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At least 19 recordsLinked to original sources

30,000 years of cosmic dust in Antarctic ice.

Polar ice provides an archive for the influx of cosmic dust. Here, we present a high-resolution, glacial-to-interglacial record of cosmic dust using helium isotope analysis of the European Project for Ice Coring in Antarctica (EPICA) ice core drilled in Dronning Maud Land. We obtained a relatively constant 3He flux over the past 30,000 years. This finding excludes 3He as a pacemaker of late Pleistocene glacial cycles. Rather, it supports 3He as a constant flux parameter in paleoclimatic studies. A last glacial-to-Holocene shift of the 4He/non-sea salt Ca2+ ratio appears to indicate a glacial-to-interglacial change in the terrestrial dust source.

Journal Article↗

Carbon and silicate grains in the laboratory as analogues of cosmic dust.

Carbon and silicate grains are the two main components of cosmic dust. There is increasing spectroscopic evidence that their composition varies according to the cosmic environment and the experienced processing. Irradiation from ultraviolet photons and cosmic rays, as well as chemical interactions with the interstellar gas play a crucial role for grain transformation. The study of 'laboratory analogues' represents a powerful tool to better understand the nature and evolution of cosmic materials. In particular, simulations of grain processing are fundamental to outline an evolutionary pathway for interstellar particles. In the present work, we discuss the ultraviolet and infrared spectral changes induced by thermal annealing, ultraviolet irradiation, ion irradiation and hydrogen atom bombardment in carbon and silicate analogue materials. The laboratory results give the opportunity to shed light on the long-standing problems of the attribution of ultraviolet and infrared interstellar spectral features.

Astronomical Phenomena↗

Cryogenic synthesis of molecules of astrobiological interest: catalytic role of cosmic dust analogues.

We have studied the effects of the substrate, namely amorphous olivine (MgFeSiO(4)) cosmic dust analogues (CDAs), in synthesis of molecules obtained after 200 keV proton irradiation of formamide (NH(2)COH). Formamide has been deposited on the olivine substrate at 20 K. The abundances of new molecular species formed after an irradiation dose of 12 eV/16 amu in formamide pure (i.e. deposited on an inert silicon substrate) and deposited on CDAs have been compared. Specifically, MgFeSiO(4) amorphous olivine is a selective catalyst preventing formation of NH(3) and CN(-) molecules and changing the relative abundances of NH4(+)OCN(-), CO(2), HNCO, CO. We have shown that the role of CDAs has to be taken into account in experiments simulating processes occurring in astronomical environments.

Ammonia↗

Accretion rates of meteorites and cosmic dust in the Early Ordovician.

Abundant fossil meteorites in marine, condensed Lower Ordovician limestones from Kinnekulle, Sweden, indicate that accretion rates of meteorites were one to two orders of magnitude higher during an interval of the Early Ordovician than at present. Osmium isotope and iridium analyses of whole-rock limestone indicate a coeval enhancement of one order of magnitude in the influx rate of cosmic dust. Enhanced accretion of cosmic matter may be related to the disruption of the L chondrite parent body around 500 million years ago.

Calcium Carbonate↗

Synthesis and degradation of nucleic Acid components by formamide and cosmic dust analogues.

We show the unprecedented one-pot synthesis of a large suite of pyrimidines (including cytosine and uracil) and purines from formamide in the presence of cosmic-dust analogues (CDAs) of olivines. Since the major problem in the origin of informational macromolecules is the instability of their precursors, we also investigate the stabilizing effect of CDAs on the intrinsic instability of oligonucleotides in formamide.

Catalysis↗

An overview of the cosmic dust analogue material production in reduced gravity: the STARDUST experience.

The formation, properties and chemical dynamics of microparticles are important in a wide variety of technical and scientific fields including synthesis of semiconductor crystals from the vapour, heterogeneous chemistry in the stratosphere and the formation of cosmic dust surrounding the stars. Gravitational effects on particle formation from vapors include gas convection and buoyancy and particle sedimentation. These processes can be significantly reduced by studying condensation and agglomeration of particles in microgravity. In addition, to accurately simulate particle formation near stars, which takes place under low gravity conditions, studies in microgravity are desired. We report here the STARDUST experience, a recent collaborative effort that brings together a successful American program of microgravity experiments on particle formation aboard NASA KC-135 Reduced Gravity Research Aircraft and several Italian research groups with expertise in microgravity research and astrophysical dust formation. The program goal is to study the formation and properties of high temperature particles and gases that are of interest in astrophysics and planetary science. To do so we are developing techniques that are generally applicable to study particle formation and properties, taking advantage of the microgravity environment to allow accurate control of system parameters.

Astronomy↗

Cosmic dust analog simulation in a microgravity environment: the STARDUST program.

We have undertaken a project called STARDUST which is a collaboration with Italian and American investigators. The goals of this program are to study the condensation and coagulation of refractory materials from the vapor and to study the properties of the resulting grains as analogs to cosmic dust particles. To reduce thermal convective currents and to develop valuable experience in designing an experiment for the Gas-Grain Simulation Facility aboard Space Station Freedom we have built and flown a new chamber to study these processes under periods of microgravity available on NASA's KC-135 Research Aircraft. Preliminary results from flights with magnesium and zinc are discussed.

Cosmic Dust↗

Optical properties of synthetic carbon nanoparticles as model of cosmic dust.

Carbon nanoparticles synthesised by laser pyrolysis of small hydrocarbons are deposited at low energy on a silicon substrate. Infrared spectroscopy of the as-formed films are studied as a function of the synthesis parameters and post-treatments, such as annealing and heavy ion irradiation. Correlation between infrared spectroscopy and multiscale organisation of the samples is made through transmission electron microscopy, including image analysis. Changes in infrared spectra are analysed in terms of the carbon network building. The relevance of the results to model the structure and spectroscopy of carbon dust in the carbon-rich circumstellar media is discussed.

Astronomical Phenomena↗

The catalytic potential of cosmic dust: implications for prebiotic chemistry in the solar nebula and other protoplanetary systems.

The synthesis of important prebiotic molecules is fundamentally reliant on basic starting ingredients: water, organic species [e.g., methane (CH(4))], and reduced nitrogen compounds [e.g., ammonia (NH(3)), methyl cyanide (CH(3)CN) etc.]. However, modern studies conclude that the primordial Earth's atmosphere was too rich in CO, CO(2), and water to permit efficient synthesis of such reduced molecules as envisioned by the classic Miller-Urey experiment. Other proposed sources of terrestrial nitrogen reduction, like those within submarine vent systems, also seem to be inadequate sources of chemically reduced C-H-O-N compounds. Here, we demonstrate that nebular dust analogs have impressive catalytic properties for synthesizing prebiotic molecules. Using a catalyst analogous to nebular iron silicate condensate, at temperatures ranging from 500K to 900K, we catalyzed both the Fischer-Tropsch conversion of CO and H(2) to methane and water, and the corresponding Haber-Bosch synthesis of ammonia from N(2) and H(2). Remarkably, when CO, N(2), and H(2) were allowed to react simultaneously, these syntheses also yielded nitrogen-containing organics such as methyl amine (CH(3)NH(2)), acetonitrile (CH(3)CN), and N-methyl methylene imine (H(3)CNCH(2)). A fundamental consequence of this work for astrobiology is the potential for a natural chemical pathway to produce complex chemical building blocks of life throughout our own Solar System and beyond.

Carbon Dioxide↗

An Experimental Study on the Structure of Cosmic Dust Aggregates and Their Alignment by Motion Relative to Gas.

We experimentally studied the shape of dust grains grown in a cluster-cluster type of aggregation (CCA) and derived characteristic axial ratios to describe the nonsphericity. CCAs might be described by an axial ratio rhoCCA=rg,max&solm0;rg,min approximately 2.0 in the limit of large aggregates, where rg,min and rg,max describe the minimum and maximum radius of gyration, while small aggregates show a somewhat larger value in their mean axial ratio up to rhoCCA approximately 3.0 but rapidly decrease to the limit rhoCCA approximately 2.0. The axial ratios for large aggregates are in agreement with the general findings of different authors for axial ratios of interstellar dust grains that are generally described by rods or spheroids. Beyond this kind of agreement, our approach does not necessarily require a special shape for individual dust grains but rather offers a physical process to generate nonsphericity. Although the simple shapes might be sufficient for first-order applications and are easier to handle analytically, our results offer a firm ground of special axial ratios for rods or spheroids on a more physical basis apart from any ad hoc assumptions. We also find an alignment of the aggregates during sedimentation in a gas along the drift axis leading to an axial ratio of rhoCCA,align=1.21+/-0.02 with respect to the drift axis and an axis perpendicular to this drift. This result is directly applicable to dust grains in protoplanetary disks and planetary atmospheres.

Journal Article↗

Metallic dust collectors for low velocity impacts.

Experiments simulating the non-destructive collection of cosmic dust are conducted at the laboratory of the Lehrstuhl fur Raumfahrttechnik (LRT) of the Technische Universitat Munchen (TUM). The electromagnetic accelerator setup is described, which is capable of obtaining an impact velocity between 10 and 400 m/s with particle masses up to 1 g. The evaluation method of the ratio of collected to impacting particles is given. Various metallic surface structures were tested with respect to their collection efficiency using different types of particles from 1 to 500 micrometers in size for simulation of cosmic dust. The simulation results are presented with emphasis on collection mechanisms. Particular influences on the collection mechanisms are discussed.

Aluminum↗

Solar wind magnetic field bending of Jovian dust trajectories.

From September 1991 to October 1992, the cosmic dust detector on the Ulysses spacecraft recorded 11 short bursts, or streams, of dust. These dust grains emanated from the jovian system, and their trajectories were strongly affected by solar wind magnetic field forces. Analyses of the on-board measurements of these fields, and of stream approach directions, show that stream-associated dust grain masses are of the order of 10(-18) gram and dust grain velocities exceed 200 kilometers per second. These masses and velocities are, respectively, about 10(3) times less massive and 5 to 10 times faster than earlier reported.

Cosmic Dust↗

Cassini dust measurements at Enceladus and implications for the origin of the E ring.

During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite. The dust impact rate peaked about 1 minute before the closest approach of the spacecraft to the moon. This asymmetric signature is consistent with a locally enhanced dust production in the south polar region of Enceladus. Other Cassini experiments revealed evidence for geophysical activities near Enceladus' south pole: a high surface temperature and a release of water gas. Production or release of dust particles related to these processes may provide the dominant source of Saturn's E ring.

Atmosphere↗

[The DARI. A unit of measurement adapted to the assessment of the effect of low-dose radiation].

A clearer understanding by a wider public of the health effects of radioactive materials arising in the nuclear industry is essential if the public interest is to served. Clear and continuous information provided to the public about radiation dose from industry is inadequate to an intuitive and correct understanding of relative risk in part because radiation exposure is expressed in units that non-specialists find difficult to comprehend. We propose the establishment of a unit of irradiation dose to the individual that is equal to that provided to a human being by the naturally occurring radioactivity of human tissue: the "Dari" from the French for "Dose Annuelle due aux Radiations Internes" annual dose from internal radioactivity. To the extent of 90%, this radiation is due to potassium 40, of mean life 1.3 billion years, that was present in the cosmic dust from which the Earth was formed about 4.5 billion years ago. The DARI amounts to less than 10% of the natural radiation to which the body is subject, arising from external irradiation from rocks and from cosmic rays. The use of this unit for expressing the individual's radiation dose from an incident or an accident involving radioactive materials would facilitate a proper judgment of its impact, and would avoid unwarranted concerns.

Humans↗

Space Station gas-grain simulation facility: application to exobiology.

The Space Station provides an environment in which the forces required to suspend particles during an experiment can be reduced by as much as six orders of magnitude. This reduction in levitation force enables us to perform many new experiments in a variety of disciplines. We have grouped these experiments into two categories: 1) those involving an individual particle or the interaction between a few particles and 2) those involving clouds in particles. We consider only particle experiments at this stage because cloud experiments suffer from electrostatic interactions and levitation-forced coalescence therefore requiring considerably more space, mass and crew interaction. The displacement of a particle resulting from g-jitter for ballistic, Knudsen and Stokes flow regimes is considered in detail and the radiation, acoustic, electrostatic and electromagnetic levitation mechanisms to control this motion are reviewed. We have selected the simulation of organic haze production ion Titan as an example experiment for detailed study. The objective of this experiment is to simulate the photolysis of methane and the subsequent formation of the organic haze particles in the upper atmosphere of Titan.

Aerosols↗