Meteors and Meteorites

Meteors and Meteorites

Meteors

No one can watch the night sky for long on a clear, moonless night without noticing one or more meteors, or sudden streaks of light popularly called “shooting stars”. These events are not stars at all but tiny pieces of stone and iron generally no larger than a grain of sand. Millions of these grains bombard the earth every day, but we are protected from them by the blanket of the Earth’s atmosphere. The grains travel so fast that they are entirely vaporized at heights of about from 80 to 25 miles by the heat of friction with the thin upper air. The great majority are too small to give rise to any visible effect, or for that matter, to undergo appreciable heating, and even the bright ones are no larger than small pebbles.

Meteorites

On rare occasions, quite sizable chunks of meteoritic materials penetrate the earth’s atmosphere to bury themselves in the ground or to explode into a number of fragments above the ground. The former are called meteorites, the latter, fireballs. The larger known meteorite weighs about 79 tonnes and still lies partly buried where it fell near Grootfontein, Namibia. But this is only a tiny fragment compared with others that had excavated great hollows or craters. One of the best preserved formations of the kind is the Barrenger crater near Winslow, Arizona. It has a diameter of about four-fifths of a mile and a floor near 1000 feet below the level of the plain. An immense number of iron fragments have been collected in the area, but the main mass, if it still exists as one whole piece, must be deeply buried.

Meteoritic craters in Canada

Several large craters in Canada are thought to be meteoritic in origin. They are extremely old and have suffered much more than the Barringer crater from the effects of erosion over geological time. Notworthy among them is Pingualuit (formerly Chubb) crater in Northern Quebec, a tremendous circular hollow nearly two miles wide and nearly one quarter of a mile deep. The crater was first investigated in 1950 by an expedition organized by the Royal Ontario Museum in partnership with the Globe and Mail Limited, and later with the National Geographic Society. Since then the Dominion Observatory, Ottawa, has done extensive research on other larger hollows, and the Holleford and Brent craters in Ontario and the Deep Bay crater in Northern Saskatchewan are now generally considered to be meteoritic.

Aerial view of Pingualuit Crater (formerly Chubb Crater), Ungava, Quebec. Most of the time floating ice covers its surface.

Meteor showers

The most beautiful and arresting aspect of meteors occurs when the Earth sweeps into the path of a really dense swarm of meteorites. Shooting stars then streak across the night sky like snowflakes driven by a cosmic wind.

Some of these “showers” are associated with comets. One of the most interesting of these associations is that between Comet Tempel-Tuttle 1866, a faint comet with a period of just over 33 years, and an annual shower known as November Leonids. The latter are so named because they appear to originate in a point in the constellation of Leo. They gave particularly magnificent displays in 1833, 1866, and as recently as 1966. The fact that the shower is an annual event indicates that the meteors are strewn along the orbit of the comet. But whether they always have had an independent existence or represent material shed by the comet remains an open question.

The Leonid shower of 1833. This depiction of the meteor storm was produced in 1889 for the Seventh-day Adventist book Bible Readings for the Home Circle