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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Isotopic composition of carbonaceous-chondrite kerogen Evidence for an interstellar origin of organic matter in meteorites

Stepwise combustion has revealed systematic patterns of isotopic heterogeneity for C, H and N in the insoluble organic fraction (m-kerogen) from the Orgueil and Murray carbonaceous chondrites. Those patterns are essentially identical for both meteorites, indicating a common source of m-kerogen. The data cannot be reconciled with a single mass-fractionation process acting upon a single precursor composition. This indicates either a multi-path history of mass-dependent processing or a significant nucleogenetic contribution, or both. If mass-fractionation were the dominant process, the magnitude of the observed isotopic variability strongly suggests that ion-molecule reactions at very low temperatures, probably in interstellar clouds, were responsible. In any case, an interstellar, rather than solar nebular, origin for at least some of the meteoritic organic matter is indicated. This has interesting implications for the origin of prebiotic molecules, temperatures in the early solar system, and the isotopic compositions of volatiles accreted by the terrestrial planets.

Kerridge, J. F.↗
NASA NTRS1983

Epsilon carbide - A low-temperature component of interplanetary dust particles

Transmission electron microscope study of a chondritic interplanetary dust particle has revealed the presence of epsilon iron-nickel carbide, a low-temperature carbide previously encountered only in metallurgical studies. In these studies epsilon-carbide was synthesized by carburization of iron or nickel grains in a stream of carbon monoxide or carbon monoxide plus hydrogen. Similar carburization of an iron-nickel metal in situ may have produced epsilon-carbide during particle heating on atmospheric entry or in solar orbit. Alternatively, the epsilon-carbide may be a by-product of Fischer-Tropsch reactions in the solar nebula. Such reactions have been proposed as the mechanism of hydrocarbon formation in the early solar system.

Christoffersen, R.↗
NASA NTRS1982

Terrestrial impact rates for long and short-period comets

The present calculations of terrestrial impact rates for longand short-period comets crossing the earth's orbit respectively yield probabilities of 2.2 x 10 to the -9th/perihelion passage (with a probable velocity of 56.6 km/sec), and 6.6 x 10 to the -9th/perihelion passage (probable velocity, 28.9 km/sec). The total cratering rate from both long- and short-period comets is about 15 percent of the observed rate derived from known terrestrial astroblemes, although there is substantial uncertainty in both estimates. The estimated cratering rate from earth-crossing asteroids given by Shoemaker et al. (1979) is about twice the observed rate, and Monte Carlo simulations of the dynamical evolution of the Oort (1950) cloud yield cometary flux rate estimates for the early solar system of the order of 200 times the current flux.

Weissman, P. R.↗
NASA NTRS1984

Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites

Ion and electron microprobes were used to examine Mg-26 excesses from Al-26 decay in four Al-rich objects from the type 3 ordinary hibonite clast in the Dhajala chondrite. The initial Al-26/Al-27 ratio was actually significantly lower than Al-rich inclusions in carbonaceous chondrites. Also, no Mg-26 excesses were found in three plagioclase-bearing chondrules that were also examined. The Mg-26 excesses in the hibonite chondrites indicated a common origin for chondrites with the excesses. The implied Al-26 content in a proposed parent body could not, however, be confirmed as a widespread heat source in the early solar system.

Hinton, R. W.↗
NASA NTRS1984

Lunar magnetic history

The origin of the lunar magnetic field remains a mystery. None of the various speculations are convincing. Suggestions of an early solar system field are not consistent with the low magnetization of the oldest samples. Models based upon a close approach of the Moon to the Earth have to account for the 300 M.Y. approach. Lunar dynamo models must explain why this dynamo which must operate in so small a core can operate so efficiently. It is concluded that it is now hard to escape from the idea that there was a relatively strong ancient lunar field between 3.9 and 3.6 B.Y. Moreover it is curious that the existence of this field coincided with the termination of the heavy bombardment of the Moon and mare basalt extrusion.

Cisowski, S. M.↗
NASA NTRS1984

Lunar origin: role of giant impacts

The explanation that lunar origin involved giant impacts remains attractive. Large planetesimals are consistent with current accretion models, and may have been widely scattered in the early solar system; their existence is a reasonable, assumption in Moon origin models. Isotopic data require the Moon's formation primarily from local material resembling Earth's upper mantle, not material from elsewhere in the solar system. Giant impacts are stochastic, class predictable events that would provide the required type of ejected Earth mantle material without requiring large moons to form near other planets (a problem with less stochastic processes). Such material may have mixed with incoming meteorites during lunar formation, affecting lunar chemistry.

Hartmann, W. K.↗
NASA NTRS1985

Lunar Origin: Role of Giant Impacts

The explanation that lunar origin involved giant impacts remains attractive. Large planetesimals are consistent with current accretion models, and may have been widely scattered in the early solar systems; their existence is a reasonably, assumption in Moon origin models. Isotopic data require the Moon's formation primarily from local material resembling Earth's upper mantle, not material from elsewhere in the solar system. Giant impacts are stochastic, class predictable events that would provide the required type of ejected Earth mantle material without requiring large moons to form near other planets (a problem with less stochastic processes). Such material may have mixed with incoming meteorites during lunar formation, affecting lunar chemistry.

Hartmann, W. K.↗
NASA NTRS1983

Meteor ablation spherules as chondrule analogs

Meteor ablation spherules are melt products of meteoroids that enter the earth's atmosphere. They are produced by aerodynamic melting, a process that surely produced chondrule-like objects in the early solar system but that apparently did not play a role in forming chondrules found in chondrites. The properties of ablation spherules do, however, provide insight into the chondrule problem because the spheres are chondrule analogs formed by a known process. Although the spheres have strong similarities to meteoritic chondrules, they also differ in significant respects. The differences between the spheres and chondrules suggest that chondrules could not have formed by flash melting of a primitive fine-grained chondritic precursor.

Brownlee, D. E.↗
NASA NTRS1984

Chemical and biological evolution in space

The formation of organic molecules in interstellar dust grains and the survival of bacterial spores in a space environment are examined, summarizing the results of experimental investigations and theoretical calculations. The interstellar medium is characterized; the production of organic yellow-stuff residues on the mantles of dust grains in molecular clouds by UV radiation is explained; an IR absorption spectrum toward a Galactic-center source is shown to confirm the presence of such residues; and the mass of such abiotically produced complex organic molecules in the Galaxy is estimated as at least 10 to the 7th solar mass, or 0.1 percent of the mass in the Galaxy. This finding is considered significant for the prebiotic chemistry of the earth, since comets containing large amounts of interstellar dust may have impacted the earth many times during comet showers in the early solar system. UV-irradiation experiments on bacterial spores show that initial exposures to solar UV, not interstellar survival, is the main factor rendering theries of panspermia questionable.

Greenberg, J. M.↗
NASA NTRS1985

Impact experiments. I - Ejecta velocity distributions and related results from regolith targets

Results are reported of laboratory measurements of the velocity distributions of powdery ejecta of 14 impacts into powders simulating regolith in near vacuum. The impact velocities ranged from 5-2321 m/sec, a velocity range believed prevalent in the early solar system. The powder was mechanically similar to lunar regolith. The projectiles comprised harder materials than the regolith, i.e., pyrex spheres, basalt spheres and cylinders, and igneous rocks. High-speed photography was employed to record the events. The differences between the present results and those from hypervelocity impacts are discussed in detail. Notably, an impact velocity threshold was detected between 10-30 m/sec, below which the amount of ejecta is less than the projectile mass.

Hartmann, W. K.↗
NASA NTRS1986

Isotopic characterisation of prebiotic synthesis of organic material

Many primitive meteorites contain an insoluble organic material, much like terrestrial kerogen, whose mode of origin is currently unknown. When sujbected to stepwise decomposition, this material, unlike its terrestrial counterpart, reveals characteristic release patterns for the stable isotopes of carbon, hydrogen and nitrogen as a function of fractional release of each element. The purpose of this study is to try to match those release patterns using organic matter synthesised in the laboratory under controlled conditions. If successful, such a study would shed light on the origin of kerogen-like organic matter in the early solar system and, by extension, on prebiotic organic synthesis in general. The range of possible syntheses, starting materials and reaction conditions to be investigated is considerable. Samples analysed to date include: a heavy oil produced by Fischer-Tropsch-type catalysis of CO + H2; a solid residue generated by a plasma discharge in CO + H2 + N2; a solid deposited on the electrodes of a Miller-Urey synthesis operating on CH4 + H2O + N2; and a solid residue formed by polymerization of light hydrocarbons procured by a Miller-Urey discharge acting on CH4. Significant structure is observed in the release patterns for the carbon and hydrogen isotopes from the synthetic samples, though there is little evidence for isotopic fractionation during the analysis itself.

Kerridge, J. F.↗
NASA NTRS1986

The reality of the secular change in solar wind nitrogen isotopes

Evidence concerning the isotopic composition of N in the early solar system currently seems to favor a picture of isotopic inhomogeneity rather than of a unique primordial composition modified by local processes. Certainly the range of N-15/N-14 ratios found in meteorites points to the existence of more than one nucleogenetic N component, though mass dependent modification of them explain the isotopic variation observed for N in the lunar regolith. The observational evidence is addressed which can be used to discriminate between such a model and one invoking a secular change in the composition of the solar wind. Three tests of this model were considered, starting with a search for light planetary N surviving in lunar rocks. Results so far are negative. The results of these tests may not eliminate the two component model for regolith N but they seriously weaken it. The alternate view, involving a secular change in solar wind N composition, has its problems but continues to survive by default.

Kerridge, J. F.↗
NASA NTRS1986

Laser microprobe study of cosmic dust (IDPs) and potential source materials

The study of cosmic dust or interplanetary dust particles (IDP) can provide vital information about primitive materials derived primarily from comets and asteroids along with a small unknown fraction from the nearby interstellar medium. The study of these particles can enhance our understanding of comets along with the decoding of the history of the early solar system. In addition the study of the cosmic dust for IDP particles can assist in the elucidation of the cosmic history of the organogenic elements which are vital to life processes. Studies to date on these particles have shown that they are complex, heterogeneous assemblages of both amorphous and crystalline components. In order to understand the nature of these particles, any analytical measurements must be able to distinguish between the possible sources of these particles. A study was undertaken using a laser microprobe interfaced to a quadrupole mass spectrometer for the analysis of the volatile components present in cosmic dust particles, terrestrial contaminants present in the upper atmosphere, and primitive carbonaceous chondrites. From the study of the volatiles released from the carbonaceous materials it is hoped that one could distinguish between components and sources in the IDP particles analyzed. The technique is briefly described and results for the CI, CM, and CV chondrites and cosmic dust particle W7027B8 are presented.

Gibson, E. K., Jr.↗
NASA NTRS1985

Carbon, hydrogen and nitrogen in carbonaceous chondrites Abundances and isotopic compositions in bulk samples

Whole-rock samples of 25 carbonaceous chondrites were analyzed for contents of C, H and N and delta C-13, delta D and delta N-15. Inhomogeneous distribution of these isotopes within individual meteorites is pronounced in several cases. Few systematic intermeteorite trends were observed; N data are suggestive of isotopic inhomogeneity in the early solar system. Several chondrites revealed unusual compositions which would repay further, more detailed study. The data are also useful for classification of carbonaceous chondrites; N abundance and isotopic compositions can differentiate existing taxonomic groups with close to 100 percent reliability; Al Rais and Renazzo clearly constitute a discrete 'grouplet', and there are hints that both CI and CM groups may each be divisible into two subgroups.

Kerridge, J. F.↗
NASA NTRS1986

Development and first flight of a sounding rocket payload to investigate the phenomena of rapidly varying space plasma

NASA Goddard Space Flight Center, Wallops Flight Facility has developed, flown, and recovered a unique plasma physics payload. This sounding rocket payload was developed to measure varying aspects of Alfven's critical velocity effect in a space plasma by using conical-shaped barium explosives. These measurements could possibly duplicate conditions that existed in the early solar system. This paper provides details of the payload and subpayload development, with specific emphasis on the extensive dynamic analysis of the barium release modules. Other key elements which are expanded on in the paper are: (1) design, development, and testing acceptance for the science/inertia booms using a viscous damping system for high spin rate deployment; (2) vehicle dynamic analysis; (3) apogee and impact dispersion analysis to satisfy the science and NASA safety requirements; (4) a comparison of predicted versus actual flight events.

Buchanan, R. P.↗
NASA NTRS1987

Al-26, Pu-244, Ti-50, REE, and trace element abundances in hibonite grains from CM and CV meteorites

Hibonites from the CM meteorites Murchison, Murray, and Cold Bokkeveld, and hibonites and Ti-rich pyroxene from the CV chondrite Allende are studied. Electron microprobe measurements of major element concentrations and track and ion probe measurements of Mg and Ti isotopic ratios, rare earth elements (REEs), and trace element abundances are analyzed. Correlations between isotopic anomalies in Ti, Al-26, Pu-244, and Mg-26(asterisk) are examined. Ti isotopic anomalies are compared with REE and trace element abundance patterns. Reasons for the lack of Al-26 in the hibonites are investigated and discussed. It is observed that there is no correlation between the Ti isotopic compositions, and the presence of Mg-26(asterisk), Pu-244, and REE and trace element patterns in individual hibonite samples. The data reveal that hibonites are not interstellar dust grains but formed on a short time scale and in localized regions of the early solar system.

Fahey, A. J.↗
NASA NTRS1988

The origin of the moon: Further studies of the giant impact

A number of technical improvements in the calculations which simulate the most violent event that has occurred to the earth during its history: its collision with the next largest body which was present in its region of accumulation in the early solar system, are discussed. This body was a planet in its own right, an object a little more massive than the planet Mars. The collision created a disk of molten and gaseous debris in orbit around the protoearth, and it is believed that the dissipation of this disk resulted in the formation of the moon. Also discussed is the serendipitous discovery that has emerged from the simulations: the role played by a huge, hot, rotating bar of rock and iron, which is formed immediately after the collision, in transferring angular momentum to much of the rock that is put into orbit, and in robbing the iron of angular momentum so that it falls promptly into the protoearth.

Benz, W.↗
NASA NTRS1987

Isotopic characterisation of kerogen-like material in the Murchison carbonaceous chondrite

Data on isotopic composition of C, H, and N in insoluble organic fraction from the Murchison CM chondrite were used to discriminate between different theories for the origin of prebiotic organic material in the early solar system. Considerable isotopic variability was found among the samples and attributed to kerogen-like organic fraction. Three to four different isotopic components, two of them of polycyclic aromatic nature, were tentatively identified. Aliphatic moieties in the kerogen-like material, most of the polycyclic aromatic network, and extractable amino acids were found to carry a highly D-enriched component believed to have originated in an interstellar molecular cloud. A least part of the polycyclic aromatic fraction may also represent interstellar material.

Kerridge, John F.↗