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Richardson, S. M.

Publications and source records attributed to Richardson, S. M..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The case for a wet, warm climate on early Mars

The conditions under which Mars could have had a warm wet climate during its early evolution are explored by means of numerical simulations, incorporating more accurate data on the opacity of gaseous CO2 and H2O in the solar and thermal spectral regions (McClatchey et al., 1971) into the one-dimensional radiative-convective greenhouse model of Kasting and Ackerman (1986). The results are presented in extensive graphs and characterized in detail, with consideration of atmospheric CO2 loss rates, sources of atmospheric CO2, CO2 partitioning between atmosphere and hydrosphere, the Mars volatile inventory, the CO2 geochemical cycle, climate evolution, and observational tests. It is concluded that greenhouse conditions (requiring atmospheric CO2 of 1-5 bar) could have existed for a period of about 1 Gyr if the total surficial inventory of CO2 was 2-10 bar.

Pollack, J. B.↗
NASA NTRS1987

The case for a wet, warm climate on early Mars

Arguments are presented in support of the idea that Mars possessed a dense CO2 atmosphere and a wet, warm climate early in its history. The plausibility of a CO2 greenhouse is tested by formulating a simple model of the CO2 geochemical cycle on early Mars. By scaling the rate of silicate weathering on Earth, researchers estimated a weathering time constant of the order of several times 10 to the 7th power years for early Mars. Thus, a dense atmosphere could have existed for a geologically significant time period (approx. 10 to the 9th power years) only if atmospheric CO2 was being continuously resupplied. The most likely mechanism by which this could have been accomplished is the thermal decomposition of carbonate rocks induced directly or indirectly by intense, global scale volcanism.

Pollack, J. B.↗
NASA NTRS1986

A hybrid model of the CO2 geochemical cycle and its application to large impact events

The effects of a large asteriod or comet impact on modern and ancient marine biospheres are analyzed. A hybrid model of the carbonate-silicate geochemical cycle, which is capable of calculating the concentrations of carbon dioxide in the atmosphere, ocean, and sedimentary rocks, is described. The differences between the Keir and Berger (1983) model and the hybrid model are discussed. Equilibrium solutions are derived for the preindustrial atmosphere/ocean system and for a system similar to that of the late Cretaceous Period. The model data reveal that globl darkening caused by a stratospheric dust veil could destroy the existing phytoplankton within a period of several weeks or months, nd the dissolution of atmospheric NO(x) compounds would lower the pH of ocean surface waters and release CO2 into the atmosphere. It is noted that the surface temperatures could be increased by several degrees and surface oceans would be uninhabitable for calcaerous organisms for approximately 20 years.

Kasting, J. F.↗
NASA NTRS1985

Seafloor hydrothermal activity and spreading rates - The Eocene carbon dioxide greenhouse revisited

A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Eocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates.

Kasting, J. F.↗
NASA NTRS1985

Water loss from Venus: Implications for the Earth's early atmosphere

The atmosphere of Venus outgassed rapidly as a result of planetary heating during accretion, resulting in massive water loss. The processes affecting atmospheric chemistry following accretion have consisted largely of hydrogen escape and internal re-equilibrium. The initial bulk composition of Venus and Earth are assumed to have been roughly similar. Chemical speciation on Venus was controlled by the temperature and oxygen buffering capacity of the surface magma. It is also assumed that the surfaces of planetary bodies of the inner solar system were partly or wholly molten during accretion with a temperature estimated at 1273 to 1573 K. To investigate the range of reasonable initial atmospheric compositions on Venus, limits have to be set for the proportion of total hydrogen and the buffered fugacity of oxygen. Using the C/H ratio of 0.033 set for Earth, virtually all of the water generated during outgassing must later have been lost in order to bring the current CO2/H2O ratio for Venus up to its observed value of 10 sup 4 to 10 sup 5. The proportion of H2O decreases in model atmospheres with successfully higher C/H values, ultimately approaching the depleted values currently observed on Venus. Increasing C/H also results in a rapid increase in CO/H2O and provides an efficient mechanism for water loss by the reaction CO+H2O = CO2 + H2. This reaction, plus water loss mechanisms involving crustal iron, could have removed a very large volume of water from the Venusian atmosphere, even at a low C/H value.

Richardson, S. M.↗
NASA NTRS1985

Seafloor hydrothermal activity and spreading rates: the Eocene carbon dioxide greenhouse revisted

A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Ecocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates.

Seawater/chemistry↗
NASA NTRS1984

Water loss on Venus - The role of carbon monoxide

The four-to-fivefold difference in water abundance between the earth and Venus may reflect either initial differences in the bulk volatile content of the two planets, or massive water loss mechanisms on Venus. These two possibilities were investigated by performing thermodynamic calculations on the heterogeneous system C-O-H-N-S, varying C/H upward from its 0.033 terrestrial value. While atmospheric H2O decreases as bulk C/H increases, the latter would have to rise to an improbably high value in order to account for the low water abundance on Venus through initial deficiency alone. Calculations suggest that if the outgassed C/H on Venus was higher than on earth by even a factor of 5, it would have been sufficient for CO to become competitive with FeO as a sink for oxygen. Together with the lower initial water abundance value that follows from a higher C/H ratio, water loss due to CO may have been a major factor.

Richardson, S. M.↗
NASA NTRS1984

Calculation of unsteady fan rotor response caused by downstream flow distortions

The present model for fan rotor/support strut airfoil interaction uses a time-marching code for the rotor flow, coupled with a potential flow model for the stator-strut region. Study of the effect of strut design variables indicates that rotor flow disturbance is increased by the primary variables of larger strut thickness and circumferential spacing, while decreasing exponentially with increased rotor-strut separation. The time-marching code predicts local rotor pressure and flow perturbations in response to an unsteady downstream boundary condition.

Obrien, W. F.↗
NASA NTRS1978

Vein formation in the C1 carbonaceous chondrites

Veins in the C1 chondrites Orgueil, Alais, and Ivuna have been deposited during an extended period of impact brecciation and leaching. At least three generations of mineralization, dominated successively by carbonates, calcium sulfate, and magnesium sulfate, can be recognized. Vein minerals are derived locally by closed-system reactions between matrix phyllosilicates and an aqueous fluid, with the result that few, if any, primitive mineral phases still exist in the C1s.

Richardson, S. M.↗
NASA NTRS1978

Textural evidence bearing on the origin of isolated olivine crystals in C2 carbonaceous chondrites

In some cases the mechanical competence of chondrules in carbonaceous chondrites has been reduced by alteration of their mesostasis glass to friable phyllosilicate, providing a mechanism by which euhedral olivines can be separated from chondrules. Morphological features of isolate olivine grains found in carbonaceous chondrites are similar to those of olivine phenocrysts in chondrules. These observations suggest that the isolated olivine grains formed in chondrules, by crystallization from a liquid, rather than by condensation from a vapor.

Richardson, S. M.↗
NASA NTRS1977

The composition of carbonaceous chondrite matrix

Matrix compositions of 32 of the approximately 40 known carbonaceous chondrites were analyzed using an electron probe defocussed-beam technique. Except in those chondrites that show evidence of metamorphism, matrices are compositionally similar and have correlation coefficients of +0.96 or greater. The implications of these analyses for the chemistry of individual matrix phases and for primitive solar system material are discussed.

Mcsween, H. Y., Jr.↗