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Meteoritic particles

Another special class of particles is meteoritic dust of cosmic origin. Smaller meteoritic particles (r < 1 m) can reach the lower layers of the atmosphere without significant modifications. However, larger meteorites falling through the atmosphere partly or totally evaporate due to frictional heating. In the troposphere, spherical droplets from the condensation of the resulting vapour can be identified (e.g. Wirth and Prodi, 1972). Pettersson estimates (see Cadle, 1973) that 14 x 10f t of meteoritic materials are collected annually by the atmosphere of our planet. [Pg.102]

It is believed by some workers that meteoritic particles may play an important role in the formation of precipitation, since they serve as ice forming nuclei in clouds of appropriate negative temperatures. Since ice crystal formation may initiate precipitation formation in mixed clouds (i.e. clouds containing liquid as well as solid phase), Bowen argues (see Fletcher, 1962) that the distribution of precipitation is controlled to some degree by meteor showers reaching the atmosphere. It is to be noted, however, that this theory is far from generally accepted by cloud physicists (Fletcher, 1962). [Pg.102]

Figure 32.8. After hypervelocity capture of meteoritic particle, this keystone was cut and removed from the bulk sample of RF aerogel. Approximate dimensions are 600 by 250 by 75 pm. Figure 32.8. After hypervelocity capture of meteoritic particle, this keystone was cut and removed from the bulk sample of RF aerogel. Approximate dimensions are 600 by 250 by 75 pm.
Pig. 6. A 0.3-mm-diameter cosmic spherule coUected from the ocean floor. The particle is composed of oUvine, glass, and magnetite and has a primary element composition similar to chondritic meteorites for nonvolatile elements. The shape is the result of melting and rapid recrystaUi2ation during... [Pg.100]

Tritium has also been observed in meteorites and material recovered from sateUites (see also Extraterrestrial materials). The tritium activity in meteorites can be reasonably well explained by the interaction of cosmic-ray particles and meteoritic material. The tritium contents of recovered sateUite materials have not in general agreed with predictions based on cosmic-ray exposure. Eor observations higher than those predicted (Discoverer XVII and sateUites), a theory of exposure to incident tritium flux in solar flares has been proposed. Eor observations lower than predicted (Sputnik 4), the suggested explanation is a diffusive loss of tritium during heating up on reentry. [Pg.14]

The number of scientific articles published on meteorites has increased dramatically in the last few years few of these, however, concern themselves with small meteorites, the size of which lies between that of the normal meteorites (from centimetres to metres in size) and that of interplanetary dust particles. In the course of an Antarctic expedition, scientists (mainly from French institutions) collected micrometeorites from 100 tons of Antarctic blue ice (Maurette et al 1991). These micrometeorites were only 100 400 pm in size five samples, each consisting of 30-35 particles, were studied to determine the amount of the extraterrestrial amino acids a-aminoisobutyric acid (AIBS) and isovaline—both of which are extremely rare on Earth—which they contained. The analysis was carried out using a well-tested and extremely sensitive HPLC system at the Scripps Institute, La Jolla. Although the micrometeorites came from an extremely clean environment, the samples must have been contaminated, as they all showed traces of L-amino acids. Only one sample showed a significantly higher concentration of AIBS (about 280 ppm). The AIBS/isovaline ratio in the samples also lay considerably above that previously found in CM-chondrites. [Pg.71]

Another feature of meteorites that proves to be important is the calcium-aluminium inclusions (CAIs), which, as the name suggests, show regions of enhanced Ca and Al. These micron- to centimetre-sized particles are some of the oldest objects known and have a similar temperature history. They probably formed at temperatures in the region 1700-2400 K and so are close to the centre line of the solar nebula. Although it is hard to be sure about the origin of these objects, there is agreement on their age based on radioisotope dating. [Pg.165]

Experiments on board the NASA Long Duration Exposure facility have been performed with spores from the bacterium Bacillus subtilis, allowing them to be exposed to the extreme conditions of space. Low pressures and highly energetic particles are dominant in space and most importantly around the Sun, including an intense UV radiation field. It is the latter that is the most destructive in terms of viability of the spores, and under controlled conditions the extreme UV exposure is four orders of magnitude more likely to kill the cells than when screened. Crucially, however, not all spores were killed. Protection of the spores from the UV field for example within the interior of the meteorite suggests that the spores... [Pg.179]

Meteoroid A particle of interplanetary debris that can enter the atmosphere of a planet to become either a meteor or a meteorite. [Pg.313]

The existence and distribution of the chemical elements and their isotopes is a consequence of nuclear processes that have taken place in the past in the Big Bang and subsequently in stars and in the interstellar medium (ISM) where they are still ongoing. These processes are studied theoretically, experimentally and obser-vationally. Theories of cosmology, stellar evolution and interstellar processes are involved, as are laboratory investigations of nuclear and particle physics, cosmo-chemical studies of elemental and isotopic abundances in the Earth and meteorites and astronomical observations of the physical nature and chemical composition of stars, galaxies and the interstellar medium. [Pg.1]

Brown LE, Clayton DD (1992) Silicon isotopic composition in large meteoritic SiC particles and Na origin of Ne. Science 258 970-972... [Pg.57]

Nittler LR, Alexander CMOD (2003) Automated isotopic measurements of micron-sized dust application to meteoritic presolar silicon carbide. Geochim Cosmochim Acta 67 4961-4980 Nuth JA(1987) Small-particle physics and interstellar diamond. Nature 329 589... [Pg.61]

These resnlts snggest that the interplanetary dust particles are among the most primitive samples available for laboratory stndies. Isotopically anomalous material constitutes only a small fraction of the investigated particles. Thus, it appears that the isotopic composition of these anomalons particles is not different from those observed in minor components of primitive meteorites. [Pg.94]

It is one of the most sensitive and specific methods available for the determination of trace quantities of a wide range elements in such diverse media as terrestial, lunar and meteoritic materials, marine sediments, air borne particles, natural water, biological material, hair, drugs, coal, petroleum, blood, etc. [Pg.210]

Cosmochemistry is the study of the chemical composition of the universe and the processes that produced those compositions. This is a tall order, to be sure. Understandably, cosmochemistry focuses primarily on the objects in our own solar system, because that is where we have direct access to the most chemical information. That part of cosmochemistry encompasses the compositions of the Sun, its retinue of planets and their satellites, the almost innumerable asteroids and comets, and the smaller samples (meteorites, interplanetary dust particles or IDPs, returned lunar samples) derived from them. From their chemistry, determined by laboratory measurements of samples or by various remote-sensing techniques, cosmochemists try to unravel the processes that formed or affected them and to fix the chronology of these events. Meteorites offer a unique window on the solar nebula - the disk-shaped cocoon of gas and dust that enveloped the early Sun some 4.57 billion years ago, and from which planetesimals and planets accreted (Fig. 1.1). [Pg.1]


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See also in sourсe #XX -- [ Pg.102 , Pg.126 ]




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