Search

The search for life in Solar System bodies such as Mars and Ocean Worlds (e.g., Europa and Enceladus) is an ongoing and high-priority endeavor in space science, even ∼ five decades after the first life detection mission at Mars performed by the twin Viking landers. However, thein situdetection of biosignatures remains highly challenging, both scientifically and technically. New instruments are being developed for detecting extinct or extant life on Mars and Ocean Worlds due to new technology and fabrication techniques. These instruments are becoming increasingly capable of both detecting and identifyingin situorganic biosignatures that are indicative of life and will play a pivotal role in the search for evidence of life through robotic lander missions. This review article gives an overview of techniques used for space missions (gas chromatography, mass spectrometry, and spectroscopy), the further ongoing developments of these techniques, and ion mobility spectrometry. In addition, current developments of techniques used in the next-generation instruments for organic biosignature detection are reviewed; these include capillary electrophoresis, liquid chromatography, biosensors (primarily immunoassays), and nanopore sensing; whereas microscopy, biological assays, and isotope analysis are beyond the scope of this paper and are not covered.

As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterr...

In situ instrumentation that can detect amino acids at parts-per-billion concentration levels and distinguish an enantiomeric excess of either d- or l-amino acids is vital for future robotic life-d...

The molecules feeding life's emergence are thought to have been provided through the hydrothermal interactions of convecting carbonic ocean waters with minerals comprising the early Hadean oceanic crust. Few laboratory experiments have simulated ancient hydrothermal conditions to test this conjecture. We used the JPL hydrothermal flow reactor to investigate CO

Editorial on the Research Topic Frontiers in astronomy and space sciences: Rising stars

As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterrestrial/non-Earth biology, biogenic structures, and chemical processes generated from biological processes. The fact that Earth is our single data point for all life, diversity, and evolution means that there is an inherent bias toward life as we know it through our own planet's history. The search for life “as we don't know it” then brings this bias forward to decision-making regarding mission instruments and payloads. Understandably, this leads to several top-level scientific, theoretical, and philosophical questions regarding the definition of life and what it means for future life detection missions. How can we decide on how and where to detect known and unknown signs of life with a single biased data point? What features could act as universal biosignatures that support Darwinian evolution in the geological context of nonterrestrial time lines? The purpose of this article is to generate an improved nomenclature for terrestrial features that have mineral/microbial interactions within structures and to confirm which features can only exist from life (biotic), features that are modified by biological processes (biogenic), features that life does not affect (abiotic), and properties that can exist or not regardless of the presence of biology (abiogenic). These four categories are critical in understanding and deciphering future returned samples from Mars, signs of potential extinct/ancient and extant life on Mars, and in situ analyses from ocean worlds to distinguish and separate what physical structures and chemical patterns are due to life and which are not. Moreover, we discuss hypothetical detection and preservation environments for extant and extinct life, respectively. These proposed environments will take into account independent active and ancient in situ detection prospects by using previous planetary exploration studies and discuss the geobiological implications within an astrobiological context.

A primary science goal of astrobiology is to understand the biological potential of Solar System bodies. Looking beyond Earth, four planetary bodies, namely Mars, Europa, Titan and Enceladus, offer numerous opportunities to investigate the chemical evolution and origin of life. These bodies may have biochemistry similar to that of life on Earth (Davila and McKay, 2014; Taubner et al., 2018; Taubner et al., 2020). In recent years, exploration strategies have been developed to pursue astrobiological objectives for these targets. Two key scientific objectives of current and planned space missions to these bodies are 1) to investigate the abundance and distribution of the organic compounds and biomolecules, as well as environmental conditions (causing alteration, degradation and even complete destruction of these compounds such as irradiation, mineralogy etc.), as these are crucial in the search of biosignatures; and 2) to identify evidence of ancient biota and to determine whether indigenous organisms currently exist anywhere on the surface and subsurface of these planetary bodies.

The detection of organic molecules that are indicative of past or present biological activity within the Solar System bodies and beyond is a key research area in astrobiology. Mars is of particular interest in this regard because of evidence of a (perhaps transient) warm and wet climate in its past. To date, space missions to Mars have primarily used pyrolysis technique to extract organic compounds from the Martian regolith, but it has not enabled a clear detection of unaltered native Martian organics. The elevated temperatures required for pyrolysis extraction can cause native Martian organics to react with perchlorate salts in the regolith, possibly resulting in the chlorohydrocarbons that have been detected by mass spectrometry, a commonly usedin situtechnique for space applications. Supercritical carbon dioxide (SCCO2) extraction technique is a powerful alternative to pyrolysis that may be capable of extracting and delivering unaltered native organic species to an analyser. In this study, we report the SCCO2extraction of unaltered amino acids (AAs) with simple laboratory analyses of extracts by capillary electrophoresis laser-induced fluorescence (CE/LIF) and liquid chromatography with mass spectrometry (LC/MS) techniques. The extraction efficiencies of several representative AAs using SCCO2with small amounts of pure water (~1–5%) as a co-solvent were determined. Glass beads were used as a model substrate to examine the effects of several experimental parameters and Johnson Space Center (JSC) Mars-1A Martian regolith simulant was used to study the effect of complex matrix on extraction efficiencies. With optimized experimental conditions (75C and 5% of water), extraction efficiencies from doped JSC Mars-1A were found to be ~40% for glycine, alanine and serine and ~10% for lysine. Extraction of native organics from undoped JSC Mars-1A suggests that SCCO2/water solvent system can extract both organics extractable with pure SCCO2and those extractable with pure water. Additionally, species not extracted by either pure SCCO2or pure water were extracted with SCCO2/water solvent. Despite the preliminary nature of this work, it paves the path for more comprehensive extraction studies of astrobiologically relevant samples with thorough analyses of resulting extracts.

Sensitive and robust in situ chemical analysis of organic biomarkers is essential in the endeavor of finding chemical signatures of life either extinct or extant on our solar system bodies such as Europa, Enceladus, or Titan. Development of new analytical instruments and accompanying methodologies are needed, especially those that are compatible with unknown and diverse samples potentially found on solar system targets and that avoid complexities involved with other wet chemistry techniques (desalting, derivatization and contamination issues, etc.). In this study, we demonstrate that online supercritical fluid extraction and supercritical fluid chromatography with water-saturated CO2 can extract and separate nonpolar analytes of astrobiological interest, such as free fatty acids, polycyclic aromatic hydrocarbons, and polycyclic aromatic compounds containing nitrogen or sulfur. Silica was used as a support material to immobilize aqueous samples during extraction. A C18 stationary phase with an embedded polar functional group and efficient end-capping in combination with water in the mobile phase allowed efficient separation of both free fatty acids and basic compounds. The total analysis time was 30 min, including extraction, equilibration, and separation. Detection was performed with a UV detector and a quadrupole mass spectrometer equipped with electrospray ionization. The method was validated in terms of lower detection limits (0.02–40 μg/L), precision (repeatability 3–13%), relative standard deviation (RSD), intermediate precision 4–26% (RSD), trueness (bias ranging from − 48 to 9%), and retention time shifts (

The analysis of the organic compounds present in the martian regolith is essential for understanding the history and habitability of Mars, as well as studying the signs of possible extant or extinct life. To date, pyrolysis, the only technique that has been used to extract organic compounds from the martian regolith, has not enabled the detection of unaltered native martian organics. The elevated temperatures required for pyrolysis extraction can cause native martian organics to react with perchlorate salts in the regolith and possibly result in the chlorohydrocarbons that have been detected by in situ instruments. Supercritical carbon dioxide (SCCO2) extraction is an alternative to pyrolysis that may be capable of delivering unaltered native organic species to an in situ detector. In this study, we report the SCCO2 extraction of unaltered coronene, a representative polycyclic aromatic hydrocarbon (PAH), from martian regolith simulants, in the presence of 3 parts per thousand (ppth) sodium perchlorate. PAHs are a class of nonpolar molecules of astrobiological interest and are delivered to the martian surface by meteoritic infall. We also determined that the extraction efficiency of coronene was unaffected by the presence of perchlorate on the regolith simulant, and that no sodium perchlorate was extracted by SCCO2. This indicates that SCCO2 extraction can provide de-salted samples that could be directly delivered to a variety of in situ detectors. SCCO2 was also used to extract trace native fluorescent organic compounds from the martian regolith simulant JSC Mars-1, providing further evidence that SCCO2 extraction may provide an alternative to pyrolysis to enable the delivery of unaltered native organic compounds to an in situ detector on a future Mars rover.Biomarkers-Carbon dioxide-In situ measurement-Mars-Search for Mars' organics. Astrobiology 16, 703-714.

One model for the emergence of life posits that ancient, low temperature, submarine alkaline hydrothermal vents, partly composed of iron-sulfides, were capable of catalyzing the synthesis of prebiotic organic molecules from CO2, H2 and CH4. Specifically, hydrothermal mackinawite (FeIIS) and greigite (FeIIFeIII2S4) have been highlighted in previous studies as analogs of the active centers of hydrogenase, ferredoxin, acetyl coenzyme-A synthase and carbon monoxide dehydrogenase featured in the biochemistry of certain autotrophic prokaryotes that occupy the base of the evolutionary tree. Despite the proposed importance of iron sulfide minerals and clusters in the synthesis of abiotic organic molecules, the mechanisms for the formation of these sulfides from solution and their preservation under the anoxic and low temperature (below 100 °C) conditions expected in off-axis submarine alkaline vent systems is not well understood ( Bourdoiseau et al., 2011 , Rickard and Luther, 2007 ). To rectify this, single hydrothermal chimneys were precipitated using a unique apparatus to simulate growth at hydrothermal vents of moderate temperature under supposed Hadean ocean-bottom conditions. Iron sulfide phases were observed through Raman spectroscopy at growth temperatures ranging from 40° to 80 °C. Fe(III)-containing mackinawite is confirmed to be present with mackinawite and greigite, supporting an FeIII-mackinawite intermediate mechanism for the transformation of mackinawite to greigite below 100 °C. Raman spectroscopy of the chimneys revealed a maximum yield of greigite at 75 °C. These results suggest abiotic production of catalytically active mackinawite and greigite are possible under early Earth hydrothermal conditions as well as on other wet, rocky worlds geochemically similar to the Earth.

We examine the electrochemical gradients that form across chemical garden membranes and investigate how self-assembling, out-of-equilibrium inorganic precipitates—mimicking in some ways those generated in far-from-equilibrium natural systems—can generate electrochemical energy. Measurements of electrical potential and current were made across membranes precipitated both by injection and solution interface methods in iron-sulfide and iron-hydroxide reaction systems. The battery-like nature of chemical gardens was demonstrated by linking multiple experiments in series which produced sufficient electrical energy to light an external light-emitting diode (LED). This work paves the way for determining relevant properties of geological precipitates that may have played a role in hydrothermal redox chemistry at the origin of life, and materials applications that utilize the electrochemical properties of self-organizing chemical systems.

Cells use three main ways of generating energy currency to drive metabolism: (i) conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) by the proton motive force through the rotor-stator ATP synthase; (ii) the synthesis of inorganic phosphate∼phosphate bonds via proton (or sodium) pyrophosphate synthase; or (iii) substrate-level phosphorylation through the direct donation from an active phosphoryl donor. A mechanism to produce a pyrophosphate bond as “energy currency” in prebiotic systems is one of the most important considerations for origin of life research. Baltscheffsky (1996) suggests that inorganic pyrophosphate (P_2O_7^(4-); PP_i) may have preceded ATP/ADP as an energy storage molecule in earliest life, produced by an H^+ pyrophosphatase. Here we test the hypothesis that PP_i could be synthesized in inorganic precipitates simulating hydrothermal chimney structures transected by thermal and/or ionic gradients. Appreciable yields of PP_i were obtained via substrate phosphorylation by acetyl phosphate within the iron sulfide/silicate precipitates at temperatures expected for an alkaline hydrothermal system.

Hydrothermal chimneys and compartments comprising transition metal sulphides and associated minerals have been proposed as likely locations for the beginnings of life. In laboratory simulations of off-axis alkaline springs, it is shown that the interaction of a simulated alkaline sulphide-bearing submarine vent solution with a primeval anoxic iron-bearing ocean leads to the formation of chimney structures reminiscent of chemical gardens. These chimneys display periodicity in their deposition and exhibit diverse morphologies and mineralogies, affording the possibilities of catalysis and molecular sequestration. The addition of peptides and RNA to the alkaline solution modifies the elemental stoichiometry of the chimneys—perhaps indicating the very initial stage of the organic takeover on the way to living cells by charged organic polymers potentially synthesized in this same environment.

A mass spectrometer system designed to measure chemical composition of gaseous, liquid, or solid samples in planetary environments must include the following components: a sampling system, an ionization source, a mass analyzer, a detection system, a vacuum system, data acquisition and processing system, and various sensors to monitor the operation of the instrument. Over the last couple of decades, research and engineering advances of mass spectrometers have undergone an evolution from room-sized instruments to portable, in situ miniature devices. The National Aeronautics and Space Administration (NASA) has been embracing these developments, given its need for small, low power, low mass, yet analytically powerful instruments to accomplish its objectives in space exploration [1]. The study of planetary atmospheric composition, including constituent species, their concentrations, and isotopic ratios, provides a better understanding of both the formation and evolution of the planets and the solar system as a whole. Beyond the principals of planetary formation and evolution lies the question regarding the existence of extinct and/or extant life elsewhere in the universe. Discoveries by previous NASA missions of a period where Mars had an extended aqueous history [2-4], evidence of oceans beneath Europa's ice crust [5-7], and the rich organic chemistry on Titan [8,9] have initiated an exciting period of solar system exploration, as an array of robotic missions might be sent to these bodies to answer questions of astrobiological significance.

Chemical gardens form when ferrous chloride hydrate seed crystals are added or concentrated solutions are injected into solutions of sodium silicate and potassium phosphate. Various precipitation morphologies are observed depending on silicate and phosphate concentrations, including hollow plumes, bulbs, and tubes. The growth of precipitates is controlled by the internal osmotic pressure, fluid buoyancy, and membrane strength. Additionally, rapid bubble-led growth is observed when silicate concentrations are high. ESEM/EDX analysis confirms compositional gradients within the membranes, and voltage measurements across the membranes during growth show a final potential of around 150-200 mV, indicating that electrochemical gradients are maintained across the membranes as growth proceeds. The characterization of chemical gardens formed with iron, silicate, and phosphate, three important components of an early earth prebiotic hydrothermal system, can help us understand the properties of analogous structures that likely formed at submarine alkaline hydrothermal vents in the Hadean-structures offering themselves as the hatchery of life.

We report on the use of a small light-weight mass spectrometer (MS) for chemical analysis of organic material directly from solution or from the solid state with potential value in future planetary missions. The mass spectrometer used in the experiments reported here is handheld and controlled from a laptop computer through custom software. Detection and identification of small organic molecules, including some that might be prebiotics, was achieved using methods relevant to in situ and remote sensing applications. The miniature MS was equipped with a discontinuous atmospheric pressure interface (DAPI) and a home-built electrosonic spray ionization (ESSI) source. Aqueous solutions of molecules of interest were examined using the ESSI technique, while desorption electrospray ionization (DESI) was applied to examine solid samples. The system performance was characterized by direct analysis of analytes belonging to several compound classes including biotic and abiotic amino acids, purines, pyrimidines, nucleosides and peptides. Detection limits in the sub-ppm range for solutions were achieved with the atmospheric pressure sampling/ionization interface. Tandem mass spectrometry (MS 2 ) was successfully applied to confirm trace detection of target compounds in mixtures. Multiple stage (MS n ) analysis, where n = 3–5, was employed for molecular structure confirmation and to demonstrate the high chemical specificity as well as the sensitivity of the instrumentation. The use of improved versions of this type of mass spectrometer on exploration missions could provide detailed chemical information on organic materials in physical states currently difficult to access. The high sensitivity and specificity, combined with rapid detection and the absence of requirements for sample preparation are encouraging features of the instrumentation.

We report photochemical studies of thin cryogenic ice films composed of N 2 , CH 4 and CO in ratios analogous to those on the surfaces of Neptune’s largest satellite, Triton, and on Pluto. Experiments were performed using a hydrogen discharge lamp, which provides an intense source of ultraviolet light to simulate the sunlight-induced photochemistry on these icy bodies. Characterization via infrared spectroscopy showed that C 2 H 6 and C 2 H 2 , and HCO are formed by the dissociation of CH 4 into H, CH 2 and CH 3 and the subsequent reaction of these radicals within the ice. Other radical species, such as C 2 , C 2 - , CN, and CNN, are observed in the visible and ultraviolet regions of the spectrum. These species imply a rich chemistry based on formation of radicals from methane and their subsequent reaction with the N 2 matrix. We discuss the implications of the formation of these radicals for the chemical evolution of Triton and Pluto. Ultimately, this work suggests that C 2 - , CN, HCO, and CNN may be found in significant quantities on the surfaces of Triton and Pluto and that new observations of these objects in the appropriate wavelength regions are warranted.

Field induced droplet ionization mass spectrometry (FIDI-MS) comprises a soft ionization method to sample ions from the surface of microliter droplets. A pulsed electric field stretches neutral droplets until they develop dual Taylor cones, emitting streams of positively and negatively charged submicrometer droplets in opposite directions, with the desired polarity being directed into a mass spectrometer for analysis. This methodology is employed to study the heterogeneous ozonolysis of 1-palmitoyl-2-oleoyl-sn-phosphatidylglycerol (POPG) at the air−liquid interface in negative ion mode using FIDI mass spectrometry. Our results demonstrate unique characteristics of the heterogeneous reactions at the air−liquid interface. We observe the hydroxyhydroperoxide and the secondary ozonide as major products of POPG ozonolysis in the FIDI-MS spectra. These products are metastable and difficult to observe in the bulk phase, using standard electrospray ionization (ESI) for mass spectrometric analysis. We also present studies of the heterogeneous ozonolysis of a mixture of saturated and unsaturated phospholipids at the air−liquid interface. A mixture of the saturated phospholipid 1,2-dipalmitoyl-sn-phosphatidylglycerol (DPPG) and unsaturated POPG is investigated in negative ion mode using FIDI-MS while a mixture of 1,2-dipalmitoyl-sn-phosphatidylcholine (DPPC) and 1-stearoyl-2-oleoyl-sn-phosphatidylcholine (SOPC) surfactant is studied in positive ion mode. In both cases FIDI-MS shows the saturated and unsaturated pulmonary surfactants form a mixed interfacial layer. Only the unsaturated phospholipid reacts with ozone, forming products that are more hydrophilic than the saturated phospholipid. With extensive ozonolysis only the saturated phospholipid remains at the droplet surface. Combining these experimental observations with the results of computational analysis provides an improved understanding of the interfacial structure and chemistry of a surfactant layer system when subject to oxidative stress.

Dissociative excitation of molecular hydrogen plays an important role in the heating of outer planet upper thermospheres. This paper addresses the role of one of the triplet states involved in the process. H2 excited to the a 3?+ g state, or higher triplet-ungerade states, is dissociated via the a 3?+ g ?b 3?+ u continuum. The kinetic energy distribution of H(1s) produced from direct X 1?+ g -a 3?+ g (v, J) excitation by electrons is investigated by an accurate theoretical evaluation of spontaneous transition probabilities of the a 3?+ g (v, J)?b 3?+ u continuum transition. It is shown that the X 1?+ g (0)-a 3?+ g (v, J) excitation primarily produces H(1s) atoms with kinetic energies lower than 2 eV. In addition to the continuum a 3?+ g (v, J)?b 3?+ u transition probabilities, spontaneous emission lifetimes of the a 3?+ g (v, J) (v = 0-20, J ? 14) levels have been calculated by considering both the a 3?+ g ?b 3?+ u and a 3?+ g -c 3? u transitions. The calculated lifetimes show a moderately strong rotational dependence, and the lifetimes for the J = 0 rotational level of the low v levels agree well with previous calculations and experimental measurements. Calculations of the a 3?+ g ?b 3?+ u continuum emission spectra from electron impact X 1?+ g -a 3?+ g excitation are included.

Rare earth elements and selected trace elements were measured in 48 samples of carbonate and chert from stromatolites and associated facies in the 3.45 billion year old Strelley Pool Formation, Pilbara Craton, Western Australia. The samples show coherent REE+Y patterns that vary systematically with sedimentary facies. Chert samples from bedded cherts beneath the Strelley Pool Formation and from the upper bedded chert members in the formation show REE+Y patterns consistent with originating by precipitation from hydrothermal and mixed marine-hydrothermal fluids. In contrast, carbonates and cherts from the stromatolitic reef member share the essential shale-normalized characteristics of other Archean marine precipitates (LREE depletion, positive La and Gd anomalies, absence of a negative Ce anomaly and a strongly superchondritic Y/Ho ratio). The close correspondence between REE+Y signatures and independent sedimentary facies interpretations is viewed as strong evidence for the primary nature of REE+Y patterns. They can thus be used as a proxy for the fluids from which sediments precipitated. Mixing hyperbolae can be constructed that reproduce the chemistry of cherts and carbonates by mixing of hydrothermal and marine fluid endmembers throughout the entire vertical succession from beneath the Strelley Pool Formation to the uppermost cherts. The mixing hyperbolae provide semi-quantitative confirmation that the trace element compositions across the suite of cherts represent different mixtures of ambient seawater and hydrothermal fluids. Our results indicate that the Earth's oldest supracrustal carbonates and associated cherts record important aspects of the REE geochemistry of the waters in which they precipitated, and provide valuable information on possible habitats of some of Earth's earliest biota.

Previous work has concluded that H-D exchange occurs readily in polycyclic aromatic hydrocarbons frozen in deuterated water (D2O) irradiated with ultraviolet light. Here, we examine H-D exchange in methane-water ices following exposure to ultraviolet radiation and analyze the products formed as a result. We find that H-D exchange also occurs in methane-water ices by means of ultraviolet photolysis. Exchange proceeds through a radical mechanism that implies that almost all organic species will undergo significant H-D exchange with the matrix in water ices exposed to ultraviolet radiation. Given sufficient energetic processing of the ice, the H/D ratio of an ice matrix may be transferred to the organic species in the ice.

The ≈3,450-million-year-old Strelley Pool Formation in Western Australia contains a reef-like assembly of laminated sedimentary accretion structures (stromatolites) that have macroscale characteristics suggestive of biological influence. However, direct microscale evidence of biology—namely, organic microbial remains or biosedimentary fabrics—has to date eluded discovery in the extensively-recrystallized rocks. Recently-identified outcrops with relatively good textural preservation record microscale evidence of primary sedimentary processes, including some that indicate probable microbial mat formation. Furthermore, we find relict fabrics and organic layers that covary with stromatolite morphology, linking morphologic diversity to changes in sedimentation, seafloor mineral precipitation, and inferred microbial mat development. Thus, the most direct and compelling signatures of life in the Strelley Pool Formation are those observed at the microscopic scale. By examining spatiotemporal changes in microscale characteristics it is possible not only to recognize the presence of probable microbial mats during stromatolite development, but also to infer aspects of the biological inputs to stromatolite morphogenesis. The persistence of an inferred biological signal through changing environmental circumstances and stromatolite types indicates that benthic microbial populations adapted to shifting environmental conditions in early oceans.

We report a study on the broadband ultraviolet photolysis of methane–water ice mixtures, at low methane concentrations and temperatures relevant to the icy satellites of the outer Solar System. The photochemistry of these mixtures is dominated by the action of hydroxyl radicals on methane and the resulting products. This implies that, given sufficient exposure time, the methane will eventually be completely oxidized to carbon dioxide. The presence of methane inhibits the formation of hydrogen peroxide by serving as a trap for hydroxyl radicals. The distribution of photochemical products is broadly similar to that previously conducted using ion and electron sources, with some differences possibly attributable to the difference in radiation source. The results are applicable to a variety of icy bodies in the Solar System. On Enceladus, where methane mixed with water is measured in the plumes, methane in the surface ices is subject to oxidation and will eventually be converted to CO 2 . The C H stretch feature detected in the VIMS spectra of the Enceladus surface ice suggests that methane is currently being supplied to the surface ice, likely from re-condensation of the plume gas.

The dissociation of a wide range of oxygen-containing molecules following impact with electrons of carefully controlled energy is critically reviewed. Molecules considered range from diatomics, like O_2 and CO, to large molecules of biological and technological interest. Dissociation mechanisms are discussed and, where possible, quantitative data for the various possible processes, ionization, attachment, dissociation, excitation, emission etc., are presented. Gaps and discrepancies in our current data base are highlighted. Both graphical and tabular data are presented.

We vapor deposit at 20 K a mixture of gases with the specific Enceladus plume composition measured in situ by the Cassini INMS [Waite, J.H., Combi, M.R., Ip, W.H., Cravens, T.E., McNutt, R.L., Kasprzak, W., Yelle, R., Luhmann, J., Niemann, H., Gell, D., Magee, B., Fletcher, G., Lunine, J., Tseng, W.L., 2006. Science 311, 1419–1422] to form a mixed molecular ice. As the sample is slowly warmed, we monitor the escaping gas quantity and composition with a mass spectrometer. Pioneering studies [Schmitt, B., Klinger, J., 1987. Different trapping mechanisms of gases by water ice and their relevance for comet nuclei. In: Rolfe, E.J., Battrick, B. (Eds.), Diversity and Similarity of Comets. SP-278. ESA, Noordwijk, The Netherlands, pp. 613–619; Bar-Nun, A., Kleinfeld, I., Kochavi, E., 1988. Phys. Rev. B 38, 7749–7754; Bar-Nun, A., Kleinfeld, I., 1989. Icarus 80, 243–253] have shown that significant quantities of volatile gases can be trapped in a water ice matrix well above the temperature at which the pure volatile ice would sublime. For our Enceladus ice mixture, a composition of escaping gases similar to that detected by Cassini in the Enceladus plume can be generated by the sublimation of the H 2 O:CO 2 :CH 4 :N 2 mixture at temperatures between 135 and 155 K, comparable to the high temperatures inferred from the CIRS measurements [Spencer, J.R., Pearl, J.C., Segura, M., Flasar, F.M., Mamoutkine, A., Romani, P., Buratti, B.J., Hendrix, A.R., Spilker, L.J., Lopes, R.M.C., 2006. Science 311, 1401–1405] of the Enceladus “tiger stripes.” This suggests that the gas escape phenomena that we measure in our experiments are an important process contributing to the gases emitted from Enceladus. A similar experiment for ice deposited at 70 K shows that both the processes of volatile trapping and release are temperature dependent over the temperature range relevant to Enceladus.

For in situ astrobiological studies of Mars or other planets, we must employ strategies that will enable us to verify whether our approach and prototype instruments are actually capable of distinguishing life from non-life. This must be done against a background of rigorously conducted scientific characterization of the environment or sample types being considered for measurement by the instruments under development. In this study we show how a combination of mineralogical and textural features can be considered a biosignature in an early Mars analogue environment, Death Valley, California. We propose that it is a combination of features in context of the geologic matrix which allows determination of biogenicity to be made. Polymineralic microbialites (organosedimentary formations constructed by microorganisms) from a spring pool at Badwater, within Death Valley National Park, are composed of alternating biogenic and abiogenic minerals in a distinct triplet sequence related to wet and dry seasons. A microbial community, occurring as a black biofilm, produced paired layers of two different mineral types: manganese oxyhydroxides and calcite. These biogenic layers are separated from the next pair by a gypsum layer and appear to be laid down in the wet season, with the gypsum (a mineral positively identified on Mars) precipitating in the dry part of the year, abiogenically (i.e., not dependent on microbial metabolic activity for its deposition). In addition, textural features (smaller grain size and less geometric morphology) unique to the biogenic vs the abiogenic layers, were consistently observed so that texture served as a biosignature in this environment.

New measurements of differential cross-sections for excitation of the a″ 1Σ+g (v' = 0, 1) state in molecular nitrogen reveal a cusp-like angular distribution. This feature is distinctly observed for the first time in the present electron energy-loss experiment as a result of finer scattering angle grid and impact energy coverage than previous measurements. This feature is similar to that observed in atomic targets such as He, Hg and Ba. The observed phenomenon suggests an interference effect related to configuration–interaction coupling between lower and excited states that are of the same symmetry. It is hoped that the present work will stimulate theoretical investigations into the physics that governs this cusp-like behaviour.

We report the rates of decomposition by ultraviolet (UV) photolysis of four amino acids in millimeter-thick crystalline water ice matrices at 100 K to constrain the survivability of these important organic molecules within ice lying near the surfaces of outer Solar System bodies. We UV-irradiated crystalline ice samples containing known concentrations of the amino acids glycine, aspartic acid, glutamic acid, and phenylalanine, then we measured the surviving concentrations using high performance liquid chromatography (HPLC) with fluorescence detection. From these experiments, we determine photolytic decomposition rates and half-lives. The half-life varies linearly with the ice thickness for all acids studied here. For example, glycine is the most resistant to photolytic destruction with a half-life of 50, 12, and 3.7 h in 1.6, 0.28, and 0.14 mm thick ices, respectively. We explain this linear variation of half-life with thickness as a consequence of extinction, mostly due to scattering, within these macroscopically thick ice samples. Applied to low latitude surface ice on Jupiter's satellite Europa, this analysis indicates that the concentration of any of these amino acids within the top meter of similar ice will be halved within a ∼10 year timescale.

Ion mobility spectrometry (IMS) has proven to be an effective tool for chemical detection and identification. Ion mobility spectrometers can be manufactured in small, rugged and portable designs and have been used in several mission critical circumstances from security screening and military preparedness. Perhaps most visible are the IMS analyzers that have been deployed in airports around the world to detect traces of explosives on passenger carry-on luggage. Intrinsic properties of ion mobility spectrometers make these analyzers suitable for both manned and robotic space exploration. In this review, we will discuss the utility, previous use and future use of ion mobility spectrometers in space environments.

Here we report experimental simulations of hydrothermal chimney growth using injection chemical garden methods. The versatility of this type of experiment allows for testing of various proposed ocean / hydrothermal fluid chemistries that could have driven reactions toward the origin of life in environments on the early Earth, early Mars, or even other worlds such as the icy moons of the outer planets. We show experiments that include growth of chemical garden structures under anoxic conditions simulating the early Earth, inclusion of trace components of phosphates / organics in the injection solution to incorporate them into the structure, a switch of the injection solution to introduce a secondary precipitating anion, and the measurement of membrane potentials generated by chemical gardens. Using this method, self-assembling chemical garden structures were formed that mimic the natural chimneys precipitated at submarine hydrothermal springs, and these precipitates can be used successfully as flow-through reactors by feeding through multiple successive “hydrothermal” injections.

In 1990, two significant reviews of electron–atomic-oxygen collision processes were published. Since that time, a large volume of both experimental and theoretical research into these processes has occurred. These data are reviewed and recommendations regarding existing data sets and future research in this area are made. Attention is given to the challenges associated with handling atomic oxygen in terms of both experiment and theory. PACS Nos.: 34.80.Bm, 34.80.Dp

A high-resolution, 33 mA (FWHM), optically thin emission study of the N2 c' 1Σ(0)-X 1Σ(0) band transition has been performed with electron impact at 100 eV. Recently measured line oscillator strengths and lifetimes have been examined by comparing model spectra with the observed emission. Good agreement between model and data indicates consistency between the measured lifetimes and oscillator strengths. Predissociation yields for various Jj levels are estimated. The calculated predissociation yield is in the range 0.2-0.5 for Jj = 4-23 and negligible for Jj = 0-2.

As part of an ongoing effort to explore the utility of high-resolution electrospray ionization ion mobility spectrometry (ESI-IMS) for the detection and identification of organic molecules on other planetary bodies, pursuant to NASA objectives, the reduced ion mobilities of 14 amino acids that have been identified in meteoritic material were determined in both N2 and CO2 drift gases. A (12,4) hard core potential model of the ion−neutral interaction was applied to a combined data set of amino acid mobilities from the present work (abiotic) and an earlier investigation of twenty common biotic amino acids (Beegle, L. W.; Kanik, I.; Matz, L.; Hill, H. H. Anal. Chem. 2001, 73, 3028−3034). The model was used to investigate the protonated amino acid mass−mobility correlation to extract details of the ion−neutral interaction and to gain insight into the structural details of these ions.

New electron-impact differential cross-section (DCS) and DCS ratio measurements for the excitation of the four levels making up the 3p54s configuration of argon are reported at incident electron energies of 14, 15, 17.5, 20, 30, 50 and 100 eV. These cross-sections were obtained using a conventional high resolution electron spectrometer. Elastic electron scattering from argon was used as a calibration standard. Electron–helium DCSs were used to determine the instrumental transmission of the spectrometer. Further checks of the relative shape of these DCS measurements were made using the method of gas mixtures (Ne mixed with Ar). We also present results from new calculations of these DCSs using the R-matrix method, the unitarized first-order many-body theory, the semi-relativistic distorted-wave Born approximation, and the relativistic distorted-wave method. Comparison with available experimental DCSs and DCS ratios is also presented.

Differential and integral cross sections (ICSs) for excitation in atomic oxygen have been measured at electron-impact energies of 15, 17.5, 20, 22.5 and 27.5 eV. Differential measurements were conducted with a conventional electron energy-loss spectrometer and a microwave discharge source of atomic oxygen. Relative differential cross sections (DCSs) were determined between 15 and 30 eV impact energy. With the help of theoretical predictions of the shape of the DCS at large angles, measured results were extrapolated to 180° scattering angle and relative ICSs were deduced. The relative excitation function was normalized to the 30 eV impact energy ICS given by Kanik et al (2001 J. Phys. B: At. Mol. Opt. Phys. 34 2647). Normalization of the ICS values allowed the measured DCSs to be put on the absolute scale. Theoretical calculations of the DCSs were carried out using the R-matrix with the pseudostates approach. A total of 22 spectroscopic bound and autoionizing states, together with 19 pseudostates, were included in the close-coupling expansion. The pseudostates were chosen to simulate continuum target states. Theoretical results, along with other available experimental data, have been compared with the current experimental results.

We report electron-impact-induced emission cross sections for the 2p4 3P–3s 3So (130.4 nm), 2p4 3P–3d 3Do (102.7 nm), 2p4 3P–3s' 3Do (98.9 nm) and 2p4 3P–3s'' 3Po (87.8 nm) transitions of atomic oxygen. Measurements were made using a magnetically confined electron beam in collision with atomic oxygen produced by an extended microwave discharge source in a crossed-beam arrangement. A 0.2 m vacuum ultraviolet diffraction spectrometer was used to record the emission. The absolute excitation functions of these transitions were determined by normalizing to the O I (130.4 nm) cross section produced by dissociative excitation of O2 at 100 eV impact energy (Noren et al 2001a Geophys. Res. Lett. 28 1379). A 60-state model of the O I electron reaction structure has been used to extract the excitation cross sections from the experimental measurements. The model process establishes analytic collision strengths to the asymptotic limit.

Using energy loss spectroscopy, normalized differential and integral cross-sections for the electron impact excitation of the lowest bound excited states of H2 from the ground X 1Σg+ state have been measured at 17.5, 20 and 30 eV impact energies and for scattering angles from 5° up to 130°. These differential cross-sections (DCSs) are an effort to improve those taken previously (Khakoo M A and Trajmar S 1986b Phys. Rev. A 34 146). Here a more sophisticated electron spectrometer and a more accurate spectrum analysis code is used to unfold the energy loss spectra. The results are compared with earlier DCS measurements for the B 1Σu+, c 3Πu, a 3Σg+, C 1Πu states of H2 and with existing theoretical results for the B 1Σu+, c 3Πu, a 3Σg+, C 1Πu, E, F 1Σg+ and e 3Σu+ states.

This investigation is a continuation of our previous work on the feasibility of utilizing ultra-high resolution electrospray ionization/ion mobility spectrometry (ESI/IMS) for in situ analysis of biomolecular compounds. The compounds we studied, in this investigation, were glycine, the smallest amino acid and four of its oligomers, namely triglycine, tetraglycine, pentaglycine, and hexaglycine. Experimental effects of drift-gas polarizability on target ions in IMS were explored by utilizing four different drift-gases with differing polarizability values (He, Ar, N 2, and CO2). The gas-phase ion radii for all five compounds were calculated from the reduced ion mobilities, K m 0 , and the effective drift-gas radii employing a simple hard-sphere model. When ion radii were plotted against the polarizabilities of the drift-gases, linear plots with different slopes were produced. This empirical observation indicated that the polarizing of drift-gas can change the calculated ion radii in a linear fashion over a limited range of polarizability values and does not affect all ions equally. This effect can be exploited in order to alter the separation factors between different ions since all ions that yield different slopes can, theoretically, be separated with IMS using different drift-gases. We demonstrated that the separation factor ( α) is highly dependent on the drift-gas. The maximum separability and, hence, unique identification of target ions was achieved when He and CO 2 were used. (Int J Mass Spectrom 216 (2002) 257–268) © 2002 Published by Elsevier Science B.V.

In this paper, we discuss how prebiotic geo-electrochemical systems can be modeled as a fuel cell and how laboratory simulations of the origin of life in general can benefit from this systems-led approach. As a specific example, the components of what we have termed the "prebiotic fuel cell" (PFC) that operates at a putative Hadean hydrothermal vent are detailed, and we used electrochemical analysis techniques and proton exchange membrane (PEM) fuel cell components to test the properties of this PFC and other geo-electrochemical systems, the results of which are reported here. The modular nature of fuel cells makes them ideal for creating geo-electrochemical reactors with which to simulate hydrothermal systems on wet rocky planets and characterize the energetic properties of the seafloor/hydrothermal interface. That electrochemical techniques should be applied to simulating the origin of life follows from the recognition of the fuel cell-like properties of prebiotic chemical systems and the earliest metabolisms. Conducting this type of laboratory simulation of the emergence of bioenergetics will not only be informative in the context of the origin of life on Earth but may help in understanding whether life might emerge in similar environments on other worlds.

We report absolute differential electron scattering cross sections (DCSs) of molecular oxygen (O2) at 20, 30, 50 and 100 eV impact energies (E0). DCSs were measured for inelastic features in the 6.5-12.5 energy-loss range including the Schumann-Runge (SR) continuum, the longest band (LB) and the second band (2B) along with the summed DCS for the third band (3B) plus the 10.76 and 11.03 eV energy-loss features. Measurements were performed at scattering angles of 0°, 5°, 10°, 15°, 20° and 25° using a conventional electrostatic electron energy-loss spectrometer. Inelastic electron energy-loss spectra of O2 were measured giving relative inelastic DCSs, which were then normalized via the relative flow technique using inelastic He and Ne transitions as standards. Past works (Trajmar et al 1972, Shyn et al 1994) have shown good relative agreement while displaying significant discrepancies in absolute terms. The current normalization technique represents an improvement over those employed in previous inelastic O2 DCS work. As such, the present results serve to firmly establish the absolute normalization of these DCSs. Furthermore, the current results are able to provide an additional test of the relative angular distributions of previous works throughout the important low-angle region where the DCSs undergo the most rapid change. This paper also represents the first measurements of inelastic O2 DCSs to extend right down to the forward-scattering limit.

We report both experimental and theoretical differential and integral excitation cross sections of atomic oxygen corresponding to the 2s22p4 3P→3s 3S (130.4 nm), 2s22p4 3P→3d 3D (102.7 nm), 2s22p4 3P→3s' 3D (98.9 nm) and 2s22p4 3P→3s'' 3P (87.8 nm) transitions at 30, 50, and 100 eV electron-impact energies. Experimental measurements have been made in the angular range from 0° to 25° with a conventional electrostatic electron energy-loss spectrometer. The atomic O differential cross sections (DCSs) were put on an absolute scale by normalization to the O2 DCS values of Johnson and Kanik (2001). Extrapolation of the measured results to larger angles was performed using theoretical calculations as a guide, and integral cross sections were derived. Theoretical calculations based on the R-matrix method, along with other available experimental data, have been compared with the current experimental results.

The optical excitation function of the O I 3So→ 3P transition (130.4 nm), produced by electron-impact excitation of atomic oxygen, has been measured over an extended energy range from threshold to 1.0 keV. Measurements were obtained in a crossed-beam experiment using both magnetically confined and electrostatically focused electrons in collision with atomic oxygen produced by a microwave discharge source. A 0.2 m vacuum ultraviolet monochromator system was used to measure the emitted O I radiation at 130.4 nm. The relative O I (130.4 nm) emission intensity corresponding to the 3So→ 3P transition was then put on the absolute scale by normalization to the O I (130.4 nm) cross section produced by dissociative excitation of O2 at 30 eV (Kanik et al 2000).

Electron-impact-induced emission spectra of Xe corresponding to the resonance transitions in the FUV spectral region from 114-165 nm at 15, 20 and 30 eV impact energies are reported. Absolute emission cross sections corresponding to the Xe I spectral features at 15, 20 and 30 eV impact energies and optical excitation functions for the two most prominent transitions at 119.2 and 147.0 nm in the 0-100 eV energy range were measured. In addition, the integral cross sections for direct electron-impact excitation of the corresponding levels in Xe, obtained by integration of the differential cross section measurements of Khakoo et al (Khakoo M A et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 3455, Khakoo M A et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 3477) are compared with the present results and the theoretical calculations of Csanak (Csanak G 1996 Private communication). A comparison of the measured emission and integrated direct excitation cross sections is made leading to indirect estimation of the cascade contributions to the emission cross sections.

In this Letter, we report for the first time, the ratio of the O I (135.6 nm)/O I (130.4 nm) absolute emission cross sections from electron-impact dissociative excitation of O-2 at 100 eV using facilities located at the University of Colorado, Laboratory for Atmospheric and Space Physics (LASP).

This paper is the second part of two back-to-back papers concerning electron-impact excitation of Kr. This part concerns excitation of the individual levels that constitute the 4p55p, 4p54d and 4p56s configurations of Kr, at incident electron energies (E0) of 20.0 and 15.0 eV, for scattering angles (θ) ranging from 10° to 130°. As in part I, excitation cross sections are measured and calculated using the R-matrix (RM) and the unitarized first-order many-body theory (UFOMBT) methods. Comparisons between the present experimental and theoretical results, and also with other experimental results, are presented.

The UV line intensities appearing in the spectra of terrestrial auroral and airglow observational data by rockets and high altitude satellites contain important diagnostic information on energy input taking place into the thermosphere. The intensities of the observed emissions are dependent on the atomic and molecular cross sections for both electrons and photons. UV extinction weakens the emission intensity along the line-of-sight to the spacecraft and is determined by the absorption cross sections of the principal constituents: O 2 , N 2 □ and O. An accurate knowledge of both excitation (emission) and photoabsorption cross sections of the dominant atmospheric molecular gases (O 2 and N 2 ) is needed for the analysis and interpretation of rocket and satellite observations of airglow and auroral emissions. The absorption cross sections of O 2 and N 2 are difficult to measure since they are highly structured in the UV from predissociation of Rydberg and valence states. The aim of this article is to focus upon certain outstanding issues concerning the available experimental excitation (emission) and photoabsorption cross section data primarily in the far UV (FUV) spectral region. These cross sections are important to terrestrial airglow and auroral observations of N 2 and O UV emission fluorescence and to critically review the available data.

We report an experimental and theoretical investigation of low-energy electron scattering from 138Ba atoms prepared in the metastable 3D2 and 1D2 levels by laser-optical pumping. Differential cross sections were measured for excitation out of these metastable levels to a variety of higher-lying levels at electron-impact energies of 10, 20 and 36.7 eV. A comparison of experimental data with the results of theoretical approaches using the unitarized distorted-wave approximation and the convergent close-coupling scheme is given.