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NASA NTRS1982

Characteristics of shocks in the solar corona, as inferred from radio, optical, and theoretical investigations

Solar radio bursts of spectral type II provide one of the chief diagnostics for the propagation of shocks through the solar corona. Radio data on the shocks are compared with computer models for propagation of fast-mode MHD shocks through the solar corona. Data on coronal shocks and high-velocity ejecta from solar flares are then discussed in terms of a general model consisting of three main velocity regimes.

Maxwell, A.↗
NASA NTRS1982

Chemical composition of HAL, an isotopically-unusual Allende inclusion

Samples of hibonite, black rim, and portions of friable rim from an unusual Allende inclusion, named HAL, were analyzed by INAA and RNAA for 37 major, minor, and trace elements. An unusually low amount of Ce was found in HAL, although it otherwise was highly enriched in REE compared to C1 chondrites. HAL is also depleted in Sr, Ba, U, V, Ru, Os, and Ir relative to other refractory elements. It is concluded that the distribution of REE between hibonite and rims was established when hibonite and other refractory minerals were removed at slightly different temperatures from a hot, oxidizing gas in which they previously coexisted as separate grains. Possible locations for the chemical and mass dependent isotopic fractionation are considered to be in ejecta from the low temperature helium-burning zone of a supernova and in the locally oxidizing environment generated by evaporation of interstellar grains of near-chondritic chemical composition.

Davis, A. M.↗
NASA NTRS1982

Volcanoes and climate

The evidence that volcanic eruptions affect climate is reviewed. Single explosive volcanic eruptions cool the surface by about 0.3 C and warm the stratosphere by several degrees. Although these changes are of small magnitude, there have been several years in which these hemispheric average temperature changes were accompanied by severely abnormal weather. An example is 1816, the "year without summer" which followed the 1815 eruption of Tambora. In addition to statistical correlations between volcanoes and climate, a good theoretical understanding exists. The magnitude of the climatic changes anticipated following volcanic explosions agrees well with the observations. Volcanoes affect climate because volcanic particles in the atmosphere upset the balance between solar energy absorbed by the Earth and infrared energy emitted by the Earth. These interactions can be observed. The most important ejecta from volcanoes is not volcanic ash but sulfur dioxide which converts into sulfuric acid droplets in the stratosphere. For an eruption with its explosive magnitude, Mount St. Helens injected surprisingly little sulfur into the stratosphere. The amount of sulfuric acid formed is much smaller than that observed following significant eruptions and is too small to create major climatic shifts. However, the Mount St. Helens eruption has provided an opportunity to measure many properties of volcanic debris not previously measured and has therefore been of significant value in improving our knowledge of the relations between volcanic activity and climate.

Toon, O. B.↗
NASA NTRS1982

Ground-based and airborne measurements of the Mount St. Helens stratospheric effluents

Shortly after the 18 May eruption, a series of airborne lidar flights were made over the Eastern United States. During the same period, ground-based systems were activated throughout the world. The available worldwide lidar data is put together in a consistent set. These data show the dispersion of material at different altitudes during the early global circuits. The material in the lower stratosphere and upper troposphere was very patchy in horizontal extent with backscattering ratio values over the east coast of the United States greater than 100 at the ruby wavelength of 0.6943. Two wavelength ratios and depolarization values for the material in the lower stratosphere (12 to 18 km) appear to have returned to the pre-18 May values within a month after the eruption and this indicated a rapid conversion to spherical shapes and normal indices of refraction. The material above 20 km moved slowly westward while most of the ejecta moved eastward at various speeds and directions which varied considerably with altitude. The westward material was detected first by the Japanese lidar system and then subsequently by the European and American ground-based systems. It circuited the globe in about 60 days. An airborne lidar flight in early September across the continental United States showed the layers to have homogenized considerably one broad layer between about 14 and 21 km peaking at 18 to 19 km and another more intermittent thin layer between 21 and 22 km. The ruby peak backscattering ratio of the broad layer was between 1.3 and 1.5.

Mccormick, M. P.↗
NASA NTRS1981

Morphometric consistency with the Hausdorff-Besicovich dimension

Studies using different measurement resolutions on a single morphologic feature may yield vastly different measured values for the perimeter. Apparent internal inconsistencies such as these have greatly impeded the numerical taxonomy, description, and modeling of landforms. Fortunately, the underlying internal consistency of measurements can often be reestablished by introducing the Hausdorff-Besicovich dimension into the analysis. This is demonstrated here by the example of perimeter-area ratio measurements made on some of the complicated ejecta deposits that surround many Martian meteorite-impact craters.

Woronow, A.↗
NASA NTRS1982

X-ray emission from young supernova remnants - Nonionization equilibrium abundances and emissivities

X-ray line emission from hot, low-density plasma in young supernova remnants is strongly enhanced by departures from ionization equilibrium. The X-ray emission from a Sedov blast wave has been calculated using a nonequilibrium evolutionary treatment of the ionization structure, and the resulting spectrum has been fitted to HEAO 2 SSS data for Tycho's remnant. These models yield dramatically different elemental abundances for heavy elements (Ne, Mg, Si, S, Ar, Ca, and Fe), compared with two-temperature component equilibrium models of Becker et al. (1979, 1980). Nonequilibrium broad-band X-ray emissivities result in lower mass determinations for the supernova ejecta. Areas of further improvement of remnant X-ray modeling are suggested.

Shull, J. M.↗
NASA NTRS1982

Grazing impacts on Mars - A record of lost satellites

Over 170 grazing impact craters, representing more than 5% of the total crater population of the ridged plains of Mars, can be identified on the basis of the elongate shape of the crater and the resulting pattern of ejecta deposits. These craters appear to occur along great circles, of which the more recent are in an east-west direction while the older ones are in more northerly directions. The large number and common impact directions of craters are interpreted as due to satellites whose orbits decayed with time. The locations of the projected orbital axes on the Martian surface indicate that the geographic poles of Mars were originally located at lower latitudes. The estimated combined mass of grazing impactors would form a satellite at least 225 km in diameter. These results may provide new clues as to the origin of Phobos and Deimos.

Schultz, P. H.↗
NASA NTRS1982

KREEP glass and the exotic provenance and formation of polymict breccia 66055

The Apollo 16 site polymict breccia 66055 contains abundant brown KREEP glass, as well as related brown glassy breccias having fluid forms. Most of the rock is composed of clasts of poikiloblastic breccia and mesostasis-rich impact melt which predate 66055's assembly, while the KREEP glass was created in the rock-producing impact. KREEP compositions are not common at the Apollo 16 site, leading to the speculation that 66055 originated in terrains to the west of the landing site. The presence of a granitic glass fragment that is embedded in the KREEP glass suggests that it is igneous, with a local volcanic origin which is more consistent with spatial relationships deduced from orbital geochemical data than with a basin ejecta deposit origin.

Ryder, G.↗
NASA NTRS1982

The Apennine Front core 15007/8 - Irradiational and depositional history

The Apennine Front core 15007/8 was subjected to ferromagnetic resonance (FMR), magnetic and noble gas measurements. Ferromagnetic resonance intensity I(s)/FeO surface exposure (maturity) index values and FeO concentrations are reported for 0.5 cm depth intervals, and noble gas and FMR data are given for 13 soils and two clasts selected from various depths in the 57 cm-long core. These data indicate four core units whose contacts are at about 18, 49 and 55 cm. The 0-18 cm unit has cosmogenic Xe-131/Xe-126 values that are higher than underlying soil and indicate irradiation at depths greater than 50 cm, showing it to probably be the ejecta from the crater on whose rim the core was collected. The 18-49 cm unit has relatively constant I(s)/FeO values and cosmogenic gas abundances, and may represent a mixed soil zone. I(s)/FeO drops by 30 units at the 49-cm contact. Comparison of the 15007/8 core to other ones suggests that soils on slopes tend to be mixed and to not contain units with long in situ radiation profiles.

Bogard, D. D.↗
NASA NTRS1983

Clay mineralogy of the Cretaceous-Tertiary boundary clay

Cretaceous-Tertiary boundary layer clay samples from four localities were subjected to analyses which imply that they are neither mineralogically exotic nor distinct from locally derived clays above and below the boundary. The anomalous iridium-rich ejecta component predicted by the asteroid impact scenario of Alvarez et al (1980) was not detected. It is proposed that volcanic material be considered as an explanation of the geochemical anomalies of the Cretaceous-Tertiary boundary. A model which involves a period of intense volcanism at the end of the Cretaceous would generate a variety of climatic and biological effects consonant with the geologic history of that period.

Rampino, M. R.↗
NASA NTRS1983

Thorium concentrations in the lunar surface. IV - Deconvolution of the Mare Imbrium, Aristarchus, and adjacent regions

Several fields of orbital gamma ray spectroscopy data have been deconvolved in order to model the distribution of Th over the Mare Imbrium and northern Oceanus Procellarum portions of the Apollo 15 lunar ground track, which in combination with a prior study of the Apenninus region covers a continuous swath from 10 deg E to 60 deg W in the northwest quadrant. The crater of the Aristarchus region dominates the Th distribution, with a concentration of 20 ppm, and substantial enhancements are also found in the mare regions around Brayley and at the ejecta blankets of Timocharis and Lambert. The existence of enhanced Th concentrations in mare basalt regions suggests that reservoirs of some late stage mare basalts incorporated KREEP-rich material during formation or transit.

Etchegaray-Ramirez, M. I.↗
NASA NTRS1983

Do oblique impacts produce Martian meteorites

It is pointed out that several achondritic meteorites, classified as shergottites, nakhlites, and chassignites, have a number of unusual characteristics. Following the suggestion of Wood and Ashwal (1981) these meteorites are collectively referred to as SNC meteorites. The major element compositions of the SNC meteorites are, in general, distinct from those of other meteorites and lunar samples, and similar to certain terrestrial rocks. The geochemical and geochronological characteristics of the SNC meteorites strongly imply that their parent body was on the order of lunar size or larger and geologically active. Serious attention must be given to the hypothesis of a Martian origin of the SNC meteorites and to dynamic processes capable of delivering Martian meteorites to earth. In connection with the present investigation, it is suggested that oblique impacts of large meteoroids can produce ejecta which is entrained with the ricocheting projectile and accelerated to velocities in excess of Martian escape velocity.

Nyquist, L. E.↗
NASA NTRS1983

Beginning and end of lunar mare volcanism

The distribution and characteristics of the early phases of mare vulcanism on the moon are discussed. Breccias have been observed that indicate the presence of magma flows before 3900 Myr BP. A mafic feature has been identified in more than 100 craters at least 1 km across. The absence of buried mare surfaces on the nearside and western hemispheres is attributed to ejecta deposits, and farside basins with no mare fill are suggested to have experienced early mare flooding. Photographs of the bright-rayed Lichtenberg crater have revealed that mare volcanism occurred within the time frame 1700-2000 Myr BP. It is concluded that the moon featured two periods of igneous activity, the last happening at 1000 Myr BP, and beginning 4300 BP.

Schultz, P. H.↗
NASA NTRS1982

The Halley dust model

The properties of dust ejecta from Comet Halley are studied on the basis of (a) evidence from the comet's past apparitions and (b) analogy with recent, physically similar comets. Specifically discussed are the light curve and spectrum, discrete phenomena in the head, the physical properties of the nucleus (size, albedo, rotation, surface temperature, and morphology), and an interaction between the nucleus and dust atmosphere. Also reviewed are constraints on the size and mass distributions of dust particles, information on submicron-size and submillimeter-size grains from the comet's dust tail and antitail, and the apparent existence of more than one particle type. Similarities between the jet patterns of Halley and the parent comet of the Perseid meteor stream are depicted, and effects of the surface heterogeneity (discrete active regions) on the dust flow are assessed. Current dust models for Halley are summarized and the existence of short-term variations in the dust content in the comet's atmosphere is suggested.

Sekanina, Z.↗
NASA NTRS1983

The geology of the terrestrial planets

Knowledge regarding the geology of the terrestrial planets has increased considerably during the last four years. The present investigation provides a brief summary of work during these years on the geology of Mercury, Venus, moon, and Mars. Following the Mariner 10 encounter with Mercury in 1974, the geologic history of the planet was broadly outlined by Strom (1979). McCauley et al. (1981) recognized several facies of ejecta around Caloris. Hostetler and Drake (1980) showed that unless Mercury received more than 60-70 percent of its thermal energy from tidal interactions, it must have undergone early, almost global melting. Knowledge of the Venusian surface has increased substantially over the last few years both through improvement of earth-based observations and in connection with the Pioneer Venus mission. A topographic map of Venus is presented. Attention is also given to the composition and character of lunar highlands, the evolution of different maria, photographs obtained of almost the entire planet Mars, and Martian craters and volcanism.

Carr, M. H.↗
NASA NTRS1983

Changes in interstellar atomic abundances from the galactic plane to the halo

A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron. Previously announced in STAR as N82-33310

Jenkins, E. B.↗
NASA NTRS1983

Asteroids and meteorites - Parent bodies and delivered samples

Asteroid physical strengths, which critically affect the quantity of ejecta that can be placed in orbits evolving so as to cross that of the earth, vary widely due to initial composition and size, and subsequent geophysical and collisional evolutions. The meteorite yield on earth additionally depends on meteorite strength, which affects longevity in space and survival through the atmosphere. It is presently shown that meteorites may be primarily derived by cratering rather than disruptive fragmentation, and from large, main-belt asteroids rather than from small, earth-approaching bodies. The model presented combines a variety of evidence from various disciplines to yield results that are consistent with meteorite statistics, although no claim is made for the uniqueness of the model and many of its elements remain uncertain.

Greenberg, R.↗
NASA NTRS1983

Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain Evidence for an oceanic impact site

The results of isotopic and trace-element-abundance analyses of Ir-enriched Cretaceous-Tertiary-boundary clay sediments from Caravaca, Spain, and of adjacent carbonate and marl layers, are presented. Acetic-acid and HCl leachates and residues were analyzed by isotope dilution to determine K, Rb, Sr, Sm, and Nd concentrations and Sr-87/Sr-86 and Nd-143/Nd-144 ratios. The stable isotope ratios delta-D, delta-(C-13), and delta-(0-18) were also determined. The results are presented in tables and graphs and compared with published data on the Caravaca sediments and on samples from other locations. The boundary clay is found to be distinguished from the adjacent layers by its isotopic ratios and to be of mainly terrestrial, lithospheric (deeper than 3-km) origin. Although submarine-weathering effects are evident and difficult to quantify, the degree of variation in Ni, Ir, Sr, and REE concentrations is considered too large to be attributed to postdepositional processes alone. These findings are seen as evidence for the ocean impact of a large single asteroid producing a worldwide blanket of ejecta, a large injection of water vapor into the atmosphere, and perhaps a gigantic tsunami, at the end of the Cretaceous period.

Depaolo, D. J.↗