The formation of Mg,Fe‐silicates by reactions between amorphous magnesiosilica smoke particles and metallic iron nanograins with implications for comet silicate origins

This thermal annealing experiment at 1000 K for up to 167 h used a physical mixture of vapor phase‐condensed magnesiosilica grains and metallic iron nanograins to test the hypothesis that a mixture of magnesiosilica grains and an Fe‐source would lead to the formation of ferromagnesiosilica grains. This exploratory study found that coagulation and thermal annealing of amorphous magnesiosilica and metallic grains yielded ferromagnesiosilica grains with the Fe/(Fe + Mg) ratios in interplanetary dust particles. Furthermore, decomposition of brucite present in the condensed magnesiosilica grains was the source for water and the cause of different iron oxidation states, and the formation of amorphous Fe³⁺‐ferrosilica, amorphous Fe³⁺‐Mg, Fe‐silicates, and magnesioferrite during thermal annealing. Fayalite and ferrosilite that formed from silica/FeO melts reacted with forsterite and enstatite to form Mg, Fe‐silicates. The presence of iron in different oxidation states in extraterrestrial materials almost certainly requires active asteroid‐like parent bodies. If so, the possible presence of trivalent Fe compounds in comet P/Halley suggests that Halley‐type comets are a mixture of preserved presolar and processed solar nebula dust. The results from this thermal annealing experiment further suggest that the Fe‐silicates detected in the impact‐induced ejecta from comet 9P/Temple 1 might be of secondary origin and related to the impact experiment or to processing in a regolith.     

Pre-accretionary and parent body histories of a cometary aggregate particle

Chondrite aggregate interplanetary dust particle IDP L2011K7, collected in the Earth’s lower stratosphere, is an agglomerate of diopside, Mg,Fe-olivine, rare Fe-sulfide and abundant amorphous Mg,Fe-silicates. The overwhelming majority of amorphous silicates have a serpentine-dehydroxylate [(Mg,Fe)₃Si₂O₇] composition; a few have a smectite-dehydroxylate [(Mg,Fe)₆Si₈O₂₂] composition. The cation ratios of the amorphous silicates are notably identical to those of serpentine and smectite phyllosilicates. This paper follows the chronological changes in the amorphous silicates that include (1) formation of nanometer scale crystalline silicates (Mg,Fe-olivine and pyroxene), (2) partial hydration and formation of antigorite-serpentine proto-phyllosilicates, (3) partial dehydration of these proto-phyllosilicates, and finally oxidation and Fe-oxide formation by flash heating during atmospheric entry. Environmental conditions capable of driving these changes in the diffuse interstellar medium or solar nebula, in a comet nucleus, or in circumsolar orbit as a cometary meteoroid were marginal at best. These changes could only proceed because of the unique amorphous silicate compositions. While this study cannot make a firm statement about an interstellar or solar nebula origin for its amorphous silicates that are irradiation-induced olivine, this study does find that amorphous silicates with serpentine and (rare) smectite compositions are an important fraction of the amorphous silicates in comets in addition to amorphous olivine and pyroxene. It is noted that an ice and water-free, millimeter-scale, structurally coherent crumb would be an ample ‘microenvironment’ to evolve micrometer-scale dust. After all IDP L2011K7 only measures 22 × 17 μm.     

SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450?C900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5?C10?AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (??2 Earth radii, ??10 M_??) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.     

Natural Variations in Comet-Aggregate Meteoroid Compositions

Bulk compositions of aggregate meteoroids made of the originally accreted dust with its highly varied in mineral content and chemistry and considerable grain size variations do not have a chondritic bulk composition. Deviations from CI element abundances reflect indigenous variations within and among comet nuclei. These unmodified meteoroids that are heterogeneous in all their properties are fundamentally different from meteoroids with a CI bulk composition that are fine-grained, equigranular materials and chemically and mineralogically homogeneous. Collection and data reduction bias exists but the compositions of individual fast meteors are entirely constrained by the measured main component meteor abundances.     

A refractory Ca-SiO-H2-O2 vapor condensation experiment with implications for calciosilica dust transforming to silicate and carbonate minerals

Condensates produced in a laboratory condensation experiment of a refractory Ca-SiO-H₂-O₂ vapor define four specific and predictable deep metastable eutectic calciosilica compositions. The condensed nanograins are amorphous solids, including those with the stoichiometric CaSiO₃ pyroxene composition. In evolving dust-condensing astronomical environments they will be highly suitable precursors for thermally supported, dust-aging reactions whereby the condensates form more complex refractory silicates, e.g., diopside and wollastonite, and calcite and dolomite carbonates. This kinetically controlled condensation experiment shows how the aging of amorphous refractory condensates could produce the same minerals that are thought to require high-temperature equilibrium condensation. We submit that evidence for this thermal annealing of dust will be the astronomical detection of silica (amorphous or crystalline) that is the common, predicted, by-product of most of these reactions.     

Environmental assessment and nano-mineralogical characterization of coal,overburden and sediment from Indian coal mining acid drainage

The deterioration of environmental conditions is the major contributory factor to poor health and quality of life that hinders sustainable development in any region.Coal mining is one of the major industries that contribute to the economy of a country but it also impacts the environment.The chemical parameters of the coal,overburden,soil and sediments along with the coal mine drainage(CMD)were investigated in order to understand the overall environmental impact from high sulphur coal mining at northeastern coalfield(India).It was found that the total sulphur content of the coal is noticeably high compared to the overburden(OB)and soil.The volatile matter of the coal is sufficiently high against the high ash content of the soil and overburden.The water samples have a High Electrical Conductivity(EC)and high Total Dissolve Solid(TDS).Lower values of pH,indicate the dissolution of minerals present in the coal as well as other minerals in the mine rejects/overburden.The chemical and nano-mineralogical composition of coal,soil and overburden samples was studied using a High Resolution-Transmission Electron Microscopy(HR-TEM),Energy Dispersive Spectroscopy(EDS),Selected-Area Diffraction(SAED),Field Emission-Scanning Electron Microscopy(FE-SEM)/EDS,X-ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),Raman and Ion-Chromatographic analysis,and Mossbauer spectroscopy.From different geochemical analysis it has been found that the mine water sample from Ledo colliery has the lowest pH value of 3.30,Tirap colliery samples have the highest electrical conductivity value of5.40 ms cm~(-1)Both Ledo and Tirap coals have total sulphur contents within the range 3-3.50%.The coal mine water from Tirap colliery(TW-15 B)has high values of Mg~(2+)(450 ppm),and Br~-(227.17 ppm).XRD analysis revealed the presence of minerals including quartz and hematite in the coals.Mineral analysis of coal mine overburden(OB)indicates the presence both of pyrite and marcasite which was also confirmed in XRD and Mossbauer spectral analysis.The presented data of the minerals and ultra/nano-particles present shows their ability to control the mobility of hazardous elements,suggesting possible use in environmental management technology,including restoration of the delicate Indian coal mine areas.     

Interstellar and Interplanetary Grains Recent Developments and New Opportunities for Experimental Chemistry

Earth, Moon, and Planets -     

Laboratory experiments on wave transmission by overtopping

Laboratory experiments with regular waves were used to investigate wave transmission by overtopping for a smooth, impermeable breakwater with a 1-in-4 slope.A resulting relationship between the transmission coefficient and a breakwater height above mean sea level normalized with a theoretical wave run-up height is reported in this paper.     

Migration dynamics of clupeoids in the Schelde estuary: A stable isotope approach

Large numbers of young of the year herring (Clupea harengus L.) and sprat (Sprattus sprattus (L.)) typically enter and remain within North Sea estuaries during the winter months. The main purpose of this study was to examine their migration dynamics between the North Sea and the Schelde estuary using C and N stable isotopes. Prior to this, stomach contents were used to verify the isotopic differences between the food sources at the sampling stations. From May 2000 to April 2001 fish were collected monthly in the upper and lower estuary. Muscle tissue and stomach contents were analyzed for δ¹³C and δ¹⁵N using an EA-IRMS. Based on the stomach contents, it was demonstrated that δ¹⁵N could not be used as a tracer for fish migration because the longitudinal estuarine δ¹⁵N gradient had reversed completely during autumn. The δ¹³C gradient, however, was found to be reliable for studying fish movement in the Schelde estuary.Seasonal movements of clupeoids in the Schelde estuary were analyzed by separating the temporal abundance patterns into migration groups based on their muscle isotopic composition. Immigration and emigration seem to occur continuously throughout the year. Most exchange occurred in November. During winter, immigration remained high but gradually decreased. Although the herring and sprat abundance further declined in the estuary during February and March, large seaward emigration was not fully demonstrated. As temporal overlap between immigration and emigration is concluded the results support the hypothesis that migration to estuarine nurseries is individually based.