Collision Course In Space

Press, Volume CIV, Issue 30847, 4 September 1965, Page 5

Collision Course In Space

(Specially written for “The Press” by G. R. LANE) THE xv orl (I of astronomy vibrates with excitement ami promise. Cameras probe Mars, radiotelescopes investigate mysterious energy sources far out in space. But astronomers in 14 observatories are currently examining a phenonemon which is of much more direct interest to us—the behaviour of hurtling rock masses which could “attack” the world at any time and lay waste a city in one smashing blow. ' It is not likely—but it is by no means impossible. For around the edges of the earth’s atmosphere are dozens of large objects, each of which has devastation potential many times more vast than man’s largest nuclear bomb. They are asteroids, huge masses of rock billions of tons in weight, erratic in orbit. All of them have one thing in common: they are veering nearer to earth. . . . Astronomers call them “earthgrazers.” In recent years, several have come to within a hair’s breadth —in space terms—of earth. And it is calculated that twice in a century, rogue asteroids actually collide with the earth. First Hint The last time was in 1908, when a small meteor fell in Siberia, doing breath-taking damage and felling trees for 20 miles around. So another “attack” could, technically, be due any time.

The first hint of near neighbours in space was uncovered some years ago by an astronomer, G. Witt, who got a glimpse of a huge asteroid orbiting between Mars and Jupiter.

Witt calculated that the asteroid named Eros circled the sun between the orbits of Mars and the earth. At one point it came within six million miles of the earth’s orbit. Then, from 1930 to 1937, the number of asteroids dramatically increased. The climax came in 1937 when an object was detected on photographic plates which turned out to be a mere 400,000 miles away. How Many? This asteriod, named Hermes, could, if both it and the earth were at the proper points of their respective orbits, approach to within 200,000 miles of the earth — closer than our own moon. And there is no reason to suppose that it will not come any closer.

Just how many “earthgrazers” are there? Scientists have no idea. When an earthgrazer approaches, and is spotted on film, it is only a matter of luck whether it can be found on other observatory plates to show how its position varies with time or observatory position, so that its' distance and orbit can be calcullated.

The earthgrazer does not stay long in our vicinity. The closer it comes, the faster it goes.

For instance, in 1937, when Hermes zoomed past us at only double the moon’s distance, it was travelling one full degree in 20 minutes. As a result, the orbit calculated for Hermes is only a rough one. Nor have astronomers been able to work out the exact chances of an earthgrazer crashing into earth. The known earthgrazers —six of them—are not, at the moment, travelling on orbits which intersect the earth’s.

But these orbits are by no means permanent. A small body like an earthgrazer can have its orbit twisted if it gets too near a large body like a planet. Such orbital changes have been regularly noticed in comets, for instance. The smaller the earthgrazer and the closer the approach, the larger the twist.

What if a particular twist brought about by Mars. Venus or earth itself changes an orbit just enough to convert an earthgrazer to an “earthcrasher?” It is unlikely, but not impossible. Monster Crater Eros, the first earthgrazer discovered, is the biggest known. It is brick-shaped—ls miles long 5 miles wide by 5 miles thick—and probably weighs about 2| trillion tons. What about Hermes, much smaller than Eros, but still some 7 million tons in mass? If Hermes struck land at its asteroidal velocity, it would be a catastrophe beyond imagination. It would gouge out a crater about a hundred miles across and cause an earthquake about a thousand times bigger than the earth has experienced in recorded history. Striking the ocean, Hermes would cause the biggest tidal wave splash ever seen. For every big earthgrazer—of billions of tons—there may be dozens of smaller ones—not yet detected —weighing thousands of tons. And after them come scores of others hundreds of tons in weight.

No Rules And some do strike: the 100,000 craters on the moon have probably been caused by them. Some of the lunar craters are 100 miles or more in diameter and objects the size Hermes may have caused them. On earth, there is the famous meteor crater in Arizona, four-fifths of a mile across and looking like a tiny crater of the moon. It was not any billion-ton earthgrazer that hit there just a tiny one of a few thousand tons. The Siberian meteor fall of 1908 involved a rock of only a few dozen tons mass, but that was enough to gouge out craters 150 feet in diameter

and to knock down trees for 20 miles around.

It was just good luck the Siberian city-buster fell in uninhabited territory. There’s nothing in the rules of the cosmic game to keep one from hitting London or New York. In fact, a destructive asteroid has, according to scientists, a 1 in 670,000 chance of hitting the world’s biggest city. Where do all asteroids come from? It seems more and more likely that there was a planetary catastrophe between Mars and Jupiter some time during the history of the solar system, after all

the planets had been forim and settled down to sobi steady life. Collisions from planets an far away galaxies may hav< contributed to the wandering asteroids.

Perhaps a hundred years from now, some astronomer will look from his computer to say, “Collision orbit!" By then we will probably be in a position to fire a nuclear charge into the path of the asteriod and divert it. But until then we must just trust to luck and hope fate doesn’t steer an earthgrazer on to a disaster course.