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Arrhenius, G.

Publications and source records attributed to Arrhenius, G..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Catalysis of carbon monoxide methanation by deep sea manganate minerals

The catalytic activity of deep sea manganese nodule minerals for the methanation of carbon monoxide was measured with a microcatalytic technique between 200 and 460 degrees C. The manganate minerals were activated at 248 degrees C by immersion into a stream of hydrogen in which pulses of carbon monoxide were injected. Activation energies for the methanation reaction and hydrogen desorption from the manganate minerals were obtained and compared with those of pure nickel. Similar energy values indicate that the activity of the nodule materials for the reaction appears to be related to the amount of reducible transition metals present in the samples (ca. 11 wt.-%). Since the activity of the nodule minerals per gram is comparable to that of pure nickel, most of the transition metal ions located between manganese oxide layers appear to be exposed and available to catalyze the reaction.

Non-NASA Center↗
NASA NTRS1989

Mixed-valence hydroxides as bioorganic host minerals

A range of naturally occurring divalent-trivalent metal cation hydroxides and modified artifical analogs have been synthesized and characterized. Structural and chemical properties of these minerals, determining their capability to selectively concentrate, order and alter molecules of prebiotic interest, include their anion exchange capacity and specificity, photochemical reactivity, production of nascent hydrogen, and catalytic efficiency. Properties relevant to these functions have been investigated and are discussed.

Kuma, K.↗
NASA NTRS1988

Photochemical fractionation of O-16 in the space medium modeled by resonance excitation of CO by H-Lyman alpha

Analyses of meteorite matter, the present structure of the solar system, and the evolution of matter in stellar systems are used to provide inferences concerning the formation of primordial matter in the solar system. Results indicate that molecular excitation processes similar to those observed today in circumstellar regions and dark interstellar clouds were operating in the early solar nebula. It is suggested that resonance excitation of broad isotopic bands by strong UV line sources may have resulted in the anomalous isotopic compositions noted in meteorites.

Arrhenius, G.↗
NASA NTRS1988

Rate of production, dissolution and accumulation of biogenic solids in the ocean

The equatorial current system, by its response to global circulation changes, provides a unique recording mechanism for long range climatic oscillations. A permanent record of the changes in rate of upwelling and organic production is generated in the equatorial deep sea sediments, particularly by such biogenic components which are unaffected by secondary dissolution. In order to determine the rates of accumulation of various sedimentary components, a reliable differential measurement of age of the strata must be obtained. Various approaches to this problem are reviewed, and sources of error discussed. Secondary dissolution of calcium carbonate introduces a substantial and variable difference between the dissolution-modified, and hence a priori unknown, rate of deposition on one hand and the rate of accumulation, derivable from the observed concentration, on the other. The cause and magnitude of these variations are of importance, particularly since some current dating schemes are based on assumed constancy in the rate of accumulation of this and, in some cases, also all other sedimentary components. The concepts used in rate evaluation are discussed with emphasis on the difference between the state of dissolution, an observable property of the sediment, and the rate of dissolution, a parameter that requires deduction of the carbonate fraction dissolved, and of the time differential. As a most likely cause of the enhanced state of dissolution of the interglacial carbonate sediments is proposed the lowered rates of biogenic production and deposition, which cause longer exposure of the carbonate microfossils to corrosion in the bioturbated surface layer of the sediment. Historical perspective is included in the discussion in view of the dedication of the Symposium to Hans Pettersson, the leader of the Swedish Deep Sea Expedition 1947-1948, an undertaking that opened a new era in deep sea research and planetary dynamics.

NASA Discipline Exobiology↗
NASA NTRS1985

Constraints on early atmosphere from planetary accretion processes

Evidence for composition and dynamics of release of the earliest volatiles was in lack of anything better being sought from the most ancient sediments known at the time, although they were recognized to be younger than three billion years. Origin of life on Earth was considered to require a lasting atmosphere with hydrogen and methane as major components. The new observations together with theoretical studies generated by the space program and by systematic exploration of the Earth's oceanic crust changed the climate of opinion in which the questions of the primordial atmosphere are discussed. Even though existing evidence does not permit conclusive choice of any specific scenario, the acceptance of specific model elements now forces the consideration of a series of consequences, some of which may be tested by observation.

Arrhenius, G.↗
NASA NTRS1985

What determines the location of satellites and planets?

The discrete structural pattern in the distribution of the satellites and planets around their primaries has since its discovery been thought to hold the key to the origin and evolution of the solar system. Different attempts to rationalize this distribution are reviewed with emphasis on theories with foundation in verifiable physical processes. Foremost among these is the band structure theory, which relates the emplacement of interstellar dust and gas source material around the magnetized primarily to the critical velocity for ionization of the four major interstellar gas components. The uncertainties, that are inevitable in all reconstructions, are in this theory compensated by the support from precise manifestations of the 2/3 effect in the Saturnian ring system and in the asteroid belt, and by the reproduction of related phenomena in laboratory and space experiments.

Arrhenius, G.↗
NASA NTRS1983

Condensation of solids in space. Isotope fractionation in the model system C-O

The reported chemical fractionation of a single isotope O-16 under simulated space conditions provides the first experimental proof for the hypothesis that the oxygen isotopic anomaly (and other similar anomalies) seen in meteorites is a product of chemical fractionation in interstellar or circumstellar space. Work proposed on this subject was discontinued because a peer review determined that such effects could not possibly exist and that continued support of this project would be a wasted effort. A bibliography is included of articles generated during research in this area.

Arrhenius, G.↗
NASA NTRS1980

Single isotope fractionation of (16)O(-) implications for early history of solar system

Chemical fractionation processes are investigated with emphasis on selective single isotope fractionation in polyisotopic systems, particularly in oxygen. The related temperature parameters of meteoritic condensates and of their source medium are investigated by a thermometric method that is independent of assumptions regarding temperatures and pressures in the solar nebula. The crucial nonlinear chemical fractionation of O-16 was demonstrated experimentally. The effect was achieved in condensed CO2 formed from CO with C-12 O-16 selectively excited by H Ly alpha. The effect was verified by mass spectrometric measurements. The meteorite paleotemperature estimates were advanced from defining only thermal exposure to evaluating time and temperature independently. Grain temperatures at condensation of refractory inclusion materials are indicated to be less than 900 K in agreement with radiation temperature considerations and observations in circumstellar dust shells.

Arrhenius, G.↗
NASA NTRS1979

Colloidal plasmas in space - Some aspects of condensation and growth of solids

The abundant occurrence of colloidal plasma clouds in the observable universe is reviewed, and the possible locales of condensation of cosmic solids identified. The physical properties of the condensation environment and the thermal physics of the plasma-cluster medium are outlined. In the light of these discussions, an attempt is made to identify the salient features of the processes of nucleation and growth in space. It is suggested that the conventional nucleation theory is inadequate when applied to the tenuous, partially excited, partially ionized multispecies cosmic vapor phase, and that studies relying on the physics of progressive molecule growth in such environments hold promise of understanding the process of transition of a cluster from the size of a few atomic mass units through the macromolecular range into what may be characterized as the bulk condensed phase.

De, B. R.↗
NASA NTRS1978

Chemical aspects of the formation of the solar system

Application of Alfven's theory for the formation of the solar system and the constraints imposed by the chemical composition of space materials are discussed with reference to chemical processes involved in the formation of the solar system. Evidence for the chemical properties of the space medium and the chemical consequences of the postulated physical differentiation processes are outlined, and interpretations based on structure and composition of meteorite material are indicated. A large range of topics, including processes involving chemical differentiation, temperature effects, and isotope fractionation, are examined.

Arrhenius, G.↗
NASA NTRS1977

The critical velocity phenomenon and the origin of the regular satellites

A theory is developed for the formation of the satellite systems which are likely to have been formed in situ, that is, not by capture of the satellite by the central planet. The foundation of the theory is the observation of the similarity between the band structure of such satellites and the band structure of cosmically abundant elements. That means that the values of the quantity log Gamma, where Gamma is the ratio of the mass of the central body to the orbital radius of the secondary body, are grouped into three bands which can be identified with the three bands into which are grouped the values of the ratio of the mass of a central body to the distance at which the kinetic energy of a freely falling cloud of atoms of a given kind equals the ionization energy. A coherent series of processes that could have led to the formation of satellites is outlined. The theory is valid also for planets, since the above-mentioned band structure is noted for the sun-planets system also.

De, B. R.↗
NASA NTRS1977

The role of plasma in the primeval nebula

The role of plasma and hydromagnetic processes in the primeval solar nebula is evaluated. In the light of the present knowledge of particles and fields in space it is difficult to avoid the conclusion that they must have played a crucial role in the emplacement of the material as well as its subsequent condensation into 'planetesimals'. Strong evidence in support of these processes in the primeval nebula is provided by the dynamical fine structure of the asteroidal belt and the Saturnian rings. The importance of current planetary magnetospheric as well as cometary research in clarifying certain physical processes believed to have occurred in the primeval nebula is stressed.

Alfven, H.↗
NASA NTRS1976

Evolution of the Solar System

The origin and evolution of the solar system are analyzed. Physical processes are first discussed, followed by experimental studies of plasma-solid reactions and chemical and mineralogical analyses of meteorites and lunar and terrestrial samples.

Alfven, H.↗
NASA NTRS1975

Structure and evolutionary history of the solar system

General principles and observational facts concerning the solar system are examined, taking into account the orbits of planets and satellites, the small bodies, the resonance structure, spin and tides, and postaccretional changes in the solar system. A description is given of the accretion of celestial bodies and the plasma phase is considered. Aspects of chemical differentiation and the matrix of the groups of bodies are also discussed, giving attention to chemical compositions in the solar system, meteorites and their precursor states, mass distribution and the critical velocity, and the structure of the groups.

Alfven, H.↗
NASA NTRS1974

Structure and evolutionary history of the solar system. IV

The chemical composition of planets and satellites, the origin of meteorites, and the location and structure of different secondary bodies are discussed in this concluding installment of the history of the Galaxy. Several traditional concepts are reviewed and rejected, and it is argued that with the empirical evidence now available it is possible to suggest a series of basic processes leading to the present structure of the planets and solar system.

Alfven, H.↗
NASA NTRS1974

The paleomagnetic record in carbonaceous chondrites - Natural remanence and magnetic properties

Recent results of an intensive study of the natural remanence (NRM) and the magnetic properties of carbonaceous chondrites (CC) are summarized. It is convincingly demonstrated that the record of ancient magnetic fields has been preserved in these least-altered old samples of solar system material known. Intensities of specific NRM in the 13 meteorites surveyed span a broad range of values from 0.00005 to 0.5 emu/g. A low-temperature cleaning technique, based on the memory effect in magnetite grains, was followed by alternating field (af) demagnetization of the residual memory to exhibit the relative stability of NRM in the CC studied. No systematic correlation was found of either intensity or stability of NRM to af demagnetization with petrologic subtype, beyond a trend of increasing stability of memory from petrologic subtype C2 to subtype C4. The intensity and stability behavior of the saturation remanence are better suited for use in a magnetic classification of CC.

Brecher, A.↗
NASA NTRS1973

Equilibrium condensation in a solar nebula

In attempts to reconstruct the environment of condensation of solar system materials, particularly exemplified by certain meteorite components, the relative temperatures of the gas and the solid are of critical importance. The relationships that determine the heat balance in a circumsolar grain-gas system are examined. Fundamental considerations show that regardless of opacity or gas density, the gas will always be at a higher temperature than the solid in such regions of the system where condensation is possible. Implications of the characteristic temperature differential between the gas and the condensing solid are discussed.

Arrhenius, G.↗