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Kerridge, J. F.

Publications and source records attributed to Kerridge, J. F..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Accretion of nitrogen during the growth of planets

The N-15/N-14 ratio measured in nitrogen of the earth's atmosphere is or was, apparently widespread in the inner solar system. Such an observation might suggest that this value (0.00361) represents that of protosolar material. The present paper argues, however, that the original ratio was at least 20% lower, the presently observed value having resulted from significant isotopic fractionation, presumably caused by nebular condensation processes.

Kerridge, J. F.↗
NASA NTRS1980

Deuterium in carbonaceous chondrites

Hydrogen isotopic compositions in seven carbonaceous chondrites lie in the range -70 to +771 per thousand relative to standard mean ocean water. These values decrease, to a range from -145 to +219 per thousand, after low-temperature oxidation in an oxygen plasma. Deuterium enrichment is therefore concentrated in the organic matter, the hydrous silicates probably lying close to the terrestrial range for such material. Calculated values for delta D of the organic fraction are +450 per thousand for Orgueil and Ivuna and up to +1600 per thousand for Renazzo. These enrichments, at least for Orgueil and Ivuna, suggest equilibration with protosolar hydrogen at very low temperatures. Assuming a value of 2.5 x 10 to the -5th for the protosolar D/H ratio, nominal equilibration temperatures of 230 K for silicates and 180 K for organic matter may be derived.

Kolodny, Y.↗
NASA NTRS1980

Secular variations in composition of the solar wind - Evidence and causes

Variations in the composition of the regolith due to irradiation by the solar wind are examined by categorizing the exposure history recorded in each sample. The history can be defined by two parameters: the duration of solar wind exposure (maturity) and a measure of how long the exposure took place (antiquity). Three partially successful methods for determining antiquity are described: the regolith contains small amounts of unsupported, trapped radiogenic noble gases, the most common being Ar-40. Assuming relatively prompt outgassing of the lunar interior, the amount of Ar-40 implanted per unit time should be proportional to the lunar content of K-40, and thus should have decayed exponentially over the lifetime of the moon. Normalization to constant exposure duration is achieved by taking the ratio Ar-40/Ar-36 in trapped gas, Ar-36 being an efficiently trapped solar wind species. The second method involves the interaction between galactic cosmic rays and lunar material producing certain spallogenic nuclides which may be analyzed in terms of a cosmic ray exposure age. The third method deals with the fact that there is a general tendency for depth within a core to be related to time deposition; two variants of this method are presented.

Kerridge, J. F.↗
NASA NTRS1979

Magnetite in CI carbonaceous meteorites - Origin by aqueous activity on a planetesimal surface

The composition and morphology of magnetite in CI carbonaceous meteorites appear incompatible with a nebular origin. Mineralization on the meteorite parent body is a more plausible mode of formation. The iodine-xenon age of this material therefore dates an episode of secondary mineralization on a planetesimal rather than the epoch of condensation in the primitive solar nebula.

Kerridge, J. F.↗
NASA NTRS1979

Clues to the origin of sulfide minerals in CI chondrites

The dominant sulfide in CI carbonaceous chondrites is an Fe-deficient pyrrhotite containing about 1% Ni, Alais, Ivuna, and Orgueil also contain minor cubanite, CuFe2S3, and Alais minor pentlandite, (Fe,Ni)9S8. All pyrrhotites contain 39.4 + or - 0.1% S; Ni contents range from 0.7 to 1.3%. The phase diagrams reveal no temperature at which the observed pentlandite-pyrrhotite assemblage is at equilibrium. Similarly, the pyrrhotite composition alone are inconsistent with equilibrium formation from a gas of solar composition. In Xe from high-purity submilligram Orgueil pyrrhotite separates, the ratios Xe-129/Xe-132 are not significantly larger than those in trapped meteoritic Xe. The lack of positive evidence for extinct I-129 in pyrrhotite does not permit any inferences regarding cooling rates in the early solar nebula. It is concluded that sulfides in CI chondrites cannot be nebular condensates formed under equilibrium conditions. Argon isotopic abundances reveal the presence of significant spallation and trapped gas components in Orgueil pyrrhotite. The Orgueil exposure age is calculated to be at least about 10 m.y.

Kerridge, J. F.↗
NASA NTRS1979

Iron-nickel sulfides in the Murchison meteorite and their relationship to phase Q1

Pentlandite from the Murchison meteorite survives HF-HCl attack and dissolves in HNO3 at room temperature, thus satisfying the operational definition of phase Q1, the proposed major carrier of carbonaceous chondrite fission xenon. However, identification of pentlandite with that phase is problematical in view of apparently differing thermal stabilities.

Kerridge, J. F.↗
NASA NTRS1979

Aqueous activity on asteroids - Evidence from carbonaceous meteorites

Carbonaceous chondrites of groups CI and CM were formed by impact brecciation and aqueous alteration of earlier generations of mineral phases within the surface regions of two or more parent bodies. Those parent bodies were probably asteroids, rather than comets, although a problem still exists in delivering such material safely to earth. Aqueous activity may have been widespread on asteroids.

Kerridge, J. F.↗
NASA NTRS1978

Light element geochemistry of the Apollo 12 site

Analytical techniques of improved sensitivity have revealed details of the concentrations and isotopic compositions of light elements for a comprehensive suite of samples from the Apollo 12 regolith. These samples show a wide spread in maturity, although maximum contents observed for solar wind elements are less than observed at other sites, possibly reflecting relative recency of craters at the Apollo 12 site. Isotopic composition of nitrogen is consistent with the idea that N-15/N-14 in the solar wind has increased with time, at least a major part of this increase having occurred in the past 3.1 Gyr. Sulfur isotope systematics support a model in which sulfur is both added to the regolith, by meteoritic influx, and lost, by an isotopically selective process. Most soils from this site are heavily contaminated with terrestrial carbon.

Kerridge, J. F.↗
NASA NTRS1978

Aspects of accretion in the early solar system

If formation of planetesimals took place by particle-particle interactions, rather than within gravitational instabilities, these interactions must have occurred at low relative velocities, leading to rates of growth which were two to three orders of magnitude slower than those characteristic of accretion within gravitational instabilities. Sticking efficiencies during particle-particle interactions are problematical, although early stages of growth were probably dominated by contact forces. Differences in accretion efficiency of metal and silicate particles probably led to the metal-silicate fractionation recorded in the composition of chondritic meteorites. It is likely that chondrules were made by particle-particle collisions prior to final accretion of planetesimals. This would have required a period of high relative velocities in an epoch otherwise characterized by low inter-particle velocities.

Kerridge, J. F.↗
NASA NTRS1978

Sputtering - Its relationship to isotopic fractionation on the lunar surface

Silicon, oxygen, sulfur and, possibly, potassium show systematic enrichment of heavier isotopes with increasing soil maturity, probably as a result of solar-wind sputtering, but such a pattern is not exhibited by solar wind-implanted species. Apparently sputter-erosion is not penetrating to their implantation depth, about 200 A. This suggests that sputtering on the moon is being impeded by deposition of vapor condensate following meteoritic impact. Although neither secular variation in the isotopic composition at the source of regolith carbon, probably the solar wind, nor isotopic fractionation of carbon after implantation in the regolith can be ruled out, carbon isotope systematics currently yield no evidence in support of either process.

Kerridge, J. F.↗
NASA NTRS1977

Cubanite - A new sulfide phase in CI meteorites

Cubanite (CuFe2S3) previously unobserved in meteorites, has been discovered in two carbonaceous chondrites, Orgueil and Alais. The association of this mineral with low-copper pyrrhotite suggests that it formed in a low-temperature environment on the meteorite parent body.

Macdougall, J. D.↗
NASA NTRS1977

Correlation between nickel and sulfur abundances in Orgueil phyllosilicates

Sympathetic variations in nickel and sulfur abundances, on a scale of micrometers, in Orgueil phyllosilicates apparently reproduce similar correlations among matrices of different carbonaceous chondrites. In Orgueil this effect probably results from aqueous alteration of a Ni-Si-bearing phase on the parent body.

Kerridge, J. F.↗
NASA NTRS1977

A constraint on impact theories of chondrule formation

The association between agglutinates and chondrule-like spherules, which characterizes the assemblage of impact-derived melt products in lunar regolith samples and some gas-rich achondrites, is not found in primitive chondrites. This observation suggests that impacts into a parent-body regolith are unlikely to have produced the chondrules. We believe that if chondrules were formed from impact melt, it was probably generated by jetting during particle-to-particle collisions, presumably in the nebula.

Kerridge, J. F.↗
NASA NTRS1977

Iron - Whence it came, where it went

Determinations of the abundances of iron and related elements in the photosphere, chromosphere, and corona of the sun as well as in solar and galactic cosmic rays are reviewed and compared with abundances derived from meteoritic data. Observed solar system abundances are found to be in accord with predictions of nucleosynthesis under either hydrostatic or explosive conditions but cannot yet be used to define these processes uniquely. The distribution of iron among planets and meteorites can probably be adequately modelled by condensation and fragmentation under equilibrium conditions above about 700 K, but below that temperature it is likely that inhibited solid-state diffusion perturbed attainment of equilibrium. Pertinent factors which are presently unknown include the mechanism responsible for metal-silicate fractionation, the grain size achieved by metallic iron in the nebula, and whether iron-bearing silicate formed prior to accretion.

Kerridge, J. F.↗
NASA NTRS1977

Solar wind nitrogen - Mechanisms for isotopic evolution

Isotope systematics of nitrogen implanted in the lunar regolith indicate that the N-15/N-14 ratio at the source of the nitrogen has increased substantially with time. This source is most plausibly identified as the solar wind reservoir. However, rigorous testing of possible mechanisms for isotopic evolution of the solar convective zone shows that they all fail, by large factors, to explain the observed effect. Evolutionary processes on the lunar surface may be similarly eliminated, leaving the lunar nitrogen isotope anomaly currently unexplained.

Kerridge, J. F.↗
NASA NTRS1976

Mafic silicates in the Orgueil carbonaceous meteorite

Iron-bearing olivines and pyroxenes occurring in Orgueil may represent a separate population distinct from the magnesian varieties previously reported. Compositions of these iron-bearing silicates are inconsistent with an origin by direct equilibrium condensation in the nebula. Such an origin is more plausible for the magnesian silicates, but lacks conclusive evidence. An extra-solar system origin for either mafic population is possible, though similarly lacking in evidence. About 15% of the olivines, randomly distributed with respect to iron content, retain particle track evidence of a precompaction irradiation.

Kerridge, J. F.↗