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NASA NTRS1977

The moment of inertia and isostasy of Mars

The systematic and large deviation of the gravitational equipotential surface (EPS) of Mars from a spheroid of revolution suggests a description of Mars in terms of a spheroid nearly in isostatic equilibrium with an extra mass in the Tharsis region. The displacement from Mars and the shape of the spheroid are calculated by using this description and a Mars gravity model. The EPS is represented as a contour map of its height above the spheroid. This representation provides the first clear demonstration that the Hellas depression coincides with a depression in the EPS. The disequilibrium contribution of Tharsis to the coefficient J2 of the second-degree harmonics of gravitational potential of Mars is estimated to be (126 + or - 5) times 10 to the minus 6th. The optical flattening and dynamic flattening calculated on this basis are in substantially better agreement than are those calculated in the usual way.

Reasenberg, R. D.↗

NASA NTRS1977

Carbon monoxide on Jupiter and implications for atmospheric convection

A study of the equilibrium and disequilibrium thermochemistry of the recently discovered carbon monoxide on Jupiter suggests that the presence of this gas in the visible atmosphere is a direct result of very rapid upward mixing from levels in the deep atmosphere where the temperature is about 1100 K and where carbon monoxide is thermodynamically much more stable. As a consequence the observed carbon monoxide mixing ratio is a sensitive function of the vertical eddy mixing coefficient. We infer a value for this latter coefficient which is about three to four orders of magnitude greater than that in the earth's troposphere. This result directly supports existing structural and dynamical theories implying very rapid convection in the deep Jovian atmosphere, driven by an internal heat source.

Prinn, R. G.↗

NASA NTRS1978

The distortion of the moon due to convection

Numerical calculations of the dynamical ellipticity of the moon due to finite-amplitude solid-state convection indicate that convection could be the cause of the nonhydrostatic gravitational figure, but only if the lunar lithosphere is capable of resisting global scale deformation. Thus lithospheric inhomogeneities and surface loads could also contribute substantially to the disequilibrium of the gravity figure. The calculations also show that it is unlikely that the geometrical distortion is due to convection.

Cassen, P.↗

NASA NTRS1978

Magma mixing at mid-ocean ridges - Evidence from legs 45 and 46-DSDP

An integrated petrologic and geochemical study of basalts recovered in Legs 45 and 46 (DSDP) has indicated, on the basis of disequilibrium mineralogy, that these moderately evolved basalts are mixtures of primitive mantle-derived tholeiites with more evolved magmas. Plagioclase phenocrysts are characterized by substantial diversity in composition and zoning pattern. Many olivine and plagioclase phenocrysts are too refractory to be in equilibrium with liquids of the host basalt composition but possess a composition consistent with crystallization from a primitive mantle-derived basalt liquid. On the basis of melt inclusions trapped in the olivine phenocrysts, features of the primitive melt are estimated. It is suggested that subvolcanic magma chambers beneath midocean ridges receive periodic injections of this primitive melt and its attendant phenocrysts which mix with fractionated chamber-bound magmas, resulting in observed moderately evolved lavas.

Dungan, M. A.↗

NASA NTRS1978

Residual glasses and melt inclusions in basalts from DSDP Legs 45 and 46 - Evidence for magma mixing

Microprobe analyses of natural glasses in basalts recovered by Legs 45 and 46 of the Deep Sea Drilling Project are reported and interpreted in the context of other geochemical, petrographic and experimental data on the same rocks (Rhodes et al., 1978). Residual glass compositions in the moderately evolved aphyritic and abundantly phyric basalts within each site indicate that none of the units is related to any other or to a common parent by simple fractional crystallization. The compositional trends, extensive disequilibrium textures in the plagioclase phenocrysts and the presence in evolved lavas of refractory plagioclase and olivine phenocrysts bearing primitive melt inclusions provide evidence that magma mixing had a major role in the genesis of the Leg 45 and 46 basalts. The magma parental to these basalts was most likely characterized by high Mg/(Mg + Fe/+2/), CaO/Al2O3, CaO/Na2O and low lithophile concentrations. A mixing model involving incremental enrichment of magmaphile elements by repeated episodes of mixing of relatively primitive and moderately evolved magmas, followed by a small amount of fractionation is consistent with the characteristics of the basalts studied.

Dungan, M. A.↗

NASA NTRS1979

Some aspects of condensation in clouds

Several general features of nucleation characteristics of low-density cosmic clouds are discussed. These are: (1) tendency for metastable condensates to form; (2) nonoccurrence of nominal refractory molecules in the gas; (3) a strong temperature dependence of condensation at relatively low temperatures; and (4) significant vibrational disequilibrium in cosmic clouds. These support previous analyses which indicate that equilibrium calculations have restricted applicability. A kinetic treatment of condensation is required for cosmic grains, and the possibility of formulating such an analysis is pointed out.

Donn, B.↗

NASA NTRS1980

A note on the Allan Hills A77278 unequilibrated ordinary chondrite

Petrographic measures of disequilibrium in the ALHA 77278 chondrite indicate that this meteorite is more equilibrated than its exceptionally high volatile element contents suggest. Based on its metal compositions, this meteorite should be classified as an LL3 rather than an L3 chondrite.

Mcsween, H. Y., Jr.↗

NASA NTRS1980

Equilibrium response of flight control systems

The steady-state behavior of an aircraft in response to control and disturbance inputs has a major impact on its performance and flying qualities, and it is, to a large extent, not readily predicted by the aircraft's stability and transient behavior. Singular as well as nonsingular response can result as a consequence of the command vector's definition, i.e., equilibrium in the command vector can imply disequilibrium in the state. The flight control structure can be modified to account for this characteristic, and it is shown that systems with identical eigenvalues and eigenvectors but dissimilar command vectors have markedly different responses.

Stengel, R. F.↗

NASA NTRS1953

Maximum Evaporation Rates of Water Droplets Approaching Obstacles in the Atmosphere Under Icing Conditions

When a closed body or a duct envelope moves through the atmosphere, air pressure and temperature rises occur ahead of the body or, under ram conditions, within the duct. If cloud water droplets are encountered, droplet evaporation will result because of the air-temperature rise and the relative velocity between the droplet and stagnating air. It is shown that the solution of the steady-state psychrometric equation provides evaporation rates which are the maximum possible when droplets are entrained in air moving along stagnation lines under such conditions. Calculations are made for a wide variety of water droplet diameters, ambient conditions, and flight Mach numbers. Droplet diameter, body size, and Mach number effects are found to predominate, whereas wide variation in ambient conditions are of relatively small significance in the determination of evaporation rates. The results are essentially exact for the case of movement of droplets having diameters smaller than about 30 microns along relatively long ducts (length at least several feet) or toward large obstacles (wings), since disequilibrium effects are then of little significance. Mass losses in the case of movement within ducts will often be significant fractions (one-fifth to one-half) of original droplet masses, while very small droplets within ducts will often disappear even though the entraining air is not fully stagnated. Wing-approach evaporation losses will usually be of the order of several percent of original droplet masses. Two numerical examples are given of the determination of local evaporation rates and total mass losses in cases involving cloud droplets approaching circular cylinders along stagnation lines. The cylinders chosen were of 3.95-inch (10.0+ cm) diameter and 39.5-inch 100+ cm) diameter. The smaller is representative of icing-rate measurement cylinders, while with the larger will be associated an air-flow field similar to that ahead of an airfoil having a leading-edge radius comparable with that of the cylinder. It is found that the losses are less than 5 percent. It is concluded that such losses are, in general, very small (less than 1 percent) in the case of smaller obstacles (of icing-rate measurement- cylinder size); the motional dynamics are such, however, that exceptions will occur by reason of failure of very small droplets (moving along stagnation lines) to impinge upon obstacle surfaces. In such cases, the droplets will evaporate completely.

Lowell, H. H.↗

NASA NTRS1981

Experimental and Theoretical Studies of Interstellar Grains

Steady state vibrational populations of SiO and CO in dilute black body radiation fields were calculated as a function of total pressure, kinetic temperature and chemical composition of the gas. Approximate calculations for polyatomic molecules are presented. Vibrational disequilibrium becomes increasingly significant as total pressure and radiation density decrease. Many regions of postulated grain formation are found to be far from thermal equilibrium before the onset of nucleation. Calculations based upon classical nucleation theory or equilibrium thermodynamics are expected to be of dubious value in such regions. Laboratory measurements of the extinction of small iron and magnetite grains were made from 195 nm to 830 nm and found to be consistent with predictions based upon published optical constants. This implies that small iron particles are not responsible for the 220 nm interstellar extinction features. Additional measurements are discussed.

Nuth, J. A., III↗

NASA NTRS1981

Primitive ultrafine matrix in ordinary chondrites

Ultrafine matrix material has been concentrated by sieving and filtering disaggregated samples of six ordinary chondrites of different classes. This component(s), 'Holy Smoke' (HS), is enriched in both volatile, e.g. Na, K, Zn, Sb, and Pb, as well as refractory elements, e.g. W and REE; however, the element ratios vary greatly among the different chondrites. SEM studies show that HS contains fragile crystals, differing in composition, and apparently in gross disequilibrium not only among themselves but also with the major mineral phases and consequently thermodynamic equilibration did not occur. Thus HS must have originated from impacting bodies and/or was inherent in the 'primitive' regolith. Subsequent impact brecciation and reheating appears to have altered, to varying degrees, the original composition of this ultrafine matrix material. Recent 'cosmic dust' studies may indicate that HS still exists in the solar system. Survival of such delicate material must be considered in all theories for the origin of chondrites.

Rambaldi, E. R.↗

NASA NTRS1980

Redistribution of volatiles during lunar metamorphism

Thermal release profiles of Pb, Zn, and Cd in sample 66095 (highly shocked breccia with melt rock matrix) showed that these volatiles were mostly present on the surface of the grains. Zn in rusty grains from 66095 was also mostly surface Zn, probably from sphalerite in grain boundaries and cracks. Simulation experiments of volatile transfer showed that Fe, FeCl2, iron phosphide, and troilite (FeS) can be produced and transported during subsolidus reactions. These results suggest that volatiles, rust, schreibersite, and possible siderophiles which are observed in lunar highland samples might have been redistributed during disequilibrium thermal metamorphism in hot ejecta blankets, and were not necessarily introduced by volcanic activity or meteoritic addition.

Cirlin, E. H.↗

NASA NTRS1982

Conditions of formation of pyroxene excentroradial chondrules

Understanding the exact mechanism of origin of chondrules and the attendant physical conditions remains a key factor in understanding the early evolution of the solar system. The present investigation is concerned with an interpretation of the range of cooling histories needed to make chondrules. Chondrule-like spherules were formed in dynamic crystallization experiments, using gas-mixing facilities. It is found that textures in pyroxene-rich chondrules are well reproduced in the laboratory by cooling melts of chondrule composition from just above the liquidus. The range of pyroxene dendrite widths is slightly greater for natural chondrules than for droplets cooled from 50 C/hr to greater than 3000 C/hr. A blanketing medium of variable thickness explains the cooling rates lower than expected for radiative cooling. Experimental results, textures indicating incomplete melting, and isotopic disequilibrium are compatible with reheating of primitive material in the early solar nebula.

Hewins, R. H.↗

NASA NTRS1983

Primordial retention of nitrogen by terrestrial planets and meteorites

Thermodynamic calculations of the amount of dissolved nitrogen in Fe-Ni alloy in a solar composition gas were done over a wide range of temperatures and pressures. The stabilities of the nitride minerals found in meteorites, a large number of other nitrides, and ammonium aluminosilicates were also calculated in a solar gas. This thorough study indicates that equilibrium mechanisms cannot account for the nitrogen contents of the terrestrial planets and meteorites. The best available data indicate that the observed nitrogen contents of planets and meteorites are several orders of magnitude greater than the predicted nitrogen contents of condensed material in a solar gas. It is suggested that the nitrogen in meteorites was originally retained as organic compounds produced by disequilibrium mechanisms. Nitrogen retention by the terrestrial planets could be due to homogeneous accretion or to accretion of a volatile-rich veneer. However, the actual mode of nitrogen accretion cannot yet be determined.

Fegley, B., Jr.↗

NASA NTRS1984

Global variation of the para hydrogen fraction in Jupiter's atmosphere and implications for dynamics on the outer planets

A detailed analysis of the Voyager infrared spectrometer measurements on Jupiter's atmosphere is presented, and possible implications of para hydrogen disequilibrium for the energetics and dynamics of that atmosphere are examined. The method of data analysis is described, and results for the large scale latitude variation of the para hydrogen fraction are presented. The Jovian results show pronounced latitude variation, and are compared with other parameters including wind fields, thermal structure, and various indicators of atmospheric clouds. The problem of equilibration rate is reexamined, and it is concluded that on Jupiter the equilibration time is longer than the radiative time constant at the level of emission to space, but that this inequality reverses at greater depths. A model for the interaction of fluid motions with the ortho-para conversion process is presented, and a consistent mixing length theory for the reacting ortho-para mixture is developed. Several implications of the Jovian data for atmospheric energetics and stability on the outer planets are presented.

Conrath, B. J.↗

NASA NTRS1984

Dynamic crystallization of silicate melts

Two types of furnaces with differing temperature range capabilities were used to provide variations in melt temperatures and cooling rates in a study of the effects of heterogeneous nucleation on crystallization. Materials of chondrule composition were used to further understanding of how the disequilibrium features displayed by minerals in rocks are formed. Results show that the textures of natural chondrules were duplicated. It is concluded that the melt history is dominant over cooling rate and composition in controlling texture. The importance of nuclei, which are most readily derived from preexisting crystalline material, support an origin for natural chondrules based on remelting of crystalline material. This would be compatible with a simple, uniform chondrule forming process having only slight variations in thermal histories resulting in the wide range of textures.

Russell, W. J.↗

NASA NTRS1985

The Evolution of CO2 on Mars

The consequences of the hypothesis that the evolution of CO2 is directly linked to the occurrence of at least transitory pockets of moisture were exposed. The current conditions preclude the existence of open bodies of liquid water and the formation of moisture in disequilibrium is not excluded by any known constraints. The water evaporation rate is inversely proportional to PCO2, and the existence of a limiting value (P*) for which liquid water can form in the Mars environment is postulated. The evolution of PCO2 is controlled largely by relatively rapid aqueous chemistry forming carbon-containing sedimentary rocks, perhaps during early history in open water, but more recently in transitory pockets of moisture in the soil. Once the total atmospheric pressure is reduced to near P*, the occurrence of transitory moisture is inhibited, and atmospheric CO2 is no longer depleted by an efficient mechanism. The role of the carbonate reservoir in the current overall carbon budget on Mars, according to this scheme, is illustrated.

Kahn, R.↗

NASA NTRS1985

Noble gases and the early history of the Earth: Inappropriate paradigms and assumptions inhibit research and communication

The development of models as tracers of nobel gases through the Earth's evolution is discussed. A new set of paradigms embodying present knowledge was developed. Several important areas for future research are: (1) measurement of the elemental and isotopic compositions of the five noble gases in a large number of terrestrial materials, thus better defining the composition and distribution of terrestrial noble gases; (2) determinations of relative diffusive behavior, chemical behavior, and the distribution between solid and melt of noble gases under mantle conditions are urgently needed; (3) disequilibrium behavior in the nebula needs investigation, and the behavior of plasmas and possible cryotrapping on cold nebular solids are considered.

Huss, G. R.↗