles were those adsorbed afresh as hydroxides together with iron and aluminum. Also, anionic elements, such as phosphorus, sulfur and chlorine, formed complexes with the hydroxides and/or were incorporated in them. Mg and/or Ca-rich aluminosilicate groups were the most effective adsorbers of such labile species. However, Si-rich and Na-, K- and Na-Ca rich aluminosilicates did not significantly adsorb the labile substance. Consequently, the remarkable selectivity was clarified in the adsorption process of labile substance to individual mineral particles in river water.     

Analysis of airborne metal containing particles with EDX/EDS detectors in electron microscopes

In years 2006–2010 particulate matter analysis was undertaken for dust samples collected from Gdansk and London area in order to compare their morphology and composition. Part of those studies was devoted to analysis of particulate matter (PM) bearing metals. Characterization of the morphology and size of the particles collected onto the filters was performed using a scanning electron microscope (SEM) and transmission electron microscope (TEM). Both electron microscopes were equipped with energy dispersive X-ray spectrometers to identify the elemental composition of the particles. On analysis of the X-ray spectra acquired by both TEM and SEM, the particles were divided into 10 groups as follows: Al-rich, Ba-rich, C-rich, Ca-rich, Cl-rich, Fe-rich, Mg-rich, Na-rich, S-rich, Si-rich. Speciation of the particles based on the major element and accompanying minor elements yielded 34 particle types. However, some pairs of elements repeat, for instance: Na-Cl and Cl-Na, Al-S and S-Al, Si-Al and Al-Si, S-Ca and Ca-S. These are undoubtedly the same types of particles; variation in peak heights of the major and minor elements is normal in a mixed particle population.     

Single-particle characterization of “Asian Dust” certified reference materials using low-Z particle electron probe X-ray microanalysis

In order to clearly elucidate whether Asian Dust particles experience chemical modification during long-range transport, it is necessary to characterize soil particles where Asian Dust particles originate. If chemical compositions of source soil particles are well characterized, then chemical compositions of Asian Dust particles collected outside source regions can be compared with those of source soil particles in order to find out the occurrence of chemical modification. Asian Dust particles are chemically and morphologically heterogeneous, and thus the average composition and the average aerodynamic diameter (obtainable by bulk analysis) are not much relevant if the chemical modifications of the particles must be followed. The major elemental composition and abundance of the particle types that are potential subjects of chemical modification can only be obtained using single-particle analysis. A single particle analytical technique, named low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA), was applied to characterize two certified reference materials (CRMs) for Asian Dust particles, which were collected from a loess plateau area and a desert of China. The CRMs were defined by bulk analyses to provide certified concentrations for 13 chemical elements. Using the low-Z particle EPMA technique, the concentrations of major chemical species such as aluminosilicates, SiO₂, CaCO₃, and carbonaceous species were obtained. Elemental concentrations obtained by the low-Z particle EPMA are close to the certified values, with considering that the single particle and bulk analyses employ very different approaches. There are still some discrepancies between those concentration values, resulting from analyses of particles with different sizes, different sample amounts analyzed, and uncertainties involved in the single particle analysis.     

The characterizations of solid specimens: Approaching the whole problem

The purpose of this paper is to demonstrate that complicated mixtures of solids can be characterized to a rather high degree if a coordinated examination by non-destructive methods is used. The techniques discussed are X-ray fluorescence, scanning electron microscopy, photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction. The application of these methods to the characterization of corrosion scale on an inconel coupon is illustrated. The types of information accumulated were elemental composition, chemical forms of elements, special distributions of elements and compounds in the scale, sizes of particles that made up the scale, variations in composition of particle surfaces from that of their interiors, and composition of scale-alloy interface.     

Miniaturized Laser-Induced Breakdown Spectroscopy for the in-situ analysis of the Martian surface: Calibration and quantification

We report on our ongoing studies to develop Laser-Induced Breakdown Spectroscopy (LIBS) for planetary surface missions to Mars and other planets and moons, like Jupiter's moon Europa or the Earth's moon. Since instruments for space missions are severely mass restricted, we are developing a light-weight miniaturized close-up LIBS instrument to be installed on a lander or rover for the in-situ geochemical analysis of planetary surface rocks and coarse fines. The total mass of the instrument will be ≈ 1 kg in flight configuration. Here we report on a systematic performance study of a LIBS instrument equipped with a prototype laser of 216 g total mass and an energy of 1.8 mJ. The LIBS measurements with the prototype laser and the comparative measurements with a regular 40 mJ laboratory laser were both performed under Martian atmospheric conditions.     

Strategies for Mars remote Laser-Induced Breakdown Spectroscopy analysis of sulfur in geological samples

The key to understanding the sulfur history on Mars is to identify and determine sulfate and sulfide compositions and then to draw from them geologic clues about their environments of formation. To lay a foundation for use of remote LIBS to sulfur analysis in planetary exploration, we have undertaken a focused study of sulfur LIBS in geological samples in a simulated Mars atmosphere, with experimental parameters replicating the ChemCam LIBS instrument. A suite of twelve samples was selected, including rocks rich in minerals representative of sulfates and sulfides that might be encountered on Mars. Univariate analysis of sulfur emission lines did not provide quantitative information. Partial least squares (PLS) analysis was successful at modeling sulfur concentrations for a subset of samples with similar matrices. Sulfide minerals were identified on the basis of other siderophile or chalcophile peaks, such as those arising from Zn and Cu. Because the S lines are very weak compared to those of other elements, optimal PLS results were obtained by restricting the wavelength range to channels close to the most intense sulfur lines ~ 540-570 nm. Principal components analysis was attempted on the dataset, but did not differentiate the samples into meaningful groups because the sulfur lines are not strong enough. However, areas of the relatively weak S, H, and O peaks may be used to correctly classify all samples. Based on these outcomes, a flowchart that outlines a possible decision tree for identification and quantification of sulfur in remote LIBS analysis was constructed. Results suggest that LIBS data acquired under Mars conditions can meet the science requirements for the ChemCam instrument.