Interplanetary dust particles (IDPs) were recovered from the stratosphere by a cryosampler flown below a balloon flying at altitudes of 20-41 km. The present study uses high-resolution scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) spectrophotometry to examine fresh samples collected at 38-41 km. The SEM observations confirm the presence of 7-32 mm sized clusters of coccoidal (0.4-1.3 mm in diameter) and rod-shaped (0.6-2.5 mm in length) objects as components of the IDP complex. Many single globules (1.6-9.0 mm in diameter) are also observed, some of which exhibit a rough surface with filamentous features of variable lengths. The spectrophotometry of the particles in aggregate reveals a prominent peak centred at 216 nm, which is remarkably similar to that of diatoms and close to the UV astronomical feature of 217.5 nm that has been identified as the spectral characteristic of aromatic hydrocarbons. The evidence presented here suggests that the stratospheric particles are IDPs comprising an assortment of materials among which are included microfossil-like features in variable sizes and forms, such as coccoids, rods and filaments.
: The interstellar absorption band centred on 2175 Å that is conventionally attributed to monodisperse graphite spheres of radii 0.02 mm is more plausibly explained as arising from biologically derived aromatic molecules. On the basis of panspermia models, interstellar dust includes a substantial fraction of biomaterial in various stages of degradation. We have modeled such an ensemble of degraded biomaterial with laboratory spectroscopy of algae, grass pigments, bituminous coal and anthracite. The average ulrtraviolet absorption profile for these materials is centred at 2175 Å with a full width at half maximum of 250 Å , in precise agreement with the interstellar extinction observations. Mid-infrared spectra also display general concordance with the unidentified interstellar absorption features found in a wide variety of astronomoical sources.
Tagish Lake meteorite, which fell in January 2000 in Canada, has provided a sample of pristine cosmic materials for laboratory studies. It is made up of loosely formed aggregates, making it one of the most friable carbonaceous chondrites. Its complex structure is composed of plaquettes of crystalized minerals, hexagon-shaped metals, chondrules and granules, all of which are embedded in a matrix of fine grains and fibril-like materials. Those components with sizes larger than 250 nm in diameter are affected to varying degrees by hydrothermal reactions, whereas the majority of smaller bodies (<350 nm in diameter) appear unscathed despite severe aqueous alterations on the parent body. A high population of granules (100-300 nm in diameter) consist of a wall (20-40 nm in thickness) and a larger core; the former is rich in organic elements, such as carbon, oxygen and sulfur, and the core contains Ni-Fe-Mg rich silicates. The organic matter has aromatic and aliphatic characteristics, and such evidence suggests that the granules may be the carriers of large organic species with distinct astrobiological implications.
Particles in the Carancas meteorite were examined by electron microscopy (transmission electron microscopy/scanning electron microscopy), energy dispersive analysis of X-rays (EDAX) and Fourier Transform Infrared spectroscopy. Scanning electron microscopical observations reveal that the particles of variable sizes have a stony appearance. Many of these particles show fractures in places, thus confirming an ealier observation that the meteorite was subjected to a high-velocity impact. The outer rim of many aggregates displays a mud crack-like texture. At high magifications, this texture shows ovoid and elongated features, which appear similar to microfossils found in other meteorites.As revealed by both scanning and transmission electron microscopy, some particles show three clearly marked zones, distinguishable by their differences in electron density and texture : a light zone, a dark zone and an intermediate zone. The EDAX analysis of these particles shows that the light zone is composed of silicates rich in Fe, Ni and S (the elements of troilite and pentlandite). The dark zone contains high concentrations of Mg and Si (the major elements of high-temperature minerals, such as forsterite, Mg 2 SiO 4 and enstatite, MgSiO 3 ) intermixed with carbonates and traces of Al, Ca and Na. The intermediate zone also contains high-temperature minerals and Fe-Ni rich silicates.The Carancas meteorite produces an infrared waveband showing prominent features of some carbonate species, amorphous and crystalline silicates, and olivine groups. Hydrated silicates and hydroxyl groups are less abundant, as shown by the presence of small humps between 2.5 and 8.0 mm.The abundance of high-temperature minerals and iron-rich metal confirms an earlier observation that the meteorite is an ordinary H4/5 chondrite. Some particles in the Carancas meteorite are found to have structural and chemical characteristics similar to those of the 81P/Wild 2 comet.
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