When Worlds Collide


An asteroid or comet is believed to have wiped out the inosaurs some 65 million years ago. A comet is expected to brush Jupiter this year. Must Earth, like the other planets, remain helplessly vulnerable to such impacts from outer space?

There is today at least a possibility that if another space object is found plunging toward the earth -- now usually predictable years in advance -- mankind can do something about it.

The hope lies in thermonuclear energy. Since the hydrogen bomb was created by Edward Teller 40 years ago, thermonuclear energy has symbolized destruction, not salvation. Now the 85-year-old Dr. Teller himself believes a thermonuclear armed missile could destroy or divert an earthbound comet or asteroid.

Collisions between the planets and errant objects from space are hardly, in astro-historical terms, a rare occurrence. The faces of the Moon, Mars and Mercury (the three heavely bodies whose surface we can see) are pockmarked from such collisions. Geologists have found at least 139 craters on the earth, with visible ones in Arizona, Quebec and Western Australia.

Nor are these impacts only from past eons. In 1908 a stony meteorite smashed into a remote area near Tunguska River in Siberia. No human lives were lost but 1,000 square miles of forest were destroyed, along with uncounted numbers of wild animals. The object had a diameter of more than 100 feet and an estimated velocity of 20 miles a second. The heat and pressure are believed to be the equivalent of a 10-megaton explosion.

ZTC Astronomers are now gearing up to watch the pyrotechnics from a collision of a fragmented comet with Jupiter next July. The comet has already been clearly photographed by the Hubble Space Telescope and ground-based instruments as it bears down on the solar system's largest planet.

And there are near-misses. Less then five years ago, March 21, 1989, a previously undetected asteroid half a mile in diameter missed the earth by just 700,000 miles, a hair's breadth, cosmologically speaking. If it had arrived just six hours later, civilization might have been wiped out.

In October 1992, astronomers discovered a comet, 6 miles in diameter and composed of ice and space dirt, bearing down on the earth. They estimated that it had a one-in-10,000 chance of hitting the earth -- comfortably high odds, considering the consequences. The estimated doomsday date was August 14, 2126. More precise calculations later indicated that the earth would be spared.

This, however, is not the end of the story. In the late 1980s scientists were finding 15 asteroids a year ''of the size that could eliminate society.'' Now, with more available telescope time, the tally is up to 35 a year -- and they are only counting asteroids that orbit close enough to the earth to pose a threat.

Dr. Teller believes that man has the opportunity, and therefore the responsibility, to protect the planet. The ''Father of the H-Bomb'' -- a title he detests -- might find a measure of redemption in his ascribed parenthood. He urges international cooperation in organizing a defense against asteroids.

''A remarkable number of technological developments,'' Dr. Teller says, ''have made it possible to do something about meteorites: computers, radar, lasers, nuclear energy -- each of these has contributed.'' He suggests that information about the conductivity of a threatening space object might be gained by use of lasers to heat its surface and then observing how long it takes to cool. Observations can now take place from earth to space, Dr. Teller believes, but preferably from a telescope on a low orbiting satellite (such as the Hubble), which avoids atmospheric disturbance.

How do we know that this thermonuclear defense would work? There could be an opportunity to test it. Dr. Teller points out that every year a potentially dangerous meteorite comes closer than the moon. He suggests that an experiment could be carried out against one of these near-miss objects as it recedes from its closest point -- striking it with a missile when there is no danger of detectable radio-activity on the earth.

If more scientists take part in thinking about the problem and working on ways to defend against it, the human race may yet escape the fate of the dinosaurs.

Stanley A. Blumberg and Gwinn Owens are the biographers of Edward Teller.

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