Seth Butler, age 11, of Tucson, Arizona, for his question:
How fast do meteors travel?
This topic takes us on a tour of the spacious Solar System and plunks us back on earth to consult figures, computers and some elaborate astronomical checking de¬vices. Meteors are meteors as long as they are space travelers and their spaceways range from inside Mercury to beyond Pluto. Out there, their speeds range from about 72,000 miles per hour to an upper limit of 93,600 miles per hour.
The average meteor has been on a non stop space voyage for perhaps five billion years. It belongs to the Solar System and' it may travel on and on, around and around through all the enormous spaces between the planets. Its speed is related to its distance from the sun. So are the orbital speeds of the earth and the other planets. The reason for this is gravity, the gravitational attraction between the sun and any member of the solar family.
The downward pull of the sun's gravity is offset by the circulating orbital paths of the planets. The strength of gravity diminishes with distance which means that the closer planets must orbit faster to keep from falling into the sun. A slow poke planet would be pulled down into the fiery furnace. So would a meteor, if it traveled so slowly that the sun's gravity could grab it. The earth's orbital speed of 18h miles per second is nicely balanced to match the sun's gravitational pull from a distance of 93 million miles.
At the other end of this balancing act is something called escape velocity. If the earth's orbital speed accelerated to 26 miles per second, it would more than off¬set the pull of the sun. In fact, it could escape the sun's gravity entirely and be free to launch us on a space voyage beyond the Solar System. This super speed is called escape velocity and it also applies to space traveling meteors.
In our neighborhood of the Solar System, 26 miles per second is the speed required to allot 7 a traveling object to escape the gravity of the sun. Hence, a meteor travel¬ing faster than this rarely if ever comes within range of our orbit. When such a speeder is checked and verified, astronomers suspect that it just might be a chance visitor from beyond the Solar System.
In several strategic places, precise instruments are set up and staffed to keep a vigilant snatch on meteors that come within range of the earth. Before they were c accelerated by the earth's gravity, most of them were traveling at about 26 miles per second, or 93,600 miles per hour. Some were traveling more slowly, but only by a dew miles per second. A space traveling meteor going faster than 26 miles per second is very rare in our region of the Solar System.