International Comet

A., Speit, G., Thybaud, V., and Tice, R. R. (2003). Recommendations for conducting the in vivo alkaline Comet assay. 4th International Comet Assay Workshop. Mutagenesis 18, 45-51. 

The era of space travel has provided astronomers with a valuable new tool for the study of comet structure, composition, and behavior. During the two-year period 1985-86, no fewer than six spacecraft made flybys of comets. The first of these was NASA s ISEE-3 (International Sun-Earth. Explorer 3), which after completing its primary mission of studying the Sun was targeted to pass through the tail of Comet Giacobini-Zinner in September of 1985. At that point, it was renamed the International Comet E q)lorer (ICE). ICE also observed Comet Halley from a distance of 17 million miles (28 million km) in March 1986. 

Figure 11.26 shows a component removed from an air-conditioning compressor. Pinhole perforations in this component had allowed cooling water to leak into the freon. Many failures of this type had occurred previously. Examinations of the internal surfaces of both the canister and the tubes entering it revealed evidence of metal loss. Tiny perforations at the bases of deep grooves were noted in the tubes. Deep, general, smooth metal loss surrounded irregular islands of intact surface (Fig. 11.27). The canister walls displayed a similar metal loss and comet-tail-shaped depressions (Fig. 11.2).

S. Faure, N. Comet, G. Gebel, R. Meicier, M. Pineri, and B. Sillion, in Proe. 2nd International Symposium on New Materials for Fuel Cell and Modem Battery Systems, Ed. by 0. Savadogo and P. R. Roberge, Ecole Polytechnique, Montreal, 1997, pp. 818-827. 

An internal one by gas emission after accretion of the Earth, and An external one, via collisions with comets and asteroids which contained... 

Puttkamer, K. V. Quack, M. 1987a Proceedings of the 10th International Conference on Molecular Energy Transfer COMET 10 195 Puttkamer, K. V. Quack, M. 1987b Mol. Phys. 62 1047... 

Spitzer, D., Comet, M., Moeglin, J.-P., Stechele, E., Werner, U., Suma, A., Yves, International Annual Conference of ICT 2006, 37th (Energetic Materials), 117/1-117/10. 

Belt (Bell et al., 1989) and are presumed to be the origin of the radial dependence of asteroid reflectance classes with increasing distance from the Sun. Once started, the internal heating process would have been enhanced by the exothermic heat from hydration processes. Some of the water must have escaped from the interiors of internally heated asteroids and perhaps a significant proportion of main Belt asteroids showed cometary activity before they turned into what are now considered to be asteroids. Had they been observed early in the history of the solar system all of the hydrated silicate-bearing asteroids would have been considered to be comets. 

Figure 3 Light scattered off a ring of dust surrounding the star HR 4796A. Presumably the dust is generated by a Kuiper Belt distribution of comets with internal and external truncations. Image taken by NASA s Hubble Space Telescope. The figure is courtesy of B. Smith (University of Hawaii), G. Schneider (University of Arizona) and NASA.

C24. Comet, A., Hartmann, L., Bignon, J., Boulu, R., and de Traverse, P. M., Etude physlcoehimique du sue striqne humain normal et dans les gastrites. 7 Congr. Intern. Assoc. Soc. Natl. Europ. et Mediterran. Gastro-enteroL, Bruxelles, 1964, pp. 137-157. Imprim. des Sciences, Bruxelles, 1964. 

Advanced by Massachusetts Institute of Technology Professor Richard P. Binzel in 1995, the Torino scale is a revision of the Near-Earth Object Hazard Index. In 1999, the International Conference on Near-Earth objects adopted the scale at a meeting in Turino (Turin), Italy (from which the name of the scale is derived). The Torino scale is used to portray the threat to Earth of an impact with a particular comet or asteroid. The measurement scale is based upon agreement between scholars as a means to categorize potential hazards. 

The primitive carbonaceous meteorites, which include the hydrated CI and CM meteorites and mostly-anhydrous meteorites such as the Allende CV meteorite [69], reach Earth from the asteroid belt between Mars and Jupiter. Asteroid reflectance properties display a remarkably systematic distribution as a function of heliocentric distance for asteroids in this belt, and hence meteorite types, with the most primitive ones located farthest from the sun. Asteroid hydration occurred when internal heating melted (water) ice that had co-accreted with dust, chondrules and refractory inclusions in the solar nebula. These asteroids form the IR spectroscopic C-class with clays, carbon and organics at the surface similar to CI and CM meteorite parent bodies [70]. They and the Allende CV parent body, which apparently did not accrete (much) ice, are from the same zone of the asteroid belt. Even more primitive asteroids closer to Jupiter still contain co-accreted ices, organic materials and silicate dust. They define the IR spectroscopic primitive (P)-and dark (D)-class [70] bodies that include comet nuclei and many near-Earth asteroids [10]. 

Poulsen HE, Loft S (1998) Interpretation of oxidative DNA modification Relation between tissue levels, excretion of urinary repair products and single cell gel electrophoresis (comet assay). In Aruoma 01, Halliwell B (eds) DNA free radicals Techniques, mechanisms and applications. OICA International, London, pp 261-70 Poulsen HE, Loft S, Weimann A (2000) Urinary measurement of 8-oxodG (8-oxo-2 -de-oxyguanosine). In Lunec J, Griffiths HR (eds) Measuring in vivo oxidative damage a practical approach. Wiley, London, pp 69-80... 

Regulatory Acceptance. The comet assay is widely accepted by regulatory agencies, even though it was only relatively recently developed and is still being validated. No OECD guidelines are yet available, but several publications provide internationally agreed protocol recommendations (Tice et al. 2000 Hartmann et al. 2003 Burhnson et al. 2007). 

Almost since the moment that the first asteroids were discovered, scientists have been intrigued by an obvious question How were these bodies first created One possible answer is that the asteroids are the fragments left of a large planet that exploded. Such an explosion, caused by internal forces, by gravitational forces exerted by a passing comet or other body, or by some other force, could have blown such a planet into millions of small pieces that eventually became the components of the asteroid belt observed today. 

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