Anhydrous Interplanetary Dust Particles Research Articles

Compositional variations of olivines and pyroxenes in chondritic interplanetary dust particles

Abstract We report here analyses of olivines and pyroxenes, and petrofabrics of 27 chondritic interplanetary dust particles (IDPs), comparing those from anhydrous and hydrous types. Approximately 40% of the hydrous particles contain diopside, a probable indicator of parent body thermal metamorphism, while this mineral is rarely present in the anhydrous particles. Based on this evidence, we find that hydrous and anhydrous IDPs are, in general, not directly related, and we conclude that olivine and pyroxene major‐element compositions can be used to help discriminate between IDPs that are (1) predominantly nebular condensates, and lately resided in anhydrous or icy (no liquids) primitive parent bodies, and (2) those originating from more geochemically active parent bodies (probably hydrous and anhydrous asteroids).

Nanometer-scale mineralogy and petrography of fine-grained aggregates in anhydrous interplanetary dust particles

Fine-grained matrices in seven (solar flare) track-rich anhydrous interplanetary dust particles (IDPs) were studied using (200 keV) analytical electron microscopy. The IDPs are U222B42, U220A19, U222B28, U230A3, W7027A11, W7027H14, U219-C2, (and U219-C11). The matrices are composed of aggregates of glass, disordered carbonaceous material, and crystalline mineral grains with diameters between 1 and 150 nm. The mineral grains were characterized using lattice fringe imaging, electron microdiffraction, and quantitative energy-dispersive X-ray spectroscopy (EDS). The glasses were studied using EDS and electron energy-loss near edge structure analysis (ELNES). Three types of aggregates were observed, unequilibrated, equilibrated, and reduced aggregates. Unequilibrated aggregates (UAs) are 0.1–0.3 μm diameter objects with bulk major element compositions that are approximately chondritic (solar) except for carbon. They contain FeNi metal and Fe-rich sulfide crystals, between 1 and 20 nm diameter, embedded in silicate glass. Equilibrated aggregates (EAs) are 0.1 to 1 μm diameter objects that exhibit melt textures and mineralogy. They contain Fe-bearing olivine and pyroxene grains, with equilibrated Fe Mg ratios, and Fe-sulfides embedded in feldspathic (alumino-silicate) glass. Reduced aggregates (RAs) are 0.1 to 1.0 μm objects with FeNi metal, FeNi carbides, and Fe-rich sulfides embedded in a carbonaceous matrix. The aggregates in the seven anhydrous IDPs appear to have formed in diverse physiochemical environments.

The genetic relationship between hydrous and anhydrous interplanetary dust particles

It is a fundamental goal of interplanetary dust particle (IDP) research to determine the sources and histories of these primitive extraterrestrial materials. Chondritic IDPs have been divided into anhydrous and hydrous varieties, with sub-classification being made on the grounds of the dominant anhydrous (olivine or pyroxene) or hydrous (smectite or serpentine) present. The presumption is that hydrated IDPs experienced aqueous alteration on parent bodies (hydrous asteroids or possibly comets); we wish to discover whether the anhydrous IDPs were the initial raw materials for these reactions. We report here analyses of olivines and pyroxenes from 22 large (>15 um) chondritic IDPs: 18 anhydrous and 4 hydrous; olivines and pyroxenes are scarce in most hydrous IDPs, when present at all Finally, we compare anhydrous to hydrous IDPs, and both to chondritic meteorites.Figure 1 shows our results for this study. We find there to exist no significant difference in the compositions of olivines from olivine vs. pyroxene dominated IDPs, which are therefore plotted together (in contrast to our preliminary results for a smaller data set).

Comparative mineral chemistry of IDPs, micrometeorites and meteorite matrices

Chondritic porous aggregates are one subclass of Interplanetary Dust Particles (IDPs). The remaining classes presently identified are hydrated IDPs consisting mainly of serpentine or smectite. We have been investigating mineral compositions in these types of IDPs, in micrometeorites from Antarctica and compared them to mineral compositions in finegrained meteorite materials, like matrices and chondrule dust mantles from several meteorite classes. Based on our mineral analyses we subdivide anhydrous IDPs into three types. Type I contains olivines and/or pyroxenes having very variable iron contents from Fa 0 to Fa 35 and Fs 0 to Fs 30. Mineral phases in these particles are truly unequilibrated. Mineral grains in several particles of type I IDPs were found to contain solar flare tracks (pers. comm. John Bradley, McCrone Associates, Chicago). Almost all type I IDPs studied contain low-iron manganese enriched (LIME) olivines and/or pyroxenes.

惑星間塵の鉱物学

Interplanetary dust particles (IDPs), collected in the Earth's stratosphere, have been a subject of intense laboratory studies for the last ten years. A significant proportion of collected IDPs has a composition close to the solar (or chondritic) elemental abundance. This paper reviews results of mineralogical, petrological and chemical studies of the chondritic IDPs. Experimental studies on mineralogy, infrared absorption spectra, and isotopic properties of the chondritic IDPs have suggested that they are primitive and may contain records of the early solar system and possibly of events that predate it. Specific mineralogical and chemical features provide indications of processes including direct condensation from the solar nebula, hydrocarbon formation in the nebula, and aqueous alteration in water-rich parent bodies. Of particular interest are the mineralogical and chemical relationships between IDPs and carbonaceous chondrites. Data of both IDPs and carbonaceous chondrites have accumulated, and it is now possible to compare the mineralogies of the IDPs and the meteorites in considerable detail. Important points of information and their implications for the origin of IDPs are discussed. The current knowledge of mineralogy and chemistry of IDPs suggests that most hydrated IDPs were derived from asteroids and most anhydrous IDPs were derived from comets.

Physical and Mineralogical Properties of Anhydrous Interplanetary Dust Particles in the Analytical Electron Microscope

AbstractThe fine grained mineralogy and petrography of anhydrous “pyroxene” and “olivine” classes of chondritic interplanetary dust have been investigated by numerous electron microscopic studies. The “pyroxene” interplanetary dust particles (IDPs) are porous, unequilibrated assemblages of mineral grains, metal, glass, and carbonaceous material. They contain enstatite whiskers, FeNi carbides, and high-Mn olivines and pyroxenes, all of which are likely to be well preserved products of nebular gas reactions. Solar flare tracks are prominent in most “pyroxene” IDPs, indicating that they were not strongly heated during atmospheric entry. The “olivine” IDPs are coarse grained, equilibrated mineral assemblages that have probably experienced strong heating. Since most “olivine” IDPs do not contain tracks, it is possible that this heating occurred during atmospheric entry.

Automated thin-film analyses of anhydrous interplanetary dust particles in the analytical electron microscope

An analytical electron microscope (AEM) equipped with digital beam control was used to obtain quantitative point count analyses from thin-sections of eight anhydrous chondritic interplanetary dust particles (IDPs). The electron beam was rastered on a two-dimensional grid over each thin-section. A preset video threshold was used to locate chondritic material. Between 200 and 500 X-ray analyses were collected from each thin-section with a total of 2804 spectra from the eight IDPs. Each spectrum was analyzed for Mg, Al, Si, S, Ca, Cr, Mn, Fe, and Ni using a Cliff-Lorimer thin-film correction procedure. Cluster analysis was used to identify major and minor mineral phases and their relative abundances. Petrographic features of each thin-section were determined from brightfield and darkfield images. Two types of anhydrous chondritic aggregates were observed in the eight IDPs. One was highly porous with an average grain size < 10 2 nm and the other was less porous with grains between 10 2 and 10 3 nm. Most IDPs were dominated either by the fine- or coarse-grained aggregates and there was a tendency towards enstatite enrichment in the fine, and olivine enrichment in the coarse components. One IDP contained both fine- and coarse-grained aggregates. Pyroxene and olivine in the fine-grained aggregates usually contain < 5 mole % Fe while those in the coarse aggregates contain up to 30 mole % Fe. The eight anhydrous IDPs are mixtures of fine- and coarse-grained aggregates, large ( > 10 3 nm) mineral grains, glass, and carbonaceous material. On a scale of less than a micrometer, elemental concentrations follow those of solar abundances, suggesting that they are chemically pristine and unperturbed by aqueous alteration. Using an automated AEM and cluster analysis we are able to rapidly characterise IDP thin-sections. It now appears possible to develop an IDP classification scheme based on AEM data.