Engineering topics

Zolensky, M. E.

Publications and source records attributed to Zolensky, M. E..

208 records · Page 12

NASA NTRS1991

Clay minerals in primitive meteorites and interplanetary dust 1

Many meteorites and interplanetary dust particles (IDPs) with primitive compositions contain significant amounts of phyllosilicate minerals, which are generally interpreted as evidence of protoplanetary aqueous alteration at an early period of the solar system. These meteorites are chondrites (near solar composition) of the carbonaceous and ordinary varieties. The former are subdivided (according to bulk composition and petrology) into CI, CM, CV, CO, CR, and ungrouped classes. IDPs are extraterrestrial particulates, collected in stratosphere, which have chemical compositions indicative of a primitive origin; they are typically distinct from the primitive meteorites. Characterization of phyllosilicates in these materials is a high priority because of the important physico-chemical information they hold. The most common phyllosilicates present in chondritic extraterrestrial materials are serpentine-group minerals, smectites, and micas. We discuss these phyllosilicates and describe the interpretation of their occurrence in meteorites and IDPs and what this indicates about history of their parent bodies, which are probably the hydrous asteroids.

Zolensky, M. E.↗

NASA NTRS1990

The Bholghati howardite - Petrography and mineral chemistry

A 10 g sample of the Bholghati howardite was disaggregated in order to separate two eucrite clasts, several small carbonaceous clasts, fragments of diogenitic pyroxene, and bulk matrix. The eucrite clasts show evidence of moderately rapid cooling from a melt, followed by prolonged subsolidus annealing. The carbonaceous clasts mostly resemble CM2 carbonaceous chondrites with low-iron silicates and Fe-Ni sulphides in a fine grained dark matrix. One clast, however, is mineralogically, petrographically, and compositionally similar to a CI1 chondrite. Both carbonaceous and eucritic clasts have a complex history prior to incorporation into the howardite matrix with no evidence of significant metamorphism since assembly. Most clasts in the howardite breccia are monomineralic, with pyroxene and plagioclase predominant. Pyroxenes range from 'diogenitic' to 'eucritic' with diogenitic compositions most abundant; a significant number of intermediate compositions are present, consistent with derivation from a series of rocks related by fractionation.

Reid, A. M.↗

NASA NTRS1989

Titanium carbide and titania phases on Antarctic ice particles of probable extraterrrestrial origin

Two unique titania-rich particles, found within ancient Antarctic ice have been discovered and characterized, and are believed to be of extraterrestrial origin. Both particles contain abundant submicron-sized crystals of Magneli phases (Ti(n)O(2n-1). In addition, one particle contains a core of TiC. Whereas the Magneli phases would have been stable in the early solar nebula, and so probably formed there, the TiC is more likely to have condensed in the cool, dusty, carbon-rich outer shell of a red giant star. It is suggested that both particles are interplanetary dust particles whose Magneli phases carry a record of the PO2-T conditions of the early solar nebula. It is further suggested that the TiC grain in particle 705 is remnant interstellar dust.

Zolensky, M. E.↗

NASA NTRS1989

The measurement of trace elements in interplanetary dust and cometary particles by ultra-high sensitivity INAA

Today the major elemental composition of interplanetary dust particles (IDPs) is routinely determined in many laboratories. These and mineralogical studies have revealed the presence of at least two major types of IDPs, chondritic and refractory. Preliminary results of a successful attempt to determine abundances of a large suite of trace elements from both chondritic and refractory IDPs are reported. The analytical procedure can be used in the grain-by-grain analysis of returned cometary samples. Chondritic and refractory IDPs are characterized by standard scanning electron microscopy and energy dispersive x ray spectroscopy (SEM-EDX) techniques. With this system, detection limits for many elements are well below picogram levels, and some approach femtogram levels. This technique is non-destructive, although some sample handling is required, so particles can be analyzed by other techniques after instrument neutron activation analysis (INAA) is completed. Data is presently being reduced from the analyses of 7 IDPs. These are U2015E10, U2015F1, W7029-A2, W7029-A3, W7013A8, LACl (all chondritic) and 705 (refractory). So far, 17 different major and trace elements were detected and measured in these particles, including rare earths and some very volatile elements (Br and Zn).

Zolensky, M. E.↗

NASA NTRS1988

Computer modeling of the mineralogy of the Martian surface, as modified by aqueous alteration

Mineralogical constraints can be placed on the Martian surface by assuming chemical equilibria among the surface rocks, atmosphere and hypothesized percolating groundwater. A study was made of possible Martian surface mineralogy, as modified by the action of aqueous alteration, using the EQ3/6 computer codes. These codes calculate gas fugacities, aqueous speciation, ionic strength, pH, Eh and concentration and degree of mineral saturation for complex aqueous systems. Thus, these codes are also able to consider mineralogical solid solutions. These codes are able to predict the likely alteration phases which will occur as the result of weathering on the Martian surface. Knowledge of the stability conditions of these phases will then assist in the definition of the specifications for the sample canister of the proposed Martian sample return mission. The model and its results are discussed.

Zolensky, M. E.↗

NASA NTRS1987

Tektite-like bodies at Lonar Crater, India - Implications for the origin of tektites

Homogeneous dense glass bodies (both irregular and splash form) with high silica contents (about 67 pct SiO2) occur in the vicinity of Lonar Crater, India. Their lack of microlites and mineral remnants and their uniform chemical composition virtually preclude a volcanic origin. They are similar to tektites reported in the literature. While such a close association of tektite-like bodies with impact craters is already known (Aouelloul Crater, Mauritania; Zhamanshin Crater, U.S.S.R.), the tektite-like bodies at Lonar Crater are unique in that they occur in an essentially basaltic terrain. Present geochemical data are consistent with these high silica glass bodies being impact melt products of two-thirds basalt and one-third local intertrappean sediment (chert). The tektite-like bodies of the impact craters Lonar, Zhamanshin, and Aouelloul are generally similar. Strong terrestrial geochemical signatures reflect the target rock REE patterns and abundance ratios and demonstrate their terrestrial origin resulting from meteorite impact, as has been suggested by earlier workers.

Murali, A. V.↗

NASA NTRS1985

Accurate stratospheric particle size distributions from a flat plate collection surface

Flat plate particle collections have revealed the presence of a remarkable variety of both terrestrial and extraterrestrial material in the stratosphere. It is found that the ratio of terrestrial to extraterrestrial material and the nature of the material collected may vary significantly over short time scales. These fluctuations may be related to massive injections of volcanic ash, emissions from solid fuel rockets, or variations in the micrometeoroid flux. The variations in particle number density can be of great importance to the earth's atmospheric radiation balance, and, therefore, its climate. With the objective to assess the number density of solid particles in the stratosphere, an examination has been conducted of all particles exceeding 1 micron in average diameter for a representative suite of particles obtained from a single flat plate collection surface. Attention is given to solid particle size distributions in the stratosphere, and the origin of important stratospheric particle types.

Zolensky, M. E.↗

NASA NTRS1984

Proposed structures for poorly characterized phases in C2M carbonaceous chondrite meteorites

A recent investigation of C2M carbonaceous chondrite meteorite matrices using electron microscopy and High-Resolution Transmission Electron Microscopy (HRTEM) has provided data on the structure and chemistry of Poorly Characterized Phases (PCP). It is suggested that a dominant matrix variety (10 A PCP) has a structure equivalent to iron-rich tochinilite (6Fe0.9S5/Fe, Mg//OHO2/), which consists of coherently intrastratified mackinawite and brucite sheets. In addition, it is proposed that 17 A PCP is a commensurate intergrowth of serpentine and tochinilite layers. Various forms of PCP observed in carbonaceous chondrites appear to be intergrowths of tochinilite, serpentine, and tochinilite-serpentine minerals.

Mackinnon, I. D. R.↗

NASA NTRS1984

Toward a complete inventory of stratospheric dust particles with implications and their classification

As the Earth travels about the Sun it continuously sweeps up material laying in its path. The material includes dust-sized fragments of the meteors, comets and asteroids that have passed by as well as much older particles from out between the stars. These grains first become caught in the mesosphere and then slowly pass down through the stratosphere and the troposphere, finally raining down upon the Earth's surface. In the stratosphere the cosmic dust particles encounter increasing amounts of contaminants from the Earth. At the highest reaches of Earth's atmosphere these contaminants consists mainly of dust from the most explosive volcanoes, rocket exhaust, and other manmade space debris. In the troposphere windborne particles and pollen become an increasingly larger fraction of the atmospheric dust load. An increased knowledge of the nature of cosmic particles is suggested.

Zolensky, M. E.↗

NASA NTRS1984

Hydrothermal alteration of CM carbonaceous chondrites: Implications of the identification of tochilinite as one type of meteoritic PCP

Poorly characterized phases (PCP's) constitute up to 30 volume percent of some CM carbonaceous chondrites, and are therefore an important key to an understanding of the physico-chemical conditions attending matrix evolution. An iron rich form of the terrestrial phase tochilinite was recently identified as a common type of PCP. Tochilinite has the general formula 6Fe(0.9)S.5(Mg,Fe)(OH)2 and consists of alternating machinawite (FeS) and brucite ((Mg,Fe)(OH)2) sheets, with iron vacancies in the sulfide sheets. In iron rich tochilinite, ferrous hydroxide, called amakinite, replaces brucite. If CM carbonaceous kchondrites have underdone hydrothermal alteration, iron rich tochilinite, at least, probably grew from aqueous solutions characterized by low FO2, high FS2, pH 10 to 12, and at a temperature at or below 170 C.

Zolensky, M. E.↗