National Geographic : 1939 Jul
THE NATIONAL GEOGRAPHIC MAGAZINE space. Occasionally we even strike a mass of meteorites or a comet head on. WHEN METEORITES HIT OUR PLANET The last time this happened was in 1908. One day, in a remote part of Siberia, a huge, luminous mass roared down out of the sky. As it struck Earth, a blast of superheated air rushed out and for miles around the countryside was charred and seared as if by a giant blowtorch, while in every direction the forest trees were uprooted, with their trunks leaning away from the central area. In the Arizona desert, too, several thou sand years ago, the same thing happened, when a large mass of meteorites or a small comet fell and formed a crater 570 feet deep and nearly a mile across (Plate III and page 13).* It almost happened again in 1937, on a vastly greater scale. The asteroid Her mes, about a mile in diameter, came within some 500,000 miles of the Earth, though its path was such that it could not have struck us. Should such a body fall on one of the world's great cities, it would dig a crater several miles wide where the city now stands, and the hot air blast would destroy all life and property for scores of miles around. But most of the Earth's surface is still empty or sparsely populated. Should Her mes strike anywhere but in a thickly settled area, it would merely dig a crater, destroy vegetation, and cause an earthquake in the vicinity, if on land, or produce a great tidal wave if at sea. Thousands of asteroids of all sizes are speeding around the Sun. The largest is 480 miles in diameter, as big as Texas, while others are no larger than small moun tains. Most of them follow a path be tween the orbits of Mars and Jupiter, and are perhaps the remnants of another planet that broke up. Only a very few of the smallest have orbits such that they ever could collide with the Earth. MESSENGERS FROM SPACE But though we could seldom collide with an asteroid, we strike "rocks" fairly often. These are the meteorites, large enough not to be consumed by the heat generated by friction as they fall through our atmosphere. * See "Mysterious Tomb of a Giant Meteorite," by William D. Boutwell, in the NATIONAL GEO GRAPHIC MAGAZINE, June, 1928. They tell us two things: first, that all of the Universe apparently is made of the same materials as our own Earth, for no element not known to us ever has been found in a meteorite; and second, that strange proc esses of mineral-making take place out in the great beyond. The familiar elements con tained in meteorites often are fused into new combinations not existing on Earth, by methods unknown to us. These visitors also bring riches from the sky. A Colorado meteorite contains enough gold to make one good tooth filling. Others contain tiny but genuine diamonds. So sure are some astronomers that there is a fortune in platinum and iridium in the great mass of meteorites that made the Arizona crater that several once invested money in a project to dig them up! Meteorites are of three kinds: iron, dif ferent from earthly iron; stone; and a mix ture of the two. You can identify them by pockmarks, like thumbprints in a cake frosting, where softer materials have been melted out, and by a smooth, glossy sur face resulting from heating. Also, they're heavy for their size (pages 29 and 32). The ancient Phrygians worshiped a me teorite as "Cybele, mother of the gods." The sacred black stone in the southeast corner of the Kaaba, the holy place of Mecca, is believed to be one. Smaller cousins of the meteorites are the countless tiny meteors. Every day the Earth collides with billions, most of them no bigger than a grain of sand.* As they speed into our atmosphere, its friction heats them and they burn to ash while they are still 40 miles or more above the Earth. All we see is a brief flash of light, a "shooting star." Vast numbers of the meteors that the Earth "sweeps up" each day come from the real depths of space, from far out between the stars, beyond the solar system. But sometimes we plunge into a thicker cloud of meteors. Then for a few hours the night sky is filled with flashing lights. And that brings us to comets, for these thicker meteor swarms are the debris of comets that are dead or dying. "From the Devil and the Comet, good Lord, deliver us," said an old prayer. In 1910, when it became known that the Earth would pass through the tail of *See "Exploring the Ice Age in Antarctica," by Richard E. Byrd, in the NATIONAL GEOGRAPHIC MAGAZINE for October, 1935.