Survival and death of the haloarchaeon Natronorubrum strain HG-1 in a simulated martian environment

Halophilic archaea are of interest to astrobiology due to their survival capabilities in desiccated and high salt environments. The detection of remnants of salty pools on Mars stimulated investigations into the response of haloarchaea to martian conditions. Natronorubrum sp. strain HG-1 is an extremely halophilic archaeon with unusual metabolic pathways, growing on acetate and stimulated by tetrathionate. We exposed Natronorubrum strain HG-1 to ultraviolet (UV) radiation, similar to levels currently prevalent on Mars. In addition, the effects of low temperature (4, −20, and −80 °C), desiccation, and exposure to a Mars soil analogue from the Atacama desert on the viability of Natronorubrum strain HG-1 cultures were investigated. The results show that Natronorubrum strain HG-1 cannot survive for more than several hours when exposed to UV radiation equivalent to that at the martian equator. Even when protected from UV radiation, viability is impaired by a combination of desiccation and low temperature. Desiccating Natronorubrum strain HG-1 cells when mixed with a Mars soil analogue impaired growth of the culture to below the detection limit. Overall, we conclude that Natronorubrum strain HG-1 cannot survive the environment currently present on Mars. Since other halophilic microorganisms were reported to survive simulated martian conditions, our results imply that survival capabilities are not necessarily shared between phylogenetically related species.     

Searching for life on Mars: selection of molecular targets for ESA's aurora ExoMars mission

The European Space Agency's ExoMars mission will seek evidence of organic compounds of biological and non-biological origin at the martian surface. One of the instruments in the Pasteur payload may be a Life Marker Chip that utilizes an immunoassay approach to detect specific organic molecules or classes of molecules. Therefore, it is necessary to define and prioritize specific molecular targets for antibody development. Target compounds have been selected to represent meteoritic input, fossil organic matter, extant (living, recently dead) organic matter, and contamination. Once organic molecules are detected on Mars, further information is likely to derive from the detailed distribution of compounds rather than from single molecular identification. This will include concentration gradients beneath the surface and gradients from generic to specific compounds. The choice of biomarkers is informed by terrestrial biology but is wide ranging, and nonterrestrial biology may be evident from unexpected molecular distributions. One of the most important requirements is to sample where irradiation and oxidation are minimized, either by drilling or by using naturally excavated exposures. Analyzing regolith samples will allow for the search of both extant and fossil biomarkers, but sequential extraction would be required to optimize the analysis of each of these in turn.     

Fullerenes in space.

The discovery and synthesis of fullerenes led to the hypothesis that they may be present and stable in interstellar space. Fullerenes have been reported in an impact crater on the LDEF spacecraft. Investigations of fullerenes in carbonaceous meteorites have yielded only small upper limits. Fullerene compounds and their ions could be interesting carrier molecules for some of the "diffuse interstellar bands" (DIBs), a long standing mystery in astronomy. We have detected two new diffuse bands that are consistent with laboratory measurements of the C60+, as first evidence for the largest molecule ever detected in space. Criteria for this identification are discussed. The inferred abundance (up to 0.9 % of cosmic carbon locked in C60+) suggests that fullerenes may play an important role in interstellar chemistry. We present new observations on DIB substructures consistent with fullerene compounds, and the search for neutral C60 in the diffuse medium.     

Cubesats: Cost-effective science and technology platforms for emerging and developing nations

The development, operation, and analysis of data from cubesats can promote science education and spur technology utilization in emerging and developing nations. This platform offers uniquely low construction and launch costs together with a comparative ubiquity of launch providers; factors that have led more than 80 universities and several emerging nations to develop programs in this field. Their small size and weight enables cubesats to “piggyback” on rocket launches and accompany orbiters travelling to Moon and Mars. It is envisaged that constellations of cubesats will be used for larger science missions. We present a brief history, technology overview, and summary of applications in science and industry for these small satellites. Cubesat technical success stories are offered along with a summary of pitfalls and challenges encountered in both developed and emerging nations. A discussion of economic and public policy issues aims to facilitate the decision-making process for those considering utilization of this unique technology.     

An ISO View on Interstellar and Cometary Ice Chemistry

The ISO-SWS instrument offering a large wavelength coverage and a resolution well adapted to the solid phase has changed our knowledge of the physical-chemical properties of ices in space. The discovery of many new ice features was reported and the comparison with dedicated laboratory experiments allowed the determination of more accurate abundances of major ice components. The presence of CO₂ ice has recently been confirmed with the SWS (Short Wavelength Spectrometer) as a dominant ice component of interstellar grain mantles. The bending mode of CO₂ ice shows a particular triple-peak structure which provides first evidence for extensive ice segregation in the line-of-sight toward massive protostars. A comparison of interstellar and cometary ices using recent ISO data and ground-based measurements has revealed important similarities but also indicated that comets contain, beside pristine interstellar material, admixtures of processed material. The investigation of molecules in interstellar clouds is essential to reveal the link between dust in the interstellar medium and in the Solar System. This revised version was published online in June 2006 with corrections to the Cover Date.     

New estimates of ionization potentials of four DIB molecular carriers.

We present a study of the behaviour and ionization properties of four Diffuse Interstellar Bands (DIBs) at lambda lambda 5780, 5797, 6379 and 6613 angstroms. In the lambda lambda 5797, 6379 and 6613 angstrom DIBs, substructures have recently been detected, indicating large gaseous molecular carriers. Studying DIBs in regions with different physical properties in terms of UV flux and density enables us to monitor the behaviour of the carriers and hence to constrain their nature. As a follow-up of Sonnentrucker et al. (1997), we add new lines of sight and generalize the results for lines of sight with 2 or 3 clouds. This refines the Ionization Potential estimates which are between 10 and 13 eV, hence reminiscent of PAH or fullerene cations for those DIBs.     

Cometary Materials: Progress Toward Understanding the Composition in the Outer Solar Nebula

A major objective of the workshop was to learn about the chemical composition, physical structure, and thermodynamic conditions of the outer parts of the solar nebula where comets formed. Here we sum up what we have learned from years of research about the molecular constituents of comet comae primarily from in situ measurements of Comet 1P/Halley and remote sensing of Comets 1P/Halley, Hale-Bopp (C/1995 O1), and Hyakutake (C/1996 B2). These three bright comets are presumably captured Oort cloud comets. We summarize the analyses of these data to predict the composition of comet nuclei and project them further to the composition, structure, and thermodynamic conditions in the nebula. Near-future comet missions are directed toward less active short-period Jupiter-family comets. Thus, future analyses will afford a better understanding of the diversity of these two major groups of comets and their respective regions of origin in the solar or presolar nebula. We conclude with recommendations for determining critical data needed to aid in further analyses. Results of the workshop provide new guidelines and constraints for modeling the solar nebula. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the possible detection of solid O2 and O3 interstellar grains with ISO

In various models of interstellar grain chemistry, solid O₂ is formed by accretion as well as by surface reactions on grains. In dense molecular cloud models, at a later stage of the evolution, the O₂ molecule may become a substantial grain mantle constituent. Since IR dipole vibrational transitions for the homonuclear diatomic molecule O₂ are forbidden, the abundance of this potentially important grain mantle component can not be determined. However, embedded in a dirty ice matrix, the fundamental vibration of O₂ at 1550 cm⁻¹ becomes observable at 10 K, due to interactions with surrounding molecules, which break the symmetry of molecular oxygen. This process might be applicable for the dust mantle environment of interstellar grains. We have studied the role of solid O₂ and O₃ in astrophysically relevant ice mixtures and discuss the possible detection of solid O₂ and its major photolysis product O₃ in interstellar grains, in dense molecular clouds. Both molecules represent a specific target to be observed by the ISO satellite in the near future.     

Experimentally tracing the key steps in the origin of life: The aromatic world

Life is generally believed to emerge on Earth, to be at least functionally similar to life as we know it today, and to be much simpler than modern life. Although minimal life is notoriously difficult to define, a molecular system can be considered alive if it turns resources into building blocks, replicates, and evolves. Primitive life may have consisted of a compartmentalized genetic system coupled with an energy-harvesting mechanism. How prebiotic building blocks self-assemble and transform themselves into a minimal living system can be broken into two questions: (1) How can prebiotic building blocks form containers, metabolic networks, and informational polymers? (2) How can these three components cooperatively organize to form a protocell that satisfies the minimal requirements for a living system? The functional integration of these components is a difficult puzzle that requires cooperation among all the aspects of protocell assembly: starting material, reaction mechanisms, thermodynamics, and the integration of the inheritance, metabolism, and container functionalities. Protocells may have been self-assembled from components different from those used in modern biochemistry. We propose that assemblies based on aromatic hydrocarbons may have been the most abundant flexible and stable organic materials on the primitive Earth and discuss their possible integration into a minimal life form. In this paper we attempt to combine current knowledge of the composition of prebiotic organic material of extraterrestrial and terrestrial origin, and put these in the context of possible prebiotic scenarios. We also describe laboratory experiments that might help clarify the transition from nonliving to living matter using aromatic material. This paper presents an interdisciplinary approach to interface state of the art knowledge in astrochemistry, prebiotic chemistry, and artificial life research.     

Spectroscopic properties of polycyclic aromatic hydrocarbons (PAHs) and astrophysical implications.

PAHs (polycyclic aromatic hydrocarbons) are probably present as a mixture of neutral and ionized species and are responsible for the set of infrared emission bands in the 2-15 microns regions, which are observed in many different objects like reflection and planetary nebulae and external galaxies. PAHs are suggested to be the most abundant free organic molecules and ubiquitous in space. PAHs might also exist in the solid phase, included in interstellar ices in dense clouds. A complex aromatic network is expected on interstellar grains in the diffuse interstellar medium. The existence of an aromatic kerogen-like structure in carbonaceous meteorites and its similarity with interstellar spectra suggests a link between interstellar matter and primitive Solar System bodies.