AbstractThe study discusses the subject involving meteors and meteorites wherein the comprising sections are its compositions, origin, classifications, and the history and records of meteorite collision on Earth. The study utilizes review of related literature in order to obtain these data and validate the statements molded by astronomers as to the exact nature and significance of meteoritic phenomena. Moreover, the study involves the records review of these incidents, most especially the significant events, in order to obtain awareness on the cause, effect and significance of these happenings to scientific embodiment especially on the field of astronomy.
Meteors and MeteoritesIntroductionThe physical and chemical properties of solar material play a central role in any discussion of the origin of the Solar System, the properties of the Jovian planets, or the Sun itself. The Sun, in turn, serves as our prototype for the study of all other parts. The raw interstellar material out of which stellar and planetary systems form has a composition essentially identical to that of the atmospheres of all Population Main Sequence stars (Lewis 2004 71). Since celestial bodies on roughly parabolic orbits in the neighborhood of the Earth have a velocity of 42 kms-1, and on the other hand, the orbital velocity of the Earth itself is 30kms-1, depending on the direction of approach (morning or evening) relative velocities between 72 and 12 kms-1 can be reached (Unsold and Baschek 2001 90).
The meteorites, being the only cosmic matter, which is directly accessible on the Earth, have been carefully investigated, at first using mineralographic and petrographic methods, and more recently, for traces of radioactive elements and anomalous isotopes. It was originally believed that the chemical analyses of a large number of meteorites by V.M. Goldschmidt and the Noddacks represented the “cosmic abundance distribution of the elements (Unsold and Baschek 2001 91).
Today, these data are used in conjunction with the quantitative analysis of the Sun to give information on the early history of the meteoritic material and of the Solar System.DiscussionDefining Meteors and MeteoritesThe bright, fast-moving streaks of light often seen in the night sky are called meteors. They are caused by the entry of small solid particles of cometary or asteroidaldebris, called meteoroids, into Earth’s upper atmosphere as such high speeds that they flash into incandescent vapor in a fraction of a second (Kerrod 2000 19). Most of the meteoroids that produce meteor displays on Earth are members of quite well defined swarms that pursue highly eccentric orbits around the Sun and encounter Earth at fixed points on Earth’s orbit, also known as fixed dates, at predictable intervals, appearing to radiate from a particular point in the sky called the radiant point (Woolfson 200 37).
Encounters of Earth with these swarms produce correlated displays of many meteors, collectively called meteor showers. Meteor showers are commonly named after the constellation front, which they appear to radiate, as In the Leonid, Perseid and Lybrid showers. In extreme cases, the display may be so intense as to merit the name meteor storm (Lewis 2004 72). Small meteorites burn up in the atmosphere as “falling stars” at an altitude of’ about 100 km (Zanda 2001 19).
On their paths through the upper atmosphere, they ionize a tube-shaped region of air. Large meteor showers, thus, contribute to the ionosphere, along with the socalled anomalous E-layer at about 100 km altitude (Unsold and Baschek 2001 90; Woolfson 200 37). Meteorites are defined as solid macroscopic bodies that survive entry into Earth’s atmosphere. They are not associated in any way with shower meteors and are so rare that they are not often observed to enter the atmosphere.
Although, an observer can see several meteors per hour on almost any clear, dark night, meteorites of recoverable size fall at an average rate of little more than one per year for each million square kilometers of Earth’s surface (Lewis 2004 72). On entering the Earth’s atmosphere, the objects are heated. In the case of larger objects, the heat cannot penetrate sufficiently rapidly to the interior, and the surface forms melt-pits anti burns off; such objects reach the ground being meteorites. The largest known meteorite is the Hobo, in Namibia, with a mass of about 60 tons.
It must have required very large masses to make some of the meteoritic craters on the Earth (Unsold and Baschek 2001 89).Types and CompositionsMeteorites are also a sample of the solid fragmented asteroidal matter that pervades the inner Solar System and that accounts for much of the cratering on the Moon and the other terrestrial planets. Some meteorites have the texture of a low-temperature mixture of solids, never severely heated or melted, with ages of about 46 billion years. These meteorites usually contain small glassy beads of silicates, called chondrules after the Greek word for droplet or seed (Kerrod 2000 20).
The meteorites that contain chondrules are called chondrites. Other meteorites show textures and compositions diagnostic of melting, density-dependent geochemical differentiation, and subsequent cooling (Draganic 1993 175). These ranges in composition from the stony achondrites, through the stony-irons, to the dense, metal-rich irons, and Of these, the oldest and chemically most primitive are the chondrites (Lewis 2004 73). The matrix of the Cl carbonaceous chondrites must have been formed at temperatures below about 360 K.
The formation of the (older) chondrites, and in particular, the separation of metals (Fe, Ni) and silicates implies complicated separation processes, which are only partially understood. J. W Larimer, E. Anders, and others (Unsold and Baschek 2001 91) have calculated the successive production of various chemical compounds and minerals depending on the pressure and temperature.
According to these results, the chondrites required formation temperatures of 500 to 700 K (Unsold and Baschek 2001 91).Significant Events of Meteorite CollisionTable 1: Meteorite StatisticsTypeFall%Find%Fall WeightFind WeightStony95.079.8152008300Stony-Iron1.
01.65258600Iron4.018.627000435000The table implicates the overall meteorite records obtained from 1740-1990 with exception to those found in Antarctica.
The approximately 10,000 known meteorites are quite varied in their properties, ranging from huge crystals of iron-nickel alloy weighing teas of tons down to 10-mg lumps of clayey material rich in organic matter (Zanda 2001 19). Most meteorites are predominantly composed of silicates, sulfides, and metal. Because, aside from the samples returned from the Moon, meteorites are the only samples of extraterrestrial matter available for study in terrestrial laboratories, they play a major role in our ideas about the chemical composition of Sobs System material. Moreover, because most meteorites are much older than the oldest known lunar and terrestrial rocks, they take on great importance in relation to questions of origin (Lewis 2004 73).
The well-known crater of Canyon Diablo in Arizona has a diameter of about 1.2 km and a depth of 170 m. According to the geologic evidence, it must have been formed about 20,000 years ago by the impact of an iron meteorite of about one million tons mass. The Nordlinger Ries in southern Germany, with a diameter of about 25km, is probably also a meteoric impact crater, which was produced 15-106 yr ago in the Tertiary Era (Draganic 1993 175).
The crater, which has been discovered under thick layers of sediment near Chicxulub in Yucatan, with a diameter of around 180 km, must have been made by the impact of a large object with a diameter of about 10km, which among other effects led to the extinction of the dinosaurs at the end of the Cretaceous Era (Unsold and Baschek 2001 90; Zanda 2001 19).Origin of Meteors/ MeteoritesMost Meteorites are too dense to have derived from comet-related meteoroids; hence, they survived the plunge to the ground. They resemble the inferred physical characteristics of asteroids. Orbits of meteorites prove to be like those of asteroids rather than of comets (Zeilik 2002 237).
The great diversity of meteorites is directly linked to that of their origin and their history within their parent bodies. In particular, their mineralogical composition reflects differing degrees of thermal evolution: most micrometeorites as well as certain carbonaceous chondrites are primitive, in the sense that they have not been subject to sufficiently high temperatures for alteration of their component minerals to have taken place. Ordinary chondrites may have been subjected to more or less pronounced metamorphism, producing solid-phase changes. Finally, the achondrites, the stony-iron and the iron meteorites have obviously been formed by complete melting, followed by recrystallization (or differentiation) (Encrenaz 2004 471).
ConclusionAs to the study, meteors/ meteorites can be classified as achondrites, chondrites, stony-iron and iron meteorites. The origin of these objects is derived from different, and probably unknown, space structures (etc. rocks, shards, etc.) that may have been due to collision or space activity.
Meteors and meteorites, significantly, possess variations of structure, form, location, and other significant feature; yet, the comparison lies in the fact that these are heavenly bodies capable of carrying the evidences of the outside space.Works CitedDraganic, I G. Radiation and Radioactivity on Earth and Beyond. CRC Press, 1993.
Encrenaz, T. The Solar System. Springer, 2004.Kerrod, R.
Asteroids, Comets, and Meteors. Lerner Publications, 2000.Lewis, J S. Physics and Chemistry of the Solar System.
Academic Press, 2004.Manuel, O. Origin of Elements in the Solar System: Implications of Post-1957. Springer, 2000.
Unsold, A, and B Baschek. The New Cosmos: An Introduction to Astronomy and Astrophysics. Springer, 2001.Woolfson, M M.
The Origin and Evolution of the Solar System. CRC Press, 2000.Zanda, B. Meteorites: Their Impact on Science and History.
Cambridge University Press, 2001.Zeilik, M. Astronomy: The Evolving Universe. Cambridge University Press, 2002.