TELEMETEORING

There used to be a quip about the difference between a journalist and a scientist: the journalist must study ever more widely until he knows nothing about everything, whereas the scientist must specialize ever more narrowly until he knows everything about nothing.

If only that were the difference, the world would be a better place. But except for the journalists who know nothing (and most know less), the quip is quite untrue. It is one of the great fascinations of science that it takes researchers extremely far afield from their specialization. Today there are no two sciences that do not share a frontier; the cold light of the glowworm is one of thousands of items studied in bioengineering, and the subject we are about to discuss is one where oil production meets astronomy.

Meteors are chunks of rock or metal that burn by friction as they whoosh into the earth's atmosphere. Radar astronomy, founded soon after World War II, proved that the vast majority of this cosmic debris does not come from outer space, but orbits the sun within the solar system. It is concentrated more densely near the ecliptic (the plane of the earth's orbit), so that the earth's atmosphere runs into it. Like a car driving in the rain that picks up more water on its windshield than on its rear window, the earth runs into more meteors on its "forward" side. Let us recall that when the earth is viewed from above its northern hemisphere, it revolves anti-clockwise round the sun, then a simple sketch (for which we have no space) will make it clear that the "forward" side is where it is sunrise. It is a simpler case than a car in the rain, for there are no aerodynamic eddies behind the vehicle nor rear wheels to throw up the water into them and onto the rear window, so that the earth does much more nearly what it "ought to," which is pick up a maximum of meteors where it is local sunrise and a minimum near sunset. But even at its minimum, the number of meteor trails usable for communication, as explained below, is still considerable.

All of this goes for "sporadic" meteors, not the "showers" which come from a definite point in the sky (they are debris from comet trails which the earth's orbit crosses at a certain time of year in a predictable direction). The showers are spectacular, but rare; it is the small, sporadic meteors that are intercepted most of the time: the earth gets more than 1,000 tons a day.

When a meteor enters the atmosphere at a cosmic velocity (the earth itself goes round the sun at almost 20 miles/sec), it is heated red-hot, leaving behind an ionized trail. Only very rarely is the meteor big enough to make it all the way to the surface of the earth, or even to ionize its trail so intensely that it emits strong light seen as a "shooting star;" but the trail is always ionized, that is, it contains free electrons torn from their atoms. That makes it an electric conductor for the rest of its life, which usually lasts only a fraction of a second, for the trail diffuses and the electrons recombine with positive ions to form neutral atoms once again. But that fraction of a second is long enough to bounce off radio waves and communicate over some 1,200 miles, for the trails form at about 50 to 60 miles above the earth. At greater heights the atmosphere is too thin to burn the meteors, and at lower heights they have all been burned up.

It is a stop-and-go communication which works like this: Both the transmitting and receiving ends of the link have a radio transmitter and receiver each, since they must not only communicate information, but also probe whether a trail is available. The transmitter at the transmitting end transmits all the time, but most of the time it sends out only a probing wave that the receiver at the receiving end cannot receive until a meteor trail has formed; as soon as the reflected (more accurately, reradiated) signal is received, the receiving end radios back "Go!" via that same meteor trail, and the transmitting end begins rattling off concentrated information as fast as it can, for it only has a fraction of a second (exceptionally up to 7 or 8 seconds) in which to communicate. When the signal is no longer received because the trail has disintegrated, the receiver's transmitter wave signals "Stop!" (by its absence) and the transmitting end goes back to sounding for a new trail.