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  • 1
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    The chemical reactivity of the Martian soil and implications for future missions (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Possible interpretations of the results of the Viking Biology Experiments suggest that greater than 1 ppm of a thermally labile oxidant, perhaps H2O2, and about 10 ppm of a thermally stable oxidant are present in the martian soil. We reexamine these results and discuss implications for future missions, the search for organics on Mars, and the possible health and engineering effects for human exploration. We conclude that further characterization of the reactivity of the martian regolith materials is warrented-although if our present understanding is correct the oxidant does not pose a hazard to humans. There are difficulties in explaining the reactivity of the Martian soil by oxidants. Most bulk phase compounds that are capable of oxidizing H2O to O2 per the Gas Exchange Experiment (GEx) are thermally labile or unstable against reduction by atmospheric CO2. Models invoking trapped O2 or peroxynitrates (NOO2(-)) require an unlikely geologic history for the Viking Lander 2 site. Most suggested oxidants, including H2O2, are expected to decompose rapidly under martian UV. Nonetheless, we conclude that the best model for the martian soil contains oxidants produced by heterogeneous chemical reactions with a photochemically produced atmospheric oxidant. The GEx results may be due to catalytic decomposition of an unstable oxidizing material by H2O. We show that interfacial reaction sites covering less than 1% of the available soil surfaces could explain the Viking Biology Experiments results.
    Keywords: SPACE BIOLOGY
    Type: ICARUS (ISSN 0019-1035); 108; 1; p. 146-157
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  • 2
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    Relevance of antarctic microbial ecosystems to exobiology (1993)
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    Publication Date: 2011-08-24
    Description: Antarctic microbial ecosystems which provide biological and physical analogs that can be used in exobiology are studied. Since the access to extraterrestrial habitats is extremely difficult, terrestrial analogs represent the best opportunity for both formulation and preliminary testing of hypothesis about life. Antarctica, as one of few suitable environments on earth is considered to be a major locus of progress in exobiology.
    Keywords: SPACE BIOLOGY
    Type: ; : Conference on the
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  • 3
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    The possibility of life on Mars during a water-rich past (1992)
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    Publication Date: 2011-08-24
    Description: Geomorphological evidence for past liquid water on Mars implies an early, warmer, epoch. In this review we compare this early warm environment to the first Gyr of Earth's history, the time within which we know life originated. We consider the key question about early Mars from the biological standpoint. How long was liquid water present? The range of answers encompasses the time interval for the origin of life on Earth. We use studies of early life on Earth as a guide, albeit a limited one, to the possible forms of evidence for past life on Mars. Presumptive evidence for microbial life on early Earth are stromatolites, layered deposits produced by microorganisms binding and trapping sediment. A search for fossils might be fruitful at sites on Mars that contained standing bodies of water over long periods of time. The ice-covered lakes of the dry valleys of Antarctica may provide analogs to the ultimate lakes on Mars as the surface pressure fell with a concomitant decrease in surface temperatures.
    Keywords: SPACE BIOLOGY
    Type: In: Mars (A93-27852 09-91); p. 1234-1245.
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  • 4
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    The implantation of life on Mars - Feasibility and motivation (1992)
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    Publication Date: 2011-08-24
    Description: Scientific concepts are reviewed regarding the potential formation and development of a life-bearing environment on Mars, and a potential ecopoiesis scenario is given. The development of the earth's biosphere is defined, and the major assumptions related to the formation of Martian life are listed. Three basic phases are described for the life-implantation concept which include determining whether sufficient quantities of volatiles are available, engineering the warming of the planet, and implanting microbial communities if necessary. Warming the planet theoretically releases liquid H2O and produces a thick CO2 atmosphere, and the implantation of biological communities is only necessary if no indigenous microbes emerge. It is concluded that a feasibility study is required to assess the possibilities of implanting life on Mars more concretely.
    Keywords: SPACE BIOLOGY
    Type: Advances in Space Research (ISSN 0273-1177); 12; 4, 19
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  • 5
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    Exobiology and future Mars missions - The search for Mars' earliest biosphere (1986)
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    Publication Date: 2011-08-19
    Description: The primordial Mars may have possessed a thick carbon dioxide atmosphere, with liquid water common on the surface, similar in many ways to the primordial earth. During this epoch, billions of years ago, the surface of Mars could have been conducive to the origin of life. It is possible that life evolved on Mars to be later eliminated as the atmospheric pressure dropped. Analysis of the surface of Mars for the traces of this early Martian biota could provide many insights into the phenomenon of life and its coupling to planetary evolution.
    Keywords: SPACE BIOLOGY
    Type: Advances in Space Research (ISSN 0273-1177); 6; 12, 1; 269-285
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  • 6
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    Space Station gas-grain simulation facility - Application to exobiology (1986)
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    Publication Date: 2011-08-19
    Description: The technical issues involved in performing experiments on the behavior and properties of aerosols in a microgravity environment provided by the Space Station are reviewed. The displacement of a particle resulting from g-jitter for ballistic, Knudsen, and Stokes flow regimes is examined in detail, and the radiation, acoustic, electrostatic, and electromagnetic mechanisms for the control of this motion are described. The simulation of organic haze production on Titan has been selected as an example experiment for detailed study. The purpose of this experiment was to simulate the photolysis of methane and the subsequent formation of the organic haze particles in the Titan upper atmosphere.
    Keywords: SPACE BIOLOGY
    Type: Advances in Space Research (ISSN 0273-1177); 6; 12, 1
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  • 7
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    The early environment and its evolution on Mars - Implications for life (1989)
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    Publication Date: 2011-08-19
    Description: There is considerable evidence that the early climate of Mars was very different from the inhospitable conditions there today. This early climate was characterized by liquid water on the surface and a dense atmosphere composed predominantly of CO2. The duration of these warm initial conditions on the surface of Mars is uncertain, but theoretical models suggest that they could have persisted for hundreds of millions up to a billion years. From studies of the earth's earliest biosphere, it is known that, by 3.5 Gyr ago, life had originated on earth and reached a fair degree of biological sophistication. If Mars did maintain a clement environment for longer than it took for life to originate on earth, then the question of the origin of life on Mars follows naturally. Since over two thirds of the Martian surface is more than 3.5 Gyr old, the possibility exists that Mars may hold the best record of the events that led to the origin of life, even though there may be no life there today.
    Keywords: SPACE BIOLOGY
    Type: Reviews of Geophysics (ISSN 8755-1209); 27; 189-214
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  • 8
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    The role of cometary particle coalescence in chemical evolution (1989)
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    Publication Date: 2011-08-19
    Description: Important prebiotic organic compounds might have been transported to earth in dust or produced in vapor clouds resulting from atmospheric explosions or impacts of comets. These compounds coalesced in the upper atmosphere with particles ejected from craters formed by impacts of large objects. Coalescence during exposure to UV radiation concentrated organic monomers and enhanced formation of oligomers. Continuing coalescence added material to the growing particles and shielded prebiotic compounds from prolonged UV radiation. These particles settled into the lower atmosphere where they were scavenged by rain. Aqueous chemistry and evaporation of raindrops containing monomers in high temperature regions near the earth's surface also promoted continued formation of oligomers. Finally, these oligomers were deposited in the oceans where continued prebiotic evolution led to the most primitive cell. Results of present studies suggest that prebiotic chemical evolution may be an inevitable consequence of impacting comets during the late accretion of planets anywhere in the universe if oceans remained on those planetary surfaces.
    Keywords: SPACE BIOLOGY
    Type: Origins of Life and Evolution of the Biosphere (ISSN 0169-6149); 19; 1, 19
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  • 9
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    Urey Prize Lecture - Planetary evolution and the origin of life (1991)
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    Publication Date: 2011-08-19
    Description: One of the principal questions concerning planetary evolution and life's origins relates to the early-earth organic material's origination in situ, outer solar system importation, or simple irrelevance to the emergence of organisms. Additional considerations encompass the character of interstellar organic material and its relationship to outer solar system organic compounds, and the possibility of life's emergence in the early Mars. Attention is given to the essentiality of liquid water for life-forms, in the role not only of a reaction medium among molecules but that of a basis for hydrophylic and hydrophobic groups' bonding.
    Keywords: SPACE BIOLOGY
    Type: Icarus (ISSN 0019-1035); 91; 93-100
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  • 10
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    History of water on Mars - A biological perspective (1992)
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    Publication Date: 2011-08-24
    Description: A general scenario is developed for the history of liquid water on the surface of Mars, according to which the history of water on Mars can be divided into four epochs based on the fundamental temperature and pressure characteristics. In Epoch I, the mean annual temperature is assumed to have been above freezing and the pressure to have been above 1 atm; liquid water was widespread and life could have arisen and become abundant. In Epoch II, the mean annual temperature fell below freezing, but peak temperatures were above freezing; In Epoch II ice-covered lakes could have provided a habitat for life. In Epoch III, both the mean and the peak temperatures were below freezing, and only transient liquid water would be possible; under these conditions, microbial ecosystems living in endolithic rock 'greenhouses' could have continued to survive. Finally, in Epoch IV, the pressure dropped to near the triple point pressure of water; at this stage, life on the surface of Mars would have become extinct.
    Keywords: SPACE BIOLOGY
    Type: Advances in Space Research (ISSN 0273-1177); 12; 4, 19
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