Preservation of glycine coordination compounds under a gamma radiation dose representative of natural mars radioactivity

The Martian subsurface is more favorable for organic preservation than its surface because of the shielding effect of rocks from cosmic rays and UV radiation with increasing depth. Nevertheless, the natural radioactivity on Mars owing to U, Th, and K must be considered to study the possible extant and/or extinct life. Here, we demonstrate the importance of natural radiation on the amino acid glycine in two different chemical environments, GlyFeSO4 5H2O and GlyMgSO4 5H2O, which are coordination compounds considered relevant to Mars. The results show that after a 600 kGy dose of gamma radiation, glycine was more stable when it bonded to Mg in the GlyMgSO4 5H2O coordination compound, it was less stable when it bonded to Fe in the GlyFeSO4 5H2O compound. Studies on the effects of gamma radiation on preservation of organic molecules bound to minerals and other potential compounds on Mars are significantly important in the search for biosignatures.

Investigating the biological potential of galactic cosmic ray-induced radiation-driven chemical disequilibrium in the Martian subsurface environment

There is growing evidence suggesting the presence of aqueous environment on ancient Mars, raising the question of the possibility of life in such an environment. Subsequently, with the erosion of the Martian atmosphere resulting in drastic changes in its climate, surface water disappeared, shrinking habitable spaces on the planet, with only a limited amount of water remaining near the surface in form of brines and water-ice deposits. Life, if it ever existed, would have had to adapt to harsh modern conditions, which includes low temperatures and surface pressure, and high radiation dose. Presently, there is no evidence of any biological activity on the planet's surface, however, the subsurface environment, which is yet to be explored, is less harsh, has traces of water in form of water-ice and brines, and undergoes radiation-driven redox chemistry. I hypothesize that Galactic Cosmic Ray (GCR)-induced radiation-driven chemical disequilibrium can be used for metabolic energy by extant life, and host organisms using mechanisms seen in similar chemical and radiation environments on Earth. I propose a GCR-induced radiolytic zone, and discuss the prospects of finding such life with Rosalind Franklin rover of the ExoMars mission.

Micro-/Nanostructured Interface for Liquid Manipulation and Its Applications

Understanding the relationship between liquid manipulation and micro-/nanostructured interfaces has gained much attention due to the wide potential applications in many fields, such as chemical and biomedical assays, environmental protection, industry, and even daily life. Much work has been done to construct various materials with interfacial liquid manipulation abilities, leading to a range of interesting applications. Herein, different fabrication methods from the top-down approach to the bottom-up approach and subsequent surface modifications of micro-/nanostructured interfaces are first introduced. Then, interactions between the surface and liquid, including liquid wetting, liquid transportation, and a number of corresponding models, together with the definition of hydrophilic/hydrophobic, oleophilic/olephobic, the definition and mechanism of superwetting, including superhydrophobicity, superhydrophilicity, and superoleophobicity, are presented. The micro-/nanostructured interface, with major applications in self-cleaning, antifogging, anti-icing, anticorrosion, drag-reduction, oil-water separation, water collection, droplet (micro)array, and surface-directed liquid transport, is summarized, and the mechanisms underlying each application are discussed. Finally, the remaining challenges and future perspectives in this area are included.

Colonization of Snow by Microorganisms as Revealed Using Miniature Raman Spectrometers-Possibilities for Detecting Carotenoids of Psychrophiles on Mars?

We tested the potential of a miniaturized Raman spectrometer for use in field detection of snow algae pigments. A miniature Raman spectrometer, equipped with an excitation laser at 532 nm, allowed for the detection of carotenoids in cells of Chloromonas nivalis and Chlamydomonas nivalis at different stages of their life cycle. Astaxanthin, the major photoprotective pigment, was detected in algal blooms originating in snows at two alpine European sites that differed in altitude (Krkonoše Mts., Czech Republic, 1502 m a.s.l., and Ötztal Alps, Austria, 2790 m a.s.l.). Comparison is made with a common microalga exclusively producing astaxanthin (Haematococcus pluvialis). The handheld Raman spectrometer is a useful tool for fast and direct field estimations of the presence of carotenoids (mainly astaxanthin) within blooms of snow algae. Application of miniature Raman instruments as well as flight prototypes in areas where microbes are surviving under extreme conditions is an important stage in preparation for successful deployment of this kind of instrumentation in the framework of forthcoming astrobiological missions to Mars. Key Words: Snow algae-Chloromonas nivalis-Chlamydomonas nivalis-On-site field detection-Raman spectroscopy-Astaxanthin. Astrobiology 16, 913-924.

Biogeological Analysis of Desert Varnish Using Portable Raman Spectrometers

Desert varnishes are thin, dark mineral coatings found on some rocks in arid or semi-arid environments on Earth. Microorganisms may play an active role in their formation, which takes many hundreds of years. Their mineral matrix may facilitate the preservation of organic matter and is therefore of great relevance to martian exploration. Miniaturized Raman spectrometers (which allow nondestructive analysis of the molecular composition of a specimen) will equip rovers in forthcoming planetary exploration missions. In that context, and for the first time, portable Raman spectrometers operating in the green visible (532 nm as currently baselined for flight) and in the near-infrared (785 nm) were used in this study to investigate the composition (and substrate) of several samples of desert varnish. Rock samples that were suspected (and later confirmed) to be coated with desert varnish were recovered from two sites in the Mojave Desert, USA. The portable spectrometers were operated in flight-representative acquisition modes to identify the key molecular components of the varnish. The results demonstrate that the coatings typically comprise silicate minerals such as quartz, plagioclase feldspars, clays, ferric oxides, and hydroxides and that successful characterization of the samples can be achieved by using flightlike portable spectrometers for both the 532 and 785 nm excitation sources. In the context of searching for spectral signatures and identifying molecules that indicate the presence of extant and/or extinct life, we also report the detection of β-carotene in some of the samples. Analysis complications caused by the presence of rare earth element photoluminescence (which overlaps with and overwhelms the organic Raman signal when a 785 nm laser is employed) are also discussed.

Biomarkers and their Raman spectroscopic signatures: a spectral challenge for analytical astrobiology

The remote robotic exploration of extraterrestrial scenarios for evidence of biological colonization in 'search for life' missions using Raman spectroscopy is critically dependent on two major factors: firstly, the Raman spectral recognition of characteristic biochemical spectral signatures in the presence of mineral matrix features; and secondly, the positive unambiguous identification of molecular biomaterials which are indicative of extinct or extant life. Both of these factors are considered here: the most important criterion is the clear definition of which biochemicals truly represent biomarkers, whose presence in the planetary geological record from an analytical astrobiological standpoint will unambiguously be indicative of life as recognized from its remote instrumental interrogation. Also discussed in this paper are chemical compounds which are associated with living systems, including biominerals, which may not in themselves be definitive signatures of life processes and origins but whose presence provides an indicator of potential life-bearing matrices.

Man and his spaceships: Vehicles for extraterrestrial colonization?

The resiliency and adaptive ability of microbial life in real time on Earth relies heavily upon horizontal gene transfer. Based on that knowledge, how likely is earth based microbial life to colonize extraterrestrial targets such as Mars? To address this question, we consider manned and unmanned space exploration, the resident microbiota that is likely to inhabit those vehicles, the adaptive potential of that microbiota in an extraterrestrial setting especially with regards to mobile genetic elements, and the likelihood that Mars like environments could initiate and sustain colonization.

Microbial stowaways: inimitable survivors or hopeless pioneers?

The resiliency of prokaryotic life has provided colonization across the globe and in the recesses of Earth's most extreme environments. Horizontal gene transfer provides access to a global bank of genetic resources that creates diversity and allows real-time adaptive potential to the clonal prokaryotic world. We assess the likelihood that this Earth-based strategy could provide survival and adaptive potential, in the case of microbial stowaways off Earth.

Bacterial growth at the high concentrations of magnesium sulfate found in martian soils

The martian surface environment exhibits extremes of salinity, temperature, desiccation, and radiation that would make it difficult for terrestrial microbes to survive. Recent evidence suggests that martian soils contain high concentrations of MgSO₄ minerals. Through warming of the soils, meltwater derived from subterranean ice-rich regolith may exist for an extended period of time and thus allow the propagation of terrestrial microbes and create significant bioburden at the near surface of Mars. The current report demonstrates that halotolerant bacteria from the Great Salt Plains (GSP) of Oklahoma are capable of growing at high concentrations of MgSO₄ in the form of 2 M solutions of epsomite. The epsotolerance of isolates in the GSP bacterial collection was determined, with 35% growing at 2 M MgSO₄. There was a complex physiological response to mixtures of MgSO₄ and NaCl coupled with other environmental stressors. Growth also was measured at 1 M concentrations of other magnesium and sulfate salts. The complex responses may be partially explained by the pattern of chaotropicity observed for high-salt solutions as measured by agar gelation temperature. Select isolates could grow at the high salt concentrations and low temperatures found on Mars. Survival during repetitive freeze-thaw or drying-rewetting cycles was used as other measures of potential success on the martian surface. Our results indicate that terrestrial microbes might survive under the high-salt, low-temperature, anaerobic conditions on Mars and present significant potential for forward contamination. Stringent planetary protection requirements are needed for future life-detection missions to Mars.

Astrobiological considerations for the selection of the geological filters on the ExoMars PanCam instrument

The Panoramic Camera (PanCam) instrument will provide visible-near IR multispectral imaging of the ExoMars rover's surroundings to identify regions of interest within the nearby terrain. This multispectral capability is dependant upon the 12 preselected "geological" filters that are integrated into two wide-angle cameras. First devised by the Imager for Mars Pathfinder team to detect iron oxides, this baseline filter set has remained largely unchanged for subsequent missions (Mars Exploration Rovers, Beagle 2, Phoenix) despite the advancing knowledge of the mineralogical diversity on Mars. Therefore, the geological filters for the ExoMars PanCam will be redesigned to accommodate the astrobiology focus of ExoMars, where hydrated mineral terrains (evidence of past liquid water) will be priority targets. Here, we conduct an initial investigation into new filter wavelengths for the ExoMars PanCam and present results from tests performed on Mars analog rocks. Two new filter sets were devised: one with filters spaced every 50 nm ("F1-12") and another that utilizes a novel filter selection method based upon hydrated mineral reflectance spectra ("F2-12"). These new filter sets, along with the Beagle 2 filter set (currently the baseline for the ExoMars PanCam), were tested on their ability to identify hydrated minerals and biosignatures present in Mars analog rocks. The filter sets, with varying degrees of ability, detected the spectral features of minerals jarosite, opaline silica, alunite, nontronite, and siderite present in these rock samples. None of the filter sets, however, were able to detect fossilized biomat structures and small (<2 mm) mineralogical heterogeneities present in silica sinters. Both new filter sets outperformed the Beagle 2 filters, with F2-12 detecting the most spectral features produced by hydrated minerals and providing the best discrimination between samples. Future work involving more extensive testing on Mars analog samples that exhibit a wider range of mineralogies would be the next step in carefully evaluating the new filter sets.

The Rio Tinto Mars analogue site: an extremophilic Raman spectroscopic study

The Rio Tinto site is recognised as a terrestrial Mars analogue because of the presence of jarosite and related sulfates which have recently been identified by the NASA Mars Exploration Rover "Opportunity" in the El Capitan region of Meridiani Planum on Mars. It has long been known that acidophilic microbial action is responsible for the deep blood-red colour of the water in Rio Tinto, where the pH varies from about 1.5 to 3.0 and the water is rich in iron and sulfur. Following recent Raman spectroscopic characterisation of the mineral phases of the Rio Tinto system, we report here a study of the biological components found in several specimens of deposited minerals and near the waterside that were collected during a GeoRaman VI Conference organized field trip in 2006. Key biosignatures were found for carotenoids, scytonemin and mycosporine-like amino acids, which are indicative of the biological colonisation of exposed mineral substrates; information from this study will be useful for targeting Martian sites using a miniaturized Raman instrument where the biosignatures of relict or extant life could remain in the geological record.

Raman and SEM analysis of a biocolonised hot spring travertine terrace in Svalbard, Norway

BACKGROUND

A profile across 8 layers from a fossil travertine terrace from a low temperature geothermal spring located in Svalbard, Norway has been studied using both Raman spectroscopy and SEM (Scanning Electron Microscopy) techniques to identify minerals and organic life signals.

RESULTS

Calcite, anatase, quartz, haematite, magnetite and graphite as well as scytonemin, three different carotenoids, chlorophyll and a chlorophyll-like compound were identified as geo- and biosignatures respectively, using 785 and/or 514 nm Raman laser excitation wavelengths. No morphological biosignatures representing remnant microbial signals were detected by high-resolution imaging, although spectral analyses indicated the presence of organics. In contrast, in all layers, Raman spectra identified a series of different organic pigments indicating little to no degradation or change of the organic signatures and thus indicating the preservation of fossil biomarker compounds throughout the life time of the springs despite the lack of remnant morphological indicators.

CONCLUSION

With a view towards planetary exploration we discuss the implications of the differences in Raman band intensities observed when spectra were collected with the different laser excitations. We show that these differences, as well as the different detection capability of the 785 and 514 nm laser, could lead to ambiguous compound identification. We show that the identification of bio and geosignatures, as well as fossil organic pigments, using Raman spectroscopy is possible. These results are relevant since both lasers have been considered for miniaturized Raman spectrometers for planetary exploration.

Comparative evaluation of Raman spectroscopy at different wavelengths for extremophile exemplars

Raman spectra have been obtained for extremophiles from several geological environments; selected examples have been taken from hot and cold deserts comprising psychrophiles, thermophiles and halophiles. The purpose of this study is the assessment of the effect of the wavelength of the laser excitation on the ability to determine unique information from the Raman spectra about the specificity of detection of biomolecules produced as a result of the survival strategies adopted by organisms in extreme terrestrial environments. It was concluded that whereas FT-Raman spectroscopy at 1064 nm gave good quality results the time required to record the data was relatively large compared with other wavelengths of excitation but that better access to the CH stretching region for organic molecules was given. Shorter wavelength excitation of biomolecules in the blue-green regions of the visible spectrum using a conventional dispersive spectrometer was more rapid but very dependent upon the type of chemical compound being studied; most relevant biomolecules fluoresced at these wavelengths but carotenoids exhibited a resonance effect which resulted in an improved detection capability. Minerals and geological materials, in contrast, were best studied at these visible wavelengths. In general, the best compromise system for the excitation of the Raman spectra of both geological and biological materials was provided using a 785 nm laser coupled with a dispersive spectrometer, especially for accessing the 1800-200 cm(-1) wavenumber shift region where much of the definitive analytical information resides. This work will have conclusions relevant to the use of miniaturised Raman spectrometers for the detection of biomolecules in extraterrestrial planetary exploration.

Raman spectroscopy in astrobiology

Raman spectroscopy is proposed as a valuable analytical technique for planetary exploration because it is sensitive to organic and inorganic compounds and able to unambiguously identify key spectral markers in a mixture of biological and geological components; furthermore, sample manipulation is not required and any size of sample can be studied without chemical or mechanical pretreatment. NASA and ESA are considering the adoption of miniaturised Raman spectrometers for inclusion in suites of analytical instrumentation to be placed on robotic landers on Mars in the near future to search for extinct or extant life signals. In this paper we review the advantages and limitations of Raman spectroscopy for the analysis of complex specimens with relevance to the detection of bio- and geomarkers in extremophilic organisms which are considered to be terrestrial analogues of possible extraterrestial life that could have developed on planetary surfaces.

The biological terraforming of Mars: planetary ecosynthesis as ecological succession on a global scale

Mars is bitterly cold and dry, but robotic spacecraft have returned abundant data that indicate Mars once had a much warmer and wetter climate in the past. These data, the basis of the search for past or present life on Mars, suggest the possibility of returning Mars to its previous climate by global engineering techniques. Greenhouse gases, such as perfluorocarbons, appear to be the best method for warming Mars and increasing its atmospheric density so that liquid water becomes stable. The process of making Mars habitable for terrestrial organisms is called terraforming or planetary ecosynthesis. The process of introducing terrestrial ecosystems to Mars can be compared with a descent down a high mountain. Each drop in elevation results in a warmer, wetter climate and more diverse biological community. Beginning with a polar desert, the sequence of ecosystems passes through tundra, boreal forest, and temperate ecosystems where moisture determines the presence of desert, grassland, or forest. This model suggests a sequence for the introduction of ecosystems to Mars and the communities to search for potential colonizing species for Mars.

Why Raman spectroscopy on Mars?--a case of the right tool for the right job

We provide a scientific rationale for the astrobiological investigation of Mars. We suggest that, given practical constraints, the most promising locations for the search for former life on Mars are palaeolake craters and the evaporite deposits that may reside within them. We suggest that Raman spectroscopy offers a promising tool for the detection of evidence of former (or extant) biota on Mars. In particular, we highlight the detection of hopanoids as long-lived bacterial cell wall products and photosynthetic pigments as the most promising targets. We further suggest that Raman spectroscopy as a fibre optic-based instrument lends itself to flexible planetary deployment.

Fluid inclusion studies of chemosynthetic carbonates: strategy for seeking life on Mars

Fluid inclusions in minerals hold the potential to provide important data on the chemistry of the ambient fluids during mineral precipitation. Especially interesting to astrobiologists are inclusions in low-temperature minerals that may have been precipitated in the presence of microorganisms. We demonstrate that it is possible to obtain data from inclusions in chemosynthetic carbonates that precipitated by the oxidation of organic carbon around methane-bearing seepages. Chemosynthetic carbonates have been identified as a target rock for astrobiological exploration. Other surficial rock types identified as targets for astrobiological exploration include hydrothermal deposits, speleothems, stromatolites, tufas, and evaporites, each of which can contain fluid inclusions. Fracture systems below impact craters would also contain precipitates of minerals with fluid inclusions. As fluid inclusions are sealed microchambers, they preserve fluids in regions where water is now absent, such as regions of the martian surface. Although most inclusions are < 5 microns, the possibility to obtain data from the fluids, including biosignatures and physical remains of life, underscores the advantages of technological advances in the study of fluid inclusions. The crushing of bulk samples could release inclusion waters for analysis, which could be undertaken in situ on Mars.

Astrobiology: exploring the origins, evolution, and distribution of life in the Universe

The search for the origins of life and its presence beyond Earth is strengthened by new technology and by evidence that life tolerates extreme conditions and that planets are widespread. Astrobiologists learn how planets develop and maintain habitable conditions. They combine biological and information sciences to decipher the origins of life. They examine how biota, particularly microorganisms, evolve, at scales from the molecular to the biosphere level, including interactions with long-term planetary changes. Astrobiologists learn how to recognize the morphological, chemical, and spectroscopic signatures of life in order to explore both extraterrestrial samples and electromagnetic spectra reflected from extrasolar planets.

The physics, biology, and environmental ethics of making mars habitable

The considerable evidence that Mars once had a wetter, more clement, environment motivates the search for past or present life on that planet. This evidence also suggests the possibility of restoring habitable conditions on Mars. While the total amounts of the key molecules--carbon dioxide, water, and nitrogen--needed for creating a biosphere on Mars are unknown, estimates suggest that there may be enough in the subsurface. Super greenhouse gases, in particular, perfluorocarbons, are currently the most effective and practical way to warm Mars and thicken its atmosphere so that liquid water is stable on the surface. This process could take approximately 100 years. If enough carbon dioxide is frozen in the South Polar Cap and absorbed in the regolith, the resulting thick and warm carbon dioxide atmosphere could support many types of microorganisms, plants, and invertebrates. If a planet-wide martian biosphere converted carbon dioxide into oxygen with an average efficiency equal to that for Earth's biosphere, it would take > 100,000 years to create Earth-like oxygen levels. Ethical issues associated with bringing life to Mars center on the possibility of indigenous martian life and the relative value of a planet with or without a global biosphere.

Exploring for a record of ancient Martian life

The immediate task facing exopaleontology is to define a strategy to explore Mars for a fossil record during the decade-long exploration program that lies ahead. Consideration of the quality of paleontological information preserved under different geological conditions is important if we are to develop a strategy with broad applicability. The preservation of microbial fossils is strongly influenced by the physical, chemical, and biological factors of the environment which, acting together, determine the types of information that will be captured and retained in the rock record. In detrital sedimentary systems, preservation is favored by rapid burial in fine-grained, clay-rich sediments. In chemical sedimentary systems, preservation is enhanced by rapid entombment in fine-grained chemical precipitates. For long-term preservation, host rocks must be composed of stable minerals that are resistant to chemical weathering and that form an impermeable matrix and closed chemical system to protect biosignatures from alteration during subsequent diagenesis or metamorphism. In this context, host rocks composed of highly ordered, chemically stable mineral phases, like silica (e.g., cherts) or phosphate (e.g., phosphorites), are especially favored. Such lithologies tend to have very long crustal residence times and, along with carbonates and shales, are the most common host rocks for the Precambrian microfossil record on Earth. Although we make the defensible assumption that Mars was more like the Earth early in its history, clearly, the geological and historical differences between the two planets are many. Such differences must be carefully considered when adapting an Earth-based strategy to Mars.