Search For Traces Of Life Research Articles

Sensitive and accurate determination of nitrogen in simulated Martian soil and environment with LIBS spectrum fusion and regression based on neural network

Nitrogen is a key element necessary for the emergence and development of life. It is one of the elements targeted by the landed missions on Mars in accordance with their scientific goal of investigation of habitability and search for traces of life. A gas chromatography mass spectrometer (GCMS) instrument on board the Mars Science Laboratory Curiosity rover has revealed the existence of oxidized nitrogen-bearing compounds on Martian surface with an equivalent nitrogen concentration up to 0.01 wt%. Although the detection with laser-induced breakdown spectroscopy (LIBS) also on board the Curiosity rover is desirable, the current performance of LIBS for nitrogen analysis does not show the capacity in terms of limit of detection (LOD) and accuracy. Research on a suitable method should therefore be first engaged in laboratory in order to guide further improvements of LIBS instrument on board Mars rover, as well as the data treatment method. Beyond the sensitivity issue, matrix effect also affects LIBS determination of nitrogen, especially due to its various chemical speciation in geological materials. Method research should answer thus double requirements of improving the sensitivity and reinforcing the robustness with respect to different nitrogen-bearing compounds. An experimental configuration of double detections with a narrow bandwidth Czerny-Tuner (CT) spectrometer and a broad bandwidth Echelle spectrometer, was implemented in this work, in such way that the first ensured a sensitive detection of emission lines from nitrogen and the second complemented with those from major elements in the sample. The fusion of the simultaneously acquired spectra took into account the emission characteristics of the both two types of elements, necessary for an effective and robust multivariate regression based on a neural network. In addition, for a better treatment of different chemical speciation of nitrogen in samples, generalized spectrum was used for training of regression models, after an unsupervised clustering having assigned a type label to each training spectrum. The trained model was tested by collections of independent test samples, resulting in a limit of detection (LOD) of 0.18 wt%, and a root mean square error of prediction (RMSEP) of 0.041 wt%, representing a step forward to nitrogen detection using LIBS on Mars.

MOSCOW INTERNATIONAL SYMPOSIA ON SOLAR SYSTEM RESEARCH (10M-S3 AND 11M-S3) REPORTS REVIEW. Part 1. Mars exploration

A review of the reports of the last two Moscow International Symposia on Solar System Research has been completed. In the first part of the review, 43 reports of the main session of the "Mars" section are considered. The works of leading experts in the field of planetary science cover a wide range of scientific and applied problems - from the study of the geological history and climate of Mars, the search for traces of life and subsurface water reserves, to new technologies in planetary research, mission planning, as well as monitoring solar activity and radiation conditions in the interplanetary space, orbit and the surface of Mars. The data obtained in the last two decades has made it possible to significantly advance in understanding the nature of Mars, but many unresolved questions remain regarding the climate in the early era, the existence of the Martian oceans in the past, biological and geological activity. The scientific results obtained by unmanned spacecraft should be fully taken into account in the development of manned deep space exploration programs. Key words: Solar system, planetology, international symposium, deep space, automatic interplanetary stations, Mars, Moon, reports review

Actinobacteria-mediated serpentine dissolution and implication for biosignatures on Mars

The search for traces of life is one of the principal objectives of Mars exploration. The global distribution of minerals associated with serpentinization in the Noachian terrains on Mars likely suggest that serpentinization commonly occurred early in the planets history. A consensus is that these reactions involved in the serpentinization may have provided the initial material and energy for the origin and early evolution of life on Earth. Comparably, the serpentine regions of Mars are potential target sites for the detection of the putative life on Mars. Herein, an actinobacterial species Streptomyces spp. FXJ8.102 is used as a model microbe to investigate the microbe-mediated dissolution of antigorite in liquid culture. The experimental results show that the strain can couple biomechanical and biochemical mechanisms in the serpentine dissolution, leading to the development of “cell-sized” and “cell-shaped” eroded pits/channels on the mineral surfaces, and the low Mg/Si ratios on the eroded sites. In addition, the cells can also induce the formation of secondary glushinskite during the dissolution process. By contrast, no distinguishable surface change on antigorite and secondary mineral formation can be observed in the control experiments without inoculation. Therefore, a collection of the features including the distinctive eroded texture and composition on serpentine surfaces, and the special mineral assemblage including the formation of secondary oxalate minerals may serve as a compelling biosignature for the search of life on Mars.

Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover.

The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures—ExoMars—Landing sites—Mars rover—Search for life. Astrobiology 17, 471–510.

Biosignatures on Mars: What, Where, and How? Implications for the Search for Martian Life.

The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is the concept of habitability, the set of conditions that allows the appearance of life and successful establishment of microorganisms in any one location. While environmental conditions may have been conducive to the appearance of life early in martian history, habitable conditions were always heterogeneous on a spatial scale and in a geological time frame. This “punctuated” scenario of habitability would have had important consequences for the evolution of martian life, as well as for the presence and preservation of traces of life at a specific landing site. We hypothesize that, given the lack of long-term, continuous habitability, if martian life developed, it was (and may still be) chemotrophic and anaerobic. Obtaining nutrition from the same kinds of sources as early terrestrial chemotrophic life and living in the same kinds of environments, the fossilized traces of the latter serve as useful proxies for understanding the potential distribution of martian chemotrophs and their fossilized traces. Thus, comparison with analog, anaerobic, volcanic terrestrial environments (Early Archean >3.5–3.33 Ga) shows that the fossil remains of chemotrophs in such environments were common, although sparsely distributed, except in the vicinity of hydrothermal activity where nutrients were readily available. Moreover, the traces of these kinds of microorganisms can be well preserved, provided that they are rapidly mineralized and that the sediments in which they occur are rapidly cemented. We evaluate the biogenicity of these signatures by comparing them to possible abiotic features. Finally, we discuss the implications of different scenarios for life on Mars for detection by in situ exploration, ranging from its non-appearance, through preserved traces of life, to the presence of living microorganisms. Key Words: Mars—Early Earth—Anaerobic chemotrophs—Biosignatures—Astrobiology missions to Mars. Astrobiology 15, 998–1029.

How Do Modern Extreme Hydrothermal Environments Inform the Identification of Martian Habitability? The Case of the El Tatio Geyser Field

Despite the success in knowledge gained by the Mars missions in the last two decades, the search for traces of life on Mars is still in progress. The reconstruction of (paleo-) environments on Mars have seen a dramatic increase, in particular with regard to the potentially habitable conditions, and it is now possible to recognize a significant role to subaerial hydrothermal processes. For this reason, and because the conditions of the primordial Earth—when these extreme environments had to be common—probably resembled Mars during its most suitable time to host life, research on terrestrial extreme hydrothermal habitats may assist in understanding how to recognize life on Mars. A number of geological and environmental reasons, and logistics opportunities, make the geothermal field of El Tatio, in the Chilean Andes an ideal location to study.

Use of miniaturized Raman spectrometer for detection of sulfates of different hydration states – Significance for Mars studies

The presence of sulfates of different hydration states, specifically magnesium sulfates, has been firmly established on Mars from data acquired by both orbital and in-situ measurements. A lander mission typically involves a variety of instruments capable of performing a wide range of experiments from mineralogical tasks to the search for traces of life. It is clear from ongoing research that Raman spectroscopy can cover all of these tasks, and it has already been decided that future mission to Mars will employ a miniature Raman spectrometer. In this paper we report and discuss the Raman spectra of various sulfate minerals, with an emphasis on the magnesium sulfates. These were acquired by a hand-held Raman instrument, using the presently uncommon 532nm excitation, the wavelength that is planned for the ESA lander mission. A sufficient quality of spectra were obtained with reasonably low spectral acquisition times, and the characteristic shift of the sulfate ν1 band in the MgSO4·n(H2O) minerals was confirmed. This was used for the unambiguous identification of magnesium sulfates of different hydration states. The present testing has confirmed the good performance of the handheld instrumentation for discrimination of structurally similar sulfates of relevance for Mars studies. This step has been proposed as the basis for subsequent testing of this instrumentation under Earth-based but Mars-analogous conditions, even using currently existing miniaturized Raman prototypes.

New insights into microbial adaptation to extreme saline environments

Extreme halophiles are microorganisms adapted to low water activity living at the upper salt concentration that life can tolerate. We review here recent data that specify the main factors, which determine their peculiar salt-dependent biochemistry. The data suggested that evolution proceeds by stage to modify the molecular dynamics properties of the entire proteome. Extreme halophiles therefore represent tractable models to understand how fast and to what extent microorganisms adapt to environmental changes. Halophiles are also robust organisms, capable to resist multiple stressors. Preliminary studies indicated that they have developed a cellular response specifically aimed to survive when the salt condition fluctuates. Because of these properties halophilic organisms deserve special attention in the search for traces of life on other planets.

Recrystallized microbial trace fossils from metamorphosed Permian basalt, southwestern Japan

Microbial trace fossils on terrestrial basalts can be used as an analogue in the search for traces of life on other terrestrial planets. This study reports on microbial trace fossils within Permian greenstones in the Maizuru Terrane, southwest Japan, which is recognized as back-arc basin oceanic crust that consists mainly of metabasalt and metagabbro. The trace fossils have been studied by means of morphology, mineralogy, elemental mapping, and carbon isotope analysis. Although minute original textures of trace fossils are recrystallized in these rocks, Granulohyalichnus vulgaris isp., Tubulohyalichnus spiralis isp., and Tubulohyalichnus annularis isp. were identified. Significant concentration of C within the trace fossils implies these are organic remnants from microbes. The δ13CPDB values <−7‰ of calcite within the greenstones indicates that the bacterial activity took place prior to the formation of calcite veins. The results support that microbial trace fossils within low-grade metamorphic basalt can be reliably identified based on their morphology and chemical composition, as reveled by elemental mapping. In this context, glassy Martian basalt may be the best rock type to investigate in terms of searching for signs of microbial activity on Earth and other planets.

From meteorites to evolution and habitability of planets

The evolution of planets is driven by the composition, structure, and thermal state of their internal core, mantle, lithosphere, and crust, and by interactions with a possible ocean and/or atmosphere. A planet’s history is a long chronology of events with possibly a sequence of apocalyptic events in which asteroids, comets and their meteorite offspring play an important role. Large meteorite impacts on the young Earth could have contributed to the conditions for life to appear, and similarly large meteorite impacts could also create the conditions to erase life or drastically decrease biodiversity on the surface of the planet. Meteorites also contain valuable information to understand the evolution of a planet through their gas inclusion, their composition, and their cosmogenic isotopes. This paper addresses the evolution of the terrestrial bodies of our Solar System, in particular through all phenomena related to meteorites and what we can learn from them. This includes our present understanding of planet formation, their interior, their atmosphere, and the effects and relations of meteorites with respect to these reservoirs. It brings further insight into the origin and sustainability of life on planets, including Earth. Particular attention is devoted to Earth and Mars, as well as to planets and satellites possessing an atmosphere (Earth, Mars, Venus, and Titan) or a subsurface ocean (e.g., Europa), because those are the best candidates for hosting life. Though the conditions on the planets Earth, Mars, and Venus were probably similar soon after their formation, their histories have diverged about 4 billion years ago. The search for traces of life on early Earth serves as a case study to refine techniques/environments allowing the detection of potential habitats and possible life on other planets. A strong emphasis is placed on impact processes, an obvious shaper of planetary evolution, and on meteorites that document early Solar System evolution and witness the geological processes taking place on other planetary bodies.

Gas chromatography–mass spectrometry of hexafluoroacetone derivatives: First time utilization of a gaseous phase derivatizing agent for analysis of extraterrestrial amino acids

Within the perspective of the current and next space missions to Mars (MSL 2011 and Exomars 2016–2018), the detection and enantioselective separation of building blocks such as the amino acids are important subjects which are becoming fundamental for the search for traces of life on the surface and subsurface of Mars. In this work, we have developed and optimized a method adapted to space experimentation to derivatize and analyze amino acids, using hexafluoroacetone as the derivatizing agent. The temperature, duration of the derivative transfer to the analyser, and chromatographic separation parameters have been optimized to meet the instrument design constraints imposed on devices for extraterrestrial experiments. The work presented in this rationale has established that hexafluoroacetone, in addition to its intrinsic qualities, such as the production of light-weight derivatives (no racemization) and great resistance to the drastic operating conditions, has indeed facilitated simple and fast derivatization that appears to be suitable for in situ analysis in space. By using hexafluoroacetone as the derivatizing agent, we successfully identified, 21 amino acids including 12 of the 20 proteinic amino acids without stirring or extraction steps. Ten of these derivatized amino acids were enantioselectively separated. The precision and accuracy measurements for the D/L ratio showed that the proposed method was also suitable for the determination of both enantioselective forms of most of the tested amino acids. The limits of detection obtained were lower than the ppb level of organic molecules detected in Martian meteorites.

The search for life on Earth and other planets

As the NASA rover Curiosity approaches Mars on its quest to look for signs of past or present life there and sophisticated instruments like the space telescopes Kepler and CoRoT keep discovering additional, more Earth-like planets orbiting distant stars, science faces the question of how to spot life on other planets. Even here on Earth biotopes remain to be discovered and explored.

Volcaniclastic habitats for early life on Earth and Mars: A case study from ∼3.5 Ga-old rocks from the Pilbara, Australia

Within the context of present and future in situ missions to Mars to investigate its habitability and to search for traces of life, we studied the habitability and traces of past life in ∼3.5 Ga-old volcanic sands deposited in littoral environments an analogue to Noachian environments on Mars. The environmental conditions on Noachian Mars (4.1–3.7 Ga) and the Early Archaean (4.0–3.3 Ga) Earth were, in many respects, similar: presence of liquid water, dense CO 2 atmosphere, availability of carbon and bio-essential elements, and availability of energy. For this reason, information contained in Early Archaean terrestrial rocks concerning habitable conditions (on a microbial scale) and traces of past life are of relevance in defining strategies to be used to identify past habitats and past life on Mars. One such example is the 3.446 Ga-old Kitty’s Gap Chert in the Pilbara Craton, NW. Australia. This formation consists of volcanic sediments deposited in a coastal mudflat environment and is thus a relevant analogue for sediments deposited in shallow water environments on Noachian Mars. Two main types of habitat are represented, a volcanic (lithic) habitat and planar stabilized sediment surfaces in sunlit shallow waters. The sediments hosted small (<1 μm in size) microorganisms that formed colonies on volcanic particle surfaces and in pore waters within the volcanic sediments, as well as biofilms on stabilised sediment surfaces. The microorganisms included coccoids, filaments and rare rod-shaped organisms associated with microbial polymer (EPS). The preserved microbial community was apparently dominated by chemotrophic organisms but some locally transported filaments and filamentous mat fragments indicate that possibly photosynthetic mats formed nearby. Both microorganisms and sediments were silicified during very early diagenesis. There are no macroscopic traces of fossilised life in these volcanic sediments and sophisticated instrumentation and specialized sample preparation techniques are required to establish the biogenicity and syngenicity of the traces of past life. The fact that the traces of life are cryptic, and the necessity of using sophisticated instrumentation, reinforces the challenges and difficulties of in situ robotic missions to identify past life on Mars. We therefore recommend the return of samples from Mars to Earth for a definitive search for traces of life.

Morphological Biosignatures in Early Terrestrial and Extraterrestrial Materials

Biosignatures in early terrestrial rocks are highly relevant in the search for traces of life on Mars because the early geological environments of the two planets were, in many respects, similar and, thus, the potential habitats for early life forms were similar. However, the identification and interpretation of biosignatures in ancient terrestrial rocks has proven contentious over the last few years. Recently, new investigations using very detailed field studies combined with highly sophisticated analytical techniques have begun to document a large range of biosignatures in Early Archaean rocks. Early life on Earth was diversified, widespread and relatively evolved, but its traces are generally, but not always, small and subtle. In this contribution I use a few examples of morphological biosignatures from the Early-Mid Archaean to demonstrate their variety in terms of size and type: macroscopic stromatolites from the 3.443 Ga Strelley Pool Chert, Pilbara; a meso-microscopic microbial mat from the 3.333 Ga Josefsdal Chert, Barberton; microscopic microbial colonies and a biofilm from the 3.446 Ga Kitty’s Gap Chert, Pilbara; and microscopic microbial corrosion pits in the glassy rinds of 3.22–3.48 Ga pillow lavas from Barberton. Some macroscopic and microscopic structures may be identifiable in an in situ robotic mission to Mars and in situ methods of organic molecule detection may be able to reveal organic traces of life. However, it is concluded that it will probably be necessary to return suitably chosen Martian rocks to Earth for the reliable identification of signs of life, since multiple observational and analytical methods will be necessary, especially if Martian life is significantly different from terrestrial life.

Living hell: Life at high temperatures

Modern hot environments, such as those found in hydrothermal vents, are of great interest to the scientific community because they resemble those ancient environments where life first arose on Earth and also share many characteristics with environments in other planets where life may have actually existed. Evidence to date strongly indicates that Fe(III) respiration may have been one of the first, if not the first, forms of respiration in a hot, early Earth. The abundance of Fe(III) minerals in many modern and ancient hot environments suggests that studies of Fe(III)-reducing hyperthermophilic micro-organisms are likely to be instrumental for our understanding of how life originated and evolved at high temperatures. The isolation and characterization of novel hyperthermophilic, Fe(III)-reducing micro-organisms has greatly increased our understanding of how microbes can live and thrive in such inhospitable environments. The study of these amazing microbes provides clues as to how life might have arisen on Earth and has implications for our search for traces of life in other planets.

The search for traces of life: the protective effect of salt on biological macromolecules.

Trapping malate dehydrogenase from the extremely halophilic archaeon Haloarcula marismortui in "dry" salt crystals protects the enzyme against thermal denaturation. Similar protection was not observed for the homologous mesophilic enzyme. In the case of transfer RNA molecules, high salt concentration plays a protective role against thermal degradation allowing activity to be recovered. The results are discussed in the context of exploring the fate of cell-free biological macromolecules in the environment and that of orienting the search for traces of life in planetary exploration.

Why biologists should support the exploration of Mars.

Physicists, chemists and geologists in the USA and Europe propose that the search for extraterrestrial life is an important justification for the exploration of Mars. Biologists, however, much more excited by the advent of the postgenome sequencing era, in general display little enthusiasm for planetary exploration. We argue that the search for traces of life on Mars represents a major thought-provoking challenge for the life sciences that should be taken up by the biological community.

Long-term preservation of microbial ecosystems in permafrost

It has been established that significant numbers (up to 10 million cells per gram of sample) of living microorganisms of various ecological and morphological groups have been preserved under permafrost conditions, at temperatures ranging from −9 to −13°C and depths of up to 100 m, for thousands and sometimes millions of years. Preserved since the formation of permafrost in sand-clay sediments of the Pliocene-Quaternary period and in paleosols and peats buried among them, these cells are the only living organisms that have survived for a geologically significant period of time. The complexity of the microbial community preserved varies with the age of the permafrost. Eukaryotes are found only in Holocene sediments; while prokaryotes are found to greater ages, i.e., Pliocene and Pleistocene. The diversity of microorganisms decreases with increasing age of sediments, and as a result cocci and corynebacteria are predominant. Enzyme activity (catalase and hydrolytic enzymes) and photosynthetic pigments (chlorophyll and pheophytin have also been detected in permafrost sediments. These results permit us to outline some approaches to the search for traces of life in the permafrost of Martian sediments by borehole core sampling. It is in the deep horizons (and not on the planet surface), isolated by permafrost from the external conditions, that results similar to those obtained on Earth can be expected.

The antarctic cold desert and the search for traces of life on Mars

The cryptoendolithic microorganisms that live inside rocks in the frigid Ross Desert of Antarctica can serve as a terrestrial model for what may have happened to life forms on Mars when the planet became dry and cold. Trace fossils of microbial rock colonization exist in Antarctica, and similar structures could ave formed on Mars. In some respects, such trace fossils could be an easier target for life-detection systems than fossils of cellular structures.