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PubMed1979

Laboratory simulations of the Viking labeled release experiment: kinetics following second nutrient injection and the nature of the gaseous end product.

Injection of 14C-labeled nutrient onto Mars soil produced an evolution of 14C gas in the Viking Labeled Release (LR) experiment. However, a second injection of nutrient seven days later was followed by an abrupt diminution of the amount of radioactive gas in the test cell. Simulation experiments performed in the LR Test Standards Module (TSM) have yielded a plausible explanation for this diminution. Radioactive carbon gases were injected into the TSM test cell in the presence and absence of two Mars analog soils. After equilibration, water was injected and its effect observed. The results indicate that the flight data following second nutrient injection can be explained on a physico-chemical basis involving a carbon dioxide/water/soil equilibrium in the test cell. The results also suggest that the gaseous end product of the Labeled Release reaction on Mars is more likely carbon dioxide than carbon monoxide.

Carbon Radioisotopes↗
PubMed1979

A model of Martian surface chemistry.

Alkaline earth and alkali metal superoxides and peroxides, gamma-Fe2O3 and carbon suboxide polymer are proposed to be constituents of the Martian surface material. These reactive substances explain the water modified reactions and thermal behaviors of the Martian samples demonstrated by all of the Viking Biology Experiments. It is also proposed that the syntheses of these substances result mainly from electrical discharges between wind-mobilized particles at Martian pressures; plasmas are initiated and maintained by these discharges. Active species in the plasma either combine to form or react with inorganic surfaces to create the reactive constitutents.

Carbon Dioxide↗
PubMed1979

The Viking Mission: implications for life on Mars.

The results of the Viking Biology experiments are best explained by non-biological phenomena: The interaction of the reagents with the materials comprising the regolith. Conditions of water activity, temperature, availability of carbon sources and others in most regions of the planet are too extreme for survival and growth of any known Earth microorganisms. Although the possibility persists that some very unusual form of life is somewhere on that planet the evidence is best interpreted as negative. Even though there is no evidence for current life on Mars, whether or not life ever originated there is not known.

Carbon↗
PubMed1979

The roots of life.

Explore the source record for details and available documents.

Extraterrestrial Environment↗
PubMed1980

Interstellar molecules.

The study of interstellar molecules broadly includes two areas of interest. One area uses the unique ability of molecules to act as probes of the physical conditions in the cold, dense, visually opaque component of the interstellar medium. The physical properties of this and other components of the interstellar medium are summarized. The other area deals with the chemistry of interstellar molecules, recent aspects of which are emphasized in this review. Gas-phase chemistry, shock chemistry, and grain surface chemistry are discussed in the context of recent observations. No present observations suggest that surface reactions are relevant, but neither can they be ruled out. Ion-molecule reactions are clearly operative, at least for the simpler species. Chemical isotope fractionation is reviewed, and it is concluded that the complexities of the chemistry allow no cosmological conclusions to be drawn from observations of deuterium in interstellar molecules, while the presence of 13C in interstellar molecules permits an estimate of the 12C/13C ratio which is consistent with the current concepts of the nucleosynthesis history of the Galaxy. Possible connections between interstellar molecules and the early molecular history of the solar system are discussed.

Biological Evolution↗
PubMed1979

Hydrogen atom initiated chemistry.

H atoms have been created by the photolysis of H2S. These then initiated reactions in mixtures involving acetylene-ammonia-water and ethylene-ammonia-water. In the case of the acetylene system, the products consisted of two amino acids, ethylene and a group of primarily cyclic thio-compounds, but no free sulfur. In the case of the ethylene systems, seven amino acids, including an aromatic one, ethane, free sulfur, and a group of solely linear thio-compounds were produced. Total quantum yields for the production of amino acids were approximately 3 x 10(-5) and approximately 2 x 10(-4) with ethylene and acetylene respectively as carbon substrates. Consideration is given of the mechanism for the formation of some of the products and implications regarding planetary atmosphere chemistry, particularly that of Jupiter, are explored.

Amino Acids↗
PubMed1982

The atmosphere of Titan.

The discovery that Titan had an atmosphere was made by the identification of methane in the satellite's spectrum in 1944. But the abundance of this gas and the identification of other major constituents required the 1980 encounter by the Voyager 1 spacecraft. in the intervening years, traces of C2H2, C2H4, C2H6 and CH3D had been posited to interpret emission bands in Titan's IR spectrum. The Voyager infrared Spectrometer confirmed that these gases were present and added seven more. The atmosphere is now known to be composed primarily of molecular nitrogen. But the derived mean molecular weight suggests the presence of a significant amount of some heavier gas, most probably argon. It is shown that this argon must be primordial, and that one can understand the evolution of Titan's atmosphere in terms of degassing of a mixed hydrate dominated by CH4, N2 and 36Ar. This model satisfactorily explains the absence of neon and makes no special requirements on the satellite's surface temperature. The organic chemistry taking place on Titan today invites comparison with chemical evolution on the primitive Earth prior to the origin of life.

Biological Evolution↗
PubMed1982

Comets: chemistry and chemical evolution.

Lasting commitment to cosmic chemistry and an awareness of the fascinating role of comets in that study was a consequence of an association with Harold Urey early in my astronomical career. Urey's influence on cometary research spread as colleagues with whom I was associated, in turn, developed their own programs in cometary chemistry. One phase of the Chicago research shows that Whipple's icy nucleus would be below about 250 K. This property, combined with their small internal pressure, means cometary interiors remain essentially unchanged during their lifetime. Observations of cometary spectra indicate that they are rich in simple organic species. Experiments on comet-like ice mixture suggests that the extensive array of interstellar molecules also may be found in comets. The capture of cometary debris by the earth or the impact of comets would have been an early source of biochemically significant molecules. Recent hypotheses on radiogenic heating and melting of water ice in the central zone of nuclei do not seem consistent with recent observations or ideas of structure. Thus comets are not a likely place for life to develop.

Astronomical Phenomena↗
PubMed1975

Ultraviolet-gas phase and -photocatalytic synthesis from CO and NH3.

The major photoproduct obtained on irradiation of gaseous NH3 and CO mixtures is ammonium cyanate; lesser amounts of urea, biurea, biuret semi-carbazide, formamide and cyanide were observed. The formation of the major gas phase photolysis product may be rationalized by the following reaction sequence: (see article). Urea is probably formed from NH4NCO in a thermal reaction while formamide may result from the disproportionation of NH2CO. Photocatalytic syntheses of 14C-urea, -formamide, and -formadehyde are effected by irradiation of 14CO and NH3 in the presence of Vycor, silica gel, or volcanic ash shale surfaces. These syntheses are catalyzed by ultraviolet wavelengths longer than those absorbed by the gaseous reactants. The syntheses are also effected when the surface material is first irradiated in the presence of CO followed by a dark incubation with NH3. Apparently, the initiating step is a light dependent formation of a reactive form of CO on the surface. A discussion is given on the possible contribution of these reactions to the abiotic synthesis of organic nitrogen compounds on Mars, on the primitive Earth and in interstellar space.

Ammonia↗
PubMed1988

Laboratory investigations of Mars: chemical and spectroscopic characteristics of a suite of clays as Mars soil analogs.

Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils.

Aluminum Silicates↗
PubMed1992

Chemical markers of prebiotic chemistry in hydrothermal systems.

The goal of this chapter is to suggest some organic compounds which may be indicative of prebiotic processes in hydrothermal systems or laboratory simulations of them. While the exact processes which led to the origins of life are not known, studies of life's origins of the past forty years have uncovered a plethora of potential precursor molecules. Some of these same molecules were probably present in hydrothermal systems if chemical processes there had a role in the origins of life. The types of molecules formed in primitive Earth simulation experiments and observed in the interstellar medium, on comets and meteorites will be reviewed in Section 2 of this chapter. Some reactions involving these molecules which may have been important in prebiotic syntheses will be outlined. Since near- to supercritical water is found in hydrothermal systems, its properties and aspects of organic chemistry in supercritical water at high temperature and pressure will be discussed in Section 3. Fischer-Tropsch type (FTT) reactions, which are a potential source of the building blocks of biological molecules in hydrothermal systems, are discussed in Section 4. In the concluding section, Section 5, the possible formation in hydrothermal systems of organic molecules that are believed to have been important for the origins of life is discussed.

Chemistry, Organic↗
PubMed1985

Photochemical reactions in interstellar grains photolysis of CO, NH3, and H2O.

A simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH2:H2O gas mixture on an Al block at 10 K, with concomitant irradiation with vacuum UV. The residues were analyzed by GC-MS, HPLC, and near IR; a reaction pathway leading from NH3 to complex alcohol, fatty acid, and amide products in 27 stages is postulated. The astronomical relevance and significance of the observations are discussed.

Ammonia↗
PubMed1996

Origins of life: a comparison of theories and application to Mars.

The field of study that deals with the origins of life does not have a consensus for a theory of life's origin. An analysis of the range of theories offered shows that they share some common features that may be reliable predictors when considering the possible origins of life on another planet. The fundamental datum dealing with the origins of life is that life appeared early in the history of the Earth, probably before 3.5 Ga and possibly before 3.8 Ga. What might be called the standard theory (the Oparin-Haldane theory) posits the production of organic molecules on the early Earth followed by chemical reactions that produced increased organic complexity leading eventually to organic life capable of reproduction, mutation, and selection using organic material as nutrients. A distinct class of other theories (panspermia theories) suggests that life was carried to Earth from elsewhere--these theories receive some support from recent work on planetary impact processes. Other alternatives to the standard model suggest that life arose as an inorganic (clay) form and/or that the initial energy source was not organic material but chemical energy or sunlight. We find that the entire range of current theories suggests that liquid water is the quintessential environmental criterion for both the origin and sustenance of life. It is therefore of interest that during the time that life appeared on Earth we have evidence for liquid water present on the surface of Mars.

Earth, Planet↗
PubMed1996

A search for interstellar oxiranecarbonitrile (C3H3NO).

We report a search in cold, quiescent and in 'hot core' type interstellar molecular clouds for the small cyclic molecule oxiranecarbonitrile (C3H3NO), which has been suggested as a precursor of important prebiotic molecules. We have determined upper limits to the column density and fractional abundance for the observed sources and find that, typically, the fractional abundance by number relative to molecular hydrogen of C3H3NO is less than a few times 10(-10). This limit is one to two orders of magnitude less than the measured abundance of such similarly complex species as CH3CH2CN and HCOOCH3 in well-studied hot cores. A number of astrochemical discoveries were made, including the first detection of the species CH3CH2CN in the massive star-forming clouds G34.3+0.2 and W51M and the first astronomical detections of some eight rotational transitions of CH3CH2CN, CH3CCH, and HCOOCH3. In addition, we found 8 emission lines in the 89 GHz region and 18 in the 102 GHz region which we were unable to assign.

Astronomy↗
PubMed1992

Comet Halley as an aggregate of interstellar dust and further evidence for the photochemical formation of organics in the interstellar medium.

Photolysis of mixtures of CO:NH3:H2O at 12 K results in the formation of an organic residue which is not volatile in high vacuum at room temperature. Analysis of this fraction by GC-MS resulted in the detection of C2-C3 hydroxy acids and hydroxy amides, glycerol, urea, glycine, hexamethylene tetramine, formamidine and ethanolamine. Use of isotopically labeled gases made it possible to establish that the observed products were not contaminants. The reaction pathways for the formation of these products were determined from the position of the isotopic labels in the mass spectral fragments. The significance of these findings to the composition of comets and the origins of life is discussed.

Dust↗
PubMed1984

On the abiotic formation of amino acids. I. HCN as a precursor of amino acids detected in extracts of lunar samples. II. Formation of HCN and amino acids from simulated mixtures of gases released from lunar samples.

Two studies on the abiotic formation of amino acids are presented. The first study demonstrates the role of hydrogen cyanide as a precursor of amino acids detected in extracts of lunar samples. The formation of several amino acids, including glycine, alanine, aspartic acid, and glutamic acid, under conditions similar to those used for the analysis of lunar samples is demonstrated. The second study investigates the formation of hydrogen cyanide as well as amino acids from lunar-sample gas mixtures under electrical discharge conditions. These results extend the possibility of synthesis of amino acids to planetary bodies with primordial atmospheres less reducing than a mixture of methane, ammonia, hydrogen and water.

Amino Acids↗