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The subsolidus cooling history of basaltic rocks can be deduced from the distribution of divalent Mg and Fe ions over the two nonequivalent positions M1 and M2 in pyroxene. The ion exchange reaction between M1 and M2 is generally characterized by rapid kinetics. It is found that the normal cooling process of basalt 14053 was interrupted at a temperature below 840 C and that the rock was then quenched extremely rapidly.
The thermal history of the lunar interior has been investigated for many sets of parameters and initial conditions by the construction of mathematical models. These models have been extended to include the effects of melting and redistribution of radioactive heat sources with time. The models considered include the possibility of heat transfer by lattice conduction, radiative transfer, removal of radioactive heat sources and, in a molten zone, fluid convection. The energy sources are divided into initial temperature sources that operate during the formation of the moon or shortly thereafter, and long-lived radioactive heat sources.
New information is used to demonstrate that better models for the thermal history of the moon are required. As a first step, account is taken of (1) a nonuniform initial composition in terms of fraction of low melting to high melting phase present, and for variation in the uranium, potassium, and thorium contents as a function of depth, (2) partitioning of the radioactive elements between the melt and the solid phases, and (3) a cutoff value of melt which must be exceeded before magma can move to the surface. The results of several attempts to determine whether reasonable conditions, composition, and thermal properties can be expected to give rise to two separate periods of volcanism are discussed. Two models with somewhat different distributions of radioactive heat sources and different conductivities are examined.
The testimony which the main features of the lunar surface bear on the cosmic environment in which the satellite acquired its principal morphological characteristics is examined. It is assumed as a working hypothesis that, in the earliest stages of the moon's history, the lunar sculpture in the continental areas was predominantly shaped by external impacts. It is considered that the argument against heliocentric orbits of particles whose collisions with the moon disfigured most of its continental areas continues to hold good. The distribution of craters due to oblique impacts appears to be essentially at random all over the lunar surface.
The Mintz-Arakawa 2-level general circulation model has been used in a series of experiments to compute the response of the model atmosphere to: (1) a positive sea surface temperature anomaly in the North Pacific Ocean in summer and in winter, (2) an identical anomaly in the South Pacific Ocean in the Southern Hemisphere winter, and (3) anomalous northward and southward displacements of the Northern Hemisphere snow line over the continents. In each case computations were carried out for 90 forecast days. Results are shown in terms of the differences between anomaly and control histories. Time series of certain regional response indices, including area-average sea level pressure and 600 mb circulation indices, as well as 30-day mean sea level pressure maps are used in the analysis. Of particular interest is the evidence of significant interhemisphere influence.
An analytical rationale for the sensitivity-insensitivity of dispersion-strengthened systems to process history is provided. In particular, the research was focussed upon the influence of the particle-matrix interface bond in TD-Nickel and TD-Nichrome, and the manner in which the differences in both elastic constants and thermal expansion coefficients between these phases stress this interface when these alloys are subjected to mechanical and thermal loads upon the mechanical properties of these alloys.
In seasonal computations, the Mintz-Arakawa two-level model is found to be sensitive to a minor alteration in the computational program. Effects of the program change on monthly mean sea level pressure fields are small in the first month, but large in the second and third months, although the meteorological histories generated by both the original and modified programs are equally credible. The inherited effects of a transient (one month) sea surface temperature (SST) anomaly on the computed monthly mean sea level pressure fields over a period of a season are about as large in absolute magnitude as those generated in the model by a persistent (seasonal) SST anomaly. The effects of a transient SST anomaly in the North Pacific Ocean on monthly and seasonal temperature and precipitation in the eastern United States may be large enough to produce a change of one or two class intervals in these predicted weather elements. The model-generated precipitation in the equatorial region is also found to be sensitive to the sea surface temperature field in the North Pacific.
The possible thermal history of the moon is investigated by means of theoretical models. The calculations include the effects of melting and time-dependent redistribution of radioactive heat sources. The known constraints can best be satisfied by a model which is characterized by relatively high initial temperatures close to the melting range; melting and, consequently, fractionation and redistribution of radionuclides would occur during the first 1.5 b.y. and would then be followed by an effective cooling process. Heat flow measurements on the lunar surface should permit a distinction between such a completely fractionated model and a nonfractionated model or a model with restricted fractionation in the outer few hundred kilometers.
Study of the distribution of magnesium and ferrous iron over the M1 and M2 positions in pyroxenes from the basaltic rocks 14053 and 14310, aimed at an analysis of the subsolidus cooling history. The results obtained suggest that the subsolidus cooling of the basalt 14310 occurred at a depth of several meters in a coherent body of appreciable size. As for the 14053, the hot debris of which it was a part were deposited after the projection from the Imbrium basin; some smaller fragments, including 14503, cooled very rapidly in the cold Fra Mauro regolith by conduction.
The lunar velocity profile and laboratory data on terrestrial and lunar rocks are constraints on models of lunar history. They show that shock-induced microcracks are absent from the rocks present in the moon today at depths of 25 to 60 kilometers. All possible causes of this observation are examined, and the most likely explanations are that either the rocks at depths of 25 to 60 kilometers formed after the major impacts ceased or the microcracks have annealed at temperatures of about 600 C over geologically long times.
A brief history is reported of the first San Marco project, a joint program of the United States and Italy. The Project was a three phase effort to investigate upper air density and associated ionosphere phenomena. The initial phase included the design and development of the spacecraft, the experiments, the launch complex, and a series of suborbital flights, from Wallops Island. The second phase, consisting of designing, fabricating, and testing a spacecraft for the first orbital mission, culminated in an orbital launch also from Wallops Island. The third phase consisted of further refining the experiments and spacecraft instrumentation and of establishing a full-bore scout complex in Kenya. The launch of San Marco B, in April 1967, from this complex into an equatorial orbit, concluded the initial San Marco effort.
The effect of tidal friction on the inclination of the lunar orbit to the earth's equator for earth-moon distances of less than 10 earth radii is examined. The results obtained bear on a conclusion drawn by Gerstenkorn and others which has been raised as a fatal objection to the fission hypothesis of lunar origin, namely, that the present nonzero inclination of the moon's orbit to the ecliptic implies a steep inclination of the moon's orbit to the earth's equatorial plane in the early history of the earth-moon system. This conclusion is shown to be valid only for particular rheological models of the earth. The earth is assumed to behave like a highly viscous fluid in response to tides raised in it by the moon. The moon is assumed to be tideless and in a circular orbit about the earth. The equations of tidal friction are integrated numerically to give inclination of the lunar orbit as a function of earth-moon distance.
All lunar samples measured to date contain a weak but stable remanent magnetization of lunar origin. The magnetization is carried by metallic iron and is considered to be caused by cooling from above the Curie point in the presence of a magnetic field. Although at present the moon does not have a global field, the remanent magnetization of the rock samples and the presence of magnetic anomalies, both on the near and far side of the moon, imply that the moon experienced a magnetic field during some portion of its history. The field could have been generated in a liquid iron core sustaining a self-exciting dynamo, but there are some basic thermal and geochemical objections that need to be resolved.
A numerical experiment was made on the Mintz-Arakawa two-level global general circulation model, investigating the effects of a transient one-month sea-surface temperature (SST) anomaly and of a persistent three-month SST anomaly. The time histories are compared with a control run that lacked the anomaly pattern. After one month, the anomaly and control synoptic patterns were as uncorrelated as any two random fields. It is found that the transient SST anomaly can alter the monthly and seasonal temperature and precipitation in the eastern U.S. by as much as two class intervals. The question of whether the real atmosphere is as sensitive to such an anomaly is raised but cannot be settled at this time.
The application of experimentally derived data on (1) the Zr partitioning between coexisting ilmenite and ulvospinel and (2) the Ti partitioning between coexisting troilite and ilmenite has allowed the discernment of differences in subsolidus cooling histories of lunar rocks - e.g., the Apollo 15 Type I Mare basalts. The rocks which show Zr partitionings reequilibrated to lower temperature (i.e., below 950 C), as a result of slow cooling, also show evidence for subsolidus reduction of ulvospinel to ilmenite + native Fe. It is suggested that the presence of ulvospinel reduction is not evidence a priori that these rocks have undergone more reducing conditions than the other Apollo 15 Mare basalts; it may only indicate that the cooling rates were slower in that subsolidus temperature range (i.e., much less than 900 C) where oxygen fugacity values were favorable for ulvospinel reduction. The rocks with higher temperature Zr partitionings and no ulvospinel reduction may have cooled under the same fugacity conditions but at a faster rate.
Particle track studies reveal an abundant record of fossil solar flare tracks in breccia components. Metamorphic events govern the degree to which this record is preserved, and studies of phases with different track retentivities allow limits to be placed on temperatures reached during a rock's history. The least affected breccias have never experienced temperatures as great as 300 C. Two breccias which contain xenon from spontaneous fission of Pu-244 (14301 and 14318) and Xe-129 (14301 only) have never been heated above about 700 C. This and evidence for a surface irradiation of some of the breccia components support a surface implantation model for the origin of the xenon in these breccias. Green glass spheres in 15086 have not been heated above about 300 C during or after breccia formation yet have retained fission tracks for less than 0.7 G.y. Argon ages of about 3.5 G.y. for similar green glass are at least five times as great and may indicate that the glass was not completely outgassed at is formation.
Cosmogenic radionuclides, including Na-22, Al-26, and Mn-54, were measured in a sample of the recently-fallen Malakal hypersthene chondrite. The high Al-26 activity, 79 plus or minus 2 dpm/kg, greatly exceeds the levels expected from elemental production rates, shielding considerations, or comparisons with other ordinary chondrites, and can only be explained by exposure to a uniquely high cosmic-ray flux. Calculations including noble gas, H-3, and Mn-53 data from other laboratories require a two-stage irradiation. Malakal's most probable history is: exposure in excess of 4 m.y. to an effective cosmic-ray flux approximately three times that experienced by other chondrites, an orbit change (very possibly caused by a collision), and a final period of about 2 m.y. during which it was exposed to a normal cosmic-ray flux.
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.