Micrometeorite

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. 

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Space-based solar ceUs are covered with a very thin layer of vitreous siHca to protect against the damaging environment of space such as atomic oxygen, micrometeorites, and radiation effects. Because the siHca is transparent to damaging uv radiation, it is normally coated with a uv-reflective thin film... 

Plastics will continue to be required in space applications from rockets to vehicles for landing on other planets. The space structures, reentry vehicles, and equipment such as antennas, sensors, and an astronaut s personal communication equipment that must operate outside the confines of a spaceship will encounter bizarre environments. Temperature extremes, thermal stresses, micrometeorites, and solar radiation are sample conditions that are being encountered successfully that include the use of plastics. 

As mentioned at the beginning of this chapter, diffusive separation of low atomic or molecular weight species into space causes them to be permanently lost from the Earth. Thus, the Earth is deficient in He and H2 relative to the best estimates of initial terrestrial composition. Some species might be accreted from space certainly, micrometeorites represent a small but identifiable flux. Published speculations exist regarding other substances, notably water. However, these would appear to be relatively unimportant at present. 

Maurette M (1998) Micrometeorites on the early earth. In Brack A (Ed.) The Molecular Origins of Life. Cambridge University Press p 147... 

Engrand C. and Maurette M. (1998). Carbonaceous Micrometeorites from Antarctica (Invited Review). Meteorites and Planetary Science 33 565-580... 

Solids Organic Particulate Matter Inorganic Particulate Matter ng/L to mg/L ng/L to mg/L Plankton biomass, fecal pellets, molts, feeding nets Atmospheric dust, riverborne clay minerals, iron oxyhydroxides, micrometeorites... 

The micrometeorites that melt during passage through Earth s atmosphere tend to solidify as spheres. These are termed cosmic spherules. The mineralogy of these spherules is given in Table 13.2. Their high iron and nickel content make them much denser (3 to 6g/cm ) than continental rock ( 2.7g/cm ). Like aeolian particles, cosmic dust deposited on the sea surface eventually settles to the seafloor via pelagic sedimentation. 

It is of interest primarily for very uniform ultra-thin films and coatings (0.002-5 mils) in applications such as electrical resistors, thermistors, thermocouples, stator cores, connectors, fast-sensing probes, photo cells, memory units, dropwise steam condensers for recovery of sea water, pellicles for beam splitters in optical instruments, windows for nuclear radiation counters, panels for micrometeorite detection, dielectric supports for planar capacitors, encapsulation of reactive powders, and supports in x-ray and optical work. Any significant growth would depend upon a major breakthrough in process techniques and a consequent lowering in price. 

The mass of the earth increases daily due to falls of extraterrestrial material. The estimates by different authors of the flux of extraterrestrial matter vary by many orders of magnitude, depending on the estimation method used. In his recent book, Dodd 5) gives an estimation of 102-103 tons per day, the largest part being in the shape of dust particles (or micrometeorites). 

Esser and Turekian (1988) estimated an accretion rate of extraterrestrial particles in ocean bottom and in varved glacial lake deposit on the basis of osmium isotope systematics and concluded a maximum accretion rate of between 4.9 x 104 and 5.6 x 104 tons/a. The discrepancy between this estimate and those derived from helium can easily be attributed to the difference in the size of the cosmic dust particles under consideration. Cosmic dusts of greater than a few ten micrometers may not be important in the helium inventory of sediments because the larger grains are likely to lose helium due to atmospheric impact heating (e.g., Brownlee, 1985). Stuart et al. (1999) concluded from studies on Antarctic micrometeorites that 50- to 1 OO-qm micrometeorites may contribute about 5% of the total flux of extraterrestrial 3He to terrestrial sediments. Therefore, the helium-based estimate deals only with these smaller particles. 

Maurette, M., Olinger, C., Christophe Michel-Levy, M. C., Kurat, G., Pourchet, M., Brandstatter, F., Bourot-Denise, M. (1991) A collection of diverse micrometeorites recovered from 100 tons of Antarctic blue ice. Nature, 351, 44-7. 

Stuart, F. M., Harrop, P. J., Knott, S., Turner, G. (1999) Laser extraction of helium isotopes from Antarctic micrometeorites Source of He and implications for the flux of extraterrestrial 3He to earth. Geochim. Cosmochim. Acta, 63, 2653-65. 

Interplanetary dust particles Micrometeorites Cosmic spherules Stardust particles... 

In addition to meteorites, three other important types of extraterrestrial material are available for analysis interplanetary dust particles (IDPs), micrometeorites, and Stardust samples. Interplanetary dust particles are collected in the stratosphere by high-altitude research aircrafts. Most of these samples are smaller than 20 pm in diameter, although some of the highly porous cluster particles probably exceeded... 

Presolar grains are found in small quantities (with concentrations of ppb to several 100 ppm, see Table 2.1) in all types of primitive Solar System materials (Lodders Amari 2005 Zinner 2007). This includes primitive meteorites (the chondrites), IDPs, some of which might originate from comets, Antarctic micrometeorites (AMMs), and samples from comet Wild 2 collected by NASA s Stardust mission. Presolar grains are nanometer to micrometer in size. The isotopic compositions, chemistry, and mineralogy of individual grains with sizes >100 nm can be studied in the laboratory. Important analysis techniques are secondary ion mass spectrometry (SIMS) and resonance ionization mass spectrometry (RIMS)... 

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