Jane Dewitt, age 11, of Transcona, Winnipeg, Canada, for her question:
How far does a meteor fall?
Andy readers are the young members of the Space Age, and he does not have to remind them that a falling star is not a falling star. It may be brighter than a real star and its moment of glory more dazzling. But it is no more than a small and solid space-traveling member of the solar system.
The fall of a stone is caused by the pull of the Earth's gravity. When the mechanics of an airplane fail, it crashes because this force of gravity hugs it down to the surface of the planet. The Earth's gravity tugs day and night with the same strength. It causes a falling body to drop at a set rate, though a long tumble through the air slows up the falling speed. The set rate of a fall to the Earth begins at 32 feet a second. Every second the falling speed increases at the rate of 32 feet a second.
Our planet's gravity reaches out in all directions into the limitless reaches of space, getting weaker as it goes. At 230,000 miles it is still strong enough to keep our captive moon in orbit. But millions of miles away it is too weak to pull very hard at the other planets. The wide spaces between the planets are occupied by space-traveling gravel, by boulders and pebbles and by clouds of debris. These solid specks and chunks of matter are the meteors.
Each orbiting planet keeps to a traffic lane, but most of the meteors zoom through the solar system with no regard for traffic laws or lanes. The Earth bowls around its orderly path at an average speed of 18.5 miles a second. The meteors travel in various directions at speeds ranging up to almost 26 miles a second. Naturally there are collisions, thousands of them every day.
As the Earth rolls along it is bashed by meteors from all sides. The planet and each little meteor rush together at collision speeds to occupy the same place at the same time. This collision course is not the same as the falling speed of a stone, and the meteor feels the downward pull of gravity only as it nears the Earth. As it enters the atmosphere it bashes into molecules of gas that force it to jam on the brakes. Its speed energy heat and the speck of matter catches fire.
A meteor begins to blaze at an average height of 70 miles and burns to ashes perhaps 40 miles above the Earth. As it descends, the Earth rotates below it, and the fiery spark arches in a curved path of 50 to 100 miles. The speed of the fall may be anything from seven to 47 miles a second, but only 3.5 miles of this velocity comes from the pull of gravity.
The descent of a meteor depends upon the direction from which it strikes the Earth. If it strikes from behind, it may be seven miles a second. This is its own interplanetary space speed minus the orbital speed of the Earth. If it strikes from ahead, the Earth and the meteor approach at maximum speed. The path of the meteor may take it plummeting down at 47 miles a second. This is its own speed of 25.5 miles a second plus the Earth's speed of 18.5 miles a second plus 3.5 miles from the downward drag of the Earth's gravity.