Infrared spectra and radiation stability of H2O2 ices relevant to Europa

In this paper we present spectra of H2O2-containing ices in the near- and mid-infrared (IR) regions. Spectral changes on warming are shown, as is a comparison of near-IR bands of H2O and H2O2-containing ices. An estimate of the A-value (absolute intensity) for the largest near- IR feature of H2O2 is given. Radiation-decay half-lives are reported for 19 K and 80 K, and are related to the surface radiation doses on Europa. The radiation data show that H2O2 destruction is slower at 80 K than 19 K, and are consistent with the claim that icy material in the outermost micrometer of Europa's surface has been heavily processed by radiation.     

Amino aciduria in weightlessness

Urinary excretion of amino acids by the 9 Skylab crewmen was studied as an indicator of the metabolic effects caused by exposure to the space flight environment. Intake was consistent in quality and quantity throughout the 28, 59 and 84-day flights for each of the crewmen and complete collections were accomplished. The results indicated an increased excretion in most amino acids during the first month of flight which remained elevated in the second and third months but to a lesser extent. Additional indications of change in muscle and skeletal metabolism were observed. These results point to the desirability of obtaining additional indices of alterations in protein synthetic processes in conjunction with future space flights.     

Thermal drilling in planetary ices: an analytic solution with application to planetary protection problems of radioisotope power sources

Abstract Thermal drilling has been applied to studies of glaciers on Earth and proposed for study of the martian ice caps and the crust of Europa. Additionally, inadvertent thermal drilling by radioisotope sources released from the breakup of a space vehicle is of astrobiological concern in that this process may form a downward-propagating "warm little pond" that could convey terrestrial biota to a habitable environment. A simple analytic solution to the asymptotic slow-speed case of thermal drilling is noted and used to show that the high thermal conductivity of the low-temperature ice on Europa and Titan makes thermal drilling qualitatively more difficult than at Mars. It is shown that an isolated General Purpose Heat Source (GPHS) "brick" can drill effectively on Earth or Mars, whereas on Titan or Europa with ice at 100 K, the source would stall and become stuck in the ice with a surface temperature of <200 K. Key Words: Planetary protection-Planetary environments-Ice-Titan. Astrobiology 12, 799-802.     

Venus, Mars, and the ices on Mercury and the moon: astrobiological implications and proposed mission designs

Venus and Mars likely had liquid water bodies on their surface early in the Solar System history. The surfaces of Venus and Mars are presently not a suitable habitat for life, but reservoirs of liquid water remain in the atmosphere of Venus and the subsurface of Mars, and with it also the possibility of microbial life. Microbial organisms may have adapted to live in these ecological niches by the evolutionary force of directional selection. Missions to our neighboring planets should therefore be planned to explore these potentially life-containing refuges and return samples for analysis. Sample return missions should also include ice samples from Mercury and the Moon, which may contain information about the biogenic material that catalyzed the early evolution of life on Earth (or elsewhere). To obtain such information, science-driven exploration is necessary through varying degrees of mission operation autonomy. A hierarchical mission design is envisioned that includes spaceborne (orbital), atmosphere (airborne), surface (mobile such as rover and stationary such as lander or sensor), and subsurface (e.g., ground-penetrating radar, drilling, etc.) agents working in concert to allow for sufficient mission safety and redundancy, to perform extensive and challenging reconnaissance, and to lead to a thorough search for evidence of life and habitability.     

Nucleobases and prebiotic molecules in organic residues produced from the ultraviolet photo-irradiation of pyrimidine in NH(3) and H(2)O+NH(3) ices

Although not yet identified in the interstellar medium (ISM), N-heterocycles including nucleobases-the information subunits of DNA and RNA-are present in carbonaceous chondrites, which indicates that molecules of biological interest can be formed in non-terrestrial environments via abiotic pathways. Recent laboratory experiments and ab initio calculations have already shown that the irradiation of pyrimidine in pure H(2)O ices leads to the formation of a suite of oxidized pyrimidine derivatives, including the nucleobase uracil. In the present work, NH(3):pyrimidine and H(2)O:NH(3):pyrimidine ice mixtures with different relative proportions were irradiated with UV photons under astrophysically relevant conditions. Liquid- and gas-chromatography analysis of the resulting organic residues has led to the detection of the nucleobases uracil and cytosine, as well as other species of prebiotic interest such as urea and small amino acids. The presence of these molecules in organic residues formed under abiotic conditions supports scenarios in which extraterrestrial organics that formed in space and were subsequently delivered to telluric planets via comets and meteorites could have contributed to the inventory of molecules that triggered the first biological reactions on their surfaces.     

Distribution and stable isotopic composition of amino acids from fungal peptaibiotics: assessing the potential for meteoritic contamination

The presence of nonprotein α-dialkyl-amino acids such as α-aminoisobutyric acid (α-AIB) and isovaline (Iva), which are considered to be relatively rare in the terrestrial biosphere, has long been used as an indication of the indigeneity of meteoritic amino acids. However, recent work showing the presence of α-AIB and Iva in peptides produced by a widespread group of filamentous fungi indicates the possibility of a terrestrial biotic source for the α-AIB observed in some meteorites. We measured the amino acid distribution and stable carbon and nitrogen isotopic composition of four α-AIB-containing fungal peptides and compared this data to similar meteoritic measurements. We show that the relatively simple distribution of the C(4) and C(5) amino acids in fungal peptides is distinct from the complex distribution observed in many carbonaceous chondrites. We also identify potentially diagnostic relationships between the stable isotopic compositions of pairs of amino acids from the fungal peptides that may aid in ruling out fungal contamination as a source of meteoritic amino acids.     

Excretion of amino acids by humans during space flight

We measured the urine amino acid distribution patterns before, during and after space flight on the Space Shuttle. The urine samples were collected on two separate flights of the space shuttle. The first flight lasted 9.5 days and the second flight 15 days. Urine was collected continuously on 8 subjects for the period beginning 10 d before launch to 6 d after landing. Results: In contrast to the earlier Skylab missions where a pronounced amino aciduria was found, on shuttle the urinary amino acids showed little change with spaceflight except for a marked decrease in all of the amino acids on FD (flight day) 1 (p<0.05) and a reduction in isoleucine and valine on FD3 and FD4 (p<0.05). Conclusions: (i) Amino aciduria is not an inevitable consequence of space flight. (ii) The occurrence of amino aciduria, like muscle protein breakdown is a mission specific effect rather than part of the general human response to microgravity.     

Survival of amino acids in micrometeorites during atmospheric entry

The delivery of amino acids by micrometeorites to the early Earth during the period of heavy bombardment could have been a significant source of the Earth's prebiotic amino acid inventory provided that these organic compounds survived atmospheric entry heating. To investigate the sublimation of amino acids from a micrometeorite analog at elevated temperature, grains from the CM-type carbonaceous chondrite Murchison were heated to 550 degrees C inside a glass sublimation apparatus (SA) under reduced pressure. The sublimed residue that had collected on the cold finger of the SA after heating was analyzed for amino acids by HPLC. We found that when the temperature of the meteorite reached approximately 150 degrees C, a large fraction of the amino acid glycine had vaporized from the meteorite, recondensed onto the end of the SA cold finger, and survived as the rest of the grains heated to 550 degrees C. alpha-Aminoisobutryic acid and isovaline, which are two of the most abundant non-protein amino acids in Murchison, did not sublime from the meteorite and were completely destroyed during the heating experiment. Our experimental results suggest that sublimation of glycine present in micrometeorite grains may provide a way for this amino acid to survive atmospheric entry heating at temperatures > 550 degrees C; all other amino acids apparently are destroyed.     

Changes in chromatin and nucleic acids in rat tissues after two-week spaceflight

The quantitative changes in nucleic acids and chromatin breakdown were followed in blood, thymus and spleen in rats after 14 day flights on board the biosatellites Cosmos-1887 and Cosmos-2044. Quantitative nucleic acid changes within 8-11 h after landing were only mild, most statistically non-significant. An analysis at 48 h after landing showed a marked decrease in a total content of DNA and RNA in spleen and thymus. Within 8-11 h after landing, the symptoms of chromatin breakdown were found as is seen in an increased concentration of its fragments-polydeoxyribonucleotides. The obtained results show that a partial adaptation to microgravity occurs up to flight day 14 in lymphoid organs. Adaptation is accompanied with a reappearing of the sensitive cells. Their chromatin breaks down, then, in a final phase of flight due to hypergravity stress manifesting itself by a temporary increase in polydeoxyribonucleotide concentration several hours after landing. The results are discussed in relation to the changes in chosen parameters after shorter or more prolonged flights.     

Amino acid distribution in meteorites: diagenesis, extraction methods, and standard metrics in the search for extraterrestrial biosignatures

The relative abundance of the protein amino acids has been previously investigated as a potential marker for biogenicity in meteoritic samples. However, these investigations were executed without a quantitative metric to evaluate distribution variations, and they did not account for the possibility of interdisciplinary systematic error arising from inter-laboratory differences in extraction and detection techniques. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and stochastic probabilistic artificial neural networks (ANNs) were used to compare the distributions for nine protein amino acids previously reported for the Murchison carbonaceous chondrite, Mars meteorites (ALH84001, Nakhla, and EETA79001), prebiotic synthesis experiments, and terrestrial biota and sediments. These techniques allowed us (1) to identify a shift in terrestrial amino acid distributions secondary to diagenesis; (2) to detect differences in terrestrial distributions that may be systematic differences between extraction and analysis techniques in biological and geological laboratories; and (3) to determine that distributions in meteoritic samples appear more similar to prebiotic chemistry samples than they do to the terrestrial unaltered or diagenetic samples. Both diagenesis and putative interdisciplinary differences in analysis complicate interpretation of meteoritic amino acid distributions. We propose that the analysis of future samples from such diverse sources as meteoritic influx, sample return missions, and in situ exploration of Mars would be less ambiguous with adoption of standardized assay techniques, systematic inclusion of assay standards, and the use of a quantitative, probabilistic metric. We present here one such metric determined by sequential feature extraction and normalization (PCA), information-driven automated exploration of classification possibilities (HCA), and prediction of classification accuracy (ANNs).     

Testing the potential for computational chemistry to quantify biophysical properties of the non-proteinaceous amino acids

Although most proteins of most living organisms are constructed from the same set of 20 amino acids, all indications are that this standard alphabet represents a mere subset of what was available to life during early evolution. However, we currently lack an appropriate quantitative framework with which to test the qualitative hypotheses that have been offered to date as explanations for nature's "choices." Specifically, although many indices have been developed to describe the 20 standard amino acids, few or no comparable data extend to prebiotically plausible alternatives because of the costly and time-consuming bench experiments that would be required. Computational chemistry (specifically quantitative structure property relationship methods) offers a potentially fast, cost-effective remedy for this knowledge gap by predicting such molecular properties in silico. Thus, we investigated the use of various freely accessible programs to predict three key amino acid properties (hydrophobicity, charge, and size). We assessed the accuracy of these predictions by comparisons with experimentally determined counterparts for appropriate test data sets. In light of these results, and factors of software accessibility and transparency, we suggest a method for further computational assessments of prebiotically plausible amino acids. The results serve as a starting point for future quantitative analysis of amino acid alphabet evolution.     

Stability of amino acids and their oligomerization under high-pressure conditions: implications for prebiotic chemistry

The polymerization of amino acids leading to the formation of peptides and proteins is a significant problem for the origin of life. This problem stems from the instability of amino acids and the difficulty of their oligomerization in aqueous environments, such as seafloor hydrothermal systems. We investigated the stability of amino acids and their oligomerization reactions under high-temperature (180-400°C) and high-pressure (1.0-5.5?GPa) conditions, based on the hypothesis that the polymerization of amino acids occurred in marine sediments during diagenesis and metamorphism, at convergent margins on early Earth. Our results show that the amino acids glycine and alanine are stabilized by high pressure. Oligomers up to pentamers were formed, which has never been reported for alanine in the absence of a catalyst. The yields of peptides at a given temperature and reaction time were higher under higher-pressure conditions. Elemental, infrared, and isotopic analyses of the reaction products indicated that deamination is a key degradation process for amino acids and peptides under high-pressure conditions. A possible NH(3)-rich environment in marine sediments on early Earth may have further stabilized amino acids and peptides by inhibiting their deamination.     

Formation routes of interstellar glycine involving carboxylic acids: possible favoritism between gas and solid phase

Despite the extensive search for glycine (NH?CH?COOH) and other amino acids in molecular clouds associated with star-forming regions, only upper limits have been derived from radio observations. Nevertheless, two of glycine's precursors, formic acid and acetic acid, have been abundantly detected. Although both precursors may lead to glycine formation, the efficiency of reaction depends on their abundance and survival in the presence of a radiation field. These facts could promote some favoritism in the reaction pathways in the gas phase and solid phase (ice). Glycine and these two simplest carboxylic acids are found in many meteorites. Recently, glycine was also observed in cometary samples returned by the Stardust space probe. The goal of this work was to perform theoretical calculations for several interstellar reactions involving the simplest carboxylic acids as well as the carboxyl radical (COOH) in both gas and solid (ice) phase to understand which reactions could be the most favorable to produce glycine in interstellar regions fully illuminated by soft X-rays and UV, such as star-forming regions. The calculations were performed at four different levels for the gas phase (B3LYP/6-31G*, B3LYP/6-31++G**, MP2/6-31G*, and MP2/6-31++G**) and at MP2/6-31++G** level for the solid phase (ice). The current two-body reactions (thermochemical calculation) were combined with previous experimental data on the photodissociation of carboxylic acids to promote possible favoritism for glycine formation in the scenario involving formic and acetic acid in both gas and solid phase. Given that formic acid is destroyed more in the gas phase by soft X-rays than acetic acid is, we suggest that in the gas phase the most favorable reactions are acetic acid with NH or NH?OH. Another possible reaction involves NH?CH? and COOH, one of the most-produced radicals from the photodissociation of acetic acid. In the solid phase, we suggest that the reactions of formic acid with NH?CH or NH?CH?OH are the most favorable from the thermochemical point of view.     

Analysis of carbonaceous biomarkers with the Mars Organic Analyzer microchip capillary electrophoresis system: carboxylic acids

The oxidizing surface chemistry on Mars argues that any comprehensive search for organic compounds indicative of life requires methods to analyze higher oxidation states of carbon with very low limits of detection. To address this goal, microchip capillary electrophoresis (μCE) methods were developed for analysis of carboxylic acids with the Mars Organic Analyzer (MOA). Fluorescent derivatization was achieved by activation with the water soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) followed by reaction with Cascade Blue hydrazide in 30 mM borate, pH 3. A standard containing 12 carboxylic acids found in terrestrial life was successfully labeled and separated in 30 mM borate at pH 9.5, 20 °C by using the MOA CE system. Limits of detection were 5-10 nM for aliphatic monoacids, 20 nM for malic acid (diacid), and 230 nM for citric acid (triacid). Polyacid benzene derivatives containing 2, 3, 4, and 6 carboxyl groups were also analyzed. In particular, mellitic acid was successfully labeled and analyzed with a limit of detection of 300 nM (5 ppb). Analyses of carboxylic acids sampled from a lava tube cave and a hydrothermal area demonstrated the versatility and robustness of our method. This work establishes that the MOA can be used for sensitive analyses of a wide range of carboxylic acids in the search for extraterrestrial organic molecules.     

The PROCESS experiment: amino and carboxylic acids under Mars-like surface UV radiation conditions in low-earth orbit

The search for organic molecules at the surface of Mars is a top priority of the next Mars exploration space missions: Mars Science Laboratory (NASA) and ExoMars (ESA). The detection of organic matter could provide information about the presence of a prebiotic chemistry or even biological activity on this planet. Therefore, a key step in interpretation of future data collected by these missions is to understand the preservation of organic matter in the martian environment. Several laboratory experiments have been devoted to quantifying and qualifying the evolution of organic molecules under simulated environmental conditions of Mars. However, these laboratory simulations are limited, and one major constraint is the reproduction of the UV spectrum that reaches the surface of Mars. As part of the PROCESS experiment of the European EXPOSE-E mission on board the International Space Station, a study was performed on the photodegradation of organics under filtered extraterrestrial solar electromagnetic radiation that mimics Mars-like surface UV radiation conditions. Glycine, serine, phthalic acid, phthalic acid in the presence of a mineral phase, and mellitic acid were exposed to these conditions for 1.5 years, and their evolution was determined by Fourier transform infrared spectroscopy after their retrieval. The results were compared with data from laboratory experiments. A 1.5-year exposure to Mars-like surface UV radiation conditions in space resulted in complete degradation of the organic compounds. Half-lives between 50 and 150?h for martian surface conditions were calculated from both laboratory and low-Earth orbit experiments. The results highlight that none of those organics are stable under low-Earth orbit solar UV radiation conditions.     

Analysis of underivatized amino acids in geological samples using ion-pairing liquid chromatography and electrospray tandem mass spectrometry

The capability of detecting biomarkers, such as amino acids, in chemically complex field samples is essential to establishing the knowledge required to search for chemical signatures of life in future planetary explorations. However, due to the complexities of in situ investigations, it is important to establish a new analytical scheme that utilizes a minimal amount of sample preparation. This paper reports the feasibility of a novel and sensitive technique, which has been established to quantitate amino acids in terrestrial crust samples directly without derivatization using volatile ion-pairing liquid chromatography and tandem mass spectrometry equipped with an electrospray ionization source. Adequate separation of 20 underivatized amino acids was achieved on a C(18) capillary column within 26 min with nonafluoropentanoic acid (NFPA) as ion-pairing reagent. Each amino acid was identified from its retention time as well as from its characteristic parent-to-daughter ion transition. Using tandem mass spectrometry as a detection technique allows co-elution of some amino acids, as it is more specific than traditional spectrophotometric methods. In the present study, terrestrial samples collected from 3 different locations were analyzed for their water-extractable free amino acid contents, following the removal of metal and organic interferences via ion exchange procedures. This is the first time that amino acids in geological samples were directly determined quantitatively without complicated derivatization steps. Depending on the amino acid, the detection limits varied from 0.02 to 5.7 pmol with the use of a 1 microl sample injection loop.     

Biochemical constraints in a protobiotic earth devoid of basic amino acids: the "BAA(-) world"

It has been hypothesized in this journal and elsewhere, based on surveys of published data from prebiotic synthesis experiments and carbonaceous meteorite analyses, that basic amino acids such as lysine and arginine were not abundant on prebiotic Earth. If the basic amino acids were incorporated only rarely into the first peptides formed in that environment, it is important to understand what protobiotic chemistry is possible in their absence. As an initial test of the hypothesis that basic amino acid negative [BAA(-)] proteins could have performed at least a subset of protobiotic chemistry, the current work reports on a survey of 13 archaeal and 13 bacterial genomes that has identified 61 modern gene sequences coding for known or putative proteins not containing arginine or lysine. Eleven of the sequences found code for proteins whose functions are well known and important in the biochemistry of modern microbial life: lysine biosynthesis protein LysW, arginine cluster proteins, copper ion binding proteins, bacterial flagellar proteins, and PE or PPE family proteins. These data indicate that the lack of basic amino acids does not prevent peptides or proteins from serving useful structural and biochemical functions. However, as would be predicted from fundamental physicochemical principles, we see no fossil evidence of prebiotic BAA(-) peptide sequences capable of interacting directly with nucleic acids.     

The PROCESS experiment: exposure of amino acids in the EXPOSE-E experiment on the international space station and in laboratory simulations

To understand the chemical behavior of organic molecules in the space environment, amino acids and a dipeptide in pure form and embedded in meteorite powder were exposed in the PROCESS experiment in the EXPOSE-E facility mounted on the European Technology Exposure Facility (EuTEF) platform on board the International Space Station (ISS). After exposure to space conditions for 18 months, the samples were returned to Earth and analyzed in the laboratory for reactions caused by solar UV and cosmic radiation. Chemical degradation and possible racemization and oligomerization, the main reactions caused by photochemistry in the vacuum ultraviolet domain (VUV, wavelength range 100-200?nm for photon energy from 6.2 to 12.4?eV) were examined in particular. The molecules were extracted and derivatized by silylation and analyzed by gas chromatograph coupled to a mass spectrometer (GC-MS) to quantify the rate of the degradation of the compounds. Laboratory exposure in several wavelength ranges from UV to VUV was carried out in parallel in the Cologne Deutsches Zentrum für Luft- und Raumfahrt (DLR) Center and Centre de biophysique moléculaire (CBM) laboratories. The results show that resistance to irradiation is a function of the chemical nature of the exposed molecules and the wavelengths of the UV light. The most altered compounds were the dipeptide, aspartic acid, and aminobutyric acid. The most resistant were alanine, valine, glycine, and aminoisobutyric acid. Our results also demonstrate the protective effect of meteorite powder, which reemphasizes the importance of exogenic contribution to the inventory of prebiotic organics on early Earth.     

Adsorption of amino acids (ALA, CYS, HIS, MET) on zeolites: fourier transform infrared and Raman spectroscopy investigations

Minerals adsorb more amino acids with charged R-groups than amino acids with uncharged R-groups. Thus, the peptides that form from the condensation of amino acids on the surface of minerals should be composed of amino acid residues that are more charged than uncharged. However, most of the amino acids (74%) in today's proteins have an uncharged R-group. One mechanism with which to solve this paradox is the use of organophilic minerals such as zeolites. Over the range of pH (pH 2.66-4.50) used in these experiments, the R-group of histidine (His) is positively charged and neutral for alanine (Ala), cysteine (Cys), and methionine (Met). In acidic hydrothermal environments, the pH could be even lower than those used in this study. For the pH range studied, the zeolites were negatively charged, and the overall charge of all amino acids was positive. The conditions used here approximate those of prebiotic Earth. The most important finding of this work is that the relative concentrations of each amino acid (X=His, Met, Cys) to alanine (X/Ala) are close to 1.00. This is an important result with regard to prebiotic chemistry because it could be a solution for the paradox stated above. Pore size did not affect the adsorption of Cys and Met on zeolites, and the Si/Al ratio did not affect the adsorption of Cys, His, and Met. ZSM-5 could be used for the purification of Cys from other amino acids (Student-Newman-Keuls test, p<0.05), and mordenite could be used for separation of amino acids from each other (Student-Newman-Keuls test, p<0.05). As shown by Fourier transform infrared (FT-IR) spectra, Ala interacts with zeolites through the [Formula: see text] group, and methionine-zeolite interactions involve the COO, [Formula: see text], and CH(3) groups. FT-IR spectra show that the interaction between the zeolites and His is weak. Cys showed higher adsorption on all zeolites; however, the hydrophobic Van der Waals interaction between zeolites and Cys is too weak to produce any structural changes in the Cys groups (amine, carboxylic, sulfhydryl, etc.); thus, the FT-IR and Raman spectra are the same as those of solid Cys.     

Observing floods from space: Experience gained from COSMO-SkyMed observations

The COSMO-SkyMed mission offers a unique opportunity to obtain all weather radar images characterized by short revisit time, thus being useful for flood evolution mapping. The COSMO-SkyMed system has been activated several times in the last few years in occasion of flood events all over the world in order to provide very high resolution X-band SAR images useful for flood detection purposes. This paper discusses the major outcomes of the experience gained, within the framework of the OPERA Pilot Project funded by the Italian Space Agency, from using COSMO-SkyMed data for the purpose of near real time generation of flood maps. A review of the mechanisms which determine the imprints of the inundation on the radar images and of the fundamental simulation tools able to predict these imprints and help image interpretation is provided. The approach developed to process the data and to generate the flood maps is also summarized. Then, the paper illustrates the experience gained with COSMO-SkyMed by describing and discussing a number of significant examples. These examples demonstrate the potential of the COSMO-SkyMed system and the suitability of the approach developed for generating the final products, but they also highlight some critical aspects that require further investigations to improve the reliability of the flood maps.