Meteorite

“ It seems as though analysing a meteorite was like questioning a messenger from the stars, and throws a glow of light on the probable structure of the sister world. When broken, their appearance inside is grey, earthy, or metallic; but the outside is invariably covered by a dark metallic shining crust, produced, perhaps, by a fusion of the constituent elements. ”

“ First of all, meteorites neither all look alike nor have the same composition. The general term “meteorite” applies to any mass that reaches the earth from space. Such masses are made up of metals and minerals in varying proportions. The term “meteorite” is nearly as general in meaning as the word “rock,” which geologists apply to bodies, large and small, that are formed by earth processes and are composed of various kinds of minerals. Actually, there are almost as many different kinds of meteorites as there are kinds of rocks ”

“ So they reject the theory that such dust found in the Podkamennaya Tunguska area is specifically connected with the meteorite that fell there a half century ago.
If sizable chunks of meteoritic material enter the atmosphere, they may produce exceptionally large and brilliant meteors. A spectacular meteor is generally known as a “fireball” if it is as bright as Venus or Jupiter. It receives the French term bolide if, in addition to showing great brilliance, its flight is accompanied by detonations like the alarming sounds heard at the time of the Ussuri and Norton meteorite falls. ”

“ This sudden generation of heat will cause fusion, and even luminosity, of the outer material of the meteorite, and in some cases a combustion of some of its constituents: the products of the thermal and mechanical action sufficiently account for the cloud from which the meteorite is generally seen to emerge as a ball of fire, and also for the visible trail often left behind. The ball of fire has often an apparent diameter larger even than that of the moon, and is sometimes too bright for the eye to gaze upon. ”

“ Have we not also seen that a meteorite projected from a globe lying in the stellar regions would almost certainly fail even to cross the orbit of our earth, inasmuch as the probability of its doing so would be only one against many thousands of millions? When, however, we locate the volcanoes which are presumed to be the origin of meteorites on the earth, these improbabilities disappear altogether. ”

“ Admitting the celestial origin of the meteorites, they surely claim our closest attention. They afford the only direct method we possess of obtaining a knowledge of the materials of bodies exterior to our planet. We can take a meteorite in our hands, we can analyse it, and find the elements of which it is composed. We shall not attempt to enter into any very detailed account of the structure of meteorites; it is rather a matter for the consideration of chemists and mineralogists than for astronomers. A few of the more obvious features will be all that we require. ”

“ Then, too, the movements of meteorites have a certain significance both for the astronomer and the mathematician. It is true that only the last stage of its wild career can be observed, for the flight of the meteorite for millions of preceding years is quite unknown, so far as any direct observations are concerned. The observer never beholds one of these bodies until that supreme moment when at the conclusion of its incalculable journey it flashes from the sky and strikes the earth beneath. ”

“ The iron and stony-iron meteorites are very heavy. A 1-inch cube of iron meteorite weighs approximately 8 times as much as a 1-inch cube of ice. Even the stones, which are only about half as dense as the irons, are much heavier than ordinary rocks.
Does your specimen show a thin blackish or brownish crust on its outer surfaces? You will recall that specimens of both the Ussuri and Norton meteorites showed a “glaze” of fused material which we call fusion crust. Most freshly-fallen meteorites are covered with such a crust. ”

“ In the geologic past, meteorite falls may not have occurred as often as they do today. For example, the primeval atmosphere of the earth may have been so much denser than at present that even quite large meteorites were totally vaporized as they passed through it and therefore never reached the ground. ”

“ Later, these pieces had to be laboriously reassembled by scientists before any idea could be gained of the original shape and surface features of the meteorite.
Even when thorough searches are made, not all the meteorite fragments in the area of fall may be found for many months. But if the people living in the region have been alerted and are on the lookout for unusual specimens or signs of meteoritic impact (such as freshly made holes or “craters” in the ground, shattered tree limbs, and so forth) , the chances of ultimately finding many or most of the fallen masses are good. ”

“ But, says another:
"If the Drift fell from a comet, why would not this clay-dust and these pebbles have been consumed before reaching the earth by the friction of our atmosphere just as we have seen the meteoroids consumed; or, if not entirely used up, why would these pebbles not show a fused surface, like the iron aërolites? "
Here is the difference: a meteorite, a small or large stone, is detached, isolated, lone-wandering, lost in space; it comes within the tremendous attractive power of our globe; it has no parental attraction to restrain it ”

“ Typical distribution of meteorite fragments according to size, within oval-shaped area of fall. The larger masses of the shower carry farther on, in the direction of the motion of the meteorite. As early as 1814, investigators had noted this peculiarity of meteorite-shower distributions. ”

“ The scientist was not allowed to touch it, but he got close enough to verify that the stone was a meteorite covered with a typical blackish fusion crust.
Not only has man worshipped meteorites, but during a period extending from approximately 300 B.C. to 300 A.D., emperors and self-governing cities frequently marked the fall of meteorites by minting special coins or medals known as betyls. ”

“ As we have already mentioned, numerous fragments of the 96 Norton meteorite (including one weighing 130 pounds) were found within two to three months after its fall on February 18, 1948. But the main mass was not discovered until the following August, when a caterpillar tractor nearly tipped over into the large impact funnel that this huge stone had made in the earth. ”

“ Where meteorites have been located as they fell and recovered, the majority of them were of this type, so that probably more than half of the meteorites which fall are of the stony type. However when the stony meteorite is exposed to weathering it takes only a very short time before the surface is eroded off and then such a meteorite looks like any other boulder and probably most of them fail to be recognized, and so have been lost. Because they have so much greater variety, they are in many ways of greater interest than the iron type. ”

“ The impact of the meteorite upon the earth not only caused an upheaval of the surface, but it also crushed and displaced the rocks beneath. As the stellar body penetrated deeper into the earth its force became more concentrated and either compressed the rocks into a denser mass or ground them to powder. ”

“ The sudden condensation of air in front of the meteorite, the consequent generation of heat and expansion of the outer shell, have been held to account not only for the break-up of the meteorite into fragments, but partly also for the crash like that of thunder which is a usual accompaniment of the fall. ”

“ This particle may be as small as a tiny dust grain or as large as one of the minor planets which are called asteroids. Fortunately for the inhabitants of the earth, most of the meteor-forming masses encountered by our globe are of the “small-fry” variety!
As the rapidly moving particle plunges earthward through denser and denser layers of atmosphere, the air molecules offer ever-increasing resistance to its passage. This resistance heats up the meteorite body until it glows. ”

“ The Mazapil, Mexico, iron meteorite fell at 9:00 p.m. on November 27, 1885, during a return of the now very weak Bielid meteor shower. Scientists still cannot decide whether or not a mere coincidence was involved in this case.
As we have already mentioned, most of the cosmic particles rushing into our atmosphere evaporate and do not reach the earth at all except as the tiny congealed droplets and spherules of their own melt. Some cosmic particles, the micro-meteorites, are so tiny that they “stall” rather than fall down. ”

“ The two accounts given also make clear that investigators of meteorite falls are almost entirely dependent upon observations made by nonscientists.
Scientists investigating meteorite falls greatly appreciate the help given them by children and adults alike. Field parties are powerless without it, and we should like to encourage people of all ages to continue this type of valuable cooperation. In Chapter 7, we shall tell more about how the individual observer of a meteorite fall can make his report really count. ”

“ The detailed investigation of them is rather the province of the chemist, the crystallographer and the mineralogist than of the astronomer whose interest is more keen in their life history before they reach the earth. To distinguish a stony meteorite from terrestrial rock substances is not always easy, but there is usually little difficulty in pronouncing upon an iron meteorite. These are most frequently found in deserts, because the dryness of the climate renders their oxidation and gradual disappearance very slow. ”

“ If irons stay in the ground long enough, they may rust away almost completely and turn into shale balls, like those found near the ancient Wolf Creek, Australia meteorite crater. (See Chapter 4.) Stone meteorites buried in the ground for any great length of time may disintegrate and become completely unrecognizable as meteorites. ”

“ The different modes of discovery of meteorites not seen to fall are interesting in themselves. The largest percentage of finds has unquestionably been made by farmers. The Plymouth, Indiana, meteorite, for example, was plowed up or, as the farmer nursing the rib bruised by his bucking plow would probably prefer to say, “plowed into.” ”

“ A meteorite, of course, cannot be claimed to be a preventive of danger on all occasions, but several who have always carried them have seemed to escape all sorts of harm. Some years ago a meteorite was given to Edward Heron Allen, the famous writer on palmistry and the violin, and this gifted man always wore it about him. ”

“ After the great meteorite had been raised out of the excavation, it was taken by truck to the University of New Mexico, in Albuquerque. There it was put on display beside the smaller 130-pound fragment found in May. By careful measurements, scientists determined the weight of the main mass to be approximately 2,360 pounds—a record weight for stony meteorites. [1] This remarkable meteorite, known as the Furnas County, Nebraska, stone, is now a prized item in the collection of the Institute of Meteoritics. ”

“ The first thing to be said on this subject is, of course, that not all holes in the ground, however large and impressive, were necessarily formed by the impact of meteorites. Features that resemble meteorite craters may result from certain ordinary earth-processes. For example, the rock layers underlying a particular area may be dissolved away by waters circulating beneath the surface of the ground. The overlying crust will eventually collapse into the empty space, and what geologists call a “sink hole” or a “sink” is formed. ”

“ The earth is being constantly bombarded with meteorites, usually of very small size. But the earth is armor-plated with its envelope of air. The impact of meteorites upon this envelope, at the enormous speed at which they are traveling through space, is fatal to them, and they are dashed to pieces and consumed upon it, as though it were a solid shield of hardest tempered steel. It is seldom, indeed, that a meteorite has sufficient size and mass to penetrate through the atmosphere to the earth's surface. ”

“ Though the surface of a meteoric stone becomes very hot during the early part of the flight through the air, it is cooled again during the later and slower part of the flight. Meteorites are generally found to be warm to the touch if immediately dug out; at the moment of their impact they are not hot enough to char woody fibre on which they chance to fall, nor is the surface then soft, for terrestrial matter with which the surface comes into contact makes no impression upon the meteorite. ”

“ Nor is it probable that they are portions of a lost satellite of the earth, or are due to a collision of two planets; for in each of these cases we should expect to have received some of the larger fragments which must at the same time have been produced.
Much light is thrown on the history of meteorites by the discovery of a relationship with shooting stars and comets.
Shooting or falling stars. 56. The meteorite-yielding fireball, referred to in Art. 17, is not the only luminous meteor, apart from lightning, with which we are acquainted. ”

“ Between the small silent shooting star visible only with the telescope and the large detonating meteorite-yielding [pg 58] fireball there is every gradation; during the star-showers themselves many fireballs of great size and brilliancy are seen, while the smaller individuals appear in no way different from the solitary shooting star. The luminous meteors, large and small, are in the upper atmosphere, few higher than 100 miles, few lower than 30 miles from the earth's surface; they all have velocities of the same order of magnitude, comparable with that of the earth in its orbit ”